Growth Analysis of Soybean Isolines Differing in Pubescence Density1

Abstract

AbstractGenetic variation in soybean plant morphology is of interest beause of its possible utility in developing cultivars adapted to unique environments. Growth analysis techniques were used to quantify and compare soybean [Glycine max(L.) Merr.] growth in genotypes differing in pubescence density. The experiment was conducted in 1980 and 1981 at Mead, NE on a Typic Argiudoll soil. Data from frequent samplings of phytomass dry weight (W), leaflet dry weight (LW), leaf area (A) and number of leaflets (N) were collected during two crop seasons from near‐isogenic lines of dense and normal pubescent types of ‘Clark’ and ‘Harosoy’ cultivars. Statistical curve‐fitting tests identified the most plausible mathematical models for describing the change of these four variables over time. Ten growth analysis parameters based on these four model equations were then computed and included crop growth rate (CGR), net assimilation rate (NAR), leaf area ratio (LAR), relative growth rate (RGR), leaf weight ratio (LWR), specific leaf area (SLA), relative leaf growth rate (RLGR), relative leaf area expansion rate (RLAER), leaf area partitioning factor (LAPF), and area per leaflet (APL). Dense pubescence affected the growth parameters differently in the two cultivars. There was no difference in any parameter between dense and normal pubescence lines in Clark. The W, LW, A, N, and CGR were, however, affected by pubescence density in Harosoy. The CGR was about 20% greater at maximum growth in the dense Harosoy isoline. The NAR was unaffected, however, indicating that the higher photosynthetic rate in the Harosoy dense pubescent isoline was due to an increase in leaf area and not an increase in photosynthetic efficiency. The fact that the gene giving rise to dense pubescence had differential effects on growth in the two cultivars suggests that the genetic background into which the gene is introduced influences the effect of the gene on growth.