The effect of arbuscular mycorrhizal root colonization on growth and nutrient uptake of two different cowpea (Vigna unguiculata [L.] Walp.) genotypes exposed to drought stress

In the present investigation, the effect of arbuscular mycorrhiza (AM) fungal root colonization on nutrient uptake, growth and soil water depletion of cowpea plants exposed to a drought stress period was studied in a greenhouse experiment. Arbuscular mycorrhizal and non- AM plants of an old, local variety from Brazil ‘Carioca’, and of the breeding improved cultivar ‘Epace-10’ were exposed to 24 days of drought, with or without a subsequent period of water resupply. Control plants remained well watered throughout the growth period. The AM symbiosis greatly enhanced nutrient uptake of drought stressed plants. However, water uptake, growth and net photosynthesis were unaffected by AM root colonization during drought stress. Recovery after water resupply was much faster when plants were inoculated with AM, probably due to an improved plant nutritional status. The cultivar Epace-10 was much more dependent on the AM symbiosis for growth and nutrient uptake compared with Carioca in all irrigation treatments. Only when roots were AM colonized, Epace-10 plants were able to recover from drought stress after water resupply. Our study suggests that the AM symbiosis constitutes an important strategy by which leguminous plants overcome periods of drought. Under conditions of low soil water and P availability, the presence of AM fungal propagules in the field soil appears to be a prerequisite for successful cultivation of cowpea, particularly with respect to the breeding improved cultivar Epace-10.