Blast disease is one of the most devastating diseases of rice. To minimize losses of production due to the disease, the use of multilines, which are groups of near-isogenic rice lines harboring various resistance genes in a common background, is considered to be a useful strategy for disease control. Blast resistant-multilines derived from Koshihikari and some other elite Japanese cultivars have been developed. In the present study, we generated five STS-based DNA markers for identifying blast-resistant Koshihikari Niigata BLs harboring either of Pia, Pii or Pita-2. It was revealed that each of these markers produced a PCR product mostly with DNAs from a Koshihikari BL and other cultivars harboring the respective resistance gene, unlike with DNAs from blast-susceptible Koshihikari and other Japanese representative rice cultivars. Based on homology search of the sequence of the markers against published Nipponbare genome sequence data, it was found that each of these markers was positioned in a chromosomal region where the respective blast gene had been reported to be located. These DNA markers, especially if the multiplex PCR procedure is used, may enable to achieve efficient discrimination of Niigata BLs 1, 2 and 3 from one another, from other Niigata BLs and from other Japanese rice cultivars.

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The expression of parthenogenesis in tetraploid Chinese leek (Allium ramosum, syn. A. tuberosum 2n=32) was analyzed by observing the cleared ovules and performing RAPD-PCR on a F₁ population generated by crossing tetraploid amphimictic individuals with a tetraploid parthenogenetic cultivar. The results from the hybridization indicated that the amphimictic and parthenogenetic reproductive behaviors segregated. RAPD analysis showed that the progeny of amphimictic individuals, except for one individual (00-03-14), displayed a completely hybrid origin. In addition, ovule analysis for four of these F₁ populations revealed that the parthenogenetic and non-parthenogenetic expression segregated in an approximately 1:1 ratio when the amphimictic cultivar was pollinated with the cv. Tender-pole. A chi-square test suggested that cv.Tender-pole harbored one locus related to parthenogenesis. Almost all the examined F₁ individuals derived from the crossing of the five non-parthenogenetic individuals (97-11-7, 97-12-43, 97-12-85, 00-02-3, 00-02-187) as seed parents, exhibited hexaploidy (namely BIII-derived hybrids). Since the RAPD marker that is specific to the pollen parent (cv.Tender-pole) had segregated in 95% of the hexaploid F₁ individuals in the (97-12-43×cv. Tender-pole) population, recombination occurred between the diplospory locus and the parthenogenesis locus in the 6× amphimictic individuals.

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