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The aim of this study was to determine the oomycetous pathogens causing root rot on sugar beet and test their control by seed treatment in Konya Province, Turkey. Oomycetous fungus-like pathogens of sugar beet were investigated using 866 plant samples collected at 2 growth stages, early seedling and late root, from fields in the Konya region of Turkey and 1 sample from the Thrace region. Herein, 10 oomycetous species belonging to 3 genera: Aphanomyces cochlioides, Phytophthora cryptogea, Ph. pseudocryptogea, Ph. megasperma, Ph. inundata, Pythium aphanidermatum, Py. helicoides, Py. heterothallicum, Py. sylvaticum, and Py. ultimum var. ultimum (Globisporangium ultimum var. ultimum) were discovered at various times with in the 2 growth periods, all of which were the first records for Turkey. A. cochlioides was the most serious pathogen, both in terms of its wide distribution and aggressiveness. The pathogen produced more than 90% disease severity when tested by soil infestation at the seedling stage, although it also occurred at the late root growth stage. Pythium species were also ascommon, such as A. cochlioides, the majority of which were very aggressive, producing more than 84% disease severity at the seedling stage, except for Py. aphanidermatum. Half-strength potato dextrose agar medium was found to be very useful for the isolation of all of the pathogens from the plant samples at both stages. Morphological features of all of the pathogens were abundantly produced when the pathogens were grown on amended grated carrot agar medium and culture disks of fungal growth of this medium were submerged in sterile and nonsterile soil extracts. Out of the 15 fungicide mixes tested, 2 mixes, thiram+metalaxyl+hymexazole and thiram+metalaxyl+hymexazole+ pyraclostrobin reduced seedling root rot caused by both A. cochlioides and Pythium ultimum var. ultimum, while the standard seed treatment fungicide mix of thiram+hymexazole was not effective against either of the pathogens. |
