Abstract:
Purple passion fruit is an important fruit, ranking third in export volumes in Kenya. lts yields drastically declined over the period 1994 to 2005 from 948,000 to 32,000 tonnes partly due o drought stresses. Without irrigation, it is difficult to maintain year-round production of purple passion fruits on a commercial basis. The present study evaluated the effects of irrigation rate and mulch type on drought stress amelioration in purple passion fruits. The experiment was set up in a plastic covered rain shelter, measuring 60mx8m and located at Egerton University, Njoro-Kenya. The experiment was set up in randomized complete block design, replicated four times, with four irrigation rates (2.5, 5, I0 and 20 L of water applied once weekly per plant) and three mulch types (black plastic, wheat straw and no mulch). Each treatment had three plants spaced at 1.5mx1.5m. Purple passion fruit seedlings, measuring 30 cm tall, were transplanted into 45cmx45cm holes and trellised onto posts and wires. A trench lined with plastic film was dug between main plots and blocks to prevent water seepage across treatments. Plants were maintained uniformly during the first four weeks to recover from transplanting shock. Treatments were applied at the beginning of the fifth week after planting (WAP). Data were recorded bi-weekly from the 9“ up to the 56th WAP on: vegetative growth, plant physiology, reproductive growth and fruit quality. Data were subjected to analysis of variance using the SAS programme. Higher irrigation rates promoted greater leaf area and weight than lower irrigation rates. Black plastic and wheat straw significantly (P<0.05) increased leaf weight. Irrigation significantly (P<0.05) increased laterals. total florals (intact flowers, dropped flowers and immature fruits) and dropped flowers. Black plastic mulch significantly increased florals, dropped flowers and immature fruits. The 20 L significantly increased stomatal conductance, while no mulch significantly increased net photosynthesis. The cumulative fruit weight of 6016 g/plant for 20 L was significantly greater than the 5052 g/plant for 2.5 L. Irrigation and mulch did not affect fruit quality. Higher irrigation rate decreased water use efficiency to 0.2 fruits/L or 5 g/L. Generally, when irrigating with over 5 L, there was no additional benefit of mulching, but mulch ameliorated drought stress when deficit irrigation rate of 2.5 L was applied. Wheat straw and 10 L per plant once per week was generally optimal and should be adopted towards mitigating drought stress effects in purple passion fruits in Kenya.
