BIOCHEMICAL AND PATHOLOGICAL STUDIES ON DOWNY MILDEW DISEASE OF CUCUMBER

Abstract

Pseudoperonospora cubensis (Berk & Curt) Rostow, the busal

pathogen of cucurbits downy mildew, attacks most cucurbit plints In I both open field and greenhouse, causing a serious damage for the infected I plants. i I I The aim of the present investigation is studying some pathological and physiological studies of the fungus on cucumber planJ The obtained result from this investigation could be summarized as foiiJws: I I I 1- The highest disease severity was recorded in autumn season in both

Tukh (Qalubia governorate) and Sakha (Kafr El-Sheikh while the lowest severity was recorded in spring season.

I governorate) I

2- The first downy mildew symptoms appsar on cucumber leaves,/as pal­

green areas separated by dark green ones, the pal-green area chapges to ' yellow angular spots bounded by leaf veins. The fungus causebright

yellow lesions on the upper surface, restricted by leaf veids with I corresponding fluffy purplish mildew on the lower sides after fhat the yellow lesion turn to the dark brown one which represent late Jtage of infection. I

I 3- The causal fungus, of downy mildew (P. cupensis), charactetized by long branched sporangiophore arises in groups of one to five thro:ugh the stomata. The branching of sporangiophore is straight and the angle of branching is more often acute. I