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Title: PARTIAL RESISTANCE TO PHYTOPHTHORA INFESTANS IN FOUR SOLANUM CROSSES

Author
item DORRANCE, A - OHIO STATE UNIVERSITY
item INGLIS, D - WSU, MT VERNON REU
item Helgeson, John
item Brown, Charles

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2000
Publication Date: 1/15/2001
Citation: DORRANCE, A.E., INGLIS, D.A., HELGESON, J.P., BROWN, C.R. PARTIAL RESISTANCE TO PHYTOPHTHORA INFESTANS IN FOUR SOLANUM CROSSES. AMERICAN JOURNAL OF POTATO RESEARCH. 78:9-17. 2001.

Interpretive Summary: Potato late blight is the most serious fungal disease of potato. The fungus kills foliage and causes tubers to rot in the field or in the storage. Annually American potato growers spend $200,000,000 on fungicide sprays to control the disease. A much better strategy would be to breed resistant varieties. Late blight fungus is quite variable and has broken varietal resistance in the past. For this reason there is an intense search for durable resistance. This study characterizes the durable resistance that can be found in four breeding populations containing new genetic sources. Durable resistance has the feature of allowing a certain amount of disease to develop, but very slowly. It requires multiple observations in multiple sites to accurately identify durable resistance. However, this study determined that it is possible to identify durable resistance early in the season by determining the number of days until 5% foliar damage occurs. This was highly negatively correlated with the tota amount of damage that was measured by a whole season of observations. Another factor was sporangia production, a measure of the degree to which the fungus reproduces, and releases infection-spreading zoospores into the environment to start infections on other leaves. However, sporangia production turned out to be a poor measure of durable resistance because it differed greatly between years. The traits discovered in this study will help breeders select new late blight resistance varieties more efficiently than in the past. New resistant varieties should increase profitability of the potato industry and reduce the fungicide load released into the environment by agriculture.

Technical Abstract: Thirty progeny from each of four Solanum crosses were evaluated in the field at Mount Vernon, WA in 1996 and 1997 for partial resistance to Phytophthora infestans. Of the four parents, three have high levels of partial resistance to P. infestans; one derived from somatic hybridization of S. bulbocastanum, the other two from traditional breeding efforts for multiple disease resistance. Data were collected from each cross to estimate area under the disease progress curve (AUDPC), days to 5% disease severity threshold (DT5), and sporangia production (SP). All of these variables differed significantly among the progeny within each cross in each year. Correlation analysis indicated that DT5 was highly correlated with AUDPC for all four populations for both years. Log-transformed SP was significantly (Pó0.001) correlated to AUDPC values for one population in both years but the significance of the correlation was variable between years for the remaining three crosses. Individual components of partial infection efficiency as well as latent period and to some extent lesion growth rate, were the most important in limiting late blight development in the progeny of all four crosses in this field study.