Are Portuguese Cowpea Genotypes Adapted to Drought? Phenological Development and Grain Quality Evaluation

SIMPLE SUMMARY: The Mediterranean region is highly vulnerable to climate change, with more prolonged and intense droughts threatening food security and biodiversity. Genetic diversity can provide plant material for breeders to develop crops capable of surviving in adverse conditions while producing nutritious and healthy foods. Cowpea [Vigna unguiculata (L.) Walp.] is a nutritionally rich legume generally considered drought tolerant. Portugal has a vast diversity of cowpea landraces that may contribute to more sustainable agrosystems; however, they remain largely unexplored. Five cowpea genotypes from different regions of the country were evaluated to understand plants’ responses to terminal drought at a phenological level. The physical and nutritional parameters of the produced grains were also assessed. Results indicate early maturation as a strategy to avoid drought in some of these varieties, combined with significant changes in the aerial part of the plants, such as reductions in the number of leaves, flowers, and fruits. Grain quality parameters also revealed adaptation to low water availability environments, with little variations found except for levels of sugars from the raffinose family. No changes were observed in grain weight, grain color, or protein content. This study reveals some fundamental traits of these genotypes to cope with drought and preserve grain quality and their importance in integrating breeding programs. ABSTRACT: Along with population growth, global climate change represents a critical threat to agricultural production, compromising the goal of achieving food and nutrition security for all. It is urgent to create sustainable and resilient agri-food systems capable of feeding the world without debilitating the planet. The Food and Agriculture Organization of the United Nations (FAO) refers to pulses as a superfood, as one of the most nutritious crops with high health benefits. Considered to be low-cost, many can be produced in arid lands and have an extended shelf-life. Their cultivation helps reduce greenhouse gases and increases carbon sequestration, also improving soil fertility. Cowpea, Vigna unguiculata (L.) Walp. is particularly drought tolerant, with a wide diversity of landraces adapted to different environments. Considering the importance of knowing and valuing the genetic variability of this species in Portugal, this study assessed the impact of drought on four landraces of cowpea (L1 to L4) from different regions of the country and a national commercial variety (CV) as a reference. The development and evaluation of morphological characteristics were monitored in response to terminal drought (imposed during the reproductive phase), and its effects were evaluated on the yield and quality of the produced grain, namely the weight of 100 grains, color, protein content, and soluble sugars. Under drought conditions, the landraces L1 and L2 showed early maturation as a strategy to avoid water deficit. Morphological alteration of the aerial part of the plants was evident in all genotypes, with a rapid reduction in the number of leaves and a reduction in the number of flowers and pods by between 44 and 72%. The parameters of grain quality, the weight of 100 grains, color, protein, and soluble sugars did not vary significantly, except for sugars of the raffinose family that is associated with the adaptive mechanisms of plants to drought. The performance and maintenance of the evaluated characteristics reflect the adaptation acquired in the past by exposure to the Mediterranean climate, highlighting the potential agronomic and genetic value, still little exploited, that could contribute to production stability, preserved nutritional value, and food safety under water stress.