Effect of Soil Moisture Management on the Development of Potato mop-top virus-Induced Tuber Necrosis.

Potato mop-top virus (PMTV), transmitted by Spongospora subterranea f. sp. subterranea, the causal agent of powdery scab in potato, has become one of the most important tuber necrosis viruses in the United States. The virus has been confirmed in six major potato-producing states in the United States since its identification in 2003. Currently, no control methods are available for PMTV or its vector. A growth-chamber experiment was conducted to investigate the potential of using moisture regime adjustments to manage tuber necrosis caused by PMTV. Two commercial potato cultivars with varying levels of sensitivity to PMTV, 'Dakota Crisp' and 'Ivory Crisp', were grown in soil obtained from a PMTV-infested field. Over the course of the plant growth cycle, plants of each cultivar were subjected to moisture regimes of wet throughout (WT), wet early/dry late (WEDL), dry early/wet late (DEWL), and dry throughout (DT). Soil moisture levels of 90 and 60% field capacity were considered wet and dry, respectively, while early and late refer to first and last 50 days after planting, respectively. Results of visual assessment conducted 3 months after storage showed significant differences in root gall formation, powdery scab on tubers, and PMTV tuber necrosis among moisture regimes. Powdery scab incidence was significantly higher in the WT and DEWL regimes than WEDL and DT regimes. PMTV tuber necrosis incidence did not differ between the WT and DEWL or between DEWL and WEDL moisture regimes. However, PMTV tuber necrosis incidence was significantly higher in WT than under WEDL and DT regimes. The incidence of PMTV tuber necrosis was significantly lower in the DT regime than in the other three moisture regimes. Severity of PMTV tuber necrosis was significantly higher in the WT than the other regimes, which did not differ statistically among themselves. A significant interaction was found between cultivar and moisture regime on root gall formation, with the highest number of galls found on Ivory Crisp grown in the WT moisture regime. A significant correlation was found between powdery scab incidence on tubers and PMTV-induced tuber necrosis incidence. The results of this study provide useful basic information upon which further work can be built for formulating irrigation management schemes that have the potential of reducing the likelihood of powdery scab infection and PMTV-induced tuber necrosis development in potato.