An Integrated Study of Potato Early Blight and Brown Spot in Wisconsin

摘要

Early blight, caused by Alternaria solani, along with brown spot caused by Alternaria alternata, have the potential to reduce quality and yield in potato production globally. One genotype of A. solani and 5 genotypes of A. alternata were identified in Wisconsin based on genetic regions of ITS, TEF1, gapdh, Alt a 1, and OPA10-2. Alternaria alternata isolates were virulent on potato cultivars Russet Burbank and Atlantic, yet caused less disease than A. solani. Alternaria alternata caused little disease on the early blight resistance breeding line 24-24-12, and A. solani caused reduced disease on 24-24-12, indicating that 24-24-12 could potentially be a good breeding source for resistance to both diseases. Isolates of A. alternata that induced chlorosis caused larger lesion areas in potatoes than isolates that did not. In 2014 to 2017, incidence of A. alternata had been recorded starting in late June, whereas incidence of A. solani started later in some fields. A correlation between disease incidence and overall disease severity in the field suggested virulence of A. alternata on potatoes, but less aggressive than A. solani. A greenhouse study showed a moderate synergistic interaction when simultaneously inoculating detached potato leaves with A. solani and A. alternata , and a slight reduction in disease severity when A. alternata was pre-inoculated prior to the introduction of A. solani . A consistently high frequency of A. solani isolates collected carried mutations conferring resistance to quinone outside inhibiting (QoI) fungicides, but the frequency of that in A. alternata started low and increased towards the end of the growing season in each year from 2015 to 2017. The dynamic pattern of QoI resistance in A. alternata may be a result of reduced QoI exposure as outsourced wild type A. alternata isolates continuously move into the potato field. Incidentally, conidia of A. alternata have a higher level of movement than conidia of A. solani was found in this study. Overall, the work of this dissertation advanced the understanding of potato early blight and brown spot in Wisconsin and may lead to more robust and sustainable disease management strategies.