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Effect of Interplot Interference on the Assessment of Partial Resistance to Stem Rust in Durum Wheat. L. H. M. Broers, Department of Plant Breeding, Wageningen Agricultural University, P.O. Box 386, 6700 AJ Wageningen, The Netherlands; CIMMYT, Lisboa 27, Apdo Postal 6-641, 06600 Mexico D.F., Mexico; R. M. Lopez-Atilano, CIMMYT, Lisboa 27, Apdo Postal 6-641, 06600 Mexico D.F., Mexico. Phytopathology 85:233-237. Accepted for publication 28 October 1994. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/Phyto-85-233.

Two experiments were carried out in which different plot designs were compared to assess the level of interplot interference of stem rust (Puccinia graminis f. sp. tritici) on durum wheat (Triticum turgidum var. durum). The resistance levels of the most resistant genotypes were on average a factor of 17.3 (experiment 1) to 31.6 (experiment 2) lower in adjacent plots than in isolated plots, which were assumed to represent the true level of resistance of a genotype (no interplot interference). According to Spearmanís rank correlation coefficients, ranging from 0.88 to 0.99, the ranking of genotypes was not affected by the presence or absence of interplot interference. Thus, selection for partial resistance in adjacent small plots is not affected by interplot interference. Using standard control cultivars with known levels of partial resistance will correct the under-estimation of true levels of partial resistance and will help breeders determine the levels of disease that are still acceptable for selecting durum wheat genotypes for partial resistance to stem rust.