A comparative assessment of the performance of a stay-green sorghum (Sorghum bicolor (L) Moench) introgression line developed by marker-assisted selection and its parental lines

A glasshouse experiment was conducted to compare the performance of a stay-green QTL introgression line (RSG 03123) and its parental lines (B35, a stay-green and R16, a high yielding cultivar with rapid senescence) after flowering, when water-limited (WL) or well-watered (WW). Flowering time and plant height were similar in RSG 03123 and the recurrent parent, R16. Under WW conditions, retention of green leaf area (GLA) and chlorophyll was similar in RSG 03123 and R16, whereas under WL conditions RSG 03123 retained significantly (P<0.05) more GLA. The rate of senescence was also lower in RSG 03123 as compared to R16 under WL conditions. B35 displayed a delayed onset of senescence under both WW and WL conditions while both R16 and RSG 01323 displayed an earlier onset of senescence under WL conditions. Photochemical efficiency of photosystem II (ΦPSII), gas exchange characteristics, and total soluble carbohydrates contents, in both leaf and stem, were higher in RSG 03123 than in R16 under WL conditions. These parameters were enhanced in RSG 03123 due to higher retention of chloroplast proteins, such as light-harvesting chlorophyll binding protein complex of PSII (LHCPII), oxygen-evolving complex 33 kDa (OEC33), phosphoenolpyruvate carboxylase (PEPC) and the large subunit of ribulose bisphosphate carboxylase-oxygenase (Rubisco). The stay-green characteristics of RSG 03123 were intermediate between R16 and B35; nonetheless, the results show that stay-green QTL are functional during senescence and improve tolerance to water limitation after flowering