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The effect of photoperiod on interval between panicle initiation and flowering in rice
Field Crops Research 57 Ž1998. 301–307
The effect of photoperiod on interval between panicle initiation and flowering in rice Xinyou Yin a
a,b,)
, Martin J. Kropff
a,c,d
Department of Theoretical Production Ecology, Agricultural UniÕersity, P.O. Box 430, 6700 AK Wageningen, Netherlands b Department of Agronomy, Jiangxi Agricultural UniÕersity, 330045 Nanchang, China c DLO-Research Institute for Agrobiology and Soil Fertility, P.O. Box 14, 6700 AA Wageningen, Netherlands d The International Rice Research Institute, P.O. Box 933, 1099 Manila, Philippines Received 24 September 1997; revised 26 December 1997; accepted 27 December 1997
Abstract An understanding of response of crops to photoperiod is essential for accurate prediction of their phenological development. This study aimed to determine whether photoperiod influences the duration from panicle initiation ŽPI. to flowering in rice Ž Oryza satiÕa L... In a greenhouse experiment, plants of 12 cultivars were grown under three short-day ŽSD. conditions 10, 11 and 12 h dayy1 or under three long-day ŽLD. conditions 13, 14, and 15 h dayy1 until PI, after which half of the plants at SD were transferred to a 3-h longer photoperiod and half of the plants at LD were moved to a 3-h shorter photoperiod. Duration from PI to flowering was positively correlated with the photoperiod experienced after PI; the effect of a 3-h change in photoperiod varied from negligible in some cases to more than 10 days in others. No consistent carryover effect of photoperiod before PI on the PI-to-flowering duration was detected. As expected, the total main-culm leaf number was influenced by photoperiod before PI, but not thereafter. Although the leaf number varied greatly both among cultivars and among pre-PI photoperiods, the number of unexpanded leaves at PI was nearly constant, with an average of about three leaves. This study further supports the earlier experimental finding that rice photoperiod sensitivity continues some days after PI, suggesting the inadequacy of the assumption in crop simulation model CERES-Rice that the PI-to-flowering duration is influenced only by a carryover effect of pre-PI photoperiod. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Rice Ž Oryza satiÕa.; Flowering; Panicle initiation; Photoperiod; Leaf number
1. Introduction An understanding of response of crops to photoperiod is essential to accurate modeling of their phenological events. In rice, the time to flowering is strongly affected by photoperiod. In general, a short )
Corresponding author. Fax: q31-317-484892; e-mail: [email protected].
photoperiod accelerates and a long photoperiod delays flowering ŽVergara and Chang, 1985.. Rice plants, however, do not respond to photoperiod during the entire vegetative period from sowing to flowering ŽVergara and Chang, 1985.. Roberts and Summerfield Ž1987. divided the vegetative period into three phases: the pre-inductive, the inductive, and the post-inductive phase. Plants are sensitive to photoperiod only during the inductive phase.
0378-4290r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 7 8 - 4 2 9 0 Ž 9 8 . 0 0 0 7 4 - 4
302
X. Yin, M.J. Kropffr Field Crops Research 57 (1998) 301–307
During the pre-inductive and inductive phase, leaf primordia are being developed. When the induction is complete, panicle initiation ŽPI. starts; but leaf initiation no longer occurs, and the final leaf number has been determined ŽMiglietta, 1991; Ritchie and NeSmith, 1991; Ritchie, 1993.. Because the subsequent growth depends on the rate of appearance of the final leaves that have differentiated but not yet appeared, the length of the remainder of the vegetative period Ži.e., between PI and flowering. is a consequence of what has happened in the pre-inductive and inductive phase ŽRitchie and NeSmith, 1991; Ritchie, 1993.. This implies that the length of the interval between PI and flowering is affected by a carryover effect of the photoperiod during the inductive phase before PI. The assumption has been used in most CERES-family models, including CERESRice ŽAlocilja and Ritchie, 1991., in which the length of the PI-flowering interval was quantified as 4508Cd plus 0.15 of the accumulated degree-days Žwith a base temperature of 88C. from emergence until PI. In contrast to the assumption in CERES-Rice ŽAlocilja and Ritchie, 1991., several early studies Že.g., Chandraratna, 1954; for others, see the review of Vergara and Chang, 1985. reported a significant effect of post-PI photoperiods on rice development from PI to flowering although the effect was not as striking as on development before PI. Those reports, however, were often based on one or few traditional cultivars with extremely high photoperiod-sensitivity. It is known that modern rice cultivars are generally less photoperiod-sensitive than the traditional ones ŽVergara and Chang, 1985.. The objective of this study was to experimentally determine whether the duration between PI and flowering in modern rice cultivars varies with photoperiod; and if so, whether it is influenced by a carryover effect of the pre-PI photoperiod or by a direct effect of the post-PI photoperiod. This was accomplished by transferring plants from short-day ŽSD. to long-day ŽLD. photoperiods and vice versa at PI.
2. Materials and methods An experiment was conducted in a greenhousedarkroom facility at the International Rice Research Institute, Philippines. A total of 12 cultivars from
contrasting rice growing environments were selected based on their photoperiod sensitivity reported elsewhere Že.g., Vergara and Chang, 1985. ŽTable 1.. Except cv. Azucena, which is traditional tall genotype with moderate photoperiod sensitivity, others are all modern semi-dwarf cultivars, with photoperiod sensitivity ranging from nearly insensitive to strongly sensitive. Seeds of each cultivar were pre-germinated and then planted on 3 June 1993 in 1-l plastic pots with five seeds per pot. Seedlings were thinned first to three and then to one plant per pot. The growing medium in pots was a loamy clay soil, which was blended with 0.21 g ŽNH 4 . 2 SO4 , 0.01 g P2 O5 and 0.04 g KCl for each pot. Additional 0.21 g ŽNH 4 . 2 SO4 was topdressed on each pot at mid-tillering and PI. Plants were irrigated daily to keep the soil saturated until 15 days after sowing ŽDAS., and were grown under continuously flooded conditions thereafter. All pot plants were arranged in a randomized complete block design on trolleys which were moved daily into an open-sided greenhouse between 08:00 and 17:00 h, after which they were distributed among darkrooms. The darkrooms were provided with different hours of 10 m mol my2 sy1 supplementary light to establish the six required photoperiods: 10, 11, 12, 13, 14 and 15 h dayy1 . The temperature in the darkrooms was maintained at 24 " 28C by forced-air ventilation, whereas the daytime temperature in the greenhouse varied generally between 27 and 378C. Table 1 Rice cultivars investigated in this study Cultivar
Ecotype
Origin
Photoperiod sensitivity
IR42 IR64 IR72 IR64616H Shan You 63 CO36 MR84 Azucena Xiu Shui 11 Koshihikari Nipponbare Hwasong
indica indica indica indica Žhybrid. indica Žhybrid. indica indica indica japonica japonica japonica japonica
IRRI IRRI IRRI IRRI China India Malaysia Philippines China Japan Japan Korea
intermediate weak weak weak weak strong intermediate intermediate strong weak intermediate intermediate
X. Yin, M.J. Kropffr Field Crops Research 57 (1998) 301–307
Initially, there were nine pots for each cultivar in each photoperiod environment; and five of them were used for dissection to observe the date of PI. PI was taken to be equivalent to stage 2 as described by Matsushima Ž1970. and Yoshida Ž1981., i.e., apex appears to the naked eye as a fuzzed white tip of 0.2–0.5 mm. When PI was first detected, two or more plants were further dissected to confirm the uniformity of development among plants. Once the date of PI was determined under a given photoperiod condition, two pots were transferred to another photoperiod until flowering, while the remaining two pots were retained under the original condition. Plants grown under SD conditions 10, 11 and 12 h dayy1 were moved to LD conditions 13, 14 and 15 h dayy1 , respectively; and those under the LD conditions 13, 14 and 15 h dayy1 were moved to the SD conditions 10, 11 and 12 h dayy1 , respectively. Because plants developed faster under SD conditions than under LD conditions, transfers from SD to LD were conducted earlier than those from LD to SD. Individual tillers were inspected daily to obtain the flowering dates. Flowering was determined when 50% of the florets of the first panicle had flowered. The appearance of individual main-culm leaves were measured, starting with the first leaf with a complete leaf blade. The main-culm leaf number was then determined at panicle emergence. However, no data for flowering dates and leaf number were obtained for those few plants of the most photoperiod-sensitive cultivar, CO36, grown in the least-inductive regimes, which remained vegetative at 365 DAS when the experiment was terminated.
303
Fig. 1. Observed days from sowing to PI in 12 rice cultivars in response to photoperiod.
ponbare and Hwasong ŽFig. 1C.. However, the 12 cultivars differed considerably in their photoperiod sensitivity, with cvs. IR72 and IR64616H being least sensitive ŽFig. 1A. and CO36 most sensitive ŽFig. 1B.. When grown under the conditions less than 13 h dayy1 , the four japonica cultivars had PI earlier than those of the indica type.
3. Results
3.2. Duration from panicle initiation to flowering
3.1. Duration from sowing to panicle initiation
Except plants of CO36 at the initial photoperiod of both 14 and 15 h dayy1 which failed to reach PI, all others provided adequate comparison for the PI to flowering interval between plants grown continuously at the same photoperiod from sowing to flowering and those transferred at PI to a different photoperiod environment ŽFig. 2.. Days from PI to flowering for plants grown at one photoperiod throughout differed significantly Ž P - 0.01. from those grown at the same pre-PI photoperiod but transferred at PI to a photoperiod with the 3-h differ-
All plants reached PI within 114 DAS, except plants of CO36 grown at both 14 and 15 h dayy1 , which failed to have PI after 365 days of growth. In all cultivars, days from sowing to PI exhibited a SD response Ži.e., the shorter the photoperiod the earlier the time of PI. ŽFig. 1., although the time of PI differed little among the constant photoperiod treatments from 10 to 13 h dayy1 in each of the four japonica cultivars, Xiu Shui 11, Koshihikari, Nip-
304
X. Yin, M.J. Kropffr Field Crops Research 57 (1998) 301–307
Fig. 2. Days from PI to flowering for plants grown at each of the six photoperiods from sowing to flowering Žfilled circles connected by lines., and for plants transferred at PI from a short photoperiod Ž10, 11 or 12 h dayy1 , respectively. to a 3 h dayy1 longer photoperiod Ži.e., 13, 14 or 15 h dayy1 , respectively. Žopen squares., or for plants transferred at PI from a long photoperiod Ž13, 14 or 15 h dayy1 , respectively. to a 3 h dayy1 shorter photoperiod Ži.e., 10, 11 or 13 h dayy1 , respectively. Žopen diamonds. in 12 rice cultivars. Plants of CO36 grown under both 14 and 15 h dayy1 had no PI after 365 days of growth, and are therefore not shown in ŽF. of this figure.
ence. A 3-h increase in photoperiod after PI generally increased the PI-to-flowering duration Žcompared open squares to the corresponding filled circles in Fig. 2.. This effect varied from often negligible to 10.5 days for Azucena grown at the pre-PI photoperiod of 10 h dayy1 ŽFig. 2H.. A 3-h decrease in photoperiod after PI almost consistently reduced the length between PI and flowering Žcompare open diamonds to filled circles.. This effect also varied among cultivars. The 3-h decrease in photoperiod had only small effect in Koshihikari ŽFig. 2K. and Hwasong ŽFig. 2L.. The effect, however, was large in CO36: plants of this cultivar transferred from 13 to 10 h dayy1 flowered 15 days earlier than those retained at 13 h dayy1 ŽFig. 2F..
The data obtained from the experiment also enabled direct comparison of the duration of PI to flowering between plants which had a common postPI photoperiod but a 3-h difference in the pre-PI photoperiod ŽFig. 3.. This figure reveals that the carryover effect of the pre-PI photoperiod on the length of the subsequent phase from PI to flowering was not consistent among cultivars, although the PI to flowering duration was often prolonged appreciably by the longer pre-PI photoperiod Že.g., Fig. 3D–F.. 3.3. Main-culm leaf number As expected, difference in photoperiod after PI had no significant effect on the total main-culm leaf
X. Yin, M.J. Kropffr Field Crops Research 57 (1998) 301–307
305
Table 3 The number of unexpanded leaves at PI in 12 rice cultivars under different photoperiod conditions Photoperiod Žh dayy1 .
Cultivar
IR42 IR64 IR72 IR64616H Shan You 63 CO36† MR84 Azucena Xiu Shui 11 Koshihikari Nipponbare Hwasong
10
11
12
13
14
15
3.2 2.8 3.5 2.7 2.6 3.5 2.9 3.2 3.2 3.5 2.5 3.5
2.7 2.5 2.9 3.1 2.8 2.7 2.3 3.5 3.0 3.5 3.0 3.0
3.5 2.7 2.9 2.4 3.5 2.3 2.9 3.2 2.3 2.3 3.2 2.9
2.3 2.8 2.6 2.9 3.3 2.5 2.3 3.0 2.3 2.9 3.5 2.9
2.4 3.0 3.2 3.0 3.0
2.5 2.3 3.0 2.3 3.0
2.3 3.0 2.5 3.0 2.3 2.3
3.0 3.2 3.5 3.1 3.2 2.3
†
No data for plants of this cultivar under both 14 and 15 h dayy1 photoperiod conditions because they did not reach PI after 365 days of growth Žsee text..
Fig. 3. Comparisons of the duration from PI to flowering between plants which had the same post-PI photoperiod wŽA. 10 h dayy1 ; ŽB. 11 h dayy1 ; ŽC. 12 h dayy1 ; ŽD. 13 h dayy1 ; ŽE. 14 h dayy1 ; ŽF. 15 h dayy1 x but with 3 h dayy1 difference in the pre-PI photoperiod. One point corresponds to the comparison for one cultivar. The diagonal line shows the 1:1 relationship.
number Ž P ) 0.10. in any cultivar ŽTable 2.. The leaf number, however, responded to the photoperiod before PI; and the responsiveness varied among cul-
tivars. The leaf number in IR64616H changed little by the pre-PI photoperiod Ž P ) 0.10., whereas the leaf number in others responded to the photoperiod to varying extents. As the appearance of individual main-culm leaves was regularly measured, it was possible to determine the main-culm leaf number at PI. As expected, the leaf number at PI also varied among photoperiods, depending on the sensitivity of a cultivar. Because
Table 2 The total number of main-culm leaves in 12 rice cultivars under different photoperiod conditions Žh dayy1 .† Pre-PI photoperiod
10
Post-PI photoperiod
10
13
11
14
12
15
13
10
14
11
15
12
IR42 IR64 IR72 IR64616H Shan You 63 CO36 ‡ MR84 Azucena Xiu Shui 11 Koshihikari Nipponbare Hwasong
14.0 13.0 13.0 13.0 13.0 12.0 13.0 13.0 10.5a 11.0 10.0 11.0
14.0 13.0 13.0 12.5a 13.0 12.5a 13.0 13.0 10.5a 10.5a 10.0 11.0
14.0 13.0 13.0 13.5a 14.5a 12.5a 13.5a 13.5a 10.5a 11.0 10.0 10.0
14.0 13.0 13.0 13.0 13.5a 12.5a 13.5a 12.5a 10.5a 11.0 9.0 10.0
15.0 13.0 13.0 13.0 15.0 13.0 14.5a 14.0 10.5a 10.5a 10.0 10.0
15.0 13.5a 13.0 13.0 14.5a 13.0 15.0 13.5a 10.0 11.0 9.0 9.0
15.0 14.0 12.5a 13.5a 15.0 17.0 15.0 14.5a 11.5a 11.0 11.0 11.0
15.0 13.0 13.0 13.5a 15.0 16.5a 15.0 14.0 10.5a 11.0 10.5a 11.0
16.5a 14.0 14.0 13.5a 15.0
16.5a 14.0 13.5a 13.0 15.0
16.0b 14.5a 14.0 13.5a 15.5a
16.5a 15.0 14.0 13.0 15.5a
15.5a 14.5a 16.0 13.0 13.5a 14.5a
16.0 15.0 15.0 13.0 14.0 14.5a
16.0 15.5a 18.0 14.0 16.0 16.0
16.0 15.5a 17.0 14.0 15.0 16.0
†
11
12
13
14
15
Letter a in this table means a standard error of 0.5 and letter b means a standard error of 1.0; otherwise, the standard error is zero. No data for plants of this cultivar under both 14 and 15 h dayy1 pre-PI photoperiod conditions because they did not reach PI after 365 days of growth Žsee text..
‡
306
X. Yin, M.J. Kropffr Field Crops Research 57 (1998) 301–307
the leaf number at PI varied in parallel with the total leaf number, the number of unexpanded leaves at PI appeared to be hardly affected by either cultivar or photoperiod ŽTable 3.. These unexpanded leaves ranged from 2.3 to 3.5 with an average of about 3.0 leaves.
4. Discussion The observation that main-culm leaf number was not affected by photoperiod after transfer ŽTable 2. confirms expectations based on dissections of companion plants, i.e., transfers did not occur before PI, because the main-culm leaf number is no longer sensitive to photoperiod after PI ŽRitchie, 1993.. The results provided the evidence of a significant effect of post-PI photoperiod on the PI-flowering duration in many modern rice cultivars. The same effect has been observed by early workers, e.g., Chandraratna Ž1954., for traditional rice cultivars. Our results with 12 rice cultivars demonstrated that the effect varies among cultivars and appear to have a trend that the stronger is the photoperiod sensitivity of a cultivar the more striking is the effect. However, the effect was nearly negligible in some relatively sensitive cultivars, e.g., Xiu Shui 11 ŽFig. 2I. and Nipponbare ŽFig. 2K.. This may reflect that transfers based on dissections of companion plants actually occurs some days after PI for the transferred plants. These results support the finding that photoperiod sensitivity continues for some days after PI but disappears thereafter ŽCollinson et al., 1992; Yin et al., 1997., based on experiments in which rice plants were serially transferred between LD and SD at various times after sowing. The effect of photoperiod on the PI-toflowering development implies the dependence of the rate of appearance of the final few leaves on photoperiod, in contrast to the common claim that leaf appearance rate in cereal crops, e.g., wheat ŽTriticum aestiÕum L.; Miglietta, 1991., is independent of photoperiod. The crop simulation model CERES-Rice ŽAlocilja and Ritchie, 1991. assumes a carryover effect of pre-PI photoperiod on subsequent development to flowering. Obviously, this carryover effect cannot explain the results of the current study. The idea of the carryover effect was developed from the expan-
sion of the main-culm leaves ŽRitchie and NeSmith, 1991; Ritchie, 1993. but the mechanism was not clearly presented. One possible explanation is that main-culm leaf appearance rate Žleaves dayy1 . decreases gradually with the leaf number ŽYin and Kropff, 1996., and hence the full appearance of the final leaves that have differentiated but not yet appeared would need longer time when more leaves had been differentiated due to the delayed PI by a long photoperiod. However, this carryover effect cannot be consistently observed in our experiment ŽFig. 3.. Matsushima Ž1970. and Yoshida Ž1981. indicated that for a normal photoperiod-insensitive rice cultivar, PI occurs at the stage when there are three unexpanded leaves. The small variation in the number of unexpanded leaves at PI in our study ŽTable 3. might be the result of some inaccuracy for the time of PI observed based on dissection of companion plants. Nevertheless, our results indicated that the mean number of unexpanded leaves at PI was about 3.0, irrespective of photoperiod and cultivar. The well established synchrony between leaf and panicle development for photoperiod-insensitive cultivars in rice ŽMatsushima, 1970; Yoshida, 1981; Nemoto et al., 1995. may, therefore, also be used for photoperiod-sensitive cultivars, provided that the number of unexpanded leaves remains an effective index. References Alocilja, E.C., Ritchie, J.T., 1991. A model for the phenology of rice. In: Hodges, T. ŽEd.., Predicting Crop Phenology. CRC Press, Boca Raton, FL, pp. 181–190. Chandraratna, M.F., 1954. Photoperiod response in rice Ž Oryza satiÕa L..: I. Effects on inflorescence initiation and emergence. New Phytol. 53, 397–405. Collinson, S.T., Ellis, R.H., Summerfield, R.J., Roberts, E.H., 1992. Durations of the photoperiod-sensitive and photoperiodinsensitive phases of development to flowering in four cultivars of rice Ž Oryza satiÕa L... Ann. Bot. 70, 339–346. Matsushima, S., 1970. Crop Science in Rice. Fuji Publ., Tokyo, 367 pp. Miglietta, F., 1991. Simulation of wheat ontogenesis: I. Appearance of main stem leaves in the field. Climate Res. 1, 145–150. Nemoto, K., Morita, S., Baba, T., 1995. Shoot and root development in rice related to the phyllochron. Crop Sci. 35, 24–29. Ritchie, J.T., 1993. Genetic specific data for crop modeling. In: Penning de Vries, F.W.T., Teng, P.S., Metselaar, K. ŽEds.., Systems Approaches for Agricultural Development. Kluwer Academic Publishers, Dordrecht, pp. 77–93.
X. Yin, M.J. Kropffr Field Crops Research 57 (1998) 301–307 Ritchie, J.T., NeSmith, D.S., 1991. Temperature and crop development. In: Hanks, R.J., Ritchie, J.T. ŽEds.., Modeling Plant and Soil Systems. Madison, WI, pp. 5–29. Roberts, E.H., Summerfield, R.J., 1987. Measurement and prediction of flowering in annual crops. In: Atherton, J.G. ŽEd.., Manipulation of Flowering. Butterworths, London, pp. 17–50. Vergara, B.S., Chang, T.T., 1985. The Flowering Response of the Rice Plant to Photoperiod, 4th edn. IRRI, Los Banos, ˜ 61 pp.
307
Yin, X., Kropff, M.J., 1996. The effect of temperature on leaf appearance in rice. Ann. Bot. 77, 215–221. Yin, X., Kropff, M.J., Ynalvez, M.A., 1997. Photoperiodically sensitive and insensitive phases of preflowering development in rice. Crop Sci. 37, 182–190. Yoshida, S., 1981. Fundamentals of Rice Crop Science. IRRI, Los Banos, ˜ 269 pp.
The effect of photoperiod on interval between panicle initiation and flowering in rice Xinyou Yin a
a,b,)
, Martin J. Kropff
a,c,d
Department of Theoretical Production Ecology, Agricultural UniÕersity, P.O. Box 430, 6700 AK Wageningen, Netherlands b Department of Agronomy, Jiangxi Agricultural UniÕersity, 330045 Nanchang, China c DLO-Research Institute for Agrobiology and Soil Fertility, P.O. Box 14, 6700 AA Wageningen, Netherlands d The International Rice Research Institute, P.O. Box 933, 1099 Manila, Philippines Received 24 September 1997; revised 26 December 1997; accepted 27 December 1997
Abstract An understanding of response of crops to photoperiod is essential for accurate prediction of their phenological development. This study aimed to determine whether photoperiod influences the duration from panicle initiation ŽPI. to flowering in rice Ž Oryza satiÕa L... In a greenhouse experiment, plants of 12 cultivars were grown under three short-day ŽSD. conditions 10, 11 and 12 h dayy1 or under three long-day ŽLD. conditions 13, 14, and 15 h dayy1 until PI, after which half of the plants at SD were transferred to a 3-h longer photoperiod and half of the plants at LD were moved to a 3-h shorter photoperiod. Duration from PI to flowering was positively correlated with the photoperiod experienced after PI; the effect of a 3-h change in photoperiod varied from negligible in some cases to more than 10 days in others. No consistent carryover effect of photoperiod before PI on the PI-to-flowering duration was detected. As expected, the total main-culm leaf number was influenced by photoperiod before PI, but not thereafter. Although the leaf number varied greatly both among cultivars and among pre-PI photoperiods, the number of unexpanded leaves at PI was nearly constant, with an average of about three leaves. This study further supports the earlier experimental finding that rice photoperiod sensitivity continues some days after PI, suggesting the inadequacy of the assumption in crop simulation model CERES-Rice that the PI-to-flowering duration is influenced only by a carryover effect of pre-PI photoperiod. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Rice Ž Oryza satiÕa.; Flowering; Panicle initiation; Photoperiod; Leaf number
1. Introduction An understanding of response of crops to photoperiod is essential to accurate modeling of their phenological events. In rice, the time to flowering is strongly affected by photoperiod. In general, a short )
Corresponding author. Fax: q31-317-484892; e-mail: [email protected].
photoperiod accelerates and a long photoperiod delays flowering ŽVergara and Chang, 1985.. Rice plants, however, do not respond to photoperiod during the entire vegetative period from sowing to flowering ŽVergara and Chang, 1985.. Roberts and Summerfield Ž1987. divided the vegetative period into three phases: the pre-inductive, the inductive, and the post-inductive phase. Plants are sensitive to photoperiod only during the inductive phase.
0378-4290r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 7 8 - 4 2 9 0 Ž 9 8 . 0 0 0 7 4 - 4
302
X. Yin, M.J. Kropffr Field Crops Research 57 (1998) 301–307
During the pre-inductive and inductive phase, leaf primordia are being developed. When the induction is complete, panicle initiation ŽPI. starts; but leaf initiation no longer occurs, and the final leaf number has been determined ŽMiglietta, 1991; Ritchie and NeSmith, 1991; Ritchie, 1993.. Because the subsequent growth depends on the rate of appearance of the final leaves that have differentiated but not yet appeared, the length of the remainder of the vegetative period Ži.e., between PI and flowering. is a consequence of what has happened in the pre-inductive and inductive phase ŽRitchie and NeSmith, 1991; Ritchie, 1993.. This implies that the length of the interval between PI and flowering is affected by a carryover effect of the photoperiod during the inductive phase before PI. The assumption has been used in most CERES-family models, including CERESRice ŽAlocilja and Ritchie, 1991., in which the length of the PI-flowering interval was quantified as 4508Cd plus 0.15 of the accumulated degree-days Žwith a base temperature of 88C. from emergence until PI. In contrast to the assumption in CERES-Rice ŽAlocilja and Ritchie, 1991., several early studies Že.g., Chandraratna, 1954; for others, see the review of Vergara and Chang, 1985. reported a significant effect of post-PI photoperiods on rice development from PI to flowering although the effect was not as striking as on development before PI. Those reports, however, were often based on one or few traditional cultivars with extremely high photoperiod-sensitivity. It is known that modern rice cultivars are generally less photoperiod-sensitive than the traditional ones ŽVergara and Chang, 1985.. The objective of this study was to experimentally determine whether the duration between PI and flowering in modern rice cultivars varies with photoperiod; and if so, whether it is influenced by a carryover effect of the pre-PI photoperiod or by a direct effect of the post-PI photoperiod. This was accomplished by transferring plants from short-day ŽSD. to long-day ŽLD. photoperiods and vice versa at PI.
2. Materials and methods An experiment was conducted in a greenhousedarkroom facility at the International Rice Research Institute, Philippines. A total of 12 cultivars from
contrasting rice growing environments were selected based on their photoperiod sensitivity reported elsewhere Že.g., Vergara and Chang, 1985. ŽTable 1.. Except cv. Azucena, which is traditional tall genotype with moderate photoperiod sensitivity, others are all modern semi-dwarf cultivars, with photoperiod sensitivity ranging from nearly insensitive to strongly sensitive. Seeds of each cultivar were pre-germinated and then planted on 3 June 1993 in 1-l plastic pots with five seeds per pot. Seedlings were thinned first to three and then to one plant per pot. The growing medium in pots was a loamy clay soil, which was blended with 0.21 g ŽNH 4 . 2 SO4 , 0.01 g P2 O5 and 0.04 g KCl for each pot. Additional 0.21 g ŽNH 4 . 2 SO4 was topdressed on each pot at mid-tillering and PI. Plants were irrigated daily to keep the soil saturated until 15 days after sowing ŽDAS., and were grown under continuously flooded conditions thereafter. All pot plants were arranged in a randomized complete block design on trolleys which were moved daily into an open-sided greenhouse between 08:00 and 17:00 h, after which they were distributed among darkrooms. The darkrooms were provided with different hours of 10 m mol my2 sy1 supplementary light to establish the six required photoperiods: 10, 11, 12, 13, 14 and 15 h dayy1 . The temperature in the darkrooms was maintained at 24 " 28C by forced-air ventilation, whereas the daytime temperature in the greenhouse varied generally between 27 and 378C. Table 1 Rice cultivars investigated in this study Cultivar
Ecotype
Origin
Photoperiod sensitivity
IR42 IR64 IR72 IR64616H Shan You 63 CO36 MR84 Azucena Xiu Shui 11 Koshihikari Nipponbare Hwasong
indica indica indica indica Žhybrid. indica Žhybrid. indica indica indica japonica japonica japonica japonica
IRRI IRRI IRRI IRRI China India Malaysia Philippines China Japan Japan Korea
intermediate weak weak weak weak strong intermediate intermediate strong weak intermediate intermediate
X. Yin, M.J. Kropffr Field Crops Research 57 (1998) 301–307
Initially, there were nine pots for each cultivar in each photoperiod environment; and five of them were used for dissection to observe the date of PI. PI was taken to be equivalent to stage 2 as described by Matsushima Ž1970. and Yoshida Ž1981., i.e., apex appears to the naked eye as a fuzzed white tip of 0.2–0.5 mm. When PI was first detected, two or more plants were further dissected to confirm the uniformity of development among plants. Once the date of PI was determined under a given photoperiod condition, two pots were transferred to another photoperiod until flowering, while the remaining two pots were retained under the original condition. Plants grown under SD conditions 10, 11 and 12 h dayy1 were moved to LD conditions 13, 14 and 15 h dayy1 , respectively; and those under the LD conditions 13, 14 and 15 h dayy1 were moved to the SD conditions 10, 11 and 12 h dayy1 , respectively. Because plants developed faster under SD conditions than under LD conditions, transfers from SD to LD were conducted earlier than those from LD to SD. Individual tillers were inspected daily to obtain the flowering dates. Flowering was determined when 50% of the florets of the first panicle had flowered. The appearance of individual main-culm leaves were measured, starting with the first leaf with a complete leaf blade. The main-culm leaf number was then determined at panicle emergence. However, no data for flowering dates and leaf number were obtained for those few plants of the most photoperiod-sensitive cultivar, CO36, grown in the least-inductive regimes, which remained vegetative at 365 DAS when the experiment was terminated.
303
Fig. 1. Observed days from sowing to PI in 12 rice cultivars in response to photoperiod.
ponbare and Hwasong ŽFig. 1C.. However, the 12 cultivars differed considerably in their photoperiod sensitivity, with cvs. IR72 and IR64616H being least sensitive ŽFig. 1A. and CO36 most sensitive ŽFig. 1B.. When grown under the conditions less than 13 h dayy1 , the four japonica cultivars had PI earlier than those of the indica type.
3. Results
3.2. Duration from panicle initiation to flowering
3.1. Duration from sowing to panicle initiation
Except plants of CO36 at the initial photoperiod of both 14 and 15 h dayy1 which failed to reach PI, all others provided adequate comparison for the PI to flowering interval between plants grown continuously at the same photoperiod from sowing to flowering and those transferred at PI to a different photoperiod environment ŽFig. 2.. Days from PI to flowering for plants grown at one photoperiod throughout differed significantly Ž P - 0.01. from those grown at the same pre-PI photoperiod but transferred at PI to a photoperiod with the 3-h differ-
All plants reached PI within 114 DAS, except plants of CO36 grown at both 14 and 15 h dayy1 , which failed to have PI after 365 days of growth. In all cultivars, days from sowing to PI exhibited a SD response Ži.e., the shorter the photoperiod the earlier the time of PI. ŽFig. 1., although the time of PI differed little among the constant photoperiod treatments from 10 to 13 h dayy1 in each of the four japonica cultivars, Xiu Shui 11, Koshihikari, Nip-
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X. Yin, M.J. Kropffr Field Crops Research 57 (1998) 301–307
Fig. 2. Days from PI to flowering for plants grown at each of the six photoperiods from sowing to flowering Žfilled circles connected by lines., and for plants transferred at PI from a short photoperiod Ž10, 11 or 12 h dayy1 , respectively. to a 3 h dayy1 longer photoperiod Ži.e., 13, 14 or 15 h dayy1 , respectively. Žopen squares., or for plants transferred at PI from a long photoperiod Ž13, 14 or 15 h dayy1 , respectively. to a 3 h dayy1 shorter photoperiod Ži.e., 10, 11 or 13 h dayy1 , respectively. Žopen diamonds. in 12 rice cultivars. Plants of CO36 grown under both 14 and 15 h dayy1 had no PI after 365 days of growth, and are therefore not shown in ŽF. of this figure.
ence. A 3-h increase in photoperiod after PI generally increased the PI-to-flowering duration Žcompared open squares to the corresponding filled circles in Fig. 2.. This effect varied from often negligible to 10.5 days for Azucena grown at the pre-PI photoperiod of 10 h dayy1 ŽFig. 2H.. A 3-h decrease in photoperiod after PI almost consistently reduced the length between PI and flowering Žcompare open diamonds to filled circles.. This effect also varied among cultivars. The 3-h decrease in photoperiod had only small effect in Koshihikari ŽFig. 2K. and Hwasong ŽFig. 2L.. The effect, however, was large in CO36: plants of this cultivar transferred from 13 to 10 h dayy1 flowered 15 days earlier than those retained at 13 h dayy1 ŽFig. 2F..
The data obtained from the experiment also enabled direct comparison of the duration of PI to flowering between plants which had a common postPI photoperiod but a 3-h difference in the pre-PI photoperiod ŽFig. 3.. This figure reveals that the carryover effect of the pre-PI photoperiod on the length of the subsequent phase from PI to flowering was not consistent among cultivars, although the PI to flowering duration was often prolonged appreciably by the longer pre-PI photoperiod Že.g., Fig. 3D–F.. 3.3. Main-culm leaf number As expected, difference in photoperiod after PI had no significant effect on the total main-culm leaf
X. Yin, M.J. Kropffr Field Crops Research 57 (1998) 301–307
305
Table 3 The number of unexpanded leaves at PI in 12 rice cultivars under different photoperiod conditions Photoperiod Žh dayy1 .
Cultivar
IR42 IR64 IR72 IR64616H Shan You 63 CO36† MR84 Azucena Xiu Shui 11 Koshihikari Nipponbare Hwasong
10
11
12
13
14
15
3.2 2.8 3.5 2.7 2.6 3.5 2.9 3.2 3.2 3.5 2.5 3.5
2.7 2.5 2.9 3.1 2.8 2.7 2.3 3.5 3.0 3.5 3.0 3.0
3.5 2.7 2.9 2.4 3.5 2.3 2.9 3.2 2.3 2.3 3.2 2.9
2.3 2.8 2.6 2.9 3.3 2.5 2.3 3.0 2.3 2.9 3.5 2.9
2.4 3.0 3.2 3.0 3.0
2.5 2.3 3.0 2.3 3.0
2.3 3.0 2.5 3.0 2.3 2.3
3.0 3.2 3.5 3.1 3.2 2.3
†
No data for plants of this cultivar under both 14 and 15 h dayy1 photoperiod conditions because they did not reach PI after 365 days of growth Žsee text..
Fig. 3. Comparisons of the duration from PI to flowering between plants which had the same post-PI photoperiod wŽA. 10 h dayy1 ; ŽB. 11 h dayy1 ; ŽC. 12 h dayy1 ; ŽD. 13 h dayy1 ; ŽE. 14 h dayy1 ; ŽF. 15 h dayy1 x but with 3 h dayy1 difference in the pre-PI photoperiod. One point corresponds to the comparison for one cultivar. The diagonal line shows the 1:1 relationship.
number Ž P ) 0.10. in any cultivar ŽTable 2.. The leaf number, however, responded to the photoperiod before PI; and the responsiveness varied among cul-
tivars. The leaf number in IR64616H changed little by the pre-PI photoperiod Ž P ) 0.10., whereas the leaf number in others responded to the photoperiod to varying extents. As the appearance of individual main-culm leaves was regularly measured, it was possible to determine the main-culm leaf number at PI. As expected, the leaf number at PI also varied among photoperiods, depending on the sensitivity of a cultivar. Because
Table 2 The total number of main-culm leaves in 12 rice cultivars under different photoperiod conditions Žh dayy1 .† Pre-PI photoperiod
10
Post-PI photoperiod
10
13
11
14
12
15
13
10
14
11
15
12
IR42 IR64 IR72 IR64616H Shan You 63 CO36 ‡ MR84 Azucena Xiu Shui 11 Koshihikari Nipponbare Hwasong
14.0 13.0 13.0 13.0 13.0 12.0 13.0 13.0 10.5a 11.0 10.0 11.0
14.0 13.0 13.0 12.5a 13.0 12.5a 13.0 13.0 10.5a 10.5a 10.0 11.0
14.0 13.0 13.0 13.5a 14.5a 12.5a 13.5a 13.5a 10.5a 11.0 10.0 10.0
14.0 13.0 13.0 13.0 13.5a 12.5a 13.5a 12.5a 10.5a 11.0 9.0 10.0
15.0 13.0 13.0 13.0 15.0 13.0 14.5a 14.0 10.5a 10.5a 10.0 10.0
15.0 13.5a 13.0 13.0 14.5a 13.0 15.0 13.5a 10.0 11.0 9.0 9.0
15.0 14.0 12.5a 13.5a 15.0 17.0 15.0 14.5a 11.5a 11.0 11.0 11.0
15.0 13.0 13.0 13.5a 15.0 16.5a 15.0 14.0 10.5a 11.0 10.5a 11.0
16.5a 14.0 14.0 13.5a 15.0
16.5a 14.0 13.5a 13.0 15.0
16.0b 14.5a 14.0 13.5a 15.5a
16.5a 15.0 14.0 13.0 15.5a
15.5a 14.5a 16.0 13.0 13.5a 14.5a
16.0 15.0 15.0 13.0 14.0 14.5a
16.0 15.5a 18.0 14.0 16.0 16.0
16.0 15.5a 17.0 14.0 15.0 16.0
†
11
12
13
14
15
Letter a in this table means a standard error of 0.5 and letter b means a standard error of 1.0; otherwise, the standard error is zero. No data for plants of this cultivar under both 14 and 15 h dayy1 pre-PI photoperiod conditions because they did not reach PI after 365 days of growth Žsee text..
‡
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X. Yin, M.J. Kropffr Field Crops Research 57 (1998) 301–307
the leaf number at PI varied in parallel with the total leaf number, the number of unexpanded leaves at PI appeared to be hardly affected by either cultivar or photoperiod ŽTable 3.. These unexpanded leaves ranged from 2.3 to 3.5 with an average of about 3.0 leaves.
4. Discussion The observation that main-culm leaf number was not affected by photoperiod after transfer ŽTable 2. confirms expectations based on dissections of companion plants, i.e., transfers did not occur before PI, because the main-culm leaf number is no longer sensitive to photoperiod after PI ŽRitchie, 1993.. The results provided the evidence of a significant effect of post-PI photoperiod on the PI-flowering duration in many modern rice cultivars. The same effect has been observed by early workers, e.g., Chandraratna Ž1954., for traditional rice cultivars. Our results with 12 rice cultivars demonstrated that the effect varies among cultivars and appear to have a trend that the stronger is the photoperiod sensitivity of a cultivar the more striking is the effect. However, the effect was nearly negligible in some relatively sensitive cultivars, e.g., Xiu Shui 11 ŽFig. 2I. and Nipponbare ŽFig. 2K.. This may reflect that transfers based on dissections of companion plants actually occurs some days after PI for the transferred plants. These results support the finding that photoperiod sensitivity continues for some days after PI but disappears thereafter ŽCollinson et al., 1992; Yin et al., 1997., based on experiments in which rice plants were serially transferred between LD and SD at various times after sowing. The effect of photoperiod on the PI-toflowering development implies the dependence of the rate of appearance of the final few leaves on photoperiod, in contrast to the common claim that leaf appearance rate in cereal crops, e.g., wheat ŽTriticum aestiÕum L.; Miglietta, 1991., is independent of photoperiod. The crop simulation model CERES-Rice ŽAlocilja and Ritchie, 1991. assumes a carryover effect of pre-PI photoperiod on subsequent development to flowering. Obviously, this carryover effect cannot explain the results of the current study. The idea of the carryover effect was developed from the expan-
sion of the main-culm leaves ŽRitchie and NeSmith, 1991; Ritchie, 1993. but the mechanism was not clearly presented. One possible explanation is that main-culm leaf appearance rate Žleaves dayy1 . decreases gradually with the leaf number ŽYin and Kropff, 1996., and hence the full appearance of the final leaves that have differentiated but not yet appeared would need longer time when more leaves had been differentiated due to the delayed PI by a long photoperiod. However, this carryover effect cannot be consistently observed in our experiment ŽFig. 3.. Matsushima Ž1970. and Yoshida Ž1981. indicated that for a normal photoperiod-insensitive rice cultivar, PI occurs at the stage when there are three unexpanded leaves. The small variation in the number of unexpanded leaves at PI in our study ŽTable 3. might be the result of some inaccuracy for the time of PI observed based on dissection of companion plants. Nevertheless, our results indicated that the mean number of unexpanded leaves at PI was about 3.0, irrespective of photoperiod and cultivar. The well established synchrony between leaf and panicle development for photoperiod-insensitive cultivars in rice ŽMatsushima, 1970; Yoshida, 1981; Nemoto et al., 1995. may, therefore, also be used for photoperiod-sensitive cultivars, provided that the number of unexpanded leaves remains an effective index. References Alocilja, E.C., Ritchie, J.T., 1991. A model for the phenology of rice. In: Hodges, T. ŽEd.., Predicting Crop Phenology. CRC Press, Boca Raton, FL, pp. 181–190. Chandraratna, M.F., 1954. Photoperiod response in rice Ž Oryza satiÕa L..: I. Effects on inflorescence initiation and emergence. New Phytol. 53, 397–405. Collinson, S.T., Ellis, R.H., Summerfield, R.J., Roberts, E.H., 1992. Durations of the photoperiod-sensitive and photoperiodinsensitive phases of development to flowering in four cultivars of rice Ž Oryza satiÕa L... Ann. Bot. 70, 339–346. Matsushima, S., 1970. Crop Science in Rice. Fuji Publ., Tokyo, 367 pp. Miglietta, F., 1991. Simulation of wheat ontogenesis: I. Appearance of main stem leaves in the field. Climate Res. 1, 145–150. Nemoto, K., Morita, S., Baba, T., 1995. Shoot and root development in rice related to the phyllochron. Crop Sci. 35, 24–29. Ritchie, J.T., 1993. Genetic specific data for crop modeling. In: Penning de Vries, F.W.T., Teng, P.S., Metselaar, K. ŽEds.., Systems Approaches for Agricultural Development. Kluwer Academic Publishers, Dordrecht, pp. 77–93.
X. Yin, M.J. Kropffr Field Crops Research 57 (1998) 301–307 Ritchie, J.T., NeSmith, D.S., 1991. Temperature and crop development. In: Hanks, R.J., Ritchie, J.T. ŽEds.., Modeling Plant and Soil Systems. Madison, WI, pp. 5–29. Roberts, E.H., Summerfield, R.J., 1987. Measurement and prediction of flowering in annual crops. In: Atherton, J.G. ŽEd.., Manipulation of Flowering. Butterworths, London, pp. 17–50. Vergara, B.S., Chang, T.T., 1985. The Flowering Response of the Rice Plant to Photoperiod, 4th edn. IRRI, Los Banos, ˜ 61 pp.
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Yin, X., Kropff, M.J., 1996. The effect of temperature on leaf appearance in rice. Ann. Bot. 77, 215–221. Yin, X., Kropff, M.J., Ynalvez, M.A., 1997. Photoperiodically sensitive and insensitive phases of preflowering development in rice. Crop Sci. 37, 182–190. Yoshida, S., 1981. Fundamentals of Rice Crop Science. IRRI, Los Banos, ˜ 269 pp.