Effects of temperature, water regime and irrigation system on the release of ascospores of Mycosphaerella nawae, causal agent of circular leaf spot of persimmon
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Experiments were conducted under controlled conditions to quantify the effects of temperature, water regime and irrigation system on the release of Mycosphaerella nawae ascospores from leaf litter in Spanish persimmon orchards. The effect of temperature on ascospore release was best described by a Gompertz model. The end of the lag phase of ascospore release occurred at 9.75 degrees C, and the end of the exponential phase at 15.75 degrees C. Few ascospores were discharged from dry leaves wetted with 0.1 or 0.5 mm water, but significant amounts were recovered with 1-50 mm water. About half of the total ascospores were released after three wetting and drying cycles, but 32 cycles were necessary for a complete discharge. No significant difference in ascospore release was detected when the leaf litter was wetted by flood and drip irrigation. However, considering the proportion of soil area wetted in both systems, inoculum release was significantly reduced by drip irrigation. The potential of drip irrigation as a cultural control measure should be investigated.