Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 7, 2008
Publication Date: November 1, 2008
Citation: Haynes, K.G., Christ, B.J., Vinyard, B.T. 2008. Determining the Importance of Combining Ability for Late Blight Resistance in Early Generations of Potato Breeding When Susceptible Clones are Discarded. American Journal of Potato Research. 85:445-454.
Interpretive Summary: Late blight is the most economically important disease of potatoes worldwide. Potato breeders are working to incorporate late blight resistance in new varieties. Once late blight resistant parents are identified, the next step is to determine how good they are in transmitting late blight resistance to their offspring. This is an intensive process that requires a great deal of resources in terms of land, time, and personnel. We developed a procedure to streamline testing that allows late blight susceptible offspring to be discarded from the breeding program as soon as they are identified but still allows the breeder to determine which parents should be utilized in future crosses. This allows us to concentrate our efforts only on those clones that are resistant. We made 32 crosses between eight female and four male parents for late blight resistance and identified one male and three female parents that were more successful than the others in producing late blight resistant offspring. This procedure should hasten the identification and development of late blight resistant varieties. This information will be used by breeders involved in breeding for resistance to diseases.
At times it may be desirable to determine the importance, rather than the actual values, of general (GCA) and specific combining ability (SCA) in parental materials. In screening large populations for disease resistance over years it may be difficult or impossible to accurately estimate these effects. Once a clone has been found to be susceptible it is usually discarded, but multiple evaluations are desired before declaring a clone resistant. The purpose of this study was to determine the importance of GCA and SCA for late blight resistance in tetraploid potatoes. Thirty-two families were generated from a design II mating scheme and progeny were evaluated for foliar late blight from 2002-2004. In the first two years progeny that had > 90% late blight infected foliage were discarded, and the remainder were retested. Sixty-seven clones had no more than 50% infected foliage each year. Separate '2 tests demonstrated the significance of GCA in all the female and one of the male parents. The proportion of resistant progeny from the female and male parents was used to calculate the expected proportion of resistant progeny for each parental combination. The probbnml function in SAS was used to calculate the probability that the actual number of resistant clones observed was as great or greater than expected. SCA was important in six of the families. Although this method does not give estimates of GCA or SCA, it does determine if GCA or SCA are significant and which parents or parental combinations have significant GCA or SCA, respectively.