| The Pythium root rot of garlic occurred in most garlic-growing areas of the Shandong Province, causing considerable financial losses, and the disease wasn't been reported at home and abroad. The garlic was infected in the seedling stage and directly affected production. The pathogens cause plants dwarf, leaves bottom-up yellowed, root and basal part of stem discolored and rot.Fifty samples of root rot of garlic were collected from the five counties in Shandong Province. According to the Koch's postulates, the main pathogen was identified as Pythium, the isolated frequency was 46.78%, and 12 pathogens were obtained. Based on the morphological identification and ITS sequence alignment, the pathogens were identified as Pythium sylvaticum Compbell & Hendrix, Pythium heterothallicum Compbell & Hendrix, Pythium paroecandrum Drechsler and Pythium violae Chesters & Hickman, two were Pythium sp. among 12 pathogens. The biological studies suggested that the optimum temperature was 20~25℃and the optimum pH was 6~7 for the mycelial growth of Pythium. In garlic field, quantity of Pythium changed with the temperature and humidity of soil. The 12 varieties of garlic from different areas were inoculated by 8 pathogens. The results showed that the garlic varieties of 03-1-kun, Dongping and Sulian-2 were resistant, Jinxiang and Jinsuan-2 were susceptibled. In addition, the inhibitory effection of 8 fungicides on the mycelial growth of Pythium was investigated. Ovraclostrobin-metiram had exhibited the highest inhibitory action to Pythium, the median inhibitory concentration was 2.612 mg/L. Famoxadone-cymoxanil, Cymoxanil-mancozeb, Copper hydroxide and Mancozeb showed better inhibition of the Pythium. Screening of fungicides in the field, Ovraclostrobin-metiram and Copper calcium sulphate were better than others, their control efficiency were 91.86% and 81.46%, respectively.
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