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Project description

Characterization of California and Australian isolates of Fusarium oxysporum f. sp. vasinfectum. (01XA001)
Program Exotic Pests and Diseases Research Program
Principal
investigator
R.M. Davis, Plant Pathology, UC Davis
Host/habitat Cotton
Pest Fusarium oxysporum f. sp. vasinfectum; Fusarium Wilt Fusarium oxysporum
Discipline Plant Pathology
Review
panel
Agricultural Systems
Start year (duration)  2001 (Two Years)
Objectives Characterize California and Australian isolates of Fusarium oxysporum f. sp. vasinfectum.

Final Report Because there is concern over the introduction of highly virulent strains of Fusarium oxysporum f. sp. vasinfectum (FOV) from Australia, it is necessary to characterize local strains of the fungus to document the movement of genotypes in and out of California. Regulatory decisions may rely on such data regarding movement of plant material between areas where different strains exist. To accurately describe the strains that presently occur in California, various genetic methods were employed. DNA from regions of the nuclear ribosomal, beta-tubulin, and elongation factor (EF) genes were sequenced and analyzed. These approaches provided clear and accurate information regarding the differences between Australia and California isolates. All methods clearly show that Australian isolates of FOV, based on our collection thus far, do not exist in California. Furthermore, a genetic analysis of these data shows that the California isolates are not related to the Australian FOV. Analysis of the IGS region of the rDNA also supports the conclusion that Australian strains are clearly unique from those in California. Californian isolates fell into four lineages. One group of several isolates consisted of the lineage of races one and two, which are closely related to each other; a second group was represented by two isolates that belong to the race three lineage; a third group, race four, was collected in two fields; and a fourth group, race eight, was represented by two isolates. Race four was highly virulent on Pima in greenhouse pathogenicity tests and was considerably less virulent on Acala; isolates belonging to the lineage of races one, two, and six were relatively virulent on Acala cotton but not Pima. Race eight and race three were weakly pathogenic on both Acala (Maxxa and Phy-72) and Pima (DP-744 and Pima S-7).

Second-year
progress
Because there is concern over the introduction of highly virulent strains of Fusarium oxysporum f. sp. vasinfectum (FOV) from Australia, it is necessary to characterize local strains of the fungus to document the movement of genotypes in and out of California. Regulatory decisions may rely on such data regarding movement of plant material between areas where different strains exist. To accurately describe the strains that presently occur in California, various genetic methods were employed. DNA from regions of the nuclear ribosomal, beta-tubulin, and elongation factor (EF) genes were sequenced and analyzed. These approaches provided clear and accurate information regarding the differences between Australia and California isolates. All methods clearly show that Australian isolates of FOV, based on our collection thus far, do not exist in California. Furthermore, a genetic analysis of these data shows that the California isolates are not related to the Australian FOV. Analysis of the IGS region of the rDNA also supports the conclusion that Australian strains are clearly unique from those in California.

Additionally, a set of primers has been developed for the detection of FOV that unambiguously amplifies a certain fragment in the ITS region unique to FOV. These primers were used to detect FOV in lots of seed imported into California for cattle feed. No FOV was detected thus far. Also, no FOV was detected in a seed grow-out of about 4,000 seedlings.

First-year
progress
Because there is concern over the introduction of highly virulent strains of Fusarium oxysporum f. sp. vasinfectum (FOV) from Australia, it is necessary to characterize local strains of the fungus to document the movement of genotypes in and out of California. Regulatory decisions may rely on such data regarding movement of plant material between areas where different strains exist. To accurately describe the strains that presently occur in California, various genetic methods were employed. DNA from regions of the nuclear ribosomal, beta-tubulin, and elongation factor (EF) genes were sequenced and analyzed. Two approaches provided clear and accurate information regarding the differences between Australia and California isolates. A number of deletions of bases in the EF gene in Australian isolates clearly showed that Australian isolates of FOV, based on our collection thus far, do not exist in California. Furthermore, a genetic analysis of these data shows that the California isolates are often related to one another but not to the Australian FOV. Analysis of the IGS region of the rDNA also supports the conclusion that Australian strains are clearly unique from those in California.

Additionally, a set of primers has been developed for the detection of FOV that unambiguously amplifies a certain fragment in the ITS region unique to FOV. These primers were used to detect FOV in lots of seed imported into California for cattle feed. No FOV was detected thus far. Also, no FOV was detected in a seed grow-out of about 4,000 seedlings.

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