Journal of Taiwan Agricultural Research

Author:Jin-Hsing Huang*, Chun-Wei Chen, and Junn-Feng Su

Abstract:

    Single conidium of Podosphaera xanthii, causal agent of powdery mildew of muskmelon, were isolated from colonies on diseased leaves and cultured on the leaf disks of muskmelon for purification and production of conidia.  The range of optimum temperature for production and germination of conidia of P. xanthii was 20 to 24℃. When conidia were inoculated on the leaf disks (1.5 cm in diam.) by the air-blow method and incubated at 20 or 24℃ for 14–16 days, the fungus produced 4.5×104–6.8×104 conidia/leaf disc with the germination rates of 24.8–42.3%.  When the inoculated leaf disks were incubated at 16℃ for 16–19 days, the number of conidia produced (3.2 × 10⁴–3.5 × 10⁴ conidia /leaf disc) and the rate of conidia germination (22.5–33.5%) were highest at the temperature.  The conidia number and germination rate were low for the cultures incubated at 12 or 28℃.  The cultures failed to produce conidia on the leaf disks incubated at 8 or 32℃ for 14–16 days or longer. Inoculation of conidia of P. xanthii on leaf disks of muskmelon by the air-blow method was more effective than the spraying method using conidia suspensions.  The germination rates and disease severity were 23.3% and 42.0%, respectively, for the inoculation method of conidia suspensions, compared with 44.5% and 70.5% for the inoculation of air-blow conidia.  Fresh conidia remained viable for 7 days at 24℃ and 30 days at 4℃ but they were unable to survive by storing at -30℃ or in liquid nitrogen.  However, air-dried conidia stored at -30℃ or in liquid nitrogen survived for at least 180 days.

Key words:Melon, Podosphaera xanthii, Powdery mildew, Propagation, Inoculation, Preservation

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