Powdery mildew severity in genera and species of Cucurbitaceae following exposure to field inoculum.

摘要

Powdery mildew is an important disease of pumpkin and other cucurbit crops in Ohio, however, substantial differences in severity of powdery mildew among the various genera and species within the Cucurbitaceae frequently have been noted. To assess powdery mildew severity in relation to that seen in commercial pumpkin varieties and experimental lines, an experiment was conducted utilizing a wide variety of genera and species of Cucurbitaceae obtained from the National Plant Germplasm System. Several commercial pumpkin cultivars and experimental lines were also tested. On 18 and 19 Aug, seeds of each entry were sown in flats filled with Metromix 360 and placed under intermittent mist in the greenhouse to allow for germination and seedling growth. Seedlings received applications of ‘MiracleGro’ (24-8-16) on 8 and 23 Sep. Individual seedlings were transplanted to 4” square pots containing MetroMix 360, 1 seedling per pot on 23 Sep. On 30 Sep, pots containing plants with two true leaves were selectedfor field inoculation and placed in flats, which were subsequently placed in the field between rows of pumpkin (Cucurbita pepo) with extensive powdery mildew development. There were 6 replicate pots of each entry. After 18 hr exposure, flats were removedfrom the field and returned to the greenhouse, incubated for 15 days at 22 - 27 C, and rated for powdery mildew severity by estimating the percent area covered with powdery mildew colonies on the upper surface of each of the first two true leaves. Fourseparate ratings taken by 4 individuals were averaged to obtain a percent estimate used in the final data analysis.