EFFECTIVENESS OF CROSS PROTECTION BY A MILD STRAIN OF ZUCCHINI YELLOW MOSAIC-VIRUS IN CUCUMBER, MELON, AND SQUASH

A mild variant of zucchini yellow mosaic virus (ZYMV-WK) that had been selected from a severe strain of ZYMV in France was used for cross-protection tests in cucurbit crops in Taiwan. Under greenhouse conditions, ZYMV-WK provided protection in cucumber, melon, and zucchini squash against four severe strains originally from Connecticut, Florida, France, and Taiwan. Cross protection was more effective against the French strain, from which the mild strain was derived. Two field trials with zucchini squach under moderate and high disease pressures showed that ZYMV-WK provided excellent cross protection against the Taiwan strain of ZYMV. Yields of marketable fruit were 2.2 and 40 times greater than those of control plants under moderate and high disease pressure conditions, respectively.