|Brown, Charles - Chuck|
Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2003
Publication Date: 3/1/2004
Citation: INGLIS, D.A., GUNDERSEN, B.G., PORTER, L.D., MILLER, J.S., JOHNSON, D.A., LOZOYA-SALDANA, H., BROWN, C.R. ASSESSMENT OF SOLANUM HOUGASII IN WASHINGTON AND MEXICO AS A NEW SOURCE OF LATE BLIGHT RESISTANCE. AMERICAN JOURNAL OF POTATO RESEARCH. pending. 2004. Interpretive Summary: Late blight of potato is perhaps the most important disease on a worldwide basis. In the U.S., 100 million dollars are spent annually to control the disease. It can cause a massive die-off of foliage in the field and can infect the potatoes in the soil, that are then stored in a state of rot. Late blight infection is difficult to assess and tuber infection often occurs without overt signs of foliar blight. The disease organism has shifted genetically in recent years with migrations of new types out of Mexico. The disease has emerged as a problem in areas where it previously was considered minor. Examples of this are in the hot irrigated growing areas of the Pacific Northwest. New isolates of the fungus have been shown to be resistant to a common fungicide, to possess greater tolerance to heat, and a shorter disease development time. Finding new genetic sources of resistance is an important part of solving this problem. Wild potatoes out of Mexico that grow and survive in the presence of the disease are sources of resistance. A rare wild species, Solanum hougasii and progeny from crosses derived from this source were found to possess resistance in different environments and different years. Some progeny displayed combined foliar and tuber resistance. These progeny are directly crossable with potato breeding clones and will contribute toward a reduction in the cost of production and amount of fungicide released into the environment when the resistance they contain is incorporated into new varieties.
Technical Abstract: Solanum hougasii is a rare wild relative of potato that that grows in the highlands of central Mexico. Late blight water mold, a pathogen of worldwide importance, is present in its zone of distribution. S. hougasii and a segregating population derived from it were evaluated in field exposures to the disease in four environments for resistance. Tubers and detached leaves from progeny of this population were examined for resistance. Approximately 13 percent of the population examined in Washington State were resistant while about 17 percent of the population was found to be resistant in the Toluca Valley of Mexico. Foliar field scores were significantly correlated to detached leaf tests but not to tuber resistance measurements. A number of clones displayed combined foliar and tuber resistance. Resistance was characterized in some cases as a leaf chlorosis accompanied by next to no sporulation, a new resistance phenotype. The ranking of the clones in the four environments was basically maintained in pairwise comparisons between environments. The most resistant clones were uniformly highly resistant in all environments. Damage to the foliage was directly proportional to the quantitative production of sporangia on leaf lesions, that is, reduced sporulation resulted in less foliar damage. Progeny of the segregating population were directly crossable to cultivated tetraploid potato. Resistant progeny constitute a new source of late blight resistance for potato breeding programs.