<p> Fusarium wilt of cotton, caused by the soilborne fungus <i>Fusarium oxysporum</i> f. sp. <i>vasinfectum,</i> is a widespread disease occurring in most cotton-growing regions of the world. Fusarium wilt occurs in all domesticated cotton. Currently, six nominal races are recognized: 1, 2, 3, 4, 6, and 8, as well as many un-named genotypes worldwide. Many are widespread in the U.S., but race 4, which is highly virulent, is apparently restricted to California. Race 4 is found in an increasing number of fields in California due in part to seed-borne dissemination. The first aim of this study was to evaluate the efficacy of hot water treatments alone or in conjunction with fungicides and other treatments to reduce the viability of FOV race 4 in infected cotton seed. The second aim was to develop and evaluate a rapid and reliable molecular diagnostic assay, the AmplifyRP<sup>®</sup> Acceler8™, for the direct detection of FOV race 4 in cotton tissue. In the seed treatment assay, a 1 hour immersion of seed in water or sterile 30% potato dextrose broth (PDB) at 24°C followed by a 20 minute immersion in a 60°C solution containing four fungicides (azoxystrobin, fludioxonil, thiabendazole, and thiophanate) or thiophanate alone were the most effective pretreatment-treatment combinations in reducing FOV in seed and avoiding loss of seed germination and vigor. The incidence of FOV in the seed was reduced by approximately 86% without reducing seed germination and vigor based on recovery of the fungus on petri plates and greenhouse grow-out assays. FOV was completely eliminated from infected seed when the seed was pretreated in water at 24°C followed by a 20 minute immersion in a solution of thiophanate heated to 70°C. With this treatment, seed germination was reduced by 36% and vigor was reduced by 38%. The AmplifyRP<sup>®</sup> Acceler8™ diagnostic assay consistently detected FOV race 4 from all infected tissue samples. The test is rapid, simple and more sensitive than conventional PCR. The AmplifyRP<sup>®</sup> Acceler8™ diagnostic assay detected DNA from FOV race 4 at concentrations of 1 ng/µL and above. In addition, it did not amplify DNA from other known FOV races (races 1, 2, 3, 6, and 8). The whole process from sample preparation to reading the results was completed in as little as 30 minutes. The test detected FOV race 4 in cotton taproots, petioles, and stems.</p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:1565656 |
| Date | 30 October 2014 |
| Creators | Doan, Hung Kim |
| Publisher | University of California, Davis |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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