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  • Author or Editor: Yutaka Sato x
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The production of hybrid-onion seed depends on cytoplasmic male sterility (CMS) systems. The male-sterile line is seed propagated using a normal (N) cytoplasmic maintainer line homozygous recessive at the nuclear male-fertility restoration locus (MS). Because of onion's biennial generation time, 4 to 8 years are required to establish the genotype at the MS locus. The development of maintainer lines would benefit greatly from a genetic marker linked to the MS locus. Such a marker would allow breeders to establish the nuclear genotype in seedlings and flower only those plants that are maintainers (N msms) or plants that can be used to develop maintainers (N MSms), reducing the number of plants to be testcrossed or backcrossed to a sterile line. We evaluated restriction fragment length polymorphisms (RFLPs), random amplification of polymorphic DNA (RAPDs), and amplified fragment length polymorphisms (AFLPs) to tag the chromosome region carrying the MS locus. No RAPDs or RFLPs cosegregated with MS. AFLP markers were identified that phenotypically correlated with restoration of male fertility.

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Cytoplasmic-genic male sterility (CMS) is used to produce hybrid onion (Allium cepa L.) seed. For the most widely used source of onion CMS, male sterility is conditioned by the interaction of the male-sterile (S) cytoplasm and the homozygous recessive genotype at a nuclear male-fertility restoration locus (Ms). Maintainer lines are used to seed propagate male-sterile lines, possess normal (N) male-fertile cytoplasm, and are homozyous recessive at the Ms locus. Due to the biennial nature of onion, it takes 4 to 8 years of crossing and scoring of progeny phenotypes to establish if maintainer lines can be extracted from an uncharacterized population or family. Identification of nuclear markers tightly linked to the Ms locus would allow for molecular-facilitated selection of maintainer lines. We evaluated testcross progenies from a segregating family for nuclear restoration of male fertility over at least three environments. Although segregations in the F2 family fit the expected 1:2:1 ratio (P = 0.973), the proportion of male-sterile testcross progenies showed significant (P < 0.01) year effects and it is therefore imperative to score male-fertility restoration over environments. Too many male-sterile testcross progenies were often observed, indicating that the dominant allele conditioning male-fertility restoration for S cytoplasm may not show complete penetrance. Segregations of amplified fragment length polymorphisms and restriction fragment length polymorphisms (RFLPs) revealed RFLPs flanking the Ms locus at 0.9 and 8.6 cM. An onion cDNA showing highly significant homology to the aldehyde dehydrogenase conditioned by the rf2 locus of maize was identified and mapped to linkage group I, independent of the Ms locus. A sample of commercial onion germplasm was evaluated for putative allelic diversity at the RFLP loci linked to Ms. The genomic region corresponding to the cDNA (AOB272) revealing the closest RFLP to Ms was sequenced to reveal numerous single nucleotide polymorphisms. Single-stranded conformational polymorphisms and single nucleotide extensions were developed that revealed genomic variation at AOB272-EcoRI. The use of these molecular markers to select maintainer lines in onion is discussed.

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In nutrient film technique (NFT) vegetable production, the use of low-concentration nutrient solutions might lead to a nutrient concentration gradient along the bed, which can translate into nonuniform plant growth. The authors modified a conventional NFT system (cNFT) and propose a modified NFT (mNFT) that enables the production of lettuce (Lactuca sativa) plants of uniform fresh weight along elongated cultural beds. Two experiments were carried out to compare the systems when long cultural beds are used (18 m) in terms of uniformity of plant and nutrient solution characteristics. The results indicated that fresh weight of plants in cNFT decreased as the distance from the nutrient inlet increased, whereas no such trend was observed in mNFT. Leaf nitrate concentration in mNFT was uniform, whereas it was higher near the outlet of cNFT. Ascorbic acid concentration was also uniform in mNFT, but it was found to be lower near the outlet of cNFT. During Expt. 2, the oxygen content along the bed decreased from inlet to outlet in cNFT; however, in mNFT, it remained relatively constant at all sampling positions. Regarding the concentration of the nutrient solution along beds, no significant differences were found between inlet and outlet in both systems. It is suggested that the lower concentration of oxygen found at the outlet of cNFT might have reduced nutrient uptake, thus attenuating the difference in concentration between inlet and outlet. The temperatures of the nutrient solution along mNFT during Expt. 2 tended to be slightly lower than those of cNFT. However, temperatures were still too high and plant growth was negatively affected. The results of this study demonstrate that plants of uniform size and quality can be achieved in long cultural beds (up to 18 m long) supplied with a low-concentration fertilizer solution by using the proposed mNFT.

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‘Porotan’ is a Japanese chestnut cultivar (Castanea crenata Sieb. et Zucc.) that was selected from offspring of the cross 550-40 × ‘Tanzawa’ and released in 2006. Its nut is distinguished by a pellicle that is easy to peel after roasting; previously, all Japanese chestnut cultivars were thought to have a pellicle that was difficult to peel. Both 550-40 and ‘Tanzawa’ are Japanese chestnuts, and 550-40 is a selection descended from ‘Tanzawa’. Both 550-40 and ‘Tanzawa’ have a pellicle that is difficult to peel. Among 59 offspring of a cross of 550-40 × ‘Tanzawa’, 12 had an easy-peeling pellicle and 47 had a difficult-peeling pellicle; this ratio is not significantly different from the 1:3 expected ratio for monogenic inheritance based on a chi-square test at P = 0.05. A half-diallel cross without selfings was made among ‘Porotan’, ‘Tanzawa’, and ‘Tsukuba’. All the offspring from ‘Tanzawa’ × ‘Tsukuba’ and from ‘Tsukuba’ × ‘Porotan’ had a difficult-peeling pellicle; in contrast, 39 offspring from ‘Tanzawa’ × ‘Porotan’ segregated in a ratio of 19 difficult-peeling pellicle to 20 easy-peeling pellicle, which is not significantly different from the expected 1:1 ratio for monogenic segregation based on a chi-square test at P = 0.05. These results suggest that the easy-peeling pellicle trait of ‘Porotan’ is controlled by a major recessive gene at a single locus. We designated the pellicle peelability locus as P/p. According to this model, the ‘Tsukuba’ genotype is homozygous-dominant (PP), the ‘Tanzawa’ genotype is heterozygous (Pp), and the ‘Porotan’ genotype is homozygous-recessive (pp).

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