JXB Advance Access originally published online on May 11, 2006
Journal of Experimental Botany 2006 57(9):2093-2100; doi:10.1093/jxb/erj166
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RESEARCH PAPER |
Powdery mildew (Podosphaera xanthii) resistance in melon is categorized into two types based on inhibition of the infection processes
1Plant Biotechnology Institute, Ibaraki Agricultural Center, Iwama, Nishi-ibaraki, Ibaraki 319-0292 Japan
2Chikusei Agricultural Extension Center, Ibaraki Agricultural Center, Chikusei, Nikinari, Ibaraki, 308-0841 Japan
3Gene Research Center, Graduate School of Life and Environmental Sciences, University of Tsukuba, Tennodai, Tsukuba, Ibaraki, 305-8572 Japan
*To whom correspondence should be addressed. E-mail: mkuzuya{at}agri.pref.ibaraki.jp
Physiological races of powdery mildew (Podosphaera xanthii) cause different symptoms in eight melon lines. Infection by races 1, 2, and 5 was examined in different melon lines. After a compatible reaction, conidia germination, haustorium initiation from the germ tube, germ tube branching, and sporulation occurred within 12, 24, 48, and 120 h, respectively, and the conidia matured within 240 h. In contrast, type i and ii inhibition were identified through incompatible reactions. The germ tube and haustorium were initiated from conidia, but no germ tube branching occurred in the lines with type i resistance within 48240 h. In type ii resistance, germ tube branching was observed within 120 h, but no sporulation was observed within 240 h. The number of fluorescing epidermal cells was higher within 24 h in type i, and within 48120 h in type ii resistance lines than in susceptible lines. Callose accumulation around the haustorium was detected in type ii resistance lines within 48120 h. This suggests that the rapid hypersensitive response (HR) within 24 h has an important role in the type i response, while HR and callose accumulation in the type ii response occur slowly between 48 and 120 h. Of the resistant lines, PMR 45 and WMR 29 showed a type i incompatible response; the PI 414723 response was entirely type ii; and PMR 5, PI 124112, and MR-1 showed different responses depending on the race. Therefore, the two types of incompatible responses were intermixed in the same germplasm.
Key words: Cucumis melo L., Podosphaera xanthii, powdery mildew resistance, stages of conidial development, type of incompatible reaction
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