Root architecture was determined together with shoot parameters under well
watered and drought conditions in the field in three soybean cultivars (A5409RG, Jackson
and Prima 2000). Morphology parameters were used to classify the cultivars into different
root phenotypes that could be important in conferring drought tolerance traits. A5409RG
is a drought-sensitive cultivar with a shallow root phenotype and a root angle of <40°. In
contrast, Jackson is a drought-escaping cultivar. It has a deep rooting phenotype with
a root angle of >60°. Prima 2000 is an intermediate drought-tolerant cultivar with a root
angle of 40°–60°. It has an intermediate root phenotype. Prima 2000 was the best performing
cultivar under drought stress, having the greatest shoot biomass and grain yield under
limited water availability. It had abundant root nodules even under drought conditions.
A positive correlation was observed between nodule size, above-ground biomass and
seed yield under well-watered and drought conditions. These findings demonstrate that root system phenotyping using markers that are easy-to-apply under field conditions can be
used to determine genotypic differences in drought tolerance in soybean. The strong
association between root and nodule parameters and whole plant productivity demonstrates
the potential application of simple root phenotypic markers in screening for drought
tolerance in soybean.