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Title: Evidence for cucurbit powdery mildew pathogen races based on watermelon differentials

item Kousik, Chandrasekar - Shaker
item Ikerd, Jennifer

Submitted to: Cucurbitaceae Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/30/2014
Publication Date: 10/12/2014
Citation: Kousik, C.S., Ikerd, J.L. 2014. Evidence for cucurbit powdery mildew pathogen races based on watermelon differentials. Cucurbitaceae Proceedings. Bay Harbor, MI. pp 32-34.

Interpretive Summary: N/A

Technical Abstract: Powdery mildew (PM) caused by Podosphaera xanthii occurs in open fields and greenhouses and can severely limit cucurbit production. Presently seven races of P. xanthii have been identified using melon (Cucumis melo) differentials. Physiological races of this pathogen have not been classified for other cucurbits because of the lack of differentials and fully resistant germplasm. We have developed several highly resistant watermelon (Citrullus lanatus var. lanatus) germplasm lines by pure line selection from plant introductions (PI). We evaluated 11 PM isolates collected from various cucurbit plants on cotyledons of 5 watermelon germplasm lines, cultivar Mickey Lee, melon differentials PMR 45 and Iran H and squash cultivar EPSN. All isolates grew and produced abundant conidia on Iran H, and EPSN. A watermelon germplasm line derived from PI 269677 (USVL677-PMS) was susceptible to all 11 isolates. None of the PM isolates grew on the four highly resistant USVL germplasm lines. Of the 11 PM isolates evaluated, 3 grew on Mickey Lee. Of these three, two were melon race 1 and one a melon race 2. Based on the reactions of Mickey Lee and USVL677-PMS to PM isolates, we can identify the presence of at least two races using two watermelon differentials.