A Survey of Soybean Cultivars for Variability in Specific Leaf Weight¹

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.

Soybean leaf photosynthesis in relation to maturity classification and stage of growth

“…Their analysis of genotypic differences indicated a positive correlation between photosynthesis and specific leaf weight and a negative correlation with diffusive resistance. Similar correlations were reported by Hesketh et al [13], Dornhoffand Skibles [7], Bowes et al [3] and Lugg and Sinclair [19].…”

Association of specific leaf weight, an estimate of chlorophyll, and chlorophyll concentration with apparent photosynthesis in soybean

“…Maximum SPAD values were attained at the R5 to R6 growth stage, which are the same growth stages where maximum SLW values (Lugg and Sinclair 1979) and AP rates (Dornhoff and Shibles 1970;Hesketh et al 1981) have been reported. The fluctuation of chlorophyll content throughout the season indicates that it was probably more sensitive to environmental conditions than either of the other two traits, however the variation within each sample date was similar for all three leaf traits.…”

Leaf area index simulation in soybean grown under near-optimal conditions

“…Specific leaf area (SLA) is the ratio of one sided leaf area to the dry matter of the leaf (cm −2 g −1 ) and is used to calculate the rate of change in leaf area based on the rate of change in leaf dry matter. SLA varies in different environments, developmental stages, and strata of leaves within the canopy (Gunn et al, 1999;Lieth et al, 1986;Lugg and Sinclair, 1979). The mechanism of such flexibility in SLA is still not known and thus the variable often becomes the source of uncertainty in models that rely on SLA in simulating LAI (Tardieu et al, 1999).…”

“…The mechanism of such flexibility in SLA is still not known and thus the variable often becomes the source of uncertainty in models that rely on SLA in simulating LAI (Tardieu et al, 1999). Lugg and Sinclair (1979) showed that SLA of the uppermost fully expanded soybean leaf varied from 0.333 cm 2 mg −1 at R1 to 0.146 cm 2 mg −1 at R6. If an average SLA is assumed under such conditions, calculated LAI based on leaf dry matter and SLA is 64% higher than the actual LAI at R6.…”