Grain growth of Pennisetum glaucum (L.) R.Br. under well-watered and drought-stressed conditions

Abstract

The objective of this study was to investigate the possibility of relationships between grain growth parameters and drought response. Grain growth parameters of more than 70 millet lines were assessed under well-watered and postflowering drought-stress conditions in two field trials at the ICRISAT Sahelian Center, Sadoré, Niger. All the grain growth parameters based on thermal time varied more than two-fold between lines in both moisture environments. Single grain mass of the lines ranged from 4.3–10.9 mg under well-watered conditions and 3.4–9.4 mg under drought stress. When averaged across trials, 51% of the accounted variance of final grain mass could be explained by differences in the grain growth rate under well-watered conditions, while differences in the duration of the linear grain growth phase accounted for 37% of the variation in final grain mass. Drought stress reduced the linear grain growth phase and, as a consequence, reduced final grain mass by up to 25%. Lines with long grain filling periods under well-watered conditions had larger reductions in the grain filling period and in final grain mass under stress. In general, there was little effect of drought stress on the grain growth rate. However, because of the negative correlation of grain growth rate and linear grain growth phase, lines with higher grain growth rates in well-watered conditions had smaller reductions in grain filling period under stress. Grain growth rate accounted with 38% for the major part of the variation in grain mass under stress conditions. Grain growth parameters in well-watered and drought-stress conditions were unrelated to drought tolerance as expressed by a drought response index, and were indicators of neither susceptibility nor tolerance to stress. However final grain mass was highly correlated to yield under stress. A feasible risk-reducing strategy in the likelihood of postflowering stress is to select pearl millet lines for drought escape with a high grain growth rate combined with a relatively short grain filling period.