EFFECTS OF SHORT-TERM WATERLOGGING ON CULTIVARS OF COWPEA [VIGNA-UNGUICULATA (L) WALP]

Greenhouse-grown plants of three cultivars of cowpea [Vigna unguiculata (L.) Walp.], with differing levels of tolerance to waterlogging, were subjected to four cycles of moderate waterlogging (MWL) or severe waterlogging. Leaf relative water content was reduced by waterlogging in the susceptible cultivar while it was increased in the tolerant cultivar, and was associated with a greater increase in stomatal resistance (r(s) and a greater reduction in dry matter production in the former. Leaf water potential (PSI(L)), leaf area (LA) per plant, transpiration rate, and net photosynthesis were all reduced by waterlogging with no cultivar difference in response. Leaf weight ratio (LWR) was reduced in the MWL treatment only and to a greater extent in the susceptible cultivar, while stem weight ratio (SWR) was increased by waterlogging and was highest in the susceptible cultivar. After the first cycle of waterlogging there was little change in PSI(L), LA, or dry weight of waterlogged plants but LWR declined while SWR increased with the number of waterlogging cycles, and the respective relative changes in LA, LWR, and SWR suggest that some adaptation to waterlogging occurred in the severely waterlogged treatment. Waterlogging greatly reduced the number of secondary roots per plant (except in the intermediate cultivar) and stimulated the development of aerenchyma within the bases of the stem and main root. It is suggested that cultivar differences in the number of secondary roots maintained and in the extent and distribution of aerenchyma may contribute to the relative tolerance of the cultivars to waterlogging.