Efeito do stress hídrico no rendimento e conteúdo protéico do grão do feijão nhemba

Abstract

Cowpea (Vigna unguiculata (L.) Walp) is a legume with high protein value that every day gains greater agro-economic value, thanks mainly to its characteristic of adaptability to adverse conditions. It is produced in a rainfed regime in most of the arid and semi-arid regions of sub-Saharan Africa. The low yields of cowpea are the result of the use of unimproved seeds, low fertility soils and irregular rainfall. The availability of water is an important factor in terms of maximizing agricultural productivity gains. Therefore, its growth and yield are reduced due to the occurrence of water stress. Knowing the response of some nhemba varieties to conditions of limited water availability may allow rural populations to be recommended to use the most resistant varieties to water stress. Therefore, a trial was conducted in Boane District, Estação Agrária de Umbelúzi, in order to test the response of 6 cowpea varieties to water stress. Seed yield and protein content were used to identify the most water-stress tolerant varieties. Growth and yield were affected because water stress reduced leaf area, which resulted in little biomass and grain production. The reduced leaf area under water stress conditions was due to the reduced number of leaves and the reduced rate of leaf expansion, but the number of leaves was the factor that most contributed to the reduction in leaf area. The low seed yield resulted from a lower number of pods per plant. The six tested varieties responded differently to water stress. Of the six varieties, three (INIA-46, TIMBAWENE MOTEADO and TIMBAWENE CRÈME), did not register yield. The variety TIMBAWENE AMANE, with local genetic status, prostrate growth, with broad leaves, showed better vigor under the conditions of water availability, but it was the variety that recorded the lowest yield, due to its larger leaf area that contributed to an excessive loss of water by sweating. The SUDAN variety showed higher yield followed by IIT 82E-16, both with erect growth, improved genetic status, due to the rapid closure of stomata and proline accumulation, which induced osmotic adjustment and contributed to maintain high water potential.