Phenotypic Changes in Grain Sorghum Over the Last Five Decades

Sorghum [Sorghum bicolor (L.) Moench] is a drought-tolerant crop, and its productivity in rain fed environments has increased since the 1950s. This increase is due to changes in agronomic practices and hybrid improvement. The objective of this study was to determine what aspects of grain sorghum morphology, physiology and water use have changed with hybrid improvement and might have contributed to this yield increase. A 2-year greenhouse experiment was conducted with one hybrid from each of the past five decades. The hybrids were studied in well-watered and pre- and post-flowering water deficit conditions. Total water use, transpiration, stomatal conductance and photosynthesis were measured during the growing period. Biomass and biomass components were measured at harvest. There was no consistent change in the leaf physiological parameters resulting from hybrid advancement. In contrast, total water use increased in rate of 8.5 cm 3 kg soil(-1) year(-1) from old to new hybrids in the well-watered treatments. Root biomass also increased in rate of 0.2 g plant(-1) year(-1). Leaf biomass and panicle length also was greater for the newest compared with the older hybrids. Hybrid advancement was related to increase in panicle length but decrease in peduncle length. Results indicated that hybrid development programmes created hybrids with improved drought avoidance, due to better root density of newly released hybrids, or hybrids with better resource use which ultimately increased yield under rain fed conditions.