The effects of drought stress on assimilate availability and metabolism in the source and sink organs of common bean (Phaseolus vulgaris L) genotypes
Changes in carbohydrate status and metabolism in the source and sink organs determine rate of growth and yield of plants subjected to drought stress. The objective of this study was to assess the effect of lost-flowering drought stress on assimilate synthesis at source level and availability of the assimilates for metabolism in the reproductive sink organs of common bean (Phaseolus vulgaris L.) genotypes differing in degree of drought resistance. A drought-resistant inbred line (SEA 15) and a drought-susceptible cultivar (BrSp) were grown under non-stress and drought stress commenced at early pod-filling stage. Plants were raised in a vegetation hall during the summer of 2005. Drought stress reduced the seed yields of BrSp and SEA 15 by 53 and 30%, respectively. Harvest index of the susceptible genotype decreased by ca. 29%, whereas no effect of drought was found for the partitioning index in the resistant genotype implying marked differences in sink strength at whole plant level between the genotypes. Drought stress did not affect the concentration of sucrose in leaves and seeds of SEA 15 during most part of the stress period. On the contrary, the stress caused 18 to 30 and 29 to 47% reductions in leaf and seed sucrose concentrations of BrSp, respectively. Relative to control treatments, drought stress decreased seed starch ccumulation of BrSp throughout the stress period (by 16 to 18%) whereas the decrease (by 20%) was found only at 20 d stress for SEA 15. The findings revealed that the underlying differences in sink establishment and yield of the bean genotypes differing in degree of drought resistance reside primarily in the capacity of the source to supply assimilates (i.e. source-strength) under drought conditions.