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Title: Assessment of Solanum hougasii in Washington and Mexico as a Source of Resistance to Late Blight

item INGLIS, D
item Brown, Charles - Chuck
item Porter, Lyndon
item MILLER, J
item Haynes, Kathleen

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2007
Publication Date: 6/15/2007
Citation: Inglis, D.A., Brown, C.R., Gundersen, B.G., Porter, L., Miller, J.S., Johnson, D.A., Lozoya-Saldana, H., Haynes, K.G. 2007. Assessment of Solanum hougasii in Washington and Mexico as a Source of Resistance to Late Blight. American Journal of Potato Research. Vol 54: 217-228.

Interpretive Summary: In 1845 a terrible disease attacked the potato crop in Ireland and spread to the rest of the world. The social costs were huge in terms of mortality and the culture of Ireland. Today there are more people of Irish descent in North America due to the huge migration of people out of Ireland, due to the Irish Potato Famine. This disease, called late blight, is the most important and damaging disease of potato worldwide today. The center of origin of the late blight organism is Central Mexico. The organism is most genetically variable there. Hence in our search for resistance, a Mexican test site is an important component for selecting durable resistance. Many wild forms of potato evolved in Mexico and have resistance genes for battling late blight. We present here our work to evaluate the value of resistance from one wild species that has been neglected over the years. In the process of testing the breeding products of the wild species we determined that it was stable over times and locations and provided a high efficient genetic control of resistance that could be incorporated into future potato varieties. Utilization of this source of resistance could reduce the estimated $150 million spent annually in North America on fungicides to control the late blight water mold. In addition, using less fungicide would improve ground water purity.

Technical Abstract: A segregating introgression population, established by crossing an accession of Solanum hougasii from the central highlands of Mexico with two successive recurrent corky ringspot resistant parental lines, was screened against Phytophthora infestans. Foliage and tuber reactions were compared under natural epidemics of US-8 and US-11 P. infestans at Mount Vernon, Washington, natural epidemics at Toluca, Mexico, and by laboratory assays with US-8 and US-11 P. infestans at Pullman, Washington RAUDPC values in the field at Mount Vernon and Toluca were significantly (P = 0.0001) correlated. Late blight severity on detached leaflets inoculated with US-8 and US-11 P. infestans in the laboratory ranged from 0 to 64% or 65%, respectively. Severity of infection on inoculated tubers ranged from 0 to 68 % for US-8, and 0 to 80 % for US-11. Disease severity on leaflets in laboratory tests was significantly correlated with field RAUDPC values, but tuber severity in laboratory tests was not, although some lines exhibited resistance in both the foliage and tubers. Foliar resistance in the field was characterized by leaf chlorosis, and limited lesion expansion and sporulation. Estimate of broad-sense heritability was relatively high, H = 0.83. Only 15% of this BC1 population showed significant instability giving little indication of specific interactions between genotypes and populations of the P. infestans pathogen that would be indicative of R-gene interactions. The introgression population (BC1) appears to be expressing highly heritable durable resistance. The high heritability estimate suggests that utilization of highly resistant and stable BC1 genotypes, such as 53.78, as a parental source of foliar late blight resistance will transmit substantial non-race specific genetic resistance to future progenies, and ultimately, after several cycles of backcrossing and selection, this genetic potential could be deployed in new potato cultivars.