CHARACTERIZATION OF SELECTED KENYAN COWPEA CULTIVARS FOR TOLERANCE TO ACIDITY

Abstract

Acid soils are normally deficient in available phosphorus and have high levels of soluble aluminium. Crops vary in sensitivity to acidity and associated stresses. Kenyan varieties of cowpea have not been tested for tolerance to acidity and phosphorus deficiency. This study was conducted to assess the response of selected cowpea cultivars to acidity and aluminium stress under laboratory and field conditions. A total of nine cowpea cultivars namely UOE-COWPEA-1, UOE-COWPEA-2, UOE-COWPEA-3, UOE-COWPEA-4, UOE-COWPEA-5, KENKUNDE-1, K-80, M-66 and KVU-27-1, were screened in culture solution containing 0 µM and 185 µM AlCl 3 at a pH of 4.3 and four which showed a greater ability to modify the culture solution pH and a higher relative net root length were further evaluated in the field. pH values of the culture solution were taken daily for a period of six days without adjustment. Root and shoot lengths were measured and recorded after six days. The field experiment were laid out in RCBD, where the two main plots were either limed (4 t/ha) or not limed. The treatments were phosphorus (TSP) (0.06 t/ha), lime, phosphorus plus lime and control (-P, -L) and four cowpea cultivars; UOE-COWPEA-2, KVU 27-1, K-80 and KENKUNDE-1 were grown for a duration of four months. Soil samples were analyzed prior to and after planting. Plant height, total number of leaves per plant, total number of branches per plant, leaf area per plant, plant biomass, number of pods per plant, pod length, number of seeds per pod, 100 seed weight and seed yield per plant were assessed using standard procedures. The nine cowpea cultivars screened increase the pH of the culture solution as the days progressed. The increase in the culture solution pH could be due to cowpea cultivars secreting chelating agents that reduce H + thereby increasing the culture solution pH and reducing Al toxicity. UOE-COWPEA-4 cultivar grown at 185 µM Al was the most tolerant with higher relative net root length (75.6%) while UOE-COWPEA-1 cultivar was the most Al sensitve (63.7%). Lime increased the soil pH from 5.23 to 6.37 while both P+L increased soil P to the maximum of 28.93 mg/kg with K-80 cultivar. UOE-COWPEA-2 produced the greatest number of leaves (52) and number of pods per plant (59) while K-80 yielded the highest total seed weight per plant (42g) with KENKUNDE-1 recording the greatest number of seeds per pod (12) all under phosphorus plus lime treatment. UOE-COWPEA- 2, UOE-COWPEA-4, UOE-COWPEA-5, K-80 and KEN-KUNDE-1 cultivars that showed greater promise in modifying the pH, superior growth and yield attributes, could be grown in acidic soils. The cultivars can be tested further to establish their stability in alleviating acidity.