|Atallah, Zahi -|
|Maruthachalam, Karun -|
|Vallad, Gary -|
|Davis, Michael -|
|Subbarao, Krishnamurthy -|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 2, 2011
Publication Date: October 1, 2011
Citation: Atallah, Z.K., Maruthachalam, K.K., Vallad, G.E., Davis, M., Klosterman, S.J., Subbarao, K.V. 2011. Analysis of Verticillium dahliae suggests a lack of correlation between genotypic diversity and virulence phenotypes. Plant Disease. 95:1224-1232. Interpretive Summary: Verticillium dahliae is a soilborne fungus that causes plant wilt diseases world-wide. V. dahliae is cross-pathogenic on many crops and can infect plant seeds as well. Analyses of two different DNA-based molecular markers between different isolates of V. dahliae indicated that neither of these marker systems correlate with their ability to cause disease in certain plants or plant varieties. The high amount of diversity observed using these markers suggests that the inclusion of diverse strains may be important in studies aimed at generating plants resistant to the fungus. Also, the degree of genetic differentiation and the influence of long distance migration among subpopulations of V. dahliae also have important practical relevance for the control of Verticillium wilt diseases. Limiting the amount of V. dahliae transported on plant materials is an important part of a comprehensive plan to control Verticillium wilt in central coastal California.
Technical Abstract: Verticillium dahliae causes severe wilt and recurring losses in numerous agricultural and ornamental hosts worldwide. Two virulence phenotypes (races) have been identified based on the Ve resistance gene and its homologs but their distribution and evolutionary history are unknown. Sequence analyses of the intergenic spacer of the ribosomal DNA and amplified fragment length polymorphism markers suggested an absence of correlation between genotypic diversity and virulence phenotypes. Additionally, both race 1 and 2 phenotypes were isolated in various geographic regions and hosts. Sustained levels of migration of both virulence phenotypes among various geographic regions were evident, and the study also suggested that both virulence phenotypes infect a variety of hosts, regardless of the availability of resistant cultivars. Given the high genotypic diversity observed in V. dahliae, more than the two known virulence phenotypes may be present in nature but not yet identified because of the current lack of sources of resistance other than the Ve gene and its homologs. The inclusion of various genotypes exhibiting the same virulence phenotype may greatly improve the long-term effectiveness of resistance to race 2 of V. dahliae regardless of the host. This study also confirms the transcontinental gene flow and high genotypic diversity of V. dahliae affecting lettuce in coastal California regardless of the molecular markers employed.