Water status and stomatal behaviour of cowpea, Vigna unguiculata (L.) Walp, plants inoculated with two Glomus species at low soil moisture levels

The effects of arbuscular mycorrhizal (AM) fungi on water status and stomatal behaviour of cowpea, Vigna unguiculata (L.) Walp. cv. B89-504, under water-stressed conditions in the greenhouse were studied. The 3 × 2 experimental design included two levels of mycorrhizal colonisation (Glomus mosseae, Glomus versiforme) and non-mycorrhizal control treatment and two soil moisture levels (well-watered pots and pots allowed to dry). Relative water content and leaf water potential values were higher in well-watered mycorrhizal and non-mycorrhizal plants than in water-stressed mycorrhizal and non-mycorrhizal plants. AM species had no significant effect on leaf osmotic potential, stomatal conductance and leaf transpiration in both well watered and water-stressed plants. The values of stomatal conductance and leaf transpiration were high during the vegetative stage and low during the flowering stage. These responses which can be related to the age of the plant suggest that mycorrhizal colonisation did not affect stomatal closure of cowpea plants during water stress. The decrease in plant growth and dry matter production in both mycorrhizal and non-mycorrhizal plants shows that drought resistance in cowpea was unaffected by mycorrhiza in the vegetative phase.