Root Characteristics of Soybean Stem-Termination Isolines.

Soybean near-isogenic lines that possess alleles conditioning various traits, including plant architectural traits, are available.  While shoot growth and yield characteristics of stem termination isolines have been investigated, little is known about the effects of the different alleles on root growth. In this study we examined the root systems of “Clark”, and it’s isolines L62-1251, and L63-3297 with indeterminate, semi-determinate, and determinate growth habits, respectively.  Plants were grown in 1.5 m long PVC pipes, installed in the field, during 2010 season. Roots were harvested destructively in 0.15-m increments at five different growth stages.  Roots were washed free of soil, scanned, and images analyzed with winRhizo software.  No significant differences for rooting depth were observed at vegetative growth stages.  During reproductive stages, Clark recorded the deepest and it’s determinate isoline the shallowest root system, and the semi-determinate isoline exhibited an intermediate root phenotype.  Root numbers of the determinate isoline were highest at the first harvest in the top 60cm, while a greater number of roots was observed for the semi-determinate line below 0.6 m.  Similar to root length, root number increased enormously for Clark in the 0-0.3-m layer during reproductive growth.  A significant correlation between root number and root volume was noticed for 0-0.6 m at all harvest dates.  Shoot characteristics assess were consistent with the growth habit of the isolines.  The leaf area and number of nodes was high, medium and low for the indeterminate, semi and determinate lines, respectively.  In agreement with previous literature, the yield of Clark was greater than that of L62-1251 and L63-3297.  These results indicate that the examined alleles conferring differences in stem termination also influence root growth.