Morphological and physiological responses of cowpea (Vigna unguiculata (L) Walp.) cultivars to induced water stress and phosphorus nutrition

[摘要] ENGLISH ABSTRACT:Cowpeas are produced under low and irregular rainfall in most of arid and semi-aridareas of sub-Saharan Africa. Growth and yield are therefore reduced due to the occurrenceof water stress during the growing season. Knowledge of the responses and adaptivemechanisms of cowpeas to water stress may help to improve the management practices forthese areas. Therefore, three glasshouse experiments were conducted at WelgevallenExperimental Farm of the University of Stellenbosch to test the responses of two cowpeacultivars to water stress. In the first experiment, physiological responses were used toidentify those physiological parameters, which can be used to distinguish between droughttolerant and susceptible cowpea cultivars. In the second experiment, some of the identifiedphysiological parameters together with some morphological growth responses, yield andgrain protein content of the same two cowpea cultivars were used to identify which is themore tolerant cultivar. Tn the third experiment, the hypothesis that increased phosphorussupply may improve the tolerance of cowpea plants to water stress and their ability ofrecover from the stress was tested. The results showed that water stress affected waterrelations, morphological growth parameters, yield and grain protein content, butincreasing P supply reduced the effect of water stress and promoted more rapid recoveryafter re-watering. Water relations were affected by water stress because it reduced relativewater content, which resulted in reduced water potential and increased leaf diffusiveresistance and proline accumulation. Morphological growth responses and yields wereaffected because water stress reduced the leaf area, which resulted in reduced biomassproduction and seed yield. Lower leaf area under water stress was the result of the reducednumber of leaves and leaf expansion rate, but the number of leaves was the mostimportant parameter. Reduced seed yield was due to reduced number of pods. Theresponses of the two cultivars tested were different. AB Wit, which performed betterunder well-watered conditions was more affected by water stress due to its larger leaf areathat resulted in excessive water loss by transpiration. ACH14 was more drought tolerantthan AB Wit due to a combination of a more rapid stomatal closure and prolineaccumulation, which induced osmotic adjustment, and which in tum helped to maintainhigher water potentials. The increased P supply reduced the effect of the water stress.High-P level plants showed higher root growth, which resulted in more water uptake andlarger leaf area during the water stress period, and after re-watering these plants recoveredmore rapidly. The more rapid recovery from stress was the result of enhanced root growthand leaf expansion rate and most probably due to increased water uptake. High-P levelplants also showed more rapid leaf appearance and plant growth at earlier stages comparedto the low-P level plants.

[发布机构] Stellenbosch University