K.G. Haynes, USDA-ARS, Beltsville, MD 20705
C.A. Thill and J.M. Bradeen, Univ. of Minnesota, St. Paul, MN 55108
G.A. Secor, North Dakota State Univ. Fargo, ND 58105
M.I. Vales, Oregon State Univ., Corvallis, OR 97331
B.J. Christ and X. Qu, The Pennsylvania State Univ., University Park, PA 16802
In 2009, 50 potato clones (5 varieties, 41 selections, 4 LB differentials) were evaluated in the field for foliar late blight at four U.S. locations: Rosemount, MN; Prosper, ND; Corvallis, OR; and, Rock Springs, PA. Plots were planted in a randomized complete block design with 3-4 replications per location. AF4121-1 was planted in only one location and dropped from subsequent analyses.
All locations except PA inoculated the plots with US-8 isolates of Phytophthora infestans. P. infestans occurred naturally in PA. In addition to US-8, an as yet unidentified isolate was found naturally in ND. Irrigation was applied as needed at all locations to provide conditions favorable for disease expression.
Percent infected foliage was recorded several times following onset of the disease. Area under the disease progress curve (AUDPC) was calculated (Shaner and Finney, 1977). At each location, clonal mean AUDPCs were ranked from 1 (lowest mean AUDPC) to 49 (highest mean AUDPC). The rankings of these AUDPCs were analyzed over all locations using nonparametric analysis of mean absolute rank differences and variance of the ranks (Huehn, 1990; Lu, 1995).
Mean AUDPCs for each clone at each location are given in Table 1. Mean AUDPC over locations ranged from a low of 134 in PA to a high of 787 in ND. The three late blight resistant checks (AWN86514-2, B0692-4, B0718-3) were highly resistant (Table 1 and Figure 1). Resistance levels in A97066-42LB, B2431-23 and MSQ176-5 were close to the resistant checks. Five clones were consistently among the most late blight susceptible over all locations: B2152-17, B2492-7, B2634-3, CO98368-2RU and CO99100-1RU. The foliar reaction of all clones was stable across locations. The incidence of tuber blight was less than 10% in all clones except Alpine Russet (20%), B2492-7 (20%), B2634-3 (17.5%), B2501-10 (15%), and A0008-1TE (12.5%).Box and whisker plot AUDPC - PDF
Huehn, M. 1990. Euphytica 47:189-194. Lu, H.Y. 1995. Agronomy J. 87:888-891. Shaner, G. and R.E. Finney. 1977. Phytopathology 67:1051-1056.
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