Abstract
Drought resistance and biological nitrogen fixation (BNF) potential of 437 diverse cowpea genotypes were determined. Plants were grown in irrigated and dryland plots in 1979 and 1980 near Lubbock, Texas. Drought resistance was determined by measuring shoot dry weight, 55 and 77 days after planting (DAP) in both dryland and irrigated plots in 1980. Genotypes were classified as either resistant or susceptible by five methods: (1) Shoot dry weight in dryland plots, 55 and 77 DAP (SDW). (2) Percent reduction in SDW, 55 and 77 DAP (SDW%). (3) Rate of growth in dryland plots (RATE). (4) Percent reduction in RATE (RATE%). (5) Mean productivity expressed as average performance in both environments (MP). MP was not found to be suitable as a screening method. Results indicated that identification of drought resistant germplasm requires screening on the basis of an absolute measurement of performance, such as SDW or RATE, in combination with a percent reduction method, such as SDW% or RATE%. BNF potential was determined by measuring plant specific activity (PSA) by the acetylene reduction assay and nodule weight in irrigated plots, 55 DAP in 1979. Using these methods, several high nitrogen fixing, drought resistant genotypes were identified. Additional evidence indicated that techniques must be developed to reduce the confounding effects of flowering and fruit development when screening for BNF potential. Several greenhouse experiments were conducted using drought resistant and susceptible genotypes with high or low nitrogen fixing potential to study the relationship between water stress and BNF. Leaf water potential (LWP), PSA, nodule weight and number, and root fresh weight were determined after stress had occurred. Results suggested that resistant genotypes are capable of maintaining higher LWP during stress. Furthermore, LWP was found to have a significant impact on PSA. Breeding for environmental adaptation to adverse conditions, such as drought, may ultimately be more beneficial than attempting to improve BNF directly. Additional experiments reported the use of a non-destructive acetylene reduction assay and evidence for differential cuticular resistance to water loss among drought resistant and susceptible genotypes.
Walker, David Wayne (1983). Influence of genotype on drought resistance and nitrogen fixation in cowpea (Vigna unguiculata (L.) Walp.). Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -400271.