Abstract
The cowpea (Vigna unguiculata (L.) Walp) it is a leguminous widely cultivated in Northeast of Brazil. In the state of Ceara, its cultivation is performed mainly by family farms who make use of traditional varieties of good adaptation to the growing region. Thus, characterizing traditional varieties with characteristics of adaptation to regions with water shortage is essential for the production of food in the world, especially in semi-arid regions. In this sense, the objective was to evaluate the physiological and biochemical responses in three genotypes of cowpea, being two traditional varieties grown in Ceara (Sempre-Verde and Cabeça-de-Gato) and a genotype characterized as a standard of drought tolerance (Pingo-de-Ouro-1,2) under three water regimes: irrigated, moderate deficit and severe water deficit. The parameters evaluated were: gas exchange, chlorophyll a fluorescence, photosynthetic pigments, organic solutes (proline, total carbohydrates, reducing and non-reducing carbohydrates), starch and enzyme activity (APX, G-POD, CAT and SOD). The genotype Pingo-de-Ouro-1,2 confirmed its tolerance pattern in a water deficit condition, presenting greater water potential, higher photosynthetic rate, high levels of total carbohydrates and high accumulation of proline. Among the traditional varieties, the Cabeça-de-Gato presented superior photosynthesis to Sempre-Verde higher Electron Transport Rate (ETR), reflecting in a greater photochemical quenching (qP) and a greater accumulation of proline, indicating that this variety presents more pronounced adaptive characteristics for water restriction conditions, which is a common condition to the Brazilian semiarid.
Highlights
The cowpea (Vigna unguiculata (L.) Walp.) is a legume originating in West Africa, having great nutritional and economic importance where it is cultivated, such as the semi-arid tropics, Asia, Africa, south-east Europe, and Central and South America
The tolerant genotype maintained constant the number of leaves (NF) and leaf area (LA) independent of the presence or absence of stress, presenting the lowest values when compared to the Sempre-Verde varieties in the severe deficit (Figures 2B and 2C)
This modulation can be considered a mechanism of escape to desiccation, once the reduction of the transpiratory area keeps the water status higher for a longer time
Summary
The cowpea (Vigna unguiculata (L.) Walp.) is a legume originating in West Africa, having great nutritional and economic importance where it is cultivated, such as the semi-arid tropics, Asia, Africa, south-east Europe, and Central and South America. Water is considered the most important and limiting resource for growth and crop productivity, making its restriction one of the most prejudicial abiotic stresses in relation to ability, survival and yield of crops (Pinheiro & Chaves, 2011; Simova-Stoilova et al, 2015; Gagné-Bourque et al, 2016). To deal with these water restriction conditions the plants developed, over time, a variety of adaptive strategies, based on the concepts of escape, avoidance and tolerance (Goufo et al, 2017). An example would be the development of mechanisms of control at the physiological level, such as, regulation of stomatal opening, directly affecting the perspiration and CO2 assimilation
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