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Evaluation of methods to detect the cotton wilt pathogen Fusarium oxysporum f. sp. vasinfectum race 4

Crutcher, Frankie K., Doan, Hung K., Bell, Alois A., Davis, R. Michael, Stipanovic, Robert D., Nichols, Robert L., Liu, Jinggao
European journal of plant pathology 2016 v.144 no.1 pp. 225-230
Fusarium oxysporum f. sp. vasinfectum, Fusarium wilt, Gossypium barbadense, Gossypium hirsutum, cotton, crop production, diagnostic techniques, fungi, genes, genotype, mycelium, pathogens, plant tissues, planting, polymerase chain reaction, races, soil, California
Fusarium wilt, caused by Fusarium oxysporum f. sp. vasinfectum (Fov), is an economically important disease of cultivated cottons (Gossypium hirsutum and G. barbadense). Recently, Fov race 4 has spread among soils planted to cotton in the San Joaquin Valley of California causing significant losses. Because Fov 4 is seedborne and persists in infested soils, it is a potential threat to all US cotton production regions. Tests have been developed to rapidly identify race 4 in the laboratory and the field, including a race 4 specific PCR and a test kit for use with fungal mycelium and infected plant tissue. Currently, the test kit is the only available method to identify race 4 in the field. Both the PCR and kit tests were evaluated on a panel of 36 Fov isolates that represented all described races and many genotypes from several geographic regions. As expected, race 4 isolates gave positive reactions, as did race 7 isolates. One race 7 isolate was not vegetatively compatible with the race 4 isolates, while the other isolate of race 7 exhibited a compatible reaction. Isolates of race 7 and race 4 have identical partial sequences in three nuclear genes. In addition, the type isolate of race 3 gave a positive reaction. All other isolates, including the highly-virulent Australian isolates, were negative. The diagnostic tests clearly distinguished race 4 from races 1, 2, 6, and 8 but not from the race 3 and race 7 isolates tested here. Race 3 and 7 are similar in etiology to that of race 4, thus a method is needed to distinguish these in the field.