A Survey of Soybean Cultivars for Variability in Specific Leaf Weight1

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Abstract
The objective of this study was to determine the variability in specific leaf weight (SLW) of 373 soybean [Glycine max (L.) Merrill] lines, to examine the seasonal changes in SLW, and to determine the consistency in the ranking of selected lines over a 3‐year period. Consistency in these data would provide a basis for selecting lines for further, intensive physiological study. The SLW was sampled in the field with a leaf punch on the uppermost fully expanded leaf that was in full sunlight. For the whole collection, SLW was sampled at two growth stages, R2 (full‐bloom) and R5 (beginning to mid‐podfill). The mean SLW increased between these stages from 3.08 to 6.46 mg/cm2, while the standard deviations were 0.36 and 0.77 mg/cm2, respectively. Significant differences among lines were found at both growth stages. Chlorophyll deficient genotypes generally had low SLWs, while dwarf types were high. Cultivars derived from ‘Harosoy’ had significantly higher. SLWs at R5 with a mean of 7.12 than those derived from ‘Lincoln,’ mean of 6.24 mg/cm2, respectively. For 20 lines in 1976 and 10 in 1977, SLW was sampled on a weekly basis. We saw an increase in SLW from flowering to after mid podfill, and then a sharp decline. The SLW at R5 in 1975 correlated well with maximum SLWs in 1976 and 1977. Solar radiation levels influenced SLW. We found a linear relationship between the mean SLW at each sampling date and the radiation received in the week before sampling at R2 in 1975, and maximum SLW was significantly affected in 1976 and 1977.