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Title: Seed transmission of Fusarium oxysporum f. sp. vasinfectum race 4 in California

item Bennett, Rebecca

Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2008
Publication Date: 7/21/2008
Citation: Bennett, R.S., Hutmacher, R.B., Davis, M.R. 2008. Seed Transmission of Fusarium oxysporum f. sp. vasinfectum Race 4 in California. J. Cotton Sci. 12:160-164.

Interpretive Summary: Fusarium wilt, which is caused by a soil-inhabiting fungus, is a major disease of cotton around the world. In 2001, a race (race 4) to which many Pima cotton varieties have little resistance was discovered in the San Joaquin Valley. Other races of Fusarium are known to infect seed, and such infections may provide a means of spreading the disease. Information regarding the ability of race 4 to infect cottonseed is not currently available. We conducted studies to determine if cottonseed could be naturally infected with race 4. Seeds from five cotton varieties were assayed for the fungus using two approaches, 1) by screening individual seeds or 2) by screening batches of seed. Fungi recovered from the seed were tested with specific chemical markers to indicate the presence of race 4. Both approaches found that Fusarium race 4 infected the seed of susceptible Pima cultivars, albeit in different amounts. These results indicate the need for additional studies to determine the potential for race 4 infected seed to spread this race of Fusarium wilt within and among cotton production regions.

Technical Abstract: Fusarium oxysporum f. sp. vasinfectum (Atk.) W.C. Snyd. & H. N. Hans. race 4, a biotype highly virulent on certain Pima cotton (Gossypium barbadense L.) cultivars, was detected in California in 2001. The propensity of this disease to appear in isolated spots in previously uninfested fields has given rise to several hypotheses regarding potential mechanisms of disease dispersal. One of these hypotheses is that the disease may be spread through the planting of infected seed. In independent assays using two methodologies, the fungus was detected in acid-delinted Pima cotton seed from plants in known race 4-infested field sites. Seed was either plated directly onto Komada’s agar or incubated en masse in a selective liquid medium. DNA isolated from the recovered fungi was amplified with race 4-specific primers. With both approaches, seed from susceptible Pima cultivars was found to be infected with race 4, albeit at different levels. These results suggest that infected seed has the potential of spreading race 4 within and among cotton production regions.