Population biology of Verticillium dahliae associated with potato agroecosystems

Open Access
- Author:
- Bautista Jalon, Laura
- Graduate Program:
- Plant Pathology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 30, 2020
- Committee Members:
- Maria Del Mar Jimenez Gasco, Dissertation Advisor/Co-Advisor
Maria Del Mar Jimenez Gasco, Committee Chair/Co-Chair
Cristina Rosa, Committee Member
Paul David Esker, Committee Member
Margarita Maria Lopez-Uribe, Outside Member
Beth Krueger Gugino, Dissertation Advisor/Co-Advisor
Beth Krueger Gugino, Committee Chair/Co-Chair
Carolee Theresa Bull, Program Head/Chair - Keywords:
- population biology
fungal plant pathogen
crop rotation
asymptomatic hosts
Verticillium wilt of potato
Verticillium dahliae
VCG - Abstract:
- Verticillium dahliae is a worldwide distributed fungal plant pathogen and the causal agent of Verticillium wilt in over 300 different plant species including potato. Because of the limited availability of disease-resistant cultivars, Verticillium wilt of potato is primarily managed with soil disinfestation using soil fumigants, and rotations with crop species traditionally considered to be non-hosts. Crop rotations are more environmentally-sustainable and commonly employed management practices. However, they often render conflicting results regarding the reduction of incidence and severity of the disease in potato crops following the rotation, indicating that they do not perform as expected. Some studies showed that V. dahliae infected asymptomatically weeds and rotational crops such as oat and barley. The overall goal of this research was to investigate the genetic diversity, evolution, and ecology of V. dahliae populations associated with potato agroecosystems with the purpose of providing information that helps improve the management of Verticillium wilt of potato using crop rotations. First, analyses were conducted to investigate the genetic diversity, structure and pathogenicity of V. dahliae populations recovered from two potato cultivars (susceptible host) and oat (asymptomatic host) cultivated under rotation in a Pennsylvania (PA) commercial potato field. We wanted to know if the V. dahliae population recovered from asymptomatic oats was genetically distinct from the population obtained from potatoes and if V. dahliae isolates recovered from asymptomatic oats could infect and cause disease on potato. Results showed that V. dahliae populations from potato and oat were not genetically distinct. Rotational oats were asymptomatically infected mainly by one genotype in VCG 4B which was also infecting the two potato cultivars. The pathogenicity test showed that an isolate of that genotype collected from asymptomatic field oats caused disease on potato and infected oat as an endophyte; whereas an isolate from VCG4A caused disease on potato but was not found in endophytic infections of oat. The second objective was to test the hypothesis that V. dahliae populations recovered from asymptomatic rotational crops and weed species were evolutionarily and genetically distinct from those causing disease to potato. This was addressed by using a single-nucleotide polymorphism (SNP) dataset generated by Genotyping-by-Sequencing (GBS) to analyze the evolutionary history and genetic differentiation of V. dahliae populations collected from potato fields with a history of Verticillium wilt in Israel and PA, US, and to compare their structure to known clonal lineages of V. dahliae. Results indicated that V. dahliae isolates infecting rotational crops and weeds as endophytes were all in lineage 4B (VCG 4B), a recognized pathogenic lineage, and were evolutionarily and genetically indistinguishable from isolates infecting symptomatic (susceptible) hosts. The third objective was to test the hypothesis that V. dahliae lineage 4A populations from northern US were highly clonal with little regional differentiation and that isolates have been dispersed with potato seed tubers. For that, the population structure, genetic differentiation and evolutionary history of 79 V. dahliae lineage 4A isolates collected from different sources, years and states in northern US potato agroecosystems was investigated using a large SNP dataset generated by GBS. Results of these analyses indicated that lineage 4A populations from northern US are highly clonal with the widespread distribution of one predominant evolutionary clade which has been disseminated probably with the use of potato seed tubers carrying propagules of the pathogen.