Canopy Development and Light Absorption of Grain Legume Species in a Short Season Mediterranean-type Environment

Leaf area index (LAI), fractional canopy light interception (F) and plant mortality at maturity, were determined for nine short-duration pigeonpea ( Cajanus cajan L.] Millsp.) genotypes in response to drought during the late-vegetative and flowering (stress 1), the flowering and early podfill (stress 2), or podfill (stress 3) stages. LAI and F were reduced, but plant mortality did not increase under drought. Stress 2 reduced LAI to the greatest extent, consistent with the effects on seed yield. At the end of stress 1, seed yield was closely related to LAI for the different genotypes in stressed but not in unstressed (control) plots. Reductions in LAI due to reproductive growth were as great or greater than those due to water stress. Indeterminate genotypes had smaller but more leaves per plant compared to the determinate genotypes. The importance of these differences to drought resistance was not apparent. Production of leaves with decreasing specific leaf area throughout plant growth may be advantageous, especially when drought is likely to occur during reproductive growth. Values of F during and following water stress gave an indication of genotypic drought resistance, with the most drought-sensitive genotype showing the largest reduction in F under water stress and the slowest rate of recovery following rewatering. For short-duration pigeonpea, where plant mortality is not a factor under water stress, the maintenance of both LAI and F appears to indicate genotypic drought resistance.