A simple screening method for drought tolerance in cowpea

A simple screening method was developed that accurately discriminates between drought and susceptible cowpea(Vigna unguiculata(L) walp). Wooden boxes (130 cm length. 65cm width. 15cm depth) made of 2.5cm thick planks were lined with polythene sheets, filled with a 12cm layer of soil and sand mixture(1.1) and kept on the table top in a screenhouse. Test materials were planted in the boxes with 10cm between rows and 5cm between plants within the row and watered daily until the partial emergence of first trifoliate, after which watering was stopped. Percent permanent wilting was recorded at various intervals for each line until the partial emergence of the first trifoliate, after which watering was stopped

Relative drought tolerance of major rainfed crops of the semiarid tropics

Ten crop species were evaluated for their relative drought tolerance at the seedling stage. Healthy seeds of each crop were planted in wooden boxes of 130 cm length, 65 cm width and 15 cm depth, filled with 3 soil types (river sand, loamy sand and sandy loam) and watered daily. A week after germination watering was stopped and the reaction to progressive water stress was observed. Based on percentage dead plants at various time intervals and days taken to 100% dead plants, soyabean (Glycine max) appeared the most drought susceptible and cowpea (Vigna unguiculata) the most drought tolerant. The overall ranking of the crops in the increasing order of drought tolerance was: soyabean < black gram (V. mungo) < green gram (V. radiata) < groundnut (Arachis hypogaea) < maize (Zea mays) < sorghum (Sorghum bicolor) < pearl millet (Pennisetum glaucum) < bambara nut (V. subterranea) < lablab bean (Lablab purpureus) < cowpea. The water stress induced using soil with a higher sand content was too severe for crops other than cowpea and lablab bean. With increased clay content and gradual water stress, it may be possible to use this method to detect varietal differences in less drought tolerant crop

Two mechanisms of drought tolerance in cowpea

Twelve cowpea (Vigna unguiculata) varieties were planted in wooden boxes of 130 cm length, 65 cm width, and 15 cm depth filled with sand and soil mixture (1:1) at 10 cm row to row and 5 cm plant-to-plant distances. The boxes were watered daily until the unifoliate leaves had fully expanded and the first trifoliates were beginning to emerge. Watering was then stopped to impose moisture stress, and effects of drought on the unifoliate and trifoliate leaves as well as growing tips were studied. Two types of drought tolerance mechanisms were observed. Under drought stress Type 1 drought tolerant lines TVu 11986 and TVu 11979 stopped growth and conserved moisture in all the plant tissues, stayed alive for over two weeks and gradually the entire plant parts dried together. The Type 2 drought tolerant lines like Dan Ila and Kanannado continued slow growth of the trifoliates. However, with continued moisture stress, the unifoliates of these varieties showed early senescence and dropped off but the growing tips remained turgid and alive for longer, suggesting that moisture was being mobilized from the unifoliates to the growing tip

Inheritance of drought tolerance in cowpea

This study was undertaken to elucidate the nature of inheritance of the two types of drought tolerance in cowpea {Vigna unguiculata (L.) Walp} so that the drought tolerant can be effectively used in breeding programme. Three cowpea lines viz TVu 11986 willi ‘Type l' drought tolerance, Dan IIa with ‘Type 2' drought tolerance and TVu 7718 as susceptible to drought were crossed in all possible combinations. The genetic segregation revealed that drought tolerance is a dominant trait and both ‘Type I' and ‘Type 2' reactions are controlled by a single dominant gene but the genes are different in the two types. These are being designated as ‘Rds 1' (resistance to drought stress) and ‘Rds 2'. Test of allelism indicated that ‘Type 1' is dominant over ‘Type 2' and the F2 population between the two types segregated to 3 ‘Type 1': 1 ‘Type 2' plants indicating that the two genes for drought tolerance are either alleles at the same locus or tightly liriked. Efforts are being made to transfer these genes into improved varieties. However, due to allelic relationship, or close lirikage, both types of drought tolerance may not be bred in the same cowpea line

Genomics-assisted breeding for drought tolerance in cowpea

Published online: 02 July 2019The importance of cowpea, Vigna unguiculata, in human and animal nutrition and sustainability of soil fertility are recognized globally especially in sub-Saharan Africa (SSA) where the crop is mainly produced in the Savanna and the Sahelian agro ecologies. However, cowpea productivity is adversely affected by both biotic (insect pests, diseases, parasitic weeds, nematodes) and abiotic (drought, heat, low soil fertility) constraints. Appreciable progress has been made in the improvement of cowpea for resistance to some biotic stresses particularly diseases such as bacterial blight, ashy stem blight, marcophomina, parasitic weeds like Striga and Alectra and some insects like aphid, leaf and flower thrips among others. There is need for intensifying research activities with focus on improving cowpea resistance to abiotic stresses. As a crop grown commonly in arid regions, cowpea is subjected to seedling stage, midseason and terminal droughts. In the recent past, the amount of rainfall, during the cropping season in the dry savannah regions of SSA, is getting less. Consequently the cropping season is getting shorter occasioned by late commencement or early cessation of the rain. Farmers in the cowpea producing areas of SSA generally have no access to irrigation hence their crops are grown under rain-fed conditions. With the impending higher frequency of drought in the dry savannah region due to climate change, efforts should be made in developing climate resilient cowpea varieties that farmers will grow. Efforts have been made in enhancing tolerance to drought in some improved cowpea varieties using conventional breeding but progress has been slow in this regard. Drought tolerance is a complex trait and many genes are involved in its inheritance. Pyramiding of these genes in improved varieties would therefore, be desirable. Such varieties with pyramided genes are likely to be stable in performance over the years and across several locations in the savannahs. Recent developments in molecular biology could play significant role in the development of such resilient varieties. In a number of crops, molecular markers associated with resistance loci have been identified and are being used in marker assisted breeding. Marker assisted backcrossing (MABC) is the choice when single traits that are simply inherited are to be moved to varieties with superior performance but lacking in the trait being transferred. Also, marker assisted recurrent selection (MARS) has shown promise in accumulating multiple genes in improved varieties of some crops. Some work has been initiated in cowpea on the use of MARS to pyramid resistance to Striga, yield and drought. Results obtained so far show the potential of this method in pyramiding desirable genes in cowpea. As more resources get committed to cowpea research a solid foundation would be established for the generation of molecular tools that should facilitate their routine application to the improvement of the crop