- Email: [email protected]
A large-grain rice cultivar, Akita 63, exhibits high yields with high physiological N-use efficiency
Field Crops Research 97 (2006) 227–237 www.elsevier.com/locate/fcr
A large-grain rice cultivar, Akita 63, exhibits high yields with high physiological N-use efficiency Tadahiko Mae a,*, Ayako Inaba a, Yoshihiro Kaneta b, Satoshi Masaki c, Mizuo Sasaki a, Mayu Aizawa a, Shigenori Okawa a, Shuichi Hasegawa a, Amane Makino a a
Department of Applied Plant Science, School of Agricultural Science, Tohoku University, 1-1 Amamiyamachi, Tsutsumidori, Aoba-ku, Sendai 981-8555, Japan b Faculty of Bioresource Sciences, Akita Prefectural University, Shimosinjyou, Akita 010-0195, Japan c The Agricultural Experimental Station of Akita Prefecture, Aikawa Yuuwamachi Kawabe-gun Akita-ken 010-1231, Japan Received 20 May 2005; received in revised form 6 October 2005; accepted 7 October 2005
Abstract A new large-grain cultivar, Akita 63, of japonica-type rice exhibited high yields with high physiological nitrogen (N)-use efficiency for grain production. Akita 63 and three reference cultivars, Yukigesyou, Toyonishiki and/or Alitakomachi were grown in a field with different levels of N supply for three years. The grain yield of Akita 63 was 22–58% greater than that of the reference cultivars. The highest yield was 9.83 t ha1 of brown (hulled) rice (approximately 12.3 t ha1 of rough (unhulled) rice). The dry weight of the aboveground part and the number of spikelets at harvest, and the total leaf area (LAI) at the full-heading stage for a given amount of N accumulated in the aboveground part (plant N) did not differ between Akita 63 and the reference cultivars. The grain yield or panicle dry weight for a given amount of plant N at harvest and for a given unit of LAI were, however, greater in Akita 63 (superior in physiological N-use efficiency) than in the reference cultivars because of a higher proportion of dry matter partitioning into panicles in Akita 63 than in the reference cultivars. As the grain size of Akita 63 was about 35% larger than that of the reference cultivars, the sink capacity (the number of spikelets per unit land area grain size) for a given amount of plant N was much larger in Akita 63. Reaccumulation of starch in the culms and leaf sheaths was very limited in Akita 63, but remarkable in the reference cultivars in the late stage of grain filling. When pot-grown Akita 63 and the reference cultivar, Toyonishiki, at different stages of ripening were fed with 13CO2 and 13C partitioning into constituent organs was examined at harvest, the proportion of 13C partitioned into panicles was much higher in Akita 63 throughout the ripening period. These results indicate that Akita 63 is a new type of high yielding cultivar of japonica-type rice, superior in physiological N-use efficiency. # 2005 Elsevier B.V. All rights reserved. Keywords: High yield; Large grain; N-use efficiency; Rice; Sink capacity
1. Introduction Rice is the staple food grain for more than half of the world’s population. More than 90% of the world’s production of rice is in Asia. It is estimated that the world’s population will increase to a level 1.4–1.5 times the present population by 2025, this projected increase being mostly in * Corresponding author. Tel.: +81 22 717 8766; fax: +81 22 717 8765. E-mail address: [email protected] (T. Mae). 0378-4290/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2005.10.003
Asia (IRRI, 1995). It is, therefore, crucial to increase rice production within a relatively short period. With little scope for expanding land area, the increase in rice production must be achieved by an increase in yield from the land currently used for rice cultivation. In addition, interest in the environmental impact of N management practices is increasing (Cassman et al., 1998; Ladha et al., 1998). Therefore, it is important in rice cultivation to both increase the grain yield and limit the environmental impact of N management practices. One solution to this problem is to use
228
T. Mae et al. / Field Crops Research 97 (2006) 227–237
a high yielding cultivar, which exhibits a higher grain yield per unit amount of plant N acquired (higher physiological N-use efficiency (NUE) for grain production). However, selection or breeding of such cultivars has not been conducted. A number of field trials on high yielding of rice have been reported. For example, high yields of around 10 t ha1 of brown (hulled) rice (approximately 13 t ha1 of rough (unhulled) rice) have been reported in northern Japan (Honya, 1989; Kamata et al., 1978; Jinbo et al., 1987). A higher yield of 15–17 t ha1 of rough rice has been reported in Yunnan Province, China (Amano et al., 1996a,b; Ying et al., 1998a,b). Only limited information, however, is available on physiological NUE in such high levels of grain yield. Recently, the Agricultural Experimental Station of Akita Prefecture in northern Japan released a new largegrain cultivar of japonica-type rice, Akita 63. In test cultivations with standard levels of N fertilization at different locations and in different years, the average yield of Akita 63 was 18% higher than that of the present leading cultivar, Akitakomachi, in Akita Prefecture (Masaki et al., unpublished data), indicating that Akita 63 might be a new type of high-yielding cultivar with high NUE. In this study, we first examined the potentiality of Akita 63 for high yield and its physiological NUE, and then analyzed the factors responsible for high yield and NUE. Akita 63 and reference cultivars of japonica-type rice were grown in a field with different levels of N supply. Akita 63 recorded a grain yield of 9.83 t ha1 of brown rice (approximately 12.3 t ha1 of rough rice), which is close to the previously recorded highest yield in Japan, and exhibited high physiological NUE for grain production.
2. Materials and methods 2.1. Plant culture and sampling Akita 63 was grown with different levels of nitrogen supply in an experimental field of the Agricultural Experimental Station of Akita Prefecture (398340 N, 1408110 E, 16 m altitude) for three years from 2000 through 2002. As reference cultivars of japonica-type rice, a highyielding local cultivar, Yukigesyou, which has previously recorded the yield of around 10 t ha1 with a high level of N supply (290 kg N ha1) (Jinbo et al. (1987), a common (old) cultivar, Toyonishiki and/or a modern cultivar, Akitakomachi, which is the present leading cultivar in Akita prefecture and known as a tasty rice, were grown with the same N treatments. Difference in growth duration (165–175days) among these cultivars was within 7 days when they were grown in the experimental station. Plant height was almost same among these cultivars (culm length of 79–84 cm). Soil type was Gley soil (Eutric Gleysols; FAO) with pH 5.3, 31.6 g total C kg1, 2.4 g total N kg1 and 25.2 cmol kg1 cation exchange capacity. Phosphorus (4.3 P g m2 as fused
Table 1 Rates of nitrogen application for rice cultivation Year
Nitrogen application (g-N m2) N treatment
Basal dressing
Top dressing
Total
2000
High level Standard level Zero-N application Single application
2a + 6 b 4a 0 10b
2a 4 times 2a 1 time 0 0
16 6 0 10
2001
High level Standard level Zero-N application Single application
4a + 7 b 4a 0 10b + 4c
2a 2 times 2a 1 time 0 0
15 6 0 14
2002
High level Standard level
4a + 7 b 4a
2a 2 times 2a 2 times
15 8
a
Ammonium sulfate. Controlled release fertilizer (LP100 Type polyolefin-coated urea, Chisso Co., Japan). c Controlled release fertilizer (LSP100 Type polyolefin-coated urea, Chisso Co., Japan). b
phosphate) was applied to all plots 30 days before transplantation. Potassium was not supplied because of its sufficient level in the soil. Two to four levels of N fertilization were conducted (Table 1) by using ammonium sulfate and controlled release fertilizers (Type LP100 and Type LPS100 polyolefin-coated urea, Chisso Co., Japan). Both Type LP100 and Type LPS100 fertilizers release 80% of its total N content until 100 days after its application at any temperature between 20 and 30 8C. Type LP100 releases N to soil solution with a zero order reaction when cumulative N release is less than 60%, and then, with a first order reaction at the cumulative N release greater than 60% of its total N. The N release from Type LPS100 follows a sigmoid curve with time (Shoji and Gandeza, 1992). For the N-single application plots only controlled release fertilizer(s) was used as a basal application. Basal applications were conducted a week before transplantation. Weeds, insects and diseases were controlled as required to avoid yield loss. All the experimental plots were arranged in a randomized design with three replicates except for N-standard and zeroN application plots (two replicates) of Toyonishiki in 2001 due to the limitation of available land area. The size of each plot was 26.25 m2 (3.5 m wide and 7.5 m long). About 35-day-old seedlings were transplanted with a rice transplanter on a day in the middle of May at a hill spacing of 0.3 m 0.14 m (24 hills per m2) with four to five seedlings per hill. In this paper, the full-heading stage was defined as the time when 80% of the panicles had emerged. The crop was considered to have reached maturity when 95% of spikelets had turned yellow. Plant height, culm (panicle) number and leaf age were examined for 20 hills of each plot at appropriate intervals (2–4 weeks) throughout the culture period, and three hills with the mean culm (panicle) number from each plot were collected at each sampling for measurements of leaf area, dry weight of constituent organs and nitrogen content. The hills were separated into leaf
T. Mae et al. / Field Crops Research 97 (2006) 227–237
blades, culms plus leaf sheaths, panicles and others (dead parts and non-reproductive tillers). After measurement of the SPAD value of individual leaves (SPAD-502, Minolta, Tokyo, Japan), leaf area was measured with a leaf area meter (Type-AMM, Hayashi-Denko, Tokyo, Japan). All samples were oven-dried at 80–105 8C for several days, weighed and powdered. At the time of harvest, three additional hills with the mean panicle number from each plot were collected and hand-threshed for measurement of the number of filled and unfilled spikelets. The filled spikelets were separated by submerging the hand-threshed spikelets in a NaCl solution with a specific gravity (g m3) of 1.06. The filled spikelets were then hulled and oven-dried at 105 8C to a constant weight for determining grain dry weight. A survey of yield was carried out as follows: 80 hills were collected from the center part of each plot. Unhulled (rough) rice was obtained after reaping, threshing and wind selection. Rough rice of 80 hills was hulled and then put through a 1.8 mm sieve to remove any immature kernels. The weight of hulled rice (brown rice) was adjusted to a moisture content of 0.14 g H2O g1 fresh weight. A conversion factor of 1.25 was used for the estimation of rough rice weight from brown rice weight. 2.2. Chemical analysis N content was determined with Nessler’s reagent after Kjeldahl digestion of powdered samples with H2SO4 and H2O2 (Mae et al., 1983). Starch content was determined as described by Nakano et al. (1995). Powdered samples were extracted several times with 80% (v/v) ethanol. Starch in the ethanol-insoluble fraction was extracted with 0.5 M KOH and neutralized with 0.5 M HClO4. After removal of KClO4 by centrifugation, starch was digested with amyloglucosidase (EC3.2.1.3, from Rhizopus, Sigma, St. Louis). Glucose in the preparation was assayed by Nelson–Somogyi’s
229
method (Somogyi, 1952). The amount of starch was taken to be 0.9 times the amount of glucose. Ribulose-1,5bisphosphate carboxylase/oxygenase (Rubisco) and chlorophyll (Chl) contents were determined as described by Makino et al. (1994). Frozen leaf blades were homogenized in 50 mM Na-phosphate buffer (pH 7) containing 0.8% (v/v) 2-mercaptoethanol, 2 mM iodoacetic acid and 5% (v/v) glycerol at a leaf to buffer ratio of 1:9 (g:ml) using a chilled mortar and pestle with acid-washed quartz sand. Homogenates were used for the determination of Chl and Rubisco. 2.3.
13
CO2 feeding and
13
C determination
Rice was grown hydroponically in a greenhouse as described by Mae and Ohira (1981). Rice seeds of Akita 63 and a reference cultivar, Toyonishiki, were soaked in tap water for 2 days at 33 8C, and the seedlings were grown for 21 days on a plastic net floating on tap water with pH adjusted to 5.3. On day 23 from seeding, eight seedlings each were transplanted into 50 pots (25 pots for each cultivar) containing 3.7 l of nutrient solution. The basal nutrient solution contained 1.0 mM NH4NO3, 0.6 mM NaH2PO4, 0.3 mM K2SO4, 0.3 mM CaCl2, 0.3 mM MgCl2, 45 mM Fe-EDTA, 50 mM H3BO3, 9 mM MnSO4, 0.3 mM CuCl2, 0.7 mM ZnSO4 and 0.1 mM Na2MoO4. The nutrient solution was renewed once a week and pH was adjusted to 5.2 with 2 M HCl. The strength of the nutrient solution ranged from 1/4 to full-strength depending on the growth period: 1/4-strength, 0–2 weeks after transplantation; 1/2strength, 2–4 weeks after transplantation; 3/4-strength, 4–8 weeks after transplantation; full-strength, 8 weeks after transplantation to heading; 1/4-strength, heading to harvest. Heading time when panicles had emerged from 40–50% of the reproductive tillers was 114 days after seeding for Akita 63 and 117 days for Toyonishiki, respectively. The time of harvest was 50 days after heading time (DAH). Plants were
Table 2 Grain yields (brown rice) of Akita 63 and the reference cultivars, i.e., Yukigesyou, Toyonishiki and Akitakomachi N treatment
Grain yield (t ha1) Akita 63
Yukigeshou
2000 High level Standard level Zeo-N application Single application
9.83 0.66 7.88 0.44 5.79 0.75 8.67 0.59
2001 High level Standard level Zero-N application Single application
9.39 0.31 (123)** 6.94 (141) 4.34 (140) 9.54 0.30 (135)*
2002 High level Standard level
7.46 0.35 (122)* 5.79 0.66 (144)*
(129)** (155)*** (158)* (135)*
7.63 0.57 5.10 0.06 3.66 0.14 6.41 0.10
Akitakomachi (100) (100) (100) (100)
Toyonishiki
5.43 0.27 (106) 4.26 0.64 (116)
7.65 0.38 (100) 4.93 (100) 3.09 (100) 7.60 0.59 (100) 6.11 0.39 (100) 4.03 0.24 (100)
Data are the mean standard deviation of three replicates except for N-standard level and zero-N application in 2001 (two replicates). Values in the parentheses show the percentage of the value of Yukigesyou (2000), Toyonishiki (2001) or Akitakomachi (2002) for the same treatment. Asterisks (*), (**) and (***) indicate significant differences between Akita 63 and the reference cultivar at the 5, 1 and 0.1% levels (t-test), respectively.
230
T. Mae et al. / Field Crops Research 97 (2006) 227–237
Fig. 1. Relationships between total dry weight (a), number of total spikelets (b), sink capacity* (c), panicle dry weight (d) or grain (brown rice) yield (e) and plant nitrogen content per unit land area at harvest in Akita 63 and the reference cultivars, i.e., Yukigeshou, Toyonishiki and Akitakomachi. (~) Akita 63 in 2000, (*) Akita 63 in 2001, (&) Akita 63 in 2002, (*) Yukigeshou in 2000, (&) Toyonishiki in 2001, (4) Akitakomachi in 2000 and (^) Akitakomachi in 2002. *Sink capacity: number of total spikelets per unit land area (m2) 1000-grain weight of each cultivar.
fed with 13CO2 at 5, 15, 20, 25, 30, 35 and 40 DAH as described by Okawa et al. (2003). One day before labeling, one pot each was transferred into a growth chamber (55 cm 55 cm 120 cm, EYELATORON FLI-301NH, Tokyo). The chamber was maintained under a 14 h (06:00– 20:00 h) photoperiod, day/night temperature of 25/20 8C, 60% relative humidity and a photosynthetic photon flux density of 850 mmol quanta m2 s1 at canopy height. Irradiance was provided by a combination of a metal halide lamp (Yoko DR, Toshiba, Tokyo), high-output fluorescent lamps (FL40ss-EX, Toshiba/Panasonic, Tokyo) and TrueLite lamps (Doro-Test, North Bergen, NJ). The plants were fed with 13CO2 for 3 h (10:00–13:00 h) at each feeding. 13 CO2 gas was produced by the reaction of HCl and Ba13CO3. Hydrochloric acid was added at a constant rate
(10 ml h1) to the Ba13CO3 (99 atom%, 10 g) suspension (200 ml) in the chamber. During feeding with 13CO2, airflow was stopped by switching off the ventilator and sealing the duct. At the end of feeding period, the plants were transferred to a greenhouse and grown there until the time of harvest. At the time of harvest plants were divided into panicles, culms and leaf sheaths, leaf blades and roots. Panicles were further separated into grains on the primary rachises and those on the remaining ones. Samples were oven-dried, weighed and ground to a fine powder in a vibrating mill. The relative amount of labeled carbon in each fraction was calculated with the following equation: (the carbon content of organ [(13C atom% of sample 13C atom% of natural abundance)]/100. Carbon content of dry matter was 42.7% for panicles, 44.2% for leaf blades, 42.6%
T. Mae et al. / Field Crops Research 97 (2006) 227–237
231
Fig. 2. Relationship between leaf area index and plant nitrogen content at the full-heading stage in Akita 63 and the reference cultivars, i.e., Yukigeshou, Toyonishiki and Akitakomachi. (~) Akita 63 in 2000, (*) Akita 63 in 2001, (&) Akita 63 in 2002, (*) Yukigeshou in 2000, (&) Toyonishiki in 2001, (4) Akitakomachi in 2000 and (^) Akitakomachi in 2002. *Sink capacity: number of total spikelets per unit land area (m2) 1000 grain weight of each cultivar.
for leaf sheaths and 41.7% for culms, respectively. Measurement of 13C atom% in the samples was performed by a combustion method using an infrared 13CO2 analyzer (EX-130S; Japan Spectoscopic Co. Ltd., Tokyo).
3. Results Table 2 shows the grain (brown rice) yields of Akita 63 and the reference cultivars. The yield of Akita 63 was 22– 58% higher than that of the reference cultivars. The highest yield of Akita 63 was 9.83 t ha1 of brown rice (approximately 12.3 t ha1 of rough rice), which was obtained with a high level of N supply in 2000, followed by 9.54 t ha1 in 2001. The difference in yield between Akita 63 and the reference cultivars was more pronounced in the plants grown with a lesser amount of N supply. The yield of Akita 63 was higher in 2000 and 2001 than in 2002, the climatic conditions during the culture period being better suited for rice cultivation in 2000 and 2001 than in 2002. The relationships between biomass production, number of total spikelets, sink capacity, panicle dry weight, grain yield and plant N content per unit land area were analyzed. Data obtained from all plots throughout the three-year period were used for analyses. The relationship between the total dry matter production and plant N content at harvest is shown in Fig. 1a. No substantial difference was found in their relationship between Akita 63 and the reference cultivars. The relationship between the number of total
Fig. 3. Relationships between sink capacity (a) or grain (brown rice) yield (b) and leaf area index at the full-heading stage in Akita 63 and the reference cultivars, i.e., Yukigeshou, Toyonishiki and Akitakomachi. (~) Akita 63 in 2000, (*) Akita 63 in 2001, (&) Akita 63 in 2002, (*) Yukigeshou in 2000, (&) Toyonishiki in 2001, (4) Akitakomachi in 2000 and (^) Akitakomachi in 2002. *Sink capacity: number of total spikelets per unit land area (m2) 1000 grain weight of each cultivar.
spikelets and plant N content per unit land area at harvest is shown in Fig. 1b. No difference was found between Akita 63 and the reference cultivars. Different from the above relationships, there was a clear difference between Akita 63 and the reference cultivars in the relationship between sink capacity (number of total spikelet per unit land area a thousand-grain (brown rice) weight) and plant N content (Fig. 1c). Sink capacity for a given amount of plant N content was 35–40% larger in Akita 63 than in the reference cultivars. The relationship between the dry weight of panicles and plant N content is shown in Fig. 1d. The dry weight of panicles for a given amount of plant N was 13– 23% greater in Akita 63 than in the reference cultivars. The
232
T. Mae et al. / Field Crops Research 97 (2006) 227–237
Fig. 4. Partitioning of 13C into constituent organs at maturity in Akita 63 and the reference cultivar Toyonishiki after photosynthetic 13CO2 assimilation at different stages of ripening. Pot-grown plants were fed with 13CO2 for a few hours at different stages of ripening. Thereafter, the plants were allowed to grow until maturity. At the time of harvest, the plants were divided into constituent organs, i.e., panicles, culms and leaf sheaths (white), leaf blades (black) and roots. Spikelets were further separated into those on the primary (gray) and the secondary rachis (lattice)) branches and their 13C contents were examined. The data are expressed as percentages of total 13C in top part.
relationship between the grain (brown rice) yield and plant N content is shown in Fig. 1e. The grain yield for a given amount of plant N content was greater in Akita 63 than in the reference cultivars. The difference was more pronounced in the plants with less amounts of plant N content. Fig. 2 shows the relationship between leaf area index (LAI) and plant N content at the full-heading stage. The difference in their relationship between Akita 63 and the reference cultivars was very small. Although the data on the relationship between sink capacity and LAI at the fullheading stage (Fig. 3a) and those on the relationship between grain yield and LAI (Fig. 3b) were somewhat
scattered, there were considerable differences in their relationships between Akita 63 and the reference cultivars. Sink capacity and grain yield for a given unit of LAI were much greater in Akita 63 than in the reference cultivars. The allocation of 13C into constituent organs at the time of harvest was examined after 13CO2 feeding of pot-grown Akita 63 and the reference cultivar Toyonishiki at different stages of ripening (Fig. 4). The proportion of 13C partitioned into panicles (spikelets) was clearly higher in Akita 63 than in the reference cultivar throughout the ripening period. Fig. 5a shows the changes in dry weight and starch content of culms and leaf sheaths during the ripening period in Akita 63
Fig. 5. Changes in the contents of dry weight and starch in the culms and leaf sheaths (a), and changes in the SPAD value, leaf-nitrogen concentration and leaf area index (b) during ripening period of Akita63 and Toyonishiki (high level-N treatment in 2001). Asterisks (*) and (**) indicate significant differences between Akita63 and Toyonishiki at the 5 and 1% levels (t-test), respectivity.
T. Mae et al. / Field Crops Research 97 (2006) 227–237
233
Fig. 6. Starch contents in the culms and leaf sheaths of Akita 63 and the reference cultivars, i.e., Yukigeshou, Toyonishiki and Akitakomachi at the full-heading and harvest stages (high level-N treatment). Closed columns indicate Akita 63 and open columns indicate the reference cultivars, i.e., Yukigesyou (2000), Toyonishiki (2001) and Akitakomachi (2002), respectively. Asterisks (*) and (**) indicate significant differences between Akita 63 and the reference cultivar at 5 and 1% levels (t-test), respectively.
and the reference cultivar Toyonishiki grown with a high level of N supply in 2001. In the reference cultivar, starch content decreased once at the early stage of ripening and then increased considerably from the middle stage through the late stage of ripening. In Akita 63, starch content decreased in the middle stage of ripening and reaccumulation of starch was slight at the late stage of ripening. Starch content in the culms and leaf sheaths was much lower at harvest than at full-heading stage in Akita 63 throughout the three years, but the content was higher at harvest than at the full-heading stage in the reference cultivars in 2000 and 2002 or the same in 2001 (Fig. 6). The increase in panicle dry weight ceased earlier in the reference cultivars than in Akita 63 during ripening (data not shown). Contents of leaf N, Chl and Rubisco in flag leaves at the full-heading stage were examined in Akita 63 and the reference cultivar Toyonishiki (Fig. 7). No difference was found in their contents between Akita 63 and Toyonishiki, irrespective of N treatments. Changes in the SPAD value and leaf N concentration in flag leaves and LAI of Akita 63 and Toyonishiki grown with a high level of N supply during ripening are shown in Fig. 5b. The SPAD value and leaf N content of flag leaves decreased in similar manners during the ripening period between Akita 63 and Toyonishiki. LAI was larger in Akita 63 than in the reference cultivar throughout ripening period.
4. Discussion 4.1. High-yielding cultivar Grain yield of field grown rice depends on many factors such as climatic conditions, cultivar, soil type, fertilizer management, skill of culture, control of weeds and insects, etc. Therefore, it is never easy to achieve high yields close to the yield potential of a cultivar. High yields of 13–17 t ha1 of rough rice have been reported in China (Amano et al., 1993, 1996a; Ying et al., 1998a) and Australia (Williams, 1992). The highest yield of Akita 63 (9.83 t ha1 of brown rice, approximately 12.3 t ha1 of rough rice) obtained in
Fig. 7. Contents of leaf nitrogen, chlorophyll and Rubisuco in the flag leaves of Akita 63 and Toyonishiki at the full-heading stage. The vertical bars indicate the S.D. (n = 3). Differences were not significant between Akita 63 and Toyoniishiki for all three parameters in all N-treatments.
Asterisks (*), (**) and (***) indicate significant differences between Akita 63 and the reference cultivar, Yukigesyou, Toyonishiki or Akitakomachi in the same treatment at the 5, 1 and 0.1% levels, respectively (ttest).
0.52 0.49 1.51 1.29 1.15 1.15 0.58*** 0.49 61 66 108 122 0.50 0.47 937 44 * 765 53 Akita 63 Akitakomachi 2002
1646 204 1419 93
15.31 0.79 11.66 1.29
0.54 0.54 1.37 1.14 1.14 1.13 0.55** 0.47 64 65 110 121 0.50 0.46 1173 39 ** 956 48 Akita 63 Toyonishiki 2001
2017 119 1792 172
18.41 2.07 14.87 1.39
0.44 0.50 1.31 1.41 1.06 1.04 0.59** 0.47 76 * 60 119 126 0.55* 0.41 1225 79 ** 954 72 Akita 63 Yukigesyou 2000
1912 60 2003 135
16.09 0.62 15.88 0.87
Leaves (%)
N concentration
Panicle (%)
Ratio of panicle-N to plant-N Grain product (g g-N1) Biomass product (g g-N1)
NUE for
N content (g-N m2) HI Grain yield (g m2) Dry matter (g m2)
Yield increase can be achieved either by increasing biomass production per unit land area or harvest index (HI) or both (Yoshida, 1981). Biomass production and N acquisition were not different between Akita 63 and the reference cultivars in 2000 and were larger in Akita 63 than in the reference cultivars in 2001 and 2002 for high N treatments (Table 3) as well as for other N treatments (data not shown). HI, defined as the ratio of grain (rough rice) dry weight to the total aboveground dry weight, was greater in Akita 63 than in the reference cultivars for all N treatments throughout the three-year period (0.43–0.64 versus 0.35– 0.48), as well as the ratio of panicle dry weight to the total aboveground dry weight (0.54–0.61 versus 0.41–0.51). The ratio of panicle N content to the total aboveground N content was also greater in Akita 63 (Table 3). The higher HI and the ratio of panicle N content to the total aboveground N content in Akita 63 can be attributed to its larger sink capacity per unit amount of plant N (Fig. 1c) and an efficient translocation of dry matter and nutrients into spikelets during the ripening period (Figs. 4, 5a and 6). In the 13C tracer experiment more efficient translocation of photosynthates into panicles was observed throughout the ripening period in Akita 63 (Fig. 4). It is not known whether an efficient translocation of photosynthate into panicles in Akita 63 is simply due to its large sink or includes some other factor(s), which promotes its efficient translocation of dry matter into panicles (Table 4). Reaccumulation of starch was very small in Akita 63 (Figs. 5a and 6). There was sufficient space in panicles for further accumulation of dry matter in Akita 63, but not in the reference cultivars from the middle to the late stage of ripening because the proportion of filled spikelets in the reference cultivars was very high over 90% for all N
Cultivar
4.2. Higher harvest index
Year
this study was close to the previously recorded highest yield (10.52 t ha1 of brown rice (about 13.3 t ha1 of rough rice)) of rice in Japan, which is almost double the current nation’s average yield (Honya, 1989). The yield of Akita 63 was 22– 58% higher than that of the reference cultivars. These results clearly indicate that Akita 63 is a new high-yielding cultivar. In addition, Akita 63 is able to grow under relatively cold climatic conditions as experienced in Akita Prefecture, the northern part of the main island of Japan, where modern high-yielding cultivars such as indica-types or japonica– indica hybrids can hardly realize their potential because of their sensitivity to cold in early spring and autumn. It has been reported that a large-grain cultivar, Oochikara, which is one of the parent cultivars of Akita 63, showed an average yield about 15% higher than those of common cultivars under warm temperate climatic conditions (Takita, 1988; Kobayashi et al., 1990). Those results and ours indicate that the trait of large-grain size and/or some other unknown traits originating from Oochikara might contribute to the highyielding characteristic of Akita 63.
Sheaths and culms (%)
T. Mae et al. / Field Crops Research 97 (2006) 227–237 Table 3 Biomass production, grain (rough rice) yield, harvest index (HI), plant N content, nitrogen-use efficiency (NUE) for biomass production and grain production, ratio of panicle-N to plant-N, and N concentrations of panicles, leaves and leaf sheaths and culms at harvest in Akita 63 and reference cultivars, i.e., Yukigesyou, Toyonishiki and Akitakomachi with high levels of N supply
234
T. Mae et al. / Field Crops Research 97 (2006) 227–237
235
Table 4 Yield components in Akita 63 and the reference cultivars, i.e., Yukigesyou, Toyonishiki and Akitakomachi grown with high levels of N supply Year
Cultivar
No. of panicles (m2)
No. of spikelets per panicle
Total no. of. spikelets (103 m2)
1000-kernel wt. (g)
Filled spikelets (%)
Sink capacity (g m2)
2000
Akita 63 Yukigesyou
456 24 432 29
91 2.0 * 80 1.0
41.5 2.8 * 34.6 2.8
31.2 0.1*** 23.1 0.0
78.5 4.8 ** 92.5 1.2
1293 86* 800 65
2001
Akita 63 Toyonishiki
455 18 436 39
94 1.2 * 79 5.9
42.6 1.5 ** 34.1 1.5
30.6 0.5*** 23.6 0.3
72.1 2.5 *** 95.0 0.7
1304 65*** 805 34
2002
Akita 63 Akitakomachi
465 13** 417 49
70 1.1 * 65 1.9
32.6 0.1 27.1 4.1
30.2 0.6*** 23.1 0.6
66.8 17.7 90.1 1.7
983 32** 624 78
Asterisks (*), (**) and (***) indicate significant differences between Akita 63 and the reference cultivar, Yukigesyou, Toyonishiki or Akitakomachi in the same treatment at the 5, 1 and 0.1% levels, respectively (t-test).
treatments. Contrary to the reference cultivars, the proportion of filled spikelets was low in Akita 63, for example, 67– 80% in high N treatment (Table 4). Reaccumulation of starch in the culms and leaf sheaths was remarkable from the middle to the late stage of ripening for all N treatments in the reference cultivars (Figs. 5a and 6). A similar difference in the reaccumulation of starch at the late stage of ripening was previously reported between a japonica-type cultivar, Nipponbare and an indica-type high-yielding cultivar, Miliyang 23 (Saito et al., 1991; Tsukaguchi et al., 1996). Reaccumulation of starch was remarkable in Nipponbare, but not in Miliyang 23. The high percentage of filled spikelets in the reference cultivars seems to be due to past selection pressure. It is likely that the pressure tended to select a cultivar having a trait of high percentage of fully ripened grains. As a result of such selection, the ratio of sink capacity to source capacity seems to have become small (Fig. 3a). The yield limit of Table 5 Agronmic nitrogen-use efficiency (NUE) and N fertilizer recovery efficiency at harvest in Akita 63 and the reference cultivars, i.e., Yukigesyou, Toyonishiki and Akitakomachi Year
N-treatment cultivar
2000
High level Akita 63 Yukigesyou
2002
Fertilizer recovery efficiency (%)
76* 60
59 57
109* 80
63 46
High level Akita 63 Toyonishiki
79* 64
78 57
Single application Akita 63 Toyonishiki
85* 68
96 53
High level Akita 63 Akitakomachi
63* 51
Single application Akita 63 Yukigesyou 2001
Agronomic NUE (g g-N1)
Asterisk (*) indicates significant difference between Akita 63 and the reference cultivar, i.e., Yukigesyou, Toyonishiki or Akitakomachi in the same treatment at the 5% level (t-test).
modern japonica-type cultivars bred in Japan can often be attributed to the shortage of sink capacity rather than to source capacity under favorable climatic conditions for rice cultivation as experienced in 2000 and 2001 in this study. The average percentage of filled spikelets of field-grown rice in Akita Prefecture increased from 78% in 1970s to 84% in 1990s (data from the Agricultural Statistics in Akita Prefecture, 2001). Although data are not shown here, the amount of root exudates was more abundant in Akita 63 than in the reference cultivars at the full-heading stage and root development was superior in Akita 63 to that in the reference cultivars, indicating that greater root activity might contribute to the high-yielding potential of Akita 63, too. The importance of root activity for high yields was previously discussed by Jiang et al. (1988). A high-yielding indica–japonica hybrid cultivar, Akenohoshi, was found to be superior in root development and its activity than a japonica-type standard cultivar, Nipponbare. Leaf N, Chl and Rubisco contents in the flag leaves did not largely differ between Akita 63 and the reference cultivar (Fig. 7). LAI at the full-heading stage in high N treatment was similar between Akita 63 and the reference cultivar (4.90 versus 5.31) in 2000 or larger in Akita 63 than in the reference cultivars in 2001 and 2002 (7.23 versus 6.09 and 4.97 versus 3.36, respectively). Therefore, photosynthetic potential throughout the ripening period was similar between Akita 63 and the reference cultivars or larger in Akita 63. 4.3. Higher N-use efficiency Data on N acquisition by rice plants show that high yields over 9 t ha1 of brown rice have been very limited (Honya, 1989; Kamata et al., 1978; Jinbo et al., 1987; Ying et al., 1998a,b). Therefore, the relationships between grain yield, yield components, LAI and plant N content have seldom been analyzed at such high yield levels. As shown in Fig. 1, there was no difference in the total dry matter production for a given amount of plant N between Akita 63 and the reference cultivars. This relationship indicates that there is no substantial difference in the physiological NUE for biomass production between Akita 63 and the reference
236
T. Mae et al. / Field Crops Research 97 (2006) 227–237
cultivars. However, the dry weight of panicles or the grain yield for a given amount of plant N was clearly greater in Akita 63 than in the reference cultivars (Fig. 1d and e), indicating that the physiological NUE for grain production is superior in Akita 63 as compared with the reference cultivars. This means that Akita 63 can produce more grains than the common and recent japonica-type cultivars with the same levels of N acquisition. The panicle dry weight for a given amount of plant N was 60.6–70.4 g g-N1 in Akita 63 and 56.9–60.1 g g-N1 in the reference cultivars for the high-N treatments, 70.2–94.7 g g-N1 in Akita 63 and 62.2– 74.4 g g-N1 in the reference cultivars for the standard-N treatments, and 80.4–84.7 g g-N1 in Akita 63 and 65.6– 67.2 g g-N1 for zero-N application treatment, respectively. Akita 63 has a larger sink capacity for a given amount of plant N (Fig. 1c) or for a given unit of LAI (Fig. 3a) as compared with the reference cultivars. These characteristics are greatly advantageous for Akita 63 to achieve a high yield. For a high yield, a larger sink capacity is required. Achievement of a larger sink capacity is generally realized by a larger amount of N application and is always accompanied by an increase in LAI, which often causes heavy self-shading and results in lodging. As the sink capacity for a given amount of plant N was greater in Akita 63 than in the reference cultivars, the amount of plant N required for achieving a sink capacity necessary for a high yield would be much less in Akita 63 than in the common cultivars (superior in physiological NUE for sink formation). Thus, the amount of N supplied can be much reduced in Akita 63. Agronomic NUE defined as grain yield for a unit amount of N supplied (fertilizer-N) and fertilizer-N recovery efficiency were greater in Akita 63 than in the reference cultivars for high N treatment and single application treatment (Table 5). Similar results were also obtained for other N treatments (data not shown). It should be noted that agronomic NUE was improved considerably in 2000 and slightly in 2001 by the use of the controlled release fertilizer in single application treatments (Table 5). Thus, with the use of controlled release fertilizer it is possible to reduce the total amount of N fertilizer supplied without substantial reduction of grain yield. Culture of Akita 63 with the use of controlled release N fertilizer would greatly reduce the environmental impact of N fertilization because of both high physiological NUE and agronomic NUE.
5. Conclusion Yield increase can be achieved either by increasing biomass production or yield capacity or both. It is controversial as to which component should be emphasized to further improve yield potential of current cultivars. Our results indicate that sink capacity rather than source capacity often limits the yield potential of current japonica-type cultivars under high-yield environmental conditions without
stresses. An increase in sink capacity, especially in grain size, is likely to be a useful way to increase the yield potential of modern japonica-type cultivars.
Acknowledgement This work was supported by a Grant-in-Aid for Scientific research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (12460028 to T.M). References Amano, T., Zhu, Q., Wang, Y., Inoue, N., Tanaka, H., 1993. Case studies on high yields of paddy rice in Jiangsu Province, China. Jpn. J. Crop Sci. 62, 267–274. Amano, T., Shi, C.J., Qin, D.L., Tsuda, M., Matsumoto, Y., 1996a. I. High yielding ability of Japonica F1 hybrid rice, Yu-Za 29. Jpn. J. Crop Sci. 65, 16–21. Amano, T., Shi, C.J., Qin, D.L., Tsuda, M., Matsumoto, Y., 1996b. II. Spikelets production of Japonica F1 hybrid rice, Yu-Za 29. Jpn. J. Crop Sci. 65, 22–28. Cassman, K.G., Peng, S., Olk, D.C., Ladha, J.K., Reichardt, W., Dobenmann, A., Singh, U., 1998. Opportunities for increased nitrogen-use efficiency from improved resource management in irrigated rice systems. Field Crops Res. 56, 7–39. Honya, K., 1989. Analysis of High-yielding Culture of Rice. Hakuyusha, Tokyo, Japan, 148 pp. (in Japanese). IRRI (International Rice Research Institute), 1995. Rice Facts. International Rice Research Institute, Los Banos, Philippines, p. 2. Jiang, C., Hirasawa, T., Ishihara, K., 1988. Physiological and ecological characteristics of high yielding varieties in rice plants. I. Yield and dry matter production. Jpn. J. Crop Sci. 57, 132–138. Jinbo, K., Yamazaki, E., Miura, H., 1987. The growth phase of 10 tons/ha rice plant and the cultivation method for high yield. Bull. Yamagata. Agric. Exp. Stn. 22, 55–64 (in Japanese). Kamata, K., Okadam, K., Yamaguchim, K., 1978. Studies on the high yielding culture of the early maturing rice plant. 1. Growth performance and yield components of the high yielding rice plant. Rep. Tohoku Br. Crop Sci. Soc. Jpn. 20, 140–142 in Japanese. Kobayashi, A., Koga, Y., Uchiyamada, H., Samoto, S., Horiuchi, H., Miura, K., Okuno, K., Fujita, Y., Uehara, Y., Ishizakam, S., Nakagaharam, M., Yamadam, T., Maruyamam, K., 1990. Breeding a new rice variety OOCHIKARA. Bull. Hokuriku Natl. Agric. Exp. Stn. 32, 85–104 (in Japanese). Ladha, J.K., Kirk, G.J.D., Bennett, J., Peng, S., Reddy, C.K., Reddy, P.M., Singh, U., 1998. Opportunities for increased nitrogen-use efficiency from improved lowland rice germplasm. Field Crops Res. 56, 41–71. Mae, T., Ohira, K., 1981. The remobilization of nitrogen related to leaf growth and senescence in rice plants (Oryza sativa L.) Plant Cell Physiol. 22, 1067–1074. Mae, T., Makino, A., Ohira, K., 1983. Changes in the amount of ribulose1,5-bisphosphate carboxylase synthesized and degraded during life span of rice leaf (Oryza sativa L.) Plant Cell Physiol. 24, 1079–1086. Makino, A., Nakano, H., Mae, T., 1994. Responses of ribulose-1,5-bisphosphate carboxylase, cytochrome f, and sucrose synthesis enzymes in rice leaves to leaf nitrogen and their relationships to photosynthesis. Plant Physiol. 105, 173–179. Nakano, H., Makino, A., Mae, T., 1995. Effects of panicle removal on the photosynthetic characteristics of the flag leaf of rice plants during the ripening stage. Plant Cell Physiol. 36, 653–659. Okawa, S., Makino, A., Mae, T., 2003. Effect of irradiance on the partitioning of assimilated carbon during the early phase of grain filling in rice. Ann. Bot. 92, 357–364.
T. Mae et al. / Field Crops Research 97 (2006) 227–237 Saito, K., Kashiwagi, N., Kinoshita, T., Ishihara, H., 1991. Characteristics of dry matter production process in high yielding rice varieties. IV. Dry matter accumulation in the panicle. Jpn. J. Crop Sci. 60, 255–263. Shoji, S., Gandeza, A.T., 1992. Properties of polyolefin-coated fertilizers. In: Shoji, S., Gandeza, A.T. (Eds.), Controlled Release Fertilizers with Polyolefin Resin Coating. Konno Printing Co., Ltd., Sendai, Japan, pp. 22–35. Somogyi, M., 1952. Notes on sugar determination. J. Biol. Chem. 195, 19– 23. Takita, T., 1988. Grain ripening of high yielding rice cultivar with very large grains. Jpn. J. Breed. 38, 443–448. Tsukaguchi, T., Horie, T., Ohnishi, M., 1996. Filling percentage of rice spikelets as affected by availability of non-structural carbohydrates at the initial phase of grain filling. Jpn. J. Crop Sci. 65, 445–452.
237
Williams, R.L., 1992. Physiological comparison of Amaroo and YRL 39. In: Breecher, H.G., Dunn, B.W. (Eds.), Yanco Agricultural Annual Report. Yanco Agricultural Institute, NSW, Australia, pp. 81–85. Ying, J., Peng, S., Yang, C., Zhou, N., Visperas, R.M., Cassman, K.G., 1998a. Comparison of high-yield rice in tropical and subtropical environments. II. Nitrogen accumulation and utilization efficiency. Field Crops Res. 57, 85–93. Ying, J., Peng, S., He, Q., Yang, H., Yang, C., Visperas, R.M., Cassman, K.G., 1998b. Comparison of high-yield rice in tropical and subtropical environments. I. Determinants of grain and dry matter yields. Field Crops Res. 57, 71–84. Yoshida, S., 1981. Yield and yield components. In: Fundamentals of Rice Crop Science, The International Rice Research Institute, Los Ban˜os, Philippines, pp. 60–63.
A large-grain rice cultivar, Akita 63, exhibits high yields with high physiological N-use efficiency Tadahiko Mae a,*, Ayako Inaba a, Yoshihiro Kaneta b, Satoshi Masaki c, Mizuo Sasaki a, Mayu Aizawa a, Shigenori Okawa a, Shuichi Hasegawa a, Amane Makino a a
Department of Applied Plant Science, School of Agricultural Science, Tohoku University, 1-1 Amamiyamachi, Tsutsumidori, Aoba-ku, Sendai 981-8555, Japan b Faculty of Bioresource Sciences, Akita Prefectural University, Shimosinjyou, Akita 010-0195, Japan c The Agricultural Experimental Station of Akita Prefecture, Aikawa Yuuwamachi Kawabe-gun Akita-ken 010-1231, Japan Received 20 May 2005; received in revised form 6 October 2005; accepted 7 October 2005
Abstract A new large-grain cultivar, Akita 63, of japonica-type rice exhibited high yields with high physiological nitrogen (N)-use efficiency for grain production. Akita 63 and three reference cultivars, Yukigesyou, Toyonishiki and/or Alitakomachi were grown in a field with different levels of N supply for three years. The grain yield of Akita 63 was 22–58% greater than that of the reference cultivars. The highest yield was 9.83 t ha1 of brown (hulled) rice (approximately 12.3 t ha1 of rough (unhulled) rice). The dry weight of the aboveground part and the number of spikelets at harvest, and the total leaf area (LAI) at the full-heading stage for a given amount of N accumulated in the aboveground part (plant N) did not differ between Akita 63 and the reference cultivars. The grain yield or panicle dry weight for a given amount of plant N at harvest and for a given unit of LAI were, however, greater in Akita 63 (superior in physiological N-use efficiency) than in the reference cultivars because of a higher proportion of dry matter partitioning into panicles in Akita 63 than in the reference cultivars. As the grain size of Akita 63 was about 35% larger than that of the reference cultivars, the sink capacity (the number of spikelets per unit land area grain size) for a given amount of plant N was much larger in Akita 63. Reaccumulation of starch in the culms and leaf sheaths was very limited in Akita 63, but remarkable in the reference cultivars in the late stage of grain filling. When pot-grown Akita 63 and the reference cultivar, Toyonishiki, at different stages of ripening were fed with 13CO2 and 13C partitioning into constituent organs was examined at harvest, the proportion of 13C partitioned into panicles was much higher in Akita 63 throughout the ripening period. These results indicate that Akita 63 is a new type of high yielding cultivar of japonica-type rice, superior in physiological N-use efficiency. # 2005 Elsevier B.V. All rights reserved. Keywords: High yield; Large grain; N-use efficiency; Rice; Sink capacity
1. Introduction Rice is the staple food grain for more than half of the world’s population. More than 90% of the world’s production of rice is in Asia. It is estimated that the world’s population will increase to a level 1.4–1.5 times the present population by 2025, this projected increase being mostly in * Corresponding author. Tel.: +81 22 717 8766; fax: +81 22 717 8765. E-mail address: [email protected] (T. Mae). 0378-4290/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2005.10.003
Asia (IRRI, 1995). It is, therefore, crucial to increase rice production within a relatively short period. With little scope for expanding land area, the increase in rice production must be achieved by an increase in yield from the land currently used for rice cultivation. In addition, interest in the environmental impact of N management practices is increasing (Cassman et al., 1998; Ladha et al., 1998). Therefore, it is important in rice cultivation to both increase the grain yield and limit the environmental impact of N management practices. One solution to this problem is to use
228
T. Mae et al. / Field Crops Research 97 (2006) 227–237
a high yielding cultivar, which exhibits a higher grain yield per unit amount of plant N acquired (higher physiological N-use efficiency (NUE) for grain production). However, selection or breeding of such cultivars has not been conducted. A number of field trials on high yielding of rice have been reported. For example, high yields of around 10 t ha1 of brown (hulled) rice (approximately 13 t ha1 of rough (unhulled) rice) have been reported in northern Japan (Honya, 1989; Kamata et al., 1978; Jinbo et al., 1987). A higher yield of 15–17 t ha1 of rough rice has been reported in Yunnan Province, China (Amano et al., 1996a,b; Ying et al., 1998a,b). Only limited information, however, is available on physiological NUE in such high levels of grain yield. Recently, the Agricultural Experimental Station of Akita Prefecture in northern Japan released a new largegrain cultivar of japonica-type rice, Akita 63. In test cultivations with standard levels of N fertilization at different locations and in different years, the average yield of Akita 63 was 18% higher than that of the present leading cultivar, Akitakomachi, in Akita Prefecture (Masaki et al., unpublished data), indicating that Akita 63 might be a new type of high-yielding cultivar with high NUE. In this study, we first examined the potentiality of Akita 63 for high yield and its physiological NUE, and then analyzed the factors responsible for high yield and NUE. Akita 63 and reference cultivars of japonica-type rice were grown in a field with different levels of N supply. Akita 63 recorded a grain yield of 9.83 t ha1 of brown rice (approximately 12.3 t ha1 of rough rice), which is close to the previously recorded highest yield in Japan, and exhibited high physiological NUE for grain production.
2. Materials and methods 2.1. Plant culture and sampling Akita 63 was grown with different levels of nitrogen supply in an experimental field of the Agricultural Experimental Station of Akita Prefecture (398340 N, 1408110 E, 16 m altitude) for three years from 2000 through 2002. As reference cultivars of japonica-type rice, a highyielding local cultivar, Yukigesyou, which has previously recorded the yield of around 10 t ha1 with a high level of N supply (290 kg N ha1) (Jinbo et al. (1987), a common (old) cultivar, Toyonishiki and/or a modern cultivar, Akitakomachi, which is the present leading cultivar in Akita prefecture and known as a tasty rice, were grown with the same N treatments. Difference in growth duration (165–175days) among these cultivars was within 7 days when they were grown in the experimental station. Plant height was almost same among these cultivars (culm length of 79–84 cm). Soil type was Gley soil (Eutric Gleysols; FAO) with pH 5.3, 31.6 g total C kg1, 2.4 g total N kg1 and 25.2 cmol kg1 cation exchange capacity. Phosphorus (4.3 P g m2 as fused
Table 1 Rates of nitrogen application for rice cultivation Year
Nitrogen application (g-N m2) N treatment
Basal dressing
Top dressing
Total
2000
High level Standard level Zero-N application Single application
2a + 6 b 4a 0 10b
2a 4 times 2a 1 time 0 0
16 6 0 10
2001
High level Standard level Zero-N application Single application
4a + 7 b 4a 0 10b + 4c
2a 2 times 2a 1 time 0 0
15 6 0 14
2002
High level Standard level
4a + 7 b 4a
2a 2 times 2a 2 times
15 8
a
Ammonium sulfate. Controlled release fertilizer (LP100 Type polyolefin-coated urea, Chisso Co., Japan). c Controlled release fertilizer (LSP100 Type polyolefin-coated urea, Chisso Co., Japan). b
phosphate) was applied to all plots 30 days before transplantation. Potassium was not supplied because of its sufficient level in the soil. Two to four levels of N fertilization were conducted (Table 1) by using ammonium sulfate and controlled release fertilizers (Type LP100 and Type LPS100 polyolefin-coated urea, Chisso Co., Japan). Both Type LP100 and Type LPS100 fertilizers release 80% of its total N content until 100 days after its application at any temperature between 20 and 30 8C. Type LP100 releases N to soil solution with a zero order reaction when cumulative N release is less than 60%, and then, with a first order reaction at the cumulative N release greater than 60% of its total N. The N release from Type LPS100 follows a sigmoid curve with time (Shoji and Gandeza, 1992). For the N-single application plots only controlled release fertilizer(s) was used as a basal application. Basal applications were conducted a week before transplantation. Weeds, insects and diseases were controlled as required to avoid yield loss. All the experimental plots were arranged in a randomized design with three replicates except for N-standard and zeroN application plots (two replicates) of Toyonishiki in 2001 due to the limitation of available land area. The size of each plot was 26.25 m2 (3.5 m wide and 7.5 m long). About 35-day-old seedlings were transplanted with a rice transplanter on a day in the middle of May at a hill spacing of 0.3 m 0.14 m (24 hills per m2) with four to five seedlings per hill. In this paper, the full-heading stage was defined as the time when 80% of the panicles had emerged. The crop was considered to have reached maturity when 95% of spikelets had turned yellow. Plant height, culm (panicle) number and leaf age were examined for 20 hills of each plot at appropriate intervals (2–4 weeks) throughout the culture period, and three hills with the mean culm (panicle) number from each plot were collected at each sampling for measurements of leaf area, dry weight of constituent organs and nitrogen content. The hills were separated into leaf
T. Mae et al. / Field Crops Research 97 (2006) 227–237
blades, culms plus leaf sheaths, panicles and others (dead parts and non-reproductive tillers). After measurement of the SPAD value of individual leaves (SPAD-502, Minolta, Tokyo, Japan), leaf area was measured with a leaf area meter (Type-AMM, Hayashi-Denko, Tokyo, Japan). All samples were oven-dried at 80–105 8C for several days, weighed and powdered. At the time of harvest, three additional hills with the mean panicle number from each plot were collected and hand-threshed for measurement of the number of filled and unfilled spikelets. The filled spikelets were separated by submerging the hand-threshed spikelets in a NaCl solution with a specific gravity (g m3) of 1.06. The filled spikelets were then hulled and oven-dried at 105 8C to a constant weight for determining grain dry weight. A survey of yield was carried out as follows: 80 hills were collected from the center part of each plot. Unhulled (rough) rice was obtained after reaping, threshing and wind selection. Rough rice of 80 hills was hulled and then put through a 1.8 mm sieve to remove any immature kernels. The weight of hulled rice (brown rice) was adjusted to a moisture content of 0.14 g H2O g1 fresh weight. A conversion factor of 1.25 was used for the estimation of rough rice weight from brown rice weight. 2.2. Chemical analysis N content was determined with Nessler’s reagent after Kjeldahl digestion of powdered samples with H2SO4 and H2O2 (Mae et al., 1983). Starch content was determined as described by Nakano et al. (1995). Powdered samples were extracted several times with 80% (v/v) ethanol. Starch in the ethanol-insoluble fraction was extracted with 0.5 M KOH and neutralized with 0.5 M HClO4. After removal of KClO4 by centrifugation, starch was digested with amyloglucosidase (EC3.2.1.3, from Rhizopus, Sigma, St. Louis). Glucose in the preparation was assayed by Nelson–Somogyi’s
229
method (Somogyi, 1952). The amount of starch was taken to be 0.9 times the amount of glucose. Ribulose-1,5bisphosphate carboxylase/oxygenase (Rubisco) and chlorophyll (Chl) contents were determined as described by Makino et al. (1994). Frozen leaf blades were homogenized in 50 mM Na-phosphate buffer (pH 7) containing 0.8% (v/v) 2-mercaptoethanol, 2 mM iodoacetic acid and 5% (v/v) glycerol at a leaf to buffer ratio of 1:9 (g:ml) using a chilled mortar and pestle with acid-washed quartz sand. Homogenates were used for the determination of Chl and Rubisco. 2.3.
13
CO2 feeding and
13
C determination
Rice was grown hydroponically in a greenhouse as described by Mae and Ohira (1981). Rice seeds of Akita 63 and a reference cultivar, Toyonishiki, were soaked in tap water for 2 days at 33 8C, and the seedlings were grown for 21 days on a plastic net floating on tap water with pH adjusted to 5.3. On day 23 from seeding, eight seedlings each were transplanted into 50 pots (25 pots for each cultivar) containing 3.7 l of nutrient solution. The basal nutrient solution contained 1.0 mM NH4NO3, 0.6 mM NaH2PO4, 0.3 mM K2SO4, 0.3 mM CaCl2, 0.3 mM MgCl2, 45 mM Fe-EDTA, 50 mM H3BO3, 9 mM MnSO4, 0.3 mM CuCl2, 0.7 mM ZnSO4 and 0.1 mM Na2MoO4. The nutrient solution was renewed once a week and pH was adjusted to 5.2 with 2 M HCl. The strength of the nutrient solution ranged from 1/4 to full-strength depending on the growth period: 1/4-strength, 0–2 weeks after transplantation; 1/2strength, 2–4 weeks after transplantation; 3/4-strength, 4–8 weeks after transplantation; full-strength, 8 weeks after transplantation to heading; 1/4-strength, heading to harvest. Heading time when panicles had emerged from 40–50% of the reproductive tillers was 114 days after seeding for Akita 63 and 117 days for Toyonishiki, respectively. The time of harvest was 50 days after heading time (DAH). Plants were
Table 2 Grain yields (brown rice) of Akita 63 and the reference cultivars, i.e., Yukigesyou, Toyonishiki and Akitakomachi N treatment
Grain yield (t ha1) Akita 63
Yukigeshou
2000 High level Standard level Zeo-N application Single application
9.83 0.66 7.88 0.44 5.79 0.75 8.67 0.59
2001 High level Standard level Zero-N application Single application
9.39 0.31 (123)** 6.94 (141) 4.34 (140) 9.54 0.30 (135)*
2002 High level Standard level
7.46 0.35 (122)* 5.79 0.66 (144)*
(129)** (155)*** (158)* (135)*
7.63 0.57 5.10 0.06 3.66 0.14 6.41 0.10
Akitakomachi (100) (100) (100) (100)
Toyonishiki
5.43 0.27 (106) 4.26 0.64 (116)
7.65 0.38 (100) 4.93 (100) 3.09 (100) 7.60 0.59 (100) 6.11 0.39 (100) 4.03 0.24 (100)
Data are the mean standard deviation of three replicates except for N-standard level and zero-N application in 2001 (two replicates). Values in the parentheses show the percentage of the value of Yukigesyou (2000), Toyonishiki (2001) or Akitakomachi (2002) for the same treatment. Asterisks (*), (**) and (***) indicate significant differences between Akita 63 and the reference cultivar at the 5, 1 and 0.1% levels (t-test), respectively.
230
T. Mae et al. / Field Crops Research 97 (2006) 227–237
Fig. 1. Relationships between total dry weight (a), number of total spikelets (b), sink capacity* (c), panicle dry weight (d) or grain (brown rice) yield (e) and plant nitrogen content per unit land area at harvest in Akita 63 and the reference cultivars, i.e., Yukigeshou, Toyonishiki and Akitakomachi. (~) Akita 63 in 2000, (*) Akita 63 in 2001, (&) Akita 63 in 2002, (*) Yukigeshou in 2000, (&) Toyonishiki in 2001, (4) Akitakomachi in 2000 and (^) Akitakomachi in 2002. *Sink capacity: number of total spikelets per unit land area (m2) 1000-grain weight of each cultivar.
fed with 13CO2 at 5, 15, 20, 25, 30, 35 and 40 DAH as described by Okawa et al. (2003). One day before labeling, one pot each was transferred into a growth chamber (55 cm 55 cm 120 cm, EYELATORON FLI-301NH, Tokyo). The chamber was maintained under a 14 h (06:00– 20:00 h) photoperiod, day/night temperature of 25/20 8C, 60% relative humidity and a photosynthetic photon flux density of 850 mmol quanta m2 s1 at canopy height. Irradiance was provided by a combination of a metal halide lamp (Yoko DR, Toshiba, Tokyo), high-output fluorescent lamps (FL40ss-EX, Toshiba/Panasonic, Tokyo) and TrueLite lamps (Doro-Test, North Bergen, NJ). The plants were fed with 13CO2 for 3 h (10:00–13:00 h) at each feeding. 13 CO2 gas was produced by the reaction of HCl and Ba13CO3. Hydrochloric acid was added at a constant rate
(10 ml h1) to the Ba13CO3 (99 atom%, 10 g) suspension (200 ml) in the chamber. During feeding with 13CO2, airflow was stopped by switching off the ventilator and sealing the duct. At the end of feeding period, the plants were transferred to a greenhouse and grown there until the time of harvest. At the time of harvest plants were divided into panicles, culms and leaf sheaths, leaf blades and roots. Panicles were further separated into grains on the primary rachises and those on the remaining ones. Samples were oven-dried, weighed and ground to a fine powder in a vibrating mill. The relative amount of labeled carbon in each fraction was calculated with the following equation: (the carbon content of organ [(13C atom% of sample 13C atom% of natural abundance)]/100. Carbon content of dry matter was 42.7% for panicles, 44.2% for leaf blades, 42.6%
T. Mae et al. / Field Crops Research 97 (2006) 227–237
231
Fig. 2. Relationship between leaf area index and plant nitrogen content at the full-heading stage in Akita 63 and the reference cultivars, i.e., Yukigeshou, Toyonishiki and Akitakomachi. (~) Akita 63 in 2000, (*) Akita 63 in 2001, (&) Akita 63 in 2002, (*) Yukigeshou in 2000, (&) Toyonishiki in 2001, (4) Akitakomachi in 2000 and (^) Akitakomachi in 2002. *Sink capacity: number of total spikelets per unit land area (m2) 1000 grain weight of each cultivar.
for leaf sheaths and 41.7% for culms, respectively. Measurement of 13C atom% in the samples was performed by a combustion method using an infrared 13CO2 analyzer (EX-130S; Japan Spectoscopic Co. Ltd., Tokyo).
3. Results Table 2 shows the grain (brown rice) yields of Akita 63 and the reference cultivars. The yield of Akita 63 was 22– 58% higher than that of the reference cultivars. The highest yield of Akita 63 was 9.83 t ha1 of brown rice (approximately 12.3 t ha1 of rough rice), which was obtained with a high level of N supply in 2000, followed by 9.54 t ha1 in 2001. The difference in yield between Akita 63 and the reference cultivars was more pronounced in the plants grown with a lesser amount of N supply. The yield of Akita 63 was higher in 2000 and 2001 than in 2002, the climatic conditions during the culture period being better suited for rice cultivation in 2000 and 2001 than in 2002. The relationships between biomass production, number of total spikelets, sink capacity, panicle dry weight, grain yield and plant N content per unit land area were analyzed. Data obtained from all plots throughout the three-year period were used for analyses. The relationship between the total dry matter production and plant N content at harvest is shown in Fig. 1a. No substantial difference was found in their relationship between Akita 63 and the reference cultivars. The relationship between the number of total
Fig. 3. Relationships between sink capacity (a) or grain (brown rice) yield (b) and leaf area index at the full-heading stage in Akita 63 and the reference cultivars, i.e., Yukigeshou, Toyonishiki and Akitakomachi. (~) Akita 63 in 2000, (*) Akita 63 in 2001, (&) Akita 63 in 2002, (*) Yukigeshou in 2000, (&) Toyonishiki in 2001, (4) Akitakomachi in 2000 and (^) Akitakomachi in 2002. *Sink capacity: number of total spikelets per unit land area (m2) 1000 grain weight of each cultivar.
spikelets and plant N content per unit land area at harvest is shown in Fig. 1b. No difference was found between Akita 63 and the reference cultivars. Different from the above relationships, there was a clear difference between Akita 63 and the reference cultivars in the relationship between sink capacity (number of total spikelet per unit land area a thousand-grain (brown rice) weight) and plant N content (Fig. 1c). Sink capacity for a given amount of plant N content was 35–40% larger in Akita 63 than in the reference cultivars. The relationship between the dry weight of panicles and plant N content is shown in Fig. 1d. The dry weight of panicles for a given amount of plant N was 13– 23% greater in Akita 63 than in the reference cultivars. The
232
T. Mae et al. / Field Crops Research 97 (2006) 227–237
Fig. 4. Partitioning of 13C into constituent organs at maturity in Akita 63 and the reference cultivar Toyonishiki after photosynthetic 13CO2 assimilation at different stages of ripening. Pot-grown plants were fed with 13CO2 for a few hours at different stages of ripening. Thereafter, the plants were allowed to grow until maturity. At the time of harvest, the plants were divided into constituent organs, i.e., panicles, culms and leaf sheaths (white), leaf blades (black) and roots. Spikelets were further separated into those on the primary (gray) and the secondary rachis (lattice)) branches and their 13C contents were examined. The data are expressed as percentages of total 13C in top part.
relationship between the grain (brown rice) yield and plant N content is shown in Fig. 1e. The grain yield for a given amount of plant N content was greater in Akita 63 than in the reference cultivars. The difference was more pronounced in the plants with less amounts of plant N content. Fig. 2 shows the relationship between leaf area index (LAI) and plant N content at the full-heading stage. The difference in their relationship between Akita 63 and the reference cultivars was very small. Although the data on the relationship between sink capacity and LAI at the fullheading stage (Fig. 3a) and those on the relationship between grain yield and LAI (Fig. 3b) were somewhat
scattered, there were considerable differences in their relationships between Akita 63 and the reference cultivars. Sink capacity and grain yield for a given unit of LAI were much greater in Akita 63 than in the reference cultivars. The allocation of 13C into constituent organs at the time of harvest was examined after 13CO2 feeding of pot-grown Akita 63 and the reference cultivar Toyonishiki at different stages of ripening (Fig. 4). The proportion of 13C partitioned into panicles (spikelets) was clearly higher in Akita 63 than in the reference cultivar throughout the ripening period. Fig. 5a shows the changes in dry weight and starch content of culms and leaf sheaths during the ripening period in Akita 63
Fig. 5. Changes in the contents of dry weight and starch in the culms and leaf sheaths (a), and changes in the SPAD value, leaf-nitrogen concentration and leaf area index (b) during ripening period of Akita63 and Toyonishiki (high level-N treatment in 2001). Asterisks (*) and (**) indicate significant differences between Akita63 and Toyonishiki at the 5 and 1% levels (t-test), respectivity.
T. Mae et al. / Field Crops Research 97 (2006) 227–237
233
Fig. 6. Starch contents in the culms and leaf sheaths of Akita 63 and the reference cultivars, i.e., Yukigeshou, Toyonishiki and Akitakomachi at the full-heading and harvest stages (high level-N treatment). Closed columns indicate Akita 63 and open columns indicate the reference cultivars, i.e., Yukigesyou (2000), Toyonishiki (2001) and Akitakomachi (2002), respectively. Asterisks (*) and (**) indicate significant differences between Akita 63 and the reference cultivar at 5 and 1% levels (t-test), respectively.
and the reference cultivar Toyonishiki grown with a high level of N supply in 2001. In the reference cultivar, starch content decreased once at the early stage of ripening and then increased considerably from the middle stage through the late stage of ripening. In Akita 63, starch content decreased in the middle stage of ripening and reaccumulation of starch was slight at the late stage of ripening. Starch content in the culms and leaf sheaths was much lower at harvest than at full-heading stage in Akita 63 throughout the three years, but the content was higher at harvest than at the full-heading stage in the reference cultivars in 2000 and 2002 or the same in 2001 (Fig. 6). The increase in panicle dry weight ceased earlier in the reference cultivars than in Akita 63 during ripening (data not shown). Contents of leaf N, Chl and Rubisco in flag leaves at the full-heading stage were examined in Akita 63 and the reference cultivar Toyonishiki (Fig. 7). No difference was found in their contents between Akita 63 and Toyonishiki, irrespective of N treatments. Changes in the SPAD value and leaf N concentration in flag leaves and LAI of Akita 63 and Toyonishiki grown with a high level of N supply during ripening are shown in Fig. 5b. The SPAD value and leaf N content of flag leaves decreased in similar manners during the ripening period between Akita 63 and Toyonishiki. LAI was larger in Akita 63 than in the reference cultivar throughout ripening period.
4. Discussion 4.1. High-yielding cultivar Grain yield of field grown rice depends on many factors such as climatic conditions, cultivar, soil type, fertilizer management, skill of culture, control of weeds and insects, etc. Therefore, it is never easy to achieve high yields close to the yield potential of a cultivar. High yields of 13–17 t ha1 of rough rice have been reported in China (Amano et al., 1993, 1996a; Ying et al., 1998a) and Australia (Williams, 1992). The highest yield of Akita 63 (9.83 t ha1 of brown rice, approximately 12.3 t ha1 of rough rice) obtained in
Fig. 7. Contents of leaf nitrogen, chlorophyll and Rubisuco in the flag leaves of Akita 63 and Toyonishiki at the full-heading stage. The vertical bars indicate the S.D. (n = 3). Differences were not significant between Akita 63 and Toyoniishiki for all three parameters in all N-treatments.
Asterisks (*), (**) and (***) indicate significant differences between Akita 63 and the reference cultivar, Yukigesyou, Toyonishiki or Akitakomachi in the same treatment at the 5, 1 and 0.1% levels, respectively (ttest).
0.52 0.49 1.51 1.29 1.15 1.15 0.58*** 0.49 61 66 108 122 0.50 0.47 937 44 * 765 53 Akita 63 Akitakomachi 2002
1646 204 1419 93
15.31 0.79 11.66 1.29
0.54 0.54 1.37 1.14 1.14 1.13 0.55** 0.47 64 65 110 121 0.50 0.46 1173 39 ** 956 48 Akita 63 Toyonishiki 2001
2017 119 1792 172
18.41 2.07 14.87 1.39
0.44 0.50 1.31 1.41 1.06 1.04 0.59** 0.47 76 * 60 119 126 0.55* 0.41 1225 79 ** 954 72 Akita 63 Yukigesyou 2000
1912 60 2003 135
16.09 0.62 15.88 0.87
Leaves (%)
N concentration
Panicle (%)
Ratio of panicle-N to plant-N Grain product (g g-N1) Biomass product (g g-N1)
NUE for
N content (g-N m2) HI Grain yield (g m2) Dry matter (g m2)
Yield increase can be achieved either by increasing biomass production per unit land area or harvest index (HI) or both (Yoshida, 1981). Biomass production and N acquisition were not different between Akita 63 and the reference cultivars in 2000 and were larger in Akita 63 than in the reference cultivars in 2001 and 2002 for high N treatments (Table 3) as well as for other N treatments (data not shown). HI, defined as the ratio of grain (rough rice) dry weight to the total aboveground dry weight, was greater in Akita 63 than in the reference cultivars for all N treatments throughout the three-year period (0.43–0.64 versus 0.35– 0.48), as well as the ratio of panicle dry weight to the total aboveground dry weight (0.54–0.61 versus 0.41–0.51). The ratio of panicle N content to the total aboveground N content was also greater in Akita 63 (Table 3). The higher HI and the ratio of panicle N content to the total aboveground N content in Akita 63 can be attributed to its larger sink capacity per unit amount of plant N (Fig. 1c) and an efficient translocation of dry matter and nutrients into spikelets during the ripening period (Figs. 4, 5a and 6). In the 13C tracer experiment more efficient translocation of photosynthates into panicles was observed throughout the ripening period in Akita 63 (Fig. 4). It is not known whether an efficient translocation of photosynthate into panicles in Akita 63 is simply due to its large sink or includes some other factor(s), which promotes its efficient translocation of dry matter into panicles (Table 4). Reaccumulation of starch was very small in Akita 63 (Figs. 5a and 6). There was sufficient space in panicles for further accumulation of dry matter in Akita 63, but not in the reference cultivars from the middle to the late stage of ripening because the proportion of filled spikelets in the reference cultivars was very high over 90% for all N
Cultivar
4.2. Higher harvest index
Year
this study was close to the previously recorded highest yield (10.52 t ha1 of brown rice (about 13.3 t ha1 of rough rice)) of rice in Japan, which is almost double the current nation’s average yield (Honya, 1989). The yield of Akita 63 was 22– 58% higher than that of the reference cultivars. These results clearly indicate that Akita 63 is a new high-yielding cultivar. In addition, Akita 63 is able to grow under relatively cold climatic conditions as experienced in Akita Prefecture, the northern part of the main island of Japan, where modern high-yielding cultivars such as indica-types or japonica– indica hybrids can hardly realize their potential because of their sensitivity to cold in early spring and autumn. It has been reported that a large-grain cultivar, Oochikara, which is one of the parent cultivars of Akita 63, showed an average yield about 15% higher than those of common cultivars under warm temperate climatic conditions (Takita, 1988; Kobayashi et al., 1990). Those results and ours indicate that the trait of large-grain size and/or some other unknown traits originating from Oochikara might contribute to the highyielding characteristic of Akita 63.
Sheaths and culms (%)
T. Mae et al. / Field Crops Research 97 (2006) 227–237 Table 3 Biomass production, grain (rough rice) yield, harvest index (HI), plant N content, nitrogen-use efficiency (NUE) for biomass production and grain production, ratio of panicle-N to plant-N, and N concentrations of panicles, leaves and leaf sheaths and culms at harvest in Akita 63 and reference cultivars, i.e., Yukigesyou, Toyonishiki and Akitakomachi with high levels of N supply
234
T. Mae et al. / Field Crops Research 97 (2006) 227–237
235
Table 4 Yield components in Akita 63 and the reference cultivars, i.e., Yukigesyou, Toyonishiki and Akitakomachi grown with high levels of N supply Year
Cultivar
No. of panicles (m2)
No. of spikelets per panicle
Total no. of. spikelets (103 m2)
1000-kernel wt. (g)
Filled spikelets (%)
Sink capacity (g m2)
2000
Akita 63 Yukigesyou
456 24 432 29
91 2.0 * 80 1.0
41.5 2.8 * 34.6 2.8
31.2 0.1*** 23.1 0.0
78.5 4.8 ** 92.5 1.2
1293 86* 800 65
2001
Akita 63 Toyonishiki
455 18 436 39
94 1.2 * 79 5.9
42.6 1.5 ** 34.1 1.5
30.6 0.5*** 23.6 0.3
72.1 2.5 *** 95.0 0.7
1304 65*** 805 34
2002
Akita 63 Akitakomachi
465 13** 417 49
70 1.1 * 65 1.9
32.6 0.1 27.1 4.1
30.2 0.6*** 23.1 0.6
66.8 17.7 90.1 1.7
983 32** 624 78
Asterisks (*), (**) and (***) indicate significant differences between Akita 63 and the reference cultivar, Yukigesyou, Toyonishiki or Akitakomachi in the same treatment at the 5, 1 and 0.1% levels, respectively (t-test).
treatments. Contrary to the reference cultivars, the proportion of filled spikelets was low in Akita 63, for example, 67– 80% in high N treatment (Table 4). Reaccumulation of starch in the culms and leaf sheaths was remarkable from the middle to the late stage of ripening for all N treatments in the reference cultivars (Figs. 5a and 6). A similar difference in the reaccumulation of starch at the late stage of ripening was previously reported between a japonica-type cultivar, Nipponbare and an indica-type high-yielding cultivar, Miliyang 23 (Saito et al., 1991; Tsukaguchi et al., 1996). Reaccumulation of starch was remarkable in Nipponbare, but not in Miliyang 23. The high percentage of filled spikelets in the reference cultivars seems to be due to past selection pressure. It is likely that the pressure tended to select a cultivar having a trait of high percentage of fully ripened grains. As a result of such selection, the ratio of sink capacity to source capacity seems to have become small (Fig. 3a). The yield limit of Table 5 Agronmic nitrogen-use efficiency (NUE) and N fertilizer recovery efficiency at harvest in Akita 63 and the reference cultivars, i.e., Yukigesyou, Toyonishiki and Akitakomachi Year
N-treatment cultivar
2000
High level Akita 63 Yukigesyou
2002
Fertilizer recovery efficiency (%)
76* 60
59 57
109* 80
63 46
High level Akita 63 Toyonishiki
79* 64
78 57
Single application Akita 63 Toyonishiki
85* 68
96 53
High level Akita 63 Akitakomachi
63* 51
Single application Akita 63 Yukigesyou 2001
Agronomic NUE (g g-N1)
Asterisk (*) indicates significant difference between Akita 63 and the reference cultivar, i.e., Yukigesyou, Toyonishiki or Akitakomachi in the same treatment at the 5% level (t-test).
modern japonica-type cultivars bred in Japan can often be attributed to the shortage of sink capacity rather than to source capacity under favorable climatic conditions for rice cultivation as experienced in 2000 and 2001 in this study. The average percentage of filled spikelets of field-grown rice in Akita Prefecture increased from 78% in 1970s to 84% in 1990s (data from the Agricultural Statistics in Akita Prefecture, 2001). Although data are not shown here, the amount of root exudates was more abundant in Akita 63 than in the reference cultivars at the full-heading stage and root development was superior in Akita 63 to that in the reference cultivars, indicating that greater root activity might contribute to the high-yielding potential of Akita 63, too. The importance of root activity for high yields was previously discussed by Jiang et al. (1988). A high-yielding indica–japonica hybrid cultivar, Akenohoshi, was found to be superior in root development and its activity than a japonica-type standard cultivar, Nipponbare. Leaf N, Chl and Rubisco contents in the flag leaves did not largely differ between Akita 63 and the reference cultivar (Fig. 7). LAI at the full-heading stage in high N treatment was similar between Akita 63 and the reference cultivar (4.90 versus 5.31) in 2000 or larger in Akita 63 than in the reference cultivars in 2001 and 2002 (7.23 versus 6.09 and 4.97 versus 3.36, respectively). Therefore, photosynthetic potential throughout the ripening period was similar between Akita 63 and the reference cultivars or larger in Akita 63. 4.3. Higher N-use efficiency Data on N acquisition by rice plants show that high yields over 9 t ha1 of brown rice have been very limited (Honya, 1989; Kamata et al., 1978; Jinbo et al., 1987; Ying et al., 1998a,b). Therefore, the relationships between grain yield, yield components, LAI and plant N content have seldom been analyzed at such high yield levels. As shown in Fig. 1, there was no difference in the total dry matter production for a given amount of plant N between Akita 63 and the reference cultivars. This relationship indicates that there is no substantial difference in the physiological NUE for biomass production between Akita 63 and the reference
236
T. Mae et al. / Field Crops Research 97 (2006) 227–237
cultivars. However, the dry weight of panicles or the grain yield for a given amount of plant N was clearly greater in Akita 63 than in the reference cultivars (Fig. 1d and e), indicating that the physiological NUE for grain production is superior in Akita 63 as compared with the reference cultivars. This means that Akita 63 can produce more grains than the common and recent japonica-type cultivars with the same levels of N acquisition. The panicle dry weight for a given amount of plant N was 60.6–70.4 g g-N1 in Akita 63 and 56.9–60.1 g g-N1 in the reference cultivars for the high-N treatments, 70.2–94.7 g g-N1 in Akita 63 and 62.2– 74.4 g g-N1 in the reference cultivars for the standard-N treatments, and 80.4–84.7 g g-N1 in Akita 63 and 65.6– 67.2 g g-N1 for zero-N application treatment, respectively. Akita 63 has a larger sink capacity for a given amount of plant N (Fig. 1c) or for a given unit of LAI (Fig. 3a) as compared with the reference cultivars. These characteristics are greatly advantageous for Akita 63 to achieve a high yield. For a high yield, a larger sink capacity is required. Achievement of a larger sink capacity is generally realized by a larger amount of N application and is always accompanied by an increase in LAI, which often causes heavy self-shading and results in lodging. As the sink capacity for a given amount of plant N was greater in Akita 63 than in the reference cultivars, the amount of plant N required for achieving a sink capacity necessary for a high yield would be much less in Akita 63 than in the common cultivars (superior in physiological NUE for sink formation). Thus, the amount of N supplied can be much reduced in Akita 63. Agronomic NUE defined as grain yield for a unit amount of N supplied (fertilizer-N) and fertilizer-N recovery efficiency were greater in Akita 63 than in the reference cultivars for high N treatment and single application treatment (Table 5). Similar results were also obtained for other N treatments (data not shown). It should be noted that agronomic NUE was improved considerably in 2000 and slightly in 2001 by the use of the controlled release fertilizer in single application treatments (Table 5). Thus, with the use of controlled release fertilizer it is possible to reduce the total amount of N fertilizer supplied without substantial reduction of grain yield. Culture of Akita 63 with the use of controlled release N fertilizer would greatly reduce the environmental impact of N fertilization because of both high physiological NUE and agronomic NUE.
5. Conclusion Yield increase can be achieved either by increasing biomass production or yield capacity or both. It is controversial as to which component should be emphasized to further improve yield potential of current cultivars. Our results indicate that sink capacity rather than source capacity often limits the yield potential of current japonica-type cultivars under high-yield environmental conditions without
stresses. An increase in sink capacity, especially in grain size, is likely to be a useful way to increase the yield potential of modern japonica-type cultivars.
Acknowledgement This work was supported by a Grant-in-Aid for Scientific research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (12460028 to T.M). References Amano, T., Zhu, Q., Wang, Y., Inoue, N., Tanaka, H., 1993. Case studies on high yields of paddy rice in Jiangsu Province, China. Jpn. J. Crop Sci. 62, 267–274. Amano, T., Shi, C.J., Qin, D.L., Tsuda, M., Matsumoto, Y., 1996a. I. High yielding ability of Japonica F1 hybrid rice, Yu-Za 29. Jpn. J. Crop Sci. 65, 16–21. Amano, T., Shi, C.J., Qin, D.L., Tsuda, M., Matsumoto, Y., 1996b. II. Spikelets production of Japonica F1 hybrid rice, Yu-Za 29. Jpn. J. Crop Sci. 65, 22–28. Cassman, K.G., Peng, S., Olk, D.C., Ladha, J.K., Reichardt, W., Dobenmann, A., Singh, U., 1998. Opportunities for increased nitrogen-use efficiency from improved resource management in irrigated rice systems. Field Crops Res. 56, 7–39. Honya, K., 1989. Analysis of High-yielding Culture of Rice. Hakuyusha, Tokyo, Japan, 148 pp. (in Japanese). IRRI (International Rice Research Institute), 1995. Rice Facts. International Rice Research Institute, Los Banos, Philippines, p. 2. Jiang, C., Hirasawa, T., Ishihara, K., 1988. Physiological and ecological characteristics of high yielding varieties in rice plants. I. Yield and dry matter production. Jpn. J. Crop Sci. 57, 132–138. Jinbo, K., Yamazaki, E., Miura, H., 1987. The growth phase of 10 tons/ha rice plant and the cultivation method for high yield. Bull. Yamagata. Agric. Exp. Stn. 22, 55–64 (in Japanese). Kamata, K., Okadam, K., Yamaguchim, K., 1978. Studies on the high yielding culture of the early maturing rice plant. 1. Growth performance and yield components of the high yielding rice plant. Rep. Tohoku Br. Crop Sci. Soc. Jpn. 20, 140–142 in Japanese. Kobayashi, A., Koga, Y., Uchiyamada, H., Samoto, S., Horiuchi, H., Miura, K., Okuno, K., Fujita, Y., Uehara, Y., Ishizakam, S., Nakagaharam, M., Yamadam, T., Maruyamam, K., 1990. Breeding a new rice variety OOCHIKARA. Bull. Hokuriku Natl. Agric. Exp. Stn. 32, 85–104 (in Japanese). Ladha, J.K., Kirk, G.J.D., Bennett, J., Peng, S., Reddy, C.K., Reddy, P.M., Singh, U., 1998. Opportunities for increased nitrogen-use efficiency from improved lowland rice germplasm. Field Crops Res. 56, 41–71. Mae, T., Ohira, K., 1981. The remobilization of nitrogen related to leaf growth and senescence in rice plants (Oryza sativa L.) Plant Cell Physiol. 22, 1067–1074. Mae, T., Makino, A., Ohira, K., 1983. Changes in the amount of ribulose1,5-bisphosphate carboxylase synthesized and degraded during life span of rice leaf (Oryza sativa L.) Plant Cell Physiol. 24, 1079–1086. Makino, A., Nakano, H., Mae, T., 1994. Responses of ribulose-1,5-bisphosphate carboxylase, cytochrome f, and sucrose synthesis enzymes in rice leaves to leaf nitrogen and their relationships to photosynthesis. Plant Physiol. 105, 173–179. Nakano, H., Makino, A., Mae, T., 1995. Effects of panicle removal on the photosynthetic characteristics of the flag leaf of rice plants during the ripening stage. Plant Cell Physiol. 36, 653–659. Okawa, S., Makino, A., Mae, T., 2003. Effect of irradiance on the partitioning of assimilated carbon during the early phase of grain filling in rice. Ann. Bot. 92, 357–364.
T. Mae et al. / Field Crops Research 97 (2006) 227–237 Saito, K., Kashiwagi, N., Kinoshita, T., Ishihara, H., 1991. Characteristics of dry matter production process in high yielding rice varieties. IV. Dry matter accumulation in the panicle. Jpn. J. Crop Sci. 60, 255–263. Shoji, S., Gandeza, A.T., 1992. Properties of polyolefin-coated fertilizers. In: Shoji, S., Gandeza, A.T. (Eds.), Controlled Release Fertilizers with Polyolefin Resin Coating. Konno Printing Co., Ltd., Sendai, Japan, pp. 22–35. Somogyi, M., 1952. Notes on sugar determination. J. Biol. Chem. 195, 19– 23. Takita, T., 1988. Grain ripening of high yielding rice cultivar with very large grains. Jpn. J. Breed. 38, 443–448. Tsukaguchi, T., Horie, T., Ohnishi, M., 1996. Filling percentage of rice spikelets as affected by availability of non-structural carbohydrates at the initial phase of grain filling. Jpn. J. Crop Sci. 65, 445–452.
237
Williams, R.L., 1992. Physiological comparison of Amaroo and YRL 39. In: Breecher, H.G., Dunn, B.W. (Eds.), Yanco Agricultural Annual Report. Yanco Agricultural Institute, NSW, Australia, pp. 81–85. Ying, J., Peng, S., Yang, C., Zhou, N., Visperas, R.M., Cassman, K.G., 1998a. Comparison of high-yield rice in tropical and subtropical environments. II. Nitrogen accumulation and utilization efficiency. Field Crops Res. 57, 85–93. Ying, J., Peng, S., He, Q., Yang, H., Yang, C., Visperas, R.M., Cassman, K.G., 1998b. Comparison of high-yield rice in tropical and subtropical environments. I. Determinants of grain and dry matter yields. Field Crops Res. 57, 71–84. Yoshida, S., 1981. Yield and yield components. In: Fundamentals of Rice Crop Science, The International Rice Research Institute, Los Ban˜os, Philippines, pp. 60–63.