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Dilatory Resistance to Rice Blast in USA Rice. M. A. Marchetti, Research plant pathologist, Agricultural Research Service, USDA, Texas A&M University Agricultural Research and Extension Center, Beaumont 77706; Phytopathology 73:645-649. Accepted for publication 1 November 1982. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1983. DOI: 10.1094/Phyto-73-645.

Differences in dilatory resistance (slower disease development) to race IG-1 of Pyricularia oryzae were detectable among closely related rice lines planted in three-row by 60-cm “miniplots” separated by two buffer rows of a resistant rice line. This technique has direct application in screening large numbers of breeding lines for dilatory resistance to rice blast. It requires only a few grams of seed, and miniplots can be planted in existing blast nursery beds designed for specific resistance screening. Southern rice lines with no major-gene resistance to race IG-1 of P. oryzae showed various degrees of dilatory resistance, and all of them were more resistant than two lines developed in blast-free California. Most of the newer rice cultivars carry major genes for resistance to race IG-1, but many have multiple sources of dilatory resistance in their recent ancestry.

Additional keywords: discriminatory resistance, general resistance, horizontal resistance, vertical resistance.