Characterizing Drought Resistance in Soybean Using Spectral Reflectance Indices.

Drought has been a problem for farmers since humans moved from hunter gatherers to producers. Soybean populations have been developed which segregate for traits related to drought tolerance. One of those populations is a mapping population of F3- and F5-derived recombinant inbred lines (RILs) from a cross between ‘KS4895’ and ‘Jackson’. Some progeny in this population maintain nitrogen fixation traits under drought better than other progeny. The objective of this research was to determine if spectral reflectance could differentiate progeny with different levels of drought tolerance. Using a multi-spectral crop canopy sensor (CropCircle AES-470), reflectance data was measured on 90 different genotypes, nine days during the growing season in 2013, between the vegetative stage V4 and the reproductive stage R6. From these readings two normalized differential vegetative indices (NDVI) were calculated and correlated to data on shoot nitrogen (gN 100g^-1), shoot ureide (umol g^-1), nodule number (no. plant^-1), nodule size (mm), individual nodule weight (mg nodule^-1), total nodule weight (g plant^-1), canopy wilting (0-100 scale), and seed yield (bu/a). NDVIs differ significantly among the genotypes during reproductive stages of development. NDVI values significantly increased with increasing shoot nitrogen, nodule number, and seed yield. Based on these observations it may be possible to predict a plant response to stress using NDVI, however accurate evaluations depended upon the growth stage of the plant, the time of day readings were taken, and the environmental conditions at the time of the readings.