Yield component analysis of grain sorghum grown under water stress

Delayed leaf senescence, or ‘stay green’, in grain sorghum (Sorghum bicolor Moench L.) allows continued photosynthesis under drought conditions which can result in normal grain fill and larger yields compared with senescent cultivars. The objective of this study was to compare the yield response of a sorghum hybrid with stay green genetics and a sorghum hybrid with senescent genetic traits grown in four soil textural classes (clay loam, silt loam, sandy loam, fine sand) to differing levels of water stress to identify traits leading to increased yield under water stress. A stay green (SG) and a senescent (SN) hybrid of grain sorghum were grown in 2010 and 2011, which had contrasting environmental conditions and soil water availability, in 48 weighing lysimeters containing soil monoliths of four regional soils at Bushland, TX, USA. Plant density was 16 plants m−2; irrigation treatments were 19 mm or 28 mm applied weekly. Under water and heat stress, the SG hybrid produced significantly more seeds (∼23,000 seeds m−2) compared with the SN hybrid (∼13,000 seed m−2), both with similar amounts of evapotranspiration. The SN hybrid yields were greater than those of the SG hybrid in the less stressful conditions. Panicle biomass growth rate from flag leaf emergence to beginning seed fill was identified as a period critical for determining seed number. Panicle mass (without grain) at maturity, as an integrated measure of panicle growth rate during this period, was linearly related to seed number for both hybrids in 2011, with the SG hybrid producing 10% more seeds m−2 compared with the SN hybrid with the same panicle mass. The seed mass of the SG hybrid was fairly constant in both minimum stress and stress environments, which was in general significantly smaller than the seed mass of the SN hybrid under all conditions. Under drought conditions, the stay green hybrid maintained yield by retaining greater seed numbers.

► Stay green (SG) and senescent (SN) hybrids of grain sorghum were grown in contrasting environments and water stress levels. ► Under stress, the SG hybrid produced significantly more seeds compared with the SN hybrid with similar water use. ► The SN hybrid yields were greater than those of the SG hybrid in the less stressful conditions. ► The seed mass of the SG hybrid was fairly constant in both minimum stress and stress environments, unlike the SN seed mass. ► Under drought conditions, the stay green hybrid maintained yield by retaining greater seed numbers.