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Leaflet expansion rates for fifteen soybean cultivars
Field Crops Research, 12 (1985) 271--279
271
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
LEAFLET EXPANSION RATES FOR FIFTEEN SOYBEAN CULTIVARS W.J. WIEBOLD and W.J. KENWORTHY i
Department of Agronomy, Ohio State University, Columbus, OH 43210 (U.S.A.) 1Department of Agronomy, University of Maryland, College Park, MD 20742 (U.S.A.) Scientific Article No. A-3124, Contribution No. 6172 of the Maryland Agric. Exp. St., Dept. of Agronomy. (Accepted 13 March 1985)
ABSTRACT Wiebold, W.J. and Kenworthy, W.J., 1985. Leaflet expansion rates for fifteen soybean cultivars. Field Crops Res., 12: 271--279. In determining soybean (Glycine max (L.) Merr.) yield, the rate of leaf area expansion may be more important than the rate of apparent photosynthesis per unit leaf area. Fifteen soybean cultivars from two Maturity Groups were surveyed for the rate at which terminal leaflets of the sixth, eighth, and tenth trifoliate leaf expanded under field conditions. Leaflet length (LL) and width (LW) were measured every day from when the leaflets were 10--15 mm long until full expansion, a period of 11 or 12 days, Leaflet length expansion (LLE) and leaflet width expansion (LWE) rates were calculated from these data. After full expansion, leaflet area (LA) and specific leaf weight (SLW) were determined. Maturity Group III cultivars differed for" LA, LW, and LWE of the sixth, eighth, and tenth leaves; SLW of the sixth and eighth leaves; LLE of the eighth and tenth leaves; and LL of the tenth leaf. Maturity Group IV cultivars differed for SLW, LA, LL, LW, LLE, and LWE for all three leaves. The tenth leaf of most cultivars was smaller and expanded at a slower rate than the sixth leaf. Highly significant correlations between LA and leaflet expansion rates were found (r = 0.55 to 0.90). F o r the eighth and tenth leaves o f Maturity Group IV, high values for SLW were associated with slow rates of leaflet expansion. Specific leaf weight of Maturity Group III was not correlated with any other leaflet characteristic. Because single leaflet expansion and total leaf area expansion rates are negatively related to SLW or apparent photosynthesis, it may be difficult to identify cultivars that combine a fast rate of leaf expansion with a fast rate of apparent photosynthesis.
INTRODUCTION
The premise that soybean (Glycine max (L.) Merr.) carbon dioxide exhange rate (CER) is related to soybean productivity, although reasonable, has not been proven true (Curtis et al., 1969; Ford et al., 1983}. The total photosynthetic performance of a soybean line is composed of the magnitude of CER, duration of CER, and leaf area (Ford et al., 1983). Negative correlations between CER and the other two components may interfere with the establishment of a relationship between CER and productivity. Of more importance than CER per unit leaf area may be the size of the
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272 photosynthesising area and the rate at which the area is established {Duncan and Hesketh, 1968; Kaplan and Koller, 1977). Kaplan and Koller {1977), using seedlings of 16 soybean cultivars grown in the growth chamber, found that leaf expansion rate was positively related to dry weight accumulation rate. Leaf expansion rate was negatively related to CER and specific leaf weight. It would be optimal if a cultivar possessed large values for CER per unit leaf area and was able to establish a large leaf area rapidly. Leaf area expansion rate is c o m p o s e d of leaf number and the rate at which individual leaves expand. The objective of this study was to determine if soybean cultivars differ for the rate at which individual leaflets expand. In addition, information on the relationship between leaf expansion rate and specific leaf weight, a characteristic related to CER (Dornhoff and Shibles, 1970), was gained. MATERIALS AND METHODS Eight soybean cultivars from Maturity Group III ('Williams', 'Williams 79', 'Hobbit', 'Pella', 'Sprite', 'Cumberland', 'Elf', 'Calland') and seven cultivars from Maturity Group IV ('Pixie', 'Cutler 71', 'Kent', 'Ware', 'Union', 'James', 'Miles') were planted 11 June 1981 at the University of Maryland Forage Research Farm near ClarksviUe, MD. Cultivars within each Maturity Group were randomly selected from the Maryland soybean variety test and arranged in the field as a randomized complete block with three replications. Plots consisted of four rows 6 m long with an inter-row spacing of 0.76 m. Following planting, alachlor (2-chloro-2'-6' diethyl-N-(methoxymethyl) acetonilide) and linuron (3-(3, 4-dichlorophenyl)-l-methoxy-l-methylurea) were applied for weed control. Soil type was a Chester silt loam {Typic Hapladult, fine loamy, mixed, mesic). On 14 July, four plants from each plot were selected from one of the center t w o rows. These plants were tagged so that repeat measurements could be made. Leaflet length (LL) and width (LW) of the terminal leaflet of the sixth trifoliolate leaf were measured every day from when the leaflet was 10--15 mm long until full expansion. Measurements were taken throughout the morning, b u t individual plants were measured at approximately the same time each day. After the leaflets had reached full egpansion, they were removed and transported back to the laboratory where leaflet area (LA) was measured with a LI-COR Model LI-3000 leaf area meter. Leaflets were dried at 60°C for specific leaf weight (SLW) calculation (SLW = leaflet dry weight/LA). Leaflet length, LW, LA, and SLW were determined for the terminal leaflet of the eighth and tenth trifoliolate leaf in an identical manner. Different plants were used for each leaf and measurements began on 29 July and 9 August for the eighth and tenth leaf, respectively. Flowering began for the Maturity Group III cultivars during the expansion of the eighth leaf. Most
273
Maturity Group IV cultivars began flowering at the beginning of expansion of the tenth leaf. Leaflet length expansion (LLE) and leaflet width expansion (LWE) rates were calculated as (X2 --X1 )/(D2 --D1 ) after the obviously non-linear data at the beginning and end of the expansion period were eliminated. X2 and XI were the measurements of the leaflet at the end and beginning of the linear expansion period. D2 and D1 were the number of days after measurements began that X2 and X1 were determined. Data from each Maturity Group and leaf were analyzed separately as a randomized complete block. Where a significant cultivar effect was found, an LSD (0.05) was calculated for mean comparison. Within each Maturity Group, data for leaves were combined and analyzed as a split plot with cultivars as the whole plots and leaves as the subplots. Where a significant leaf effect was found an LSD (0.05) was calculated to compare leaves within a cultivar. RESULTS AND DISCUSSION
Each leaflet for all cultivars possessed a short lag period of two to three days (after first measurement) for leaf expansion. Thereafter, leaflet width and length increased in a linear manner for 6 or 7 days. Leaflet expansion slowed abruptly 8--11 days after the first measurement, depending on the leaf, with a slight increase in length and width for several additional days. Similar data were provided for 'Wayne' by Hofstra et al. (1977). Cultivars did not differ for total number of days of linear leaf growth. Regression analysis of LLE and LWE on days after first measurement, performed after excluding the non-linear data at the beginning and end of the expansion period, produced R 2 values which exceeded 0.99 for all cultivars. Several studies have demonstrated that SLW increases for successively higher leaves within the soybean canopy (Dornhoff and Shibles, 1970; Lugg and Sinclair, 1979, 1980). In this study, only three of the 15 cultivars had greater SLW values for leaf ten than for leaf six (Tables 1 and 2). Consistent with other research (Dornhoff and Shibles, 1970; Lugg and Sinclair, 1979), cultivars differed for SLW of all three leaflets (Tables 1, 2). Terminal leaflet size (LA) of most cultivars decreased from leaf six to leaf ten (Tables 1, 2). This is a typical response of indeterminate soybean cultivars (Wiebold, 1975). Green et al. (1977) measured the size of terminal leaflets of the last fully expanded leaves of 60 indeterminate soybean lines at beginning pod and beginning seed stages of development. They found that leaflets measured at beginning seed were 55% of the size of leaflets measured at beginning pod. Exceptions to the trend of smaller LA with increased leaf number in our study were three Maturity Group IV cultivars: Miles, Ware, and James. Miles contains the gene pair In In for narrow leaflets; Ware has a determinate growth habit; and James was the latest maturing cultivar studied. The semi-dwarf cultivars: Sprite, Hobbit, Elf, and Pixie,
0.6 8
LSD (0.05) c CV d
0.4 6
4.6a 4.4a 4.5b 4.3a 4.4a 3.9a 3.9a 4.2a 0.5 5
4.3a 4.3a 4.1a 4.0a 4.2a 4.3b 4.2ab 4.1a 10 11
55c 47c 62b 58b 55b 50c 45c 48c 8 14
31b 37a 33a 36a 40a 30b 27b 27b 9 19
24a 32a 31a 31a 38a 14a 12a 17a N.S. 6
104b 93a 106c 105b 102b 103c 101c 106c
N.S. 6
87a 93a 94b 91a 95ab 90b 88b 88b
8
6
10
6
8
LL a ( r a m )
LA a (cm 2 )
10 7
81a 88a 83a 85a 92a 71a 65a 79a
10
a
SLW -~ specific leaf weight, L A = leaflet area, LL ~- leaflet l e n g t h , LW = leaflet w i d t h . b w i t h i n a leaflet characteristic, m e a n s in a r o w f o l l o w e d b y t h e s a m e l e t t e r are n o t d i f f e r e n t b y LSD 0.05. c LSD to c o m p a r e cultivar m e a n s w i t h i n a c o l u m n . dCV -- c o e f f i c i e n t o f variability e x p r e s s e d as p e r c e n t .
6.4a b 5.0b 4.6b 4.0a 4.5a 4.2ab 4.4b 3.9a
SLW a ( m g / c m 2 ) Leaf number: 6 8 10
Cumberland Pella Williams 79 Williams Calland Sprite Hobbit Elf
Cultivar
8 6
76c 73c 83c 81c 78c 73c 66c 69c
6
8 8
57b 61b 59b 62b 66b 50b 47b 48b
8
LW a (ram)
6 8
47a 54a 49a 53a 60a 31a 30a 33a
10
Cultivar m e a n s o f SLW, LA, LL, a n d LW f o r t h e t e r m i n a l leaflet o f t h e sixth, e i g h t h , a n d t e n t h t r i f o l i o l a t e leaves o f t h e eight M a t u r i t y G r o u p III cultivars
TABLE 1
b~
0.4 6
LSD (0.05) c CV d
0.4 5
4.5b 4.7b 4.5b 4.8a 3.7a 4.2a 4.2b 0.4 6
4.5b 4.6b 4.8c 4.7a 3.8a 4.4a 3.8a 10 11
65b 62b 40b 28a 73a 55a 53a 14 18
39a 46a 25a 33a 49a 50a 75b 16 21
32a 39a 16a 29a 45a 56a 75b 11 6
106a 105a 93a 99a l13a ll0a 97a 16 9
95a 100a 80a l14a 102a l13a l16b
8
6
10
6
8
LL a (ram)
LA a (cm 2 )
25 15
88a 95a 74a ll0ab 99a 122a 108ab
10
a S L W = specific leaf w e i g h t , L A = leaflet area, L L -- leaflet length, LW = leaflet w i d t h . b w i t h i n a leaflet c h a r a c t e r i s t i c , m e a n s in a r o w f o l l o w e d b y t h e s a m e l e t t e r are n o t d i f f e r e n t b y LSD 0.05. c LSD t o c o m p a r e cultivar m e a n s w i t h i n a c o l u m n . dCV = c o e f f i c i e n t o f variability e x p r e s s e d as p e r c e n t .
3.8a b 3.7a 3.5a 4.6a 3.9a 4.3a 4.5c
SLW a ( m g / c m 2 ) Leaf number: 6 8 10
Cutler71 Umon Pixie Miles Kent Ware James
Cultivar
7 6
85b 81b 63a 41a 91b 74a 79a
6
10 10
62a 70ab 46ab 42a 72a 71a 94a
8
LW a ( r a m )
13 12
56a 62a 34a 39a 71a 73a 93a
10
Cultivar m e a n s o f SLW, LA, LL a n d LW for t h e t e r m i n a l leaflet o f t h e s i x t h , e i g h t h , a n d t e n t h t r i f o l i o l a t e leaves o f t h e s e v e n M a t u r i t y G r o u p IV cultivars
TABLE 2
¢J1
t~
276
exhibited the decrease in leaflet size although t h e y have a determinate .growth habit. Cultivars differed for LA of all three leaves. Terminal leaflet dimensions (LL and LW) were related to LA and usually decreased from leaf six to leaf ten (Tables 1, 2). All Maturity Group III cultivars, except Pella, had a shorter LL for leaf ten than for leaf six. Leaflet length for leaf ten did not differ from LL of leaf six for any of the Maturity Group IV cultivars. Leaflet width decreased with leaf number for all but three cultivars: Miles, Ware, and James. These were the same cultivars for which there was no change in LA with leaf number. Maturity Group III cultivars differed for LL of the tenth leaf and LW of all three leaves. Maturity Group IV cultivars differed for LL and LW of all three leaves. Significant differences among leaves of all 15 cultivars were found for LLE and LWE (Tables 3 and 4). In general, the tenth leaf had the lowest rates of expansion. For 13 of the 15 cultivars, the leaf with the fastest rates of expansion was either leaf six or eight. Highly significant correlations between ultimate leaflet size and expansion rates were f o u n d (r = 0.55--0.90). Hofstra et al. (1977) reported a positive relationship between soybean leaf expansion rate and ultimate leaf size for Wayne soybeans. Cultivars differed from LLE and LWE of all leaves except LLE of the sixth leaf of the Maturity Group III cultivars. To enhance productivity, it would be o p t i m u m if cultivars with rapid leaf expansion rates also possessed high CER. Specific leaf weight has been correlated with soybean CER (Dornhoff and Shibles, 1970, 1976; Wiebold TABLE 3 Cultivar m e a n s o f LLE a n d LWE f o r t h e t e r m i n a l leaflet o f t h e sixth, eighth, and t e n t h trifoliolate leaves o f t h e eight M a t u r i t y G r o u p III cultivars Cultivar
LL a ( m m / d a y ) Leaf number: 6 8
Cumberland Pella Williams 79 Williams Calland Sprite Hobbit Elf
10.1b b 10.0a 10.8b ll.0b 10.3a 10.7b 10.7b 10.3c
8.8ab 11.8b 10.5b 9.8b 12.2b 9.8ab 7.1a 8.2b
LSD (0.05) c CV d
N.S. 9
3.2 18
LWE a ( m m / d a y ) 10 8.0a 8.7a 7.3a 6.5a 8.7a 8.1a 7.4a 5.5a 2.0 15
6 7.4b 8.4b 8.2b 8.2c 7.8b 7.2b 6.6b 6.8c 1.2 9
8
10 5.6a 7.5b 7.5b 6.9b 9.3c 5.7a 5.4a 4.6b
2.1 18
4.7a 5.0a 4.3a 4.3a 6.0a 6.9b 7.1b 3.1a 0.3 10
a L L E ----leaflet length e x p a n s i o n , LWE ----leaflet w i d t h e x p a n s i o n . b w i t h i n a leaflet characteristic, m e a n s in a r o w f o l l o w e d b y t h e same letter are n o t d i f f e r e n t by LSD 0.05. c LSD t o c o m p a r e cultivar m e a n s w i t h i n a c o l u m n . dCV ----c o e f f i c i e n t o f variability e x p r e s s e d as p e r c e n t .
277 TABLE 4 Cultivar m e a n s o f L L E a n d LWE f o r t h e t e r m i n a l leaflet o f t h e s i x t h , e i g h t h , a n d t e n t h t r i f o l i o l a t e leaves o f t h e s e v e n M a t u r i t y G r o u p I V cultivars Cultivar
LLE a (ram]day) Leaf number: 6 8
LWE a ( m m / d a y ) 10
6
8
10
C u t l e r 71 Union Pixie Miles Kent Ware James
10.5b b 11.2b 8.8b ll.3b 12.0b 10.5a ll.0a
11.6b ll.9b 6.4ab 14.4c 10.7ab 13.8b 15.9b
6.7a 7.4a 4.9a 8.8a 8.8a 10.7a 9.4a
8.5b 8.5b 5.4b 4.3ab 9.2b 7.2a 9.1a
8.8b 8.8b 3.9ab 5.4b 8.7b 9.2b 12.6b
LSD (0.05) c CV d
1.9 10
4.6 22
2.6 19
1.0 8
3.4 24
4.6a 5.0a 2.4a 3.2a 6.0a 6.5a 8.5a 1.6 17
a L L E ----leaflet l e n g t h e x p a n s i o n , LWE = leaflet w i d t h e x p a n s i o n . b w i t h i n a leaflet c h a r a c t e r i s t i c , m e a n s in a r o w f o l l o w e d b y t h e same l e t t e r are n o t d i f f e r e n t b y L S D 0.05. c LSD to compare cultivar means within a column. d C V ----c o e f f i c i e n t of v a r i a b i l i t y e x p r e s s e d as p e r c e n t .
et al., 1981) and was used in this study as a measure of relative CER values of the 15 cultivars. For the Maturity Group III cultivars, SLW was not related to any of the other leaflet characteristics (Table 5). Specific leaf weight of the eighth leaf of the Maturity Group IV cultivars was negatively correlated to LA and LWE. F o r the tenth leaf, SLW was negatively correlated to LA, LW, LLE, and LWE. In other words, at least for the Maturity Group IV cultivars, cultivars with fast rates of leaflet expansion may also TABLE 5 S i m p l e c o r r e l a t i o n c o e f f i c i e n c e b e t w e e n specific leaf w e i g h t a n d t h e various leaflet c h a r a c t e r i s t i c s for t h e s i x t h , e i g h t h , a n d t e n t h leaves o f t h e eight M a t u r i t y G r o u p III cultivars a n d t h e s e v e n M a t u r i t y G r o u p I V cultivars Leaflet characteristic a LA LL LW LLE LWE
M a t u r i t y G r o u p III Leaf number: 6 8 10 --0.06 b --0.34 0.07 --0.30 0.17
0.13 --0.09 0.36 0.22 0.17
--0.14 --0.14 --0.03 0.20 0.36
M a t u r i t y G r o u p IV 6
8
10
--0.28 b --0.03 --0.33 0.26 --0.14
--0.46* --0.20 --0.22 --0.10 --0.42*
--0.69** --0.37 --0.72** --0.51"* --0.73**
*,** s i g n i f i c a n t a t P = 0.05, 0.01. a L A --- leaflet area, LL = leaflet l e n g t h , LW = leaflet w i d t h , L L E ----- leaflet l e n g t h ~ x p a n s i o n , LWE ----leaflet w i d t h e x p a n s i o n . n ---- 24 a n d 21 f o r M a t u r i t y G r o u p s III a n d IV, respectively.
278
have slow CER. Kaplan and Koller {1977), using seedlings of 16 soybean cultivars grown in the growth chamber, found that leaf area growth rate was negatively related to CER (r = - - 0 . 4 2 ) and SLW (r = - - 0 . 4 5 ) . They found that crop growth rate was positively correlated to leaf growth rate b u t negatively correlated to CER. Similar data have been reported for other species (Potter and Jones, 1977; Muramoto et al., 1965, Duncan and Hesketh, 1968; Delaney and Dobrenz, 1974; Nelson et al., 1975). To maximize yield, it would be optimal to combine in one cultivar high values for apparent photosynthesis and a fast rate of leaf area expansion. Of these two characteristics, leaf area expansion rate may be more important. One c o m p o n e n t of leaf area expansion rate is the rate at which individual leaves expand. This study showed that soybean cultivars differ for leaflet expansion rate. However, because single leaflet expansion and total leaf area expansion rates are negatively related to SLW or CER it may be difficult to identify cultivars that combine a fast rate of leaf expansion with a fast rate of apparent photosynthesis. REFERENCES Curtis, P.E., Ogren, W.L. and Hageman, R.H., 1969. Varietal differences in soybean photosynthesis. Crop Sci., 9: 323--327. Delaney, R.H. and Dobrenz, A.K., 1974. Morphological and anatomical features of alfalfa leaves as related to CO2 exchanges. Crop Sci., 14: 444--447. Dornhoff, G.M. and Shibles, R.M., 1970. Varietal differences in net photosynthesis of soybean leaves. Crop Sci., 10: 42--45. Dornhoff, G.M. and Shibles, R.M., 1976. Leaf morphology and anatomy in relation to CO2-exchange of soybean leaves. Crop Sci., 16: 377--381. Duncan, W.G. and Hesketh, J.D., 1968. Net photosynthetic rates, relative leaf growth rates, and leaf number of 22 races of maize grown at eight temperatures. Crop Sci., 8: 670--674. Ford, D.M., Shibles, R. and Green, D.E., 1983. Growth and yield of soybean lines selected for divergent leaf photosynthetic ability. Crop Sci., 2 3 : 5 1 7 - - 5 2 0 . Green, D.E., Burlamaque, P.F. and Shibles, R., 1977. Performance of randomly selected soybean lines with semideterminate and indeterminate growth habits. Crop Sci., 17: 335--339. Hofstra, G., Hesketh, J.D. and Myhre, D.L., 1977. A plastochron model for soybean leaf and stem growth. Can. J. Plant Sci., 57: 167--175. Kaplan, S.L. and Koller, H.R., 1977. Leaf area and CO2-exchange rate as determinates of the rate of vegetative growth in soybean plants. Crop Sci., 17: 35--38. Lugg, D.G. and Sinclair, T.R., 1979. A survey of soybean cultivars for variability in specific leaf weight. Crop Sci., 19: 887--892. Lugg, D.G. and Sinclair, T.R., 1980. Seasonal changes in morphology and anatomy of field-grown soybean leaves. Crop Sci., 20: 191--196. Muramoto, H., Hesketh, J. and E1-Sharkawy, M., 1965. Relationship among rate of leaf area development, photosynthetic rate, and rate of dry matter production among American cultivated cottons and other species. Crop Sci., 5: 163--166. Nelson, C.J., Assay, K.H. and Horst, G.L., 1975. Relationship of leaf photosynthesis to forage yield of tall rescue. Crop Sci., 15: 476--482. Potter, J.R. and Jones, J.W., 1977. Leaf area partitioning as an important factor in growth. Plant Physiol., 59: 10--14.
279 Wiebold, W.J., 1975. Heritability of net photosynthesis and related leaf characters in soybeans. MSc Thesis, Iowa State University, Ames, IA. Wiebold, W., Shibles, R.M., Green, D.E. and Morgan, T., 1981. Selection of net CO2exchange and related leaf characters in early generations of soybeans. Crop Sci., 21: 969--973.
271
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
LEAFLET EXPANSION RATES FOR FIFTEEN SOYBEAN CULTIVARS W.J. WIEBOLD and W.J. KENWORTHY i
Department of Agronomy, Ohio State University, Columbus, OH 43210 (U.S.A.) 1Department of Agronomy, University of Maryland, College Park, MD 20742 (U.S.A.) Scientific Article No. A-3124, Contribution No. 6172 of the Maryland Agric. Exp. St., Dept. of Agronomy. (Accepted 13 March 1985)
ABSTRACT Wiebold, W.J. and Kenworthy, W.J., 1985. Leaflet expansion rates for fifteen soybean cultivars. Field Crops Res., 12: 271--279. In determining soybean (Glycine max (L.) Merr.) yield, the rate of leaf area expansion may be more important than the rate of apparent photosynthesis per unit leaf area. Fifteen soybean cultivars from two Maturity Groups were surveyed for the rate at which terminal leaflets of the sixth, eighth, and tenth trifoliate leaf expanded under field conditions. Leaflet length (LL) and width (LW) were measured every day from when the leaflets were 10--15 mm long until full expansion, a period of 11 or 12 days, Leaflet length expansion (LLE) and leaflet width expansion (LWE) rates were calculated from these data. After full expansion, leaflet area (LA) and specific leaf weight (SLW) were determined. Maturity Group III cultivars differed for" LA, LW, and LWE of the sixth, eighth, and tenth leaves; SLW of the sixth and eighth leaves; LLE of the eighth and tenth leaves; and LL of the tenth leaf. Maturity Group IV cultivars differed for SLW, LA, LL, LW, LLE, and LWE for all three leaves. The tenth leaf of most cultivars was smaller and expanded at a slower rate than the sixth leaf. Highly significant correlations between LA and leaflet expansion rates were found (r = 0.55 to 0.90). F o r the eighth and tenth leaves o f Maturity Group IV, high values for SLW were associated with slow rates of leaflet expansion. Specific leaf weight of Maturity Group III was not correlated with any other leaflet characteristic. Because single leaflet expansion and total leaf area expansion rates are negatively related to SLW or apparent photosynthesis, it may be difficult to identify cultivars that combine a fast rate of leaf expansion with a fast rate of apparent photosynthesis.
INTRODUCTION
The premise that soybean (Glycine max (L.) Merr.) carbon dioxide exhange rate (CER) is related to soybean productivity, although reasonable, has not been proven true (Curtis et al., 1969; Ford et al., 1983}. The total photosynthetic performance of a soybean line is composed of the magnitude of CER, duration of CER, and leaf area (Ford et al., 1983). Negative correlations between CER and the other two components may interfere with the establishment of a relationship between CER and productivity. Of more importance than CER per unit leaf area may be the size of the
0378-4290/85/$03.30
© 1 9 8 5 Elsevier S c i e n c e Publishers B.V.
272 photosynthesising area and the rate at which the area is established {Duncan and Hesketh, 1968; Kaplan and Koller, 1977). Kaplan and Koller {1977), using seedlings of 16 soybean cultivars grown in the growth chamber, found that leaf expansion rate was positively related to dry weight accumulation rate. Leaf expansion rate was negatively related to CER and specific leaf weight. It would be optimal if a cultivar possessed large values for CER per unit leaf area and was able to establish a large leaf area rapidly. Leaf area expansion rate is c o m p o s e d of leaf number and the rate at which individual leaves expand. The objective of this study was to determine if soybean cultivars differ for the rate at which individual leaflets expand. In addition, information on the relationship between leaf expansion rate and specific leaf weight, a characteristic related to CER (Dornhoff and Shibles, 1970), was gained. MATERIALS AND METHODS Eight soybean cultivars from Maturity Group III ('Williams', 'Williams 79', 'Hobbit', 'Pella', 'Sprite', 'Cumberland', 'Elf', 'Calland') and seven cultivars from Maturity Group IV ('Pixie', 'Cutler 71', 'Kent', 'Ware', 'Union', 'James', 'Miles') were planted 11 June 1981 at the University of Maryland Forage Research Farm near ClarksviUe, MD. Cultivars within each Maturity Group were randomly selected from the Maryland soybean variety test and arranged in the field as a randomized complete block with three replications. Plots consisted of four rows 6 m long with an inter-row spacing of 0.76 m. Following planting, alachlor (2-chloro-2'-6' diethyl-N-(methoxymethyl) acetonilide) and linuron (3-(3, 4-dichlorophenyl)-l-methoxy-l-methylurea) were applied for weed control. Soil type was a Chester silt loam {Typic Hapladult, fine loamy, mixed, mesic). On 14 July, four plants from each plot were selected from one of the center t w o rows. These plants were tagged so that repeat measurements could be made. Leaflet length (LL) and width (LW) of the terminal leaflet of the sixth trifoliolate leaf were measured every day from when the leaflet was 10--15 mm long until full expansion. Measurements were taken throughout the morning, b u t individual plants were measured at approximately the same time each day. After the leaflets had reached full egpansion, they were removed and transported back to the laboratory where leaflet area (LA) was measured with a LI-COR Model LI-3000 leaf area meter. Leaflets were dried at 60°C for specific leaf weight (SLW) calculation (SLW = leaflet dry weight/LA). Leaflet length, LW, LA, and SLW were determined for the terminal leaflet of the eighth and tenth trifoliolate leaf in an identical manner. Different plants were used for each leaf and measurements began on 29 July and 9 August for the eighth and tenth leaf, respectively. Flowering began for the Maturity Group III cultivars during the expansion of the eighth leaf. Most
273
Maturity Group IV cultivars began flowering at the beginning of expansion of the tenth leaf. Leaflet length expansion (LLE) and leaflet width expansion (LWE) rates were calculated as (X2 --X1 )/(D2 --D1 ) after the obviously non-linear data at the beginning and end of the expansion period were eliminated. X2 and XI were the measurements of the leaflet at the end and beginning of the linear expansion period. D2 and D1 were the number of days after measurements began that X2 and X1 were determined. Data from each Maturity Group and leaf were analyzed separately as a randomized complete block. Where a significant cultivar effect was found, an LSD (0.05) was calculated for mean comparison. Within each Maturity Group, data for leaves were combined and analyzed as a split plot with cultivars as the whole plots and leaves as the subplots. Where a significant leaf effect was found an LSD (0.05) was calculated to compare leaves within a cultivar. RESULTS AND DISCUSSION
Each leaflet for all cultivars possessed a short lag period of two to three days (after first measurement) for leaf expansion. Thereafter, leaflet width and length increased in a linear manner for 6 or 7 days. Leaflet expansion slowed abruptly 8--11 days after the first measurement, depending on the leaf, with a slight increase in length and width for several additional days. Similar data were provided for 'Wayne' by Hofstra et al. (1977). Cultivars did not differ for total number of days of linear leaf growth. Regression analysis of LLE and LWE on days after first measurement, performed after excluding the non-linear data at the beginning and end of the expansion period, produced R 2 values which exceeded 0.99 for all cultivars. Several studies have demonstrated that SLW increases for successively higher leaves within the soybean canopy (Dornhoff and Shibles, 1970; Lugg and Sinclair, 1979, 1980). In this study, only three of the 15 cultivars had greater SLW values for leaf ten than for leaf six (Tables 1 and 2). Consistent with other research (Dornhoff and Shibles, 1970; Lugg and Sinclair, 1979), cultivars differed for SLW of all three leaflets (Tables 1, 2). Terminal leaflet size (LA) of most cultivars decreased from leaf six to leaf ten (Tables 1, 2). This is a typical response of indeterminate soybean cultivars (Wiebold, 1975). Green et al. (1977) measured the size of terminal leaflets of the last fully expanded leaves of 60 indeterminate soybean lines at beginning pod and beginning seed stages of development. They found that leaflets measured at beginning seed were 55% of the size of leaflets measured at beginning pod. Exceptions to the trend of smaller LA with increased leaf number in our study were three Maturity Group IV cultivars: Miles, Ware, and James. Miles contains the gene pair In In for narrow leaflets; Ware has a determinate growth habit; and James was the latest maturing cultivar studied. The semi-dwarf cultivars: Sprite, Hobbit, Elf, and Pixie,
0.6 8
LSD (0.05) c CV d
0.4 6
4.6a 4.4a 4.5b 4.3a 4.4a 3.9a 3.9a 4.2a 0.5 5
4.3a 4.3a 4.1a 4.0a 4.2a 4.3b 4.2ab 4.1a 10 11
55c 47c 62b 58b 55b 50c 45c 48c 8 14
31b 37a 33a 36a 40a 30b 27b 27b 9 19
24a 32a 31a 31a 38a 14a 12a 17a N.S. 6
104b 93a 106c 105b 102b 103c 101c 106c
N.S. 6
87a 93a 94b 91a 95ab 90b 88b 88b
8
6
10
6
8
LL a ( r a m )
LA a (cm 2 )
10 7
81a 88a 83a 85a 92a 71a 65a 79a
10
a
SLW -~ specific leaf weight, L A = leaflet area, LL ~- leaflet l e n g t h , LW = leaflet w i d t h . b w i t h i n a leaflet characteristic, m e a n s in a r o w f o l l o w e d b y t h e s a m e l e t t e r are n o t d i f f e r e n t b y LSD 0.05. c LSD to c o m p a r e cultivar m e a n s w i t h i n a c o l u m n . dCV -- c o e f f i c i e n t o f variability e x p r e s s e d as p e r c e n t .
6.4a b 5.0b 4.6b 4.0a 4.5a 4.2ab 4.4b 3.9a
SLW a ( m g / c m 2 ) Leaf number: 6 8 10
Cumberland Pella Williams 79 Williams Calland Sprite Hobbit Elf
Cultivar
8 6
76c 73c 83c 81c 78c 73c 66c 69c
6
8 8
57b 61b 59b 62b 66b 50b 47b 48b
8
LW a (ram)
6 8
47a 54a 49a 53a 60a 31a 30a 33a
10
Cultivar m e a n s o f SLW, LA, LL, a n d LW f o r t h e t e r m i n a l leaflet o f t h e sixth, e i g h t h , a n d t e n t h t r i f o l i o l a t e leaves o f t h e eight M a t u r i t y G r o u p III cultivars
TABLE 1
b~
0.4 6
LSD (0.05) c CV d
0.4 5
4.5b 4.7b 4.5b 4.8a 3.7a 4.2a 4.2b 0.4 6
4.5b 4.6b 4.8c 4.7a 3.8a 4.4a 3.8a 10 11
65b 62b 40b 28a 73a 55a 53a 14 18
39a 46a 25a 33a 49a 50a 75b 16 21
32a 39a 16a 29a 45a 56a 75b 11 6
106a 105a 93a 99a l13a ll0a 97a 16 9
95a 100a 80a l14a 102a l13a l16b
8
6
10
6
8
LL a (ram)
LA a (cm 2 )
25 15
88a 95a 74a ll0ab 99a 122a 108ab
10
a S L W = specific leaf w e i g h t , L A = leaflet area, L L -- leaflet length, LW = leaflet w i d t h . b w i t h i n a leaflet c h a r a c t e r i s t i c , m e a n s in a r o w f o l l o w e d b y t h e s a m e l e t t e r are n o t d i f f e r e n t b y LSD 0.05. c LSD t o c o m p a r e cultivar m e a n s w i t h i n a c o l u m n . dCV = c o e f f i c i e n t o f variability e x p r e s s e d as p e r c e n t .
3.8a b 3.7a 3.5a 4.6a 3.9a 4.3a 4.5c
SLW a ( m g / c m 2 ) Leaf number: 6 8 10
Cutler71 Umon Pixie Miles Kent Ware James
Cultivar
7 6
85b 81b 63a 41a 91b 74a 79a
6
10 10
62a 70ab 46ab 42a 72a 71a 94a
8
LW a ( r a m )
13 12
56a 62a 34a 39a 71a 73a 93a
10
Cultivar m e a n s o f SLW, LA, LL a n d LW for t h e t e r m i n a l leaflet o f t h e s i x t h , e i g h t h , a n d t e n t h t r i f o l i o l a t e leaves o f t h e s e v e n M a t u r i t y G r o u p IV cultivars
TABLE 2
¢J1
t~
276
exhibited the decrease in leaflet size although t h e y have a determinate .growth habit. Cultivars differed for LA of all three leaves. Terminal leaflet dimensions (LL and LW) were related to LA and usually decreased from leaf six to leaf ten (Tables 1, 2). All Maturity Group III cultivars, except Pella, had a shorter LL for leaf ten than for leaf six. Leaflet length for leaf ten did not differ from LL of leaf six for any of the Maturity Group IV cultivars. Leaflet width decreased with leaf number for all but three cultivars: Miles, Ware, and James. These were the same cultivars for which there was no change in LA with leaf number. Maturity Group III cultivars differed for LL of the tenth leaf and LW of all three leaves. Maturity Group IV cultivars differed for LL and LW of all three leaves. Significant differences among leaves of all 15 cultivars were found for LLE and LWE (Tables 3 and 4). In general, the tenth leaf had the lowest rates of expansion. For 13 of the 15 cultivars, the leaf with the fastest rates of expansion was either leaf six or eight. Highly significant correlations between ultimate leaflet size and expansion rates were f o u n d (r = 0.55--0.90). Hofstra et al. (1977) reported a positive relationship between soybean leaf expansion rate and ultimate leaf size for Wayne soybeans. Cultivars differed from LLE and LWE of all leaves except LLE of the sixth leaf of the Maturity Group III cultivars. To enhance productivity, it would be o p t i m u m if cultivars with rapid leaf expansion rates also possessed high CER. Specific leaf weight has been correlated with soybean CER (Dornhoff and Shibles, 1970, 1976; Wiebold TABLE 3 Cultivar m e a n s o f LLE a n d LWE f o r t h e t e r m i n a l leaflet o f t h e sixth, eighth, and t e n t h trifoliolate leaves o f t h e eight M a t u r i t y G r o u p III cultivars Cultivar
LL a ( m m / d a y ) Leaf number: 6 8
Cumberland Pella Williams 79 Williams Calland Sprite Hobbit Elf
10.1b b 10.0a 10.8b ll.0b 10.3a 10.7b 10.7b 10.3c
8.8ab 11.8b 10.5b 9.8b 12.2b 9.8ab 7.1a 8.2b
LSD (0.05) c CV d
N.S. 9
3.2 18
LWE a ( m m / d a y ) 10 8.0a 8.7a 7.3a 6.5a 8.7a 8.1a 7.4a 5.5a 2.0 15
6 7.4b 8.4b 8.2b 8.2c 7.8b 7.2b 6.6b 6.8c 1.2 9
8
10 5.6a 7.5b 7.5b 6.9b 9.3c 5.7a 5.4a 4.6b
2.1 18
4.7a 5.0a 4.3a 4.3a 6.0a 6.9b 7.1b 3.1a 0.3 10
a L L E ----leaflet length e x p a n s i o n , LWE ----leaflet w i d t h e x p a n s i o n . b w i t h i n a leaflet characteristic, m e a n s in a r o w f o l l o w e d b y t h e same letter are n o t d i f f e r e n t by LSD 0.05. c LSD t o c o m p a r e cultivar m e a n s w i t h i n a c o l u m n . dCV ----c o e f f i c i e n t o f variability e x p r e s s e d as p e r c e n t .
277 TABLE 4 Cultivar m e a n s o f L L E a n d LWE f o r t h e t e r m i n a l leaflet o f t h e s i x t h , e i g h t h , a n d t e n t h t r i f o l i o l a t e leaves o f t h e s e v e n M a t u r i t y G r o u p I V cultivars Cultivar
LLE a (ram]day) Leaf number: 6 8
LWE a ( m m / d a y ) 10
6
8
10
C u t l e r 71 Union Pixie Miles Kent Ware James
10.5b b 11.2b 8.8b ll.3b 12.0b 10.5a ll.0a
11.6b ll.9b 6.4ab 14.4c 10.7ab 13.8b 15.9b
6.7a 7.4a 4.9a 8.8a 8.8a 10.7a 9.4a
8.5b 8.5b 5.4b 4.3ab 9.2b 7.2a 9.1a
8.8b 8.8b 3.9ab 5.4b 8.7b 9.2b 12.6b
LSD (0.05) c CV d
1.9 10
4.6 22
2.6 19
1.0 8
3.4 24
4.6a 5.0a 2.4a 3.2a 6.0a 6.5a 8.5a 1.6 17
a L L E ----leaflet l e n g t h e x p a n s i o n , LWE = leaflet w i d t h e x p a n s i o n . b w i t h i n a leaflet c h a r a c t e r i s t i c , m e a n s in a r o w f o l l o w e d b y t h e same l e t t e r are n o t d i f f e r e n t b y L S D 0.05. c LSD to compare cultivar means within a column. d C V ----c o e f f i c i e n t of v a r i a b i l i t y e x p r e s s e d as p e r c e n t .
et al., 1981) and was used in this study as a measure of relative CER values of the 15 cultivars. For the Maturity Group III cultivars, SLW was not related to any of the other leaflet characteristics (Table 5). Specific leaf weight of the eighth leaf of the Maturity Group IV cultivars was negatively correlated to LA and LWE. F o r the tenth leaf, SLW was negatively correlated to LA, LW, LLE, and LWE. In other words, at least for the Maturity Group IV cultivars, cultivars with fast rates of leaflet expansion may also TABLE 5 S i m p l e c o r r e l a t i o n c o e f f i c i e n c e b e t w e e n specific leaf w e i g h t a n d t h e various leaflet c h a r a c t e r i s t i c s for t h e s i x t h , e i g h t h , a n d t e n t h leaves o f t h e eight M a t u r i t y G r o u p III cultivars a n d t h e s e v e n M a t u r i t y G r o u p I V cultivars Leaflet characteristic a LA LL LW LLE LWE
M a t u r i t y G r o u p III Leaf number: 6 8 10 --0.06 b --0.34 0.07 --0.30 0.17
0.13 --0.09 0.36 0.22 0.17
--0.14 --0.14 --0.03 0.20 0.36
M a t u r i t y G r o u p IV 6
8
10
--0.28 b --0.03 --0.33 0.26 --0.14
--0.46* --0.20 --0.22 --0.10 --0.42*
--0.69** --0.37 --0.72** --0.51"* --0.73**
*,** s i g n i f i c a n t a t P = 0.05, 0.01. a L A --- leaflet area, LL = leaflet l e n g t h , LW = leaflet w i d t h , L L E ----- leaflet l e n g t h ~ x p a n s i o n , LWE ----leaflet w i d t h e x p a n s i o n . n ---- 24 a n d 21 f o r M a t u r i t y G r o u p s III a n d IV, respectively.
278
have slow CER. Kaplan and Koller {1977), using seedlings of 16 soybean cultivars grown in the growth chamber, found that leaf area growth rate was negatively related to CER (r = - - 0 . 4 2 ) and SLW (r = - - 0 . 4 5 ) . They found that crop growth rate was positively correlated to leaf growth rate b u t negatively correlated to CER. Similar data have been reported for other species (Potter and Jones, 1977; Muramoto et al., 1965, Duncan and Hesketh, 1968; Delaney and Dobrenz, 1974; Nelson et al., 1975). To maximize yield, it would be optimal to combine in one cultivar high values for apparent photosynthesis and a fast rate of leaf area expansion. Of these two characteristics, leaf area expansion rate may be more important. One c o m p o n e n t of leaf area expansion rate is the rate at which individual leaves expand. This study showed that soybean cultivars differ for leaflet expansion rate. However, because single leaflet expansion and total leaf area expansion rates are negatively related to SLW or CER it may be difficult to identify cultivars that combine a fast rate of leaf expansion with a fast rate of apparent photosynthesis. REFERENCES Curtis, P.E., Ogren, W.L. and Hageman, R.H., 1969. Varietal differences in soybean photosynthesis. Crop Sci., 9: 323--327. Delaney, R.H. and Dobrenz, A.K., 1974. Morphological and anatomical features of alfalfa leaves as related to CO2 exchanges. Crop Sci., 14: 444--447. Dornhoff, G.M. and Shibles, R.M., 1970. Varietal differences in net photosynthesis of soybean leaves. Crop Sci., 10: 42--45. Dornhoff, G.M. and Shibles, R.M., 1976. Leaf morphology and anatomy in relation to CO2-exchange of soybean leaves. Crop Sci., 16: 377--381. Duncan, W.G. and Hesketh, J.D., 1968. Net photosynthetic rates, relative leaf growth rates, and leaf number of 22 races of maize grown at eight temperatures. Crop Sci., 8: 670--674. Ford, D.M., Shibles, R. and Green, D.E., 1983. Growth and yield of soybean lines selected for divergent leaf photosynthetic ability. Crop Sci., 2 3 : 5 1 7 - - 5 2 0 . Green, D.E., Burlamaque, P.F. and Shibles, R., 1977. Performance of randomly selected soybean lines with semideterminate and indeterminate growth habits. Crop Sci., 17: 335--339. Hofstra, G., Hesketh, J.D. and Myhre, D.L., 1977. A plastochron model for soybean leaf and stem growth. Can. J. Plant Sci., 57: 167--175. Kaplan, S.L. and Koller, H.R., 1977. Leaf area and CO2-exchange rate as determinates of the rate of vegetative growth in soybean plants. Crop Sci., 17: 35--38. Lugg, D.G. and Sinclair, T.R., 1979. A survey of soybean cultivars for variability in specific leaf weight. Crop Sci., 19: 887--892. Lugg, D.G. and Sinclair, T.R., 1980. Seasonal changes in morphology and anatomy of field-grown soybean leaves. Crop Sci., 20: 191--196. Muramoto, H., Hesketh, J. and E1-Sharkawy, M., 1965. Relationship among rate of leaf area development, photosynthetic rate, and rate of dry matter production among American cultivated cottons and other species. Crop Sci., 5: 163--166. Nelson, C.J., Assay, K.H. and Horst, G.L., 1975. Relationship of leaf photosynthesis to forage yield of tall rescue. Crop Sci., 15: 476--482. Potter, J.R. and Jones, J.W., 1977. Leaf area partitioning as an important factor in growth. Plant Physiol., 59: 10--14.
279 Wiebold, W.J., 1975. Heritability of net photosynthesis and related leaf characters in soybeans. MSc Thesis, Iowa State University, Ames, IA. Wiebold, W., Shibles, R.M., Green, D.E. and Morgan, T., 1981. Selection of net CO2exchange and related leaf characters in early generations of soybeans. Crop Sci., 21: 969--973.