Expression and Segregation of Stay- Green in Pearl Millet

摘要

Drought stress can occur any time during the crop cycle, but drought stress during flowering through grain fill results in low and unstable yield of pearl millet [Pennisetum glaucum (L.) R. Br.] (Yadav et al. 2002). Delayed senescence, or stay-green (Borrell et al. 2003; Mahalakshmi and Bidinger 2002; Thomas and Howarth 2000), is a mechanism of drought tolerance characterized by the retention of green leaf area at crop maturity under water-stressed environments (Borrell et al. 2000). Scientific literature concerning stay-green in pearl millet is minimal, so the sorghum model may provide useful information. In sorghum, stay-green is genetically and physiologically complex, expressing a variety of patterns and environmental sensitivities depending onthe background genotype (Thomas and Howarth 2000). Stay-green hybrids partition more carbon and nitrogen to leaves during early growth compared to their senescent types resulting in greater specific leaf nitrogen (Borrell et al. 2003). Higher specific leaf nitrogen after anthesis delays the onset and reduces the rate of leaf senescence. Delayed senescence effectively increases cereal production under water-limited conditions (Yadav et al. 2002). Under post-anthesis water stress-grain, yield is positively correlated with green leaf area at maturity and negatively correlated with rate of leaf senescence (Borrell et al. 2000). Grain yield in cereals is basically a reflection of starch accumulation, which relies on current photosynthate and a non-senescentcanopy (Thomas et al. 2000). Under post-anthesis water stress, stay-green genotypes remain photosynthetically active and continue to fill grain as opposed to the senescent types (Thomas and Howarth 2000), leading to increased grain yield and lodging resistance (Borrell et al. 2003) and disease resistance (Hash et al. 2003). Stay-green sorghums contain more cytokinins and basal stem sugars than do senescent genotypes (Borrell et al. 2000). Increased accumulation of soluble sugar in stay-green types is associated with greater functional leaf area during grain fill, reducing the dependence on stem reserves in grain fill. Higher concentrations of stem sugars improve the digestible energy content of the straw or stalk (Borrell et al. 2000), making stay-green valuable for grain and fodder production (Hash et al. 2003). Since stay-green genotypes remain photosynthetically active during grain fill, their leaves tend to maintain more nitrogen than the senescent types, which may also improve stover quality.