Kedi LiFollow

Date of Award

Fall 12-17-2021

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)


Plant, Soil, and Environmental Sciences


Jianjun Hao

Second Committee Member

Robert P. Larkin

Third Committee Member

Alicyn Smart


Potato early dying (PED) is a yield-constraining soilborne disease of potato, caused by Verticillium spp. with V. dahliae being the predominant causal agent. Since the pathogen inhabits soil for long periods, PED management aims to reduce the population of V. dahliae in soil. Benzovindiflupyr and azoxystrobin are effective chemicals and frequently used in the control of V. dahliae. In this study, field trials were conducted at Aroostook Farm, Presque Isle, ME in 2019 and 2020. Chemical and biological products have been studied for PED control, and fungicide resistance was also examined. To evaluate fungicide resistance, benzovindiflupyr was characterized on sensitivity baseline and resistance risk development in V. dahliae. Benzovindiflupyr-resistant mutants of V. dahliae were generated, and evaluated for resistance stability, fitness, and pathogenicity. Results showed that most mutants maintained a high level of resistance and the same fitness and pathogenicity compared to their parents, indicating a high risk of resistance in fields. Therefore, the resistance of V. dahliae to benzovindiflupyr should be monitored in disease management. In field trials, Elatus (a.i. azoxystrobin and benzovindiflupyr), Aprovia (benzovindiflupyr), Stargus (Bacillus amyloliquefaciens) and Regalia (Reynoutria sachalinensis extract) were examined. In a second field trial, Vapam (a.i. metam sodium) was studied at three rates for soil fumigation. Disease was evaluated during the growing season and postharvest. Bulked soil was sampled at different time points of the season. Soil DNA was extracted from the soil and root samples. Quantity of V. dahliae in soil was measured using quantitative polymerase chain reaction (qPCR). Soil microbial communities of soil from plots applied with Elatus at 280.9 ml/A and Vapam at 35 gal/A and 50 gal/A were examined using Illumina sequencing targeting the V4 region of the 16S rRNA gene for bacteria and ITS1 region for fungi. Results showed that all the fungicides and the fumigant significantly reduced PED disease incidences and V. dahliae population. Soil microbial community richness, abundance, and diversity were affected after Elatus and Vapam applications, and most bacterial and fungal families that recovered rapidly were non-pathogenic. All products can be used for PED control, but the impact on soil microbiome needs to be addressed.