Water-Deficit Stress Alters Intra-Panicle Grain Number In Sorghum

Despite the ability of sorghum [Sorghum bicolor (L.) Moench] to withstand harsh environmental conditions, it is susceptible to water-deficit stress during grain filling. To identify postflowering, drought-tolerant sorghum genotypes, parents of nested association mapping populations were evaluated under controlled and water-deficit conditions in greenhouse and field conditions. In both experiments, water-deficit stress was imposed by withholding water during the grain-filling period. In field experiments, rootzone soil moisture was measured weekly using a neutron probe to quantify the plant available water under well-watered and water-deficit conditions. Investigations were focused on determining the variability in the grain-filling pattern across different positions within the panicles (intra-panicle) of 11 different sorghum genotypes. Water-deficit conditions characterized by low plant available water had a consistently negative association with grain number along different positions in the panicle. Our findings indicate that maintaining grain numbers per panicle under postflowering water deficit is more important than increasing individual grain weight. Among the tested genotypes, SC35 and SC1103 were most tolerant to water-deficit conditions under greenhouse and field conditions, respectively. Currently available biparental populations developed using these genotypes provide an opportunity to enhance tolerance to postflowering water-deficit stress in sorghum.