INHERITANCE OF A DISEASE LESION MIMIC MUTANT IN SOYBEAN

Disease lesion mimic mutants have been identified in several plant spe cies, including one that affects the primary root in soybean [Glycine max (L.) Merr.]. These mutants display chlorotic and/or necrotic lesio ns despite the absence of any detectable pathogen. A soybean mutant ex hibiting this phenotype in its leaves was observed as a single M-2 pla nt among the bulked progeny of about 150,000 M-1 plants grown from mut agenized (i.e., gamma-irradiated) seed of the determinate cultivar Hob bit 87. Leaves of the identified mutant plant became more necrotic and chlorotic as they aged, eventually undergoing an earlier than normal leaf senescence. No pathogen was detectable in the affected leaves. Th e self ed progeny of the mutant bred true for this phenotype. Reciproc al crosses were made between the mutant and its Hobbit 87 parent. The mutant also was crossed to a determinate isoline of the cultivar Haros oy. The F-1 phenotype and the F-2 and F-2:3 segregation data indicated that the mutant behaved as a single recessive allele, designated dim tan acronym for disease lesion mimic). About two-thirds of the F-2 pla nts classified as nonmutant displayed a faint freckling on some of the ir leaves, but this was not a reliable indicator of heterozygosity at the Dim locus based on F-3 progeny tests. Disease lesion mimicry mutan ts may be useful in basic research aimed at better understanding disea se hypersensitive response and programmed cell death in plants.