![]() ![]() The conidia (spores produced asexually) of E. xanthii appears to progress most rapidly during the warmer months. cichoracearum may have a lower temperature optimum since this species is found mainly during cooler spring and early summer periods and P. xanthii is a more aggressive pathogen than E. A shift in the predominance of these two fungi may have occurred or the causal organism may have been misidentified. xanthii is found more commonly worldwide. cichoracearum was considered to be the primary causal organism throughout most of the world before 1958. fusca) and Erysiphe cichoracearum are the two most commonly recorded fungi causing cucurbit powdery mildew. Podosphaera xanthii (previously known as Sphaerotheca fuliginea and S. In addition, powdery mildew infection predisposes plants to other diseases, in particular, gummy stem blight. Stress from disease can lead to imperfections on fruit rind such as speckling, raised indentations, and oedema. Such fruit have poor storability (winter squash), low soluble solids with consequent poor flavor (melon), poor rind color (pumpkin), and shriveled, discolored handles (pumpkin). Premature senescence of infected leaves can result in reduced market quality because fruit become sunburnt or ripen prematurely or incompletely. Quantity of yield is reduced due to a decrease in the size or number of fruit or a decrease in the length of the harvest period. This disease can be a major production problem. Although all cucurbits are susceptible, symptoms are less common on cucumber and melon because many commercial cultivars have resistance. Powdery mildew is a common disease of cucurbits under field and greenhouse conditions in most areas of the world.
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