Submitted to: HortScience
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/6/2008
Publication Date: 8/1/2008
Citation: Nyankanga, R.O., Olanya, O.M., Wien, H.C., El-Bedewy, R., Ojiambo, P.S., Karinga, J. 2008. Development of Tuber Blight (Phytophthora infestans) on Potato Cultivars Based on In-Vitro Assays and Field Evaluations. HortScience.43:1501-1508. Interpretive Summary: Potato late blight is a devastating plant disease in both field and potato storage environments. We evaluated the relationship between laboratory assessments of late blight and its occurrence in the field for potato varieties with different levels of resistance to the disease. We determined that laboratory evaluations had limited utility for estimating late blight in the field. However, laboratory assessments were useful for predicting late blight on potatoes in storage environments.
Technical Abstract: Tuber blight may result from infection of wounded or unwounded potato tubers, exposed to sporangia from foliar blight, soil, or blighted tubers. However, there is limited data on the prediction of tuber blight in field or storage environments based on in-vitro assays. To assess this relationship, potato genotypes with foliar blight resistance (R-genes) and general resistance were evaluated for tuber blight incited by Phytophthora infestans (US 1) based on wound-induced and unwounded tuber inoculations. Surface lesion diameter, lesion depth, and frequency distribution of blighted tubers were assessed in in-vitro assays, and tuber blight incidence determined in field experiments. Significant differences (P<0.05) in lesion diameter and depth were recorded among genotypes. Surface lesion diameter, depth and index ranged from 5-40, 2-16.3 and 15-656 mm respectively, in wound-inoculated tubers. In non-wounded tuber assays, the incidence of blighted tubers ranged from 0 to 8.7% in both years. Tuber blight infection of potato cultivars varied between years in field studies. Although tuber infection differed among cultivars, the frequency of blighted tubers had normal distribution irrespective of R-genes, implying that foliar resistance may have limited effect on tuber blight occurrence based on in-vitro experiments. Prediction of tuber blight based on inoculation assays can be effectively utilized to estimate and manage blight development in storage environments.