Progress in Breeding for Tolerance to Fusarium Wilt (FOV) Races 1 and 4 in the San Joaquin Valley (SJV) of California

The vulnerability of cotton production in California to Fusarium wilt [Fusarium oxysporum f. sp. vasinfectum (FOV)] highlights the need for comprehensive research to protect the future of the cotton industry in the San Joaquin Valley (SJV). A recently identified problematic strain of Fusarium (race 4) has proven especially damaging to most varieties of Pima cotton. Development of host-plant resistance is currently the most economic and effective strategy for managing FOV in the SJV. For the last seven years, we have conducted field and greenhouse evaluations for FOV resistance. In addition to indentifying resistant/tolerant entries, we developed progeny to assess for resistance against FOV races 1 and 4 as well as root-knot nematode. More than 16,000 plants have been assayed in multiple greenhouse and field evaluations representing more than 1000 progeny of selected crosses, germplasm lines, and commercial cultivars. Approximately 1200 molecular markers located on different cotton chromosomes were analyzed in different mapping populations from crosses of Upland-by-Upland, Upland-by-Pima, and Pima-by-Pima cottons. Preliminary analyses suggested that different genes were active in the plant disease response under different environmental conditions. Greenhouse and field evaluations revealed interactions in disease response between breeding lines, FOV races (1 and 4), and evaluation sites (greenhouse and infested field). Preliminary molecular analyses revealed several markers associated with FOV resistance. Ten candidate markers showing associations with susceptible or resistant cottons have been identified on four chromosomes. These data are being further evaluated to investigate the inheritance and gene interactions involved in resistance to FOV races 1 and 4. Results from these studies provide a better understanding of cotton-Fusarium interactions and should facilitate the development of molecular markers for marker assisted selection for FOV resistant cotton-genotypes.