There is evidence that high-tillering, small-panicled pearl millet landraces are better adapted to the severe, unpredictable drought stress of the arid zones of northwestern (NW) India than low-tillering, large-panicled modern varieties, which significantly outyield the landraces under favourable conditions. In an experiment conducted in Jodhpur, Rajasthan, India, during the rainy seasons of 1988 and 1989, we analysed the relationship of arid zone adaptation with the expression, under optimum conditions, of yield components that determine either the potential sink size or the ability to realize this potential. The objective was to test whether selection under optimum conditions for yield components can identify germplasm with adaptation to arid zones in NW India, as this could potentially improve the efficiency of pearl millet improvement programmes targeting arid zones. We used data from an evaluation of more than 100 landraces from NW India (Rajasthan, Punjab and Gujarat), conducted under both severe drought stress and favourable conditions. The average grain yields ranged from 14 to 182 g m-2. The landraces were grouped into clusters based on their phenology and yield components, as measured under well-watered conditions in south India. In environments without pre-flowering drought stress, the tillering type had no effect on potential sink size, but low-tillering, large-panicled landraces had higher grain yields, as they were better able to realize their potential sink size. In 2 low-yielding arid zone environments which experienced pre-anthesis drought stress, low-tillering, large-panicled landraces had lower grain yields than high-tillering ones with comparable phenology, because of both a reduced potential sink size and a reduced ability to realize this potential. The results indicated that the high grain yield of low-tillering, large-panicled landraces under favourable conditions is due to improved partitioning rather than resource capture. However, under severe stress with restricted assimilate supply, high-tillering, small-panicled landraces are better able to produce a reproductive sink than are large-panicled ones. Selection under optimum conditions for yield components representing a resource allocation pattern favouring high yield under severe drought stress, combined with a capability to increase grain yield if assimilates are available, was more effective than direct selection for grain yield in identifying germplasm adapted to arid zones. Incorporating such selection in early generations of variety testing could reduce the reliance on random stress environments. This should improve the efficiency of millet breeding programmes targeting arid zones
