Effects of Watering Regime and Mycorrhizal Inoculation on Seedling Growth and Drought Tolerant Traits of Cocoa ( Theobroma cacao L.) Varieties

Two experiments were conducted to examine the effects of watering regime and mycorrhizal inoculation on growth, development and drought tolerant traits of seedlings of five cocoa varieties ( Theobroma cacao ) obtained from the Cocoa research Institute Nigeria (CRIN), Ibadan, Nigeria. For each experiment, treatments were 5 x 3 x 2 factorial scheme consisting of cocoa hybrids/varieties, watering regimes in addition to mycorrhizal inoculation or without. Treatments were arranged using Completely Randomized Design with five replications. In experiment one, cocoa hybrids: CRIN: (TC1, TC2, TC3, TC4 and TC5) were subjected to watering regimes (100, 60 and 40% field capacity (FC) equivalent to 1.5 0.9 and 0.6 litres of water per pot) and were applied twice per week. Treatment effects were significant (P ≤ 0.05) for the measured growth variables of cocoa such as plant height, stem girth, root length, root and shoot weight were enhanced by 100 and 60% FC watering regime. Variety TC2 that were watered at 100 and 60% FC were taller in height and produced higher number of leaves and stem girth compared to those watered at 40% FC. Among varieties, increasing orders of water use by seedlings were TC1, TC2, TC5, TC3 and TC4. The 100 and 60% FC TC1 and TC2 had taller plants and produced higher number of leaves and stem girth compared to those watered at 40% FC. The response of cocoa varieties to mycorrhizal inoculation varied, inoculated seedlings of TC1, TC2 and TC3 had enhance vigor than the non-inoculated. Across varieties, both inoculated and non-inoculated seedlings that were subjected to 100% FC and 60% FC watering regimes enhanced growth and development. Cocoa variety TC3 showed best response to 100% FC and 60% FC watering and AMF inoculation. Watering regime and AMF Inoculation affected the concentration of chlorophyll and water soluble carbohydrate and water use efficiency of cocoa varieties. In experiment two, the elite varieties: T65/7 x N38, T65/7 x T57/22, T82/27 x T12/11, PA150 x T60/887 and T82/27 x T16/17 were subjected to watering regimes (4-, 8- and 14- day watering intervals). Cocoa seedling water use, plant height, stem girth, plant biomass and number of leaves and branches were enhanced by the 4- and 8- day watering intervals and with or without mycorrhizal inoculation compared with 14- day watering. Varieties T82/27 x T12/11 and PA150 x T60/887 watered at 4- and 8- day intervals was consistently taller in height, had enhanced biomass and produced higher number of leaves and branches compared with those watered at 14- day intervals. The variety PA150 x T60/887 consumed more water and had wider stem girth. The inoculated seedlings of varieties T82/27 x T12/11 and T65/7 x N38 were taller than the non-inoculated seedlings. The interaction effects of watering regime and variety enhanced the growth parameters of varieties T82/27 x T12/11 and PA150 x T60/887 that were watered at 4- and 8- day intervals. Mycorrhizal inoculation enhanced vigour of growth and survival of seedlings of tested cacao varieties that were subjected to the evaluated watering regimes in the nursery in the dry season.