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Title: Fusarium Race 4: Commercial cultivar screening for resistance

item Ulloa, Mauricio
item Bennett, Rebecca

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 9/30/2006
Publication Date: 1/8/2007
Citation: Hutmacher, R.B., Ulloa, M., Wright, S., Davis, M.R., Bennett, R., Marsh, B.H., Keeley, M.P. 2007. Fusarium Race 4: Commercial cultivar screening for resistance. National Cotton Council Beltwide Cotton Conference. p. 764.

Interpretive Summary: The soilborne fungus Fusarium oxysporum f. sp. vasinfectum causes vascular wilt in cotton, a disease of increasing significance in California’s San Joaquin Valley (SJV). A new highly virulent race (race 4) appeared in the SJV several years ago and is continuing to spread and cause serious yield losses throughout the valley. Use of resistant plants is the most sustainable method of managing this disease over the long term, so efforts are being made to screen available cotton germplasm for resistance. Screening results have shown that most Pima cotton varieties are highly susceptible, although one commercial variety and several USDA experimental varieties appear to be resistant. Results have also shown that Upland cotton varieties are less susceptible that most Pima varieties but they are not completely resistant to race 4. These data can be used to make recommendations to growers with fields infested with race 4, as well as to aid plant breeders in developing more resistant varieties.

Technical Abstract: Fusarium wilt (FOV) of cotton in California has been considered a potentially serious fungal disease for many decades in areas of the San Joaquin Valley (SJV). In the past, damage from Fusarium has been notable only in areas with the combination of: (a) moderate to high populations of one or more specific races of FOV (usually race 1); (b) soils with a coarse texture; and (c) where root knot nematodes existed in populations adequate to cause significant root damage. While most cotton crop loss in the SJV from Fusarium wilt likely remains associated with nematode damage and race 1 FOV, field investigations recently have found Fusarium symptoms across a range of soil textures in which root knot nematode populations were very low. This more-recently identified FOV identified in these studies has been identified as race 4. Field and greenhouse studies were initiated to conduct germplasm screening trials to identify useful genetic differences in susceptibility / resistance to race 4 FOV that can be utilized in further genetic evaluations and to identify sources of host plant resistance useful to growers and breeders. Screening efforts have included Gossypium hirsutum (Upland) and Gossypium barbadense (Pima) plantings as well as other, more exotic Gossypium species to gain a broader perspective of susceptibility and host plant resistance. Screening efforts can be summarized as follows: (1) most Pima varieties show more severe symptoms and suffer higher levels of stunting and plant mortality than Acala/Uplands; (2) one highly-resistant commercial Pima variety and several USDA experimentals have been identified; (3) most Acala / Upland germplasm tested, while less severely impacted than most Pima varieties, were still infected by the race 4 FOV when tested at infested field sites or when inoculated in greenhouse trials.