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Seeds of common buckwheat usually mature while leaves are still green, causing problems for harvest machinery and limiting yields. We developed an early leaf-senescence line, Kyushu 1, from spontaneous mutants. To characterize this mutant line physiologically and genetically, we measured the change in leaf chlorophyll content in two regions of Japan with different environments, and performed genetic analyses with self-compatible lines. The chlorophyll content of Kyushu 1 was lower than that of the wild type at seed maturity in both regions. F1 progeny of the cross between wild-type plants and Kyushu 1 showed a wild-type phenotype. F2 progeny segregated into wild-type and early leaf-senescence phenotypes in a 3:1 or 13:3 ratio, suggesting that the early leaf senescence of Kyushu 1 is controlled by either a single recessive gene or an epistatic interaction between two loci. Discipline: Plant breeding Additional key words: chlorophyll, genetic analysis, mutant, SPAD

Common buckwheat plants have heteromorphic self-incompatibility. Using two self-fertilizing lines, we revealed that there are two distinct systems of sell-compatibility, one using a self-compatible allele, S', the other using modifier genes located outside the S locus and suppressing the functions of the S-locus genes. S h appears to have been produced by recombination in the S supergene (gi s I P PA/gi S I p PA), in which each gene is functional. The modifier genes control the intensity of self-incompatibility and have three distinctive features: (1) Pollen shows cross-compatibility with styles of all flower types, although the compatibility is influenced by the genetic background of those plants. (2) Flower morphology of F 1 plants is controlled by the genotype of the S locus. (3) F 1 plants show high self-compatibility, although the level of self-compatibility is influenced by genetic background. The use of these genes for buckwheat breeding is discussed.