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