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Atsushi Kono, Akihiko Sato, Yusuke Ban and Nobuhito Mitani

We evaluated the resistance of 133 grapevine cultivars or selections, including Vitis vinifera and American hybrids, on the basis of lesion number and length to identify sources of resistance to grapevine anthracnose. All germplasms tested in this study showed anthracnose symptoms to some extent, and the distribution of lesion number and diameter was continuous. Most table grape V. vinifera cultivars were highly susceptible, showing many large lesions. However, V. vinifera wine grapes were more resistant with smaller lesions. Some American hybrid grapes such as ‘Ontario’ showed very few and small lesions. There was a significant positive correlation between lesion number and size in American (r = 0.63, P = 0.0041) and Japanese hybrids (r = 0.56, P < 0.001), whereas there was no correlation between these characters in V. vinifera. Japanese tetraploid cultivars were neither highly susceptible nor resistant. High anthracnose susceptibility of most well-known table grape V. vinifera cultivars, including ‘Muscat of Alexandria’, ‘Italia’, ‘Rizamat’, ‘Kattakurgan’, and ‘Thompson Seedless’, indicates that resistance should be introgressed from other cultivars such as American hybrids or wine grapes when these susceptible table grapes or their descendants are used in breeding anthracnose-resistant table grapes.

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Atsushi Kono, Akihiko Sato, Bruce Reisch and Lance Cadle-Davidson

Grapevine downy mildew (DM), caused by the oomycete Plasmopara viticola (Berk. & Curt.) Berlese & de Toni, is a major disease, especially in humid viticultural areas. Development of resistant cultivars is an important objective for grapevine breeding. To establish a reliable and inexpensive quantitative method to aid in breeding for DM resistance, we improved the method for counting the number of sporangia on leaf discs, and developed a method for counting the number of sporangia in solution. To prevent the loss of DM sporangia from adhesion onto plastic ware, we found as little as 0.01% Tween 20 was effective. On the other hand, this detergent was shown to have a severe inhibitory effect upon DM infection of leaves. We developed a sporangia counting method using dried droplets of DM suspensions, and the method was highly correlated with counting by hemacytometer (R 2 > 0.96). The nonparametric Spearman’s rank correlations between visual rating and the number of the sporangia were as high as ρ = 0.82 to 0.91, suggesting that evaluation by the visual rating could provide a good estimate of the sporangia numbers on leaf discs. We established a high-throughput and inexpensive method with acceptable accuracy for DM resistance evaluation based on a leaf disc assay, and our results suggested that visual ratings of infected leaf discs provide a good estimate of sporangia numbers.

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Takashi Akagi, Yumi Takeda, Keizo Yonemori, Ayako Ikegami, Atsushi Kono, Masahiko Yamada and Shinya Kanzaki

Persimmon (Diospyros kaki Thunb.) is generally hexaploid, and a single AST locus controls the pollination-constant non-astringency trait on each of six corresponding chromosomes. The pollination-constant non-astringent (PCNA) genotype is nulliplex and requires homozygous recessive alleles (ast) at the AST locus. There are several non-PCNA cultivars/selections that could be cross parents; however, the probability of yielding nulliplex offspring depends on the number of recessive alleles (ast). In genotyping for the AST locus in hexaploid persimmon, in contrast to the situation in diploid plants, we need to detect the AST/ast allele dosage; this cannot be detected by common codominant markers. In this study, we detected the allele dosage of Mast, which is a marker allele strongly linked to the ast allele among cultivars, by quantitative real-time polymerase chain reaction (qPCR) using three reference sites, actin (DkAct), anthocyanin reductase (DkANR), and L5R, whose sequences are conserved in the genome of persimmon cultivars. Based on the allele dosage of the Mast, AST/ast genotypes were estimated for 63 non-astringent cultivars/selections, of which only five cultivars/selections were estimated to be simplex or duplex. The quantitative genotyping method using qPCR may be generally effective for polyploid plants.

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Nobuhito Mitani, Atsushi Kono, Masahiko Yamada, Akihiko Sato, Shozo Kobayashi, Yusuke Ban, Toshihito Ueno, Mikio Shiraishi, Shinya Kanzaki, Tomoyuki Tsujimoto and Keizo Yonemori

Persimmon (Diospyros kaki Thunb) is hexaploid, and the pollination-constant, non-astringent (PCNA)/non-PCNA trait of Japanese origin is qualitatively controlled by the AST/ast alleles at a single locus and the PCNA trait is recessive to the non-PCNA trait. To avoid inbreeding depression led by repeated crosses among PCNA genotypes, non-PCNA genotypes should be used as cross parents. The marker-assisted selection system has been developed for the selection of PCNA offspring in the progeny derived from the cross of non-PCNA ‘Taigetsu’ (non-PCNA ‘Kurokuma’ × PCNA ‘Taishu’) to PCNA ‘Kanshu’. The primer pairs E8.5/E9r and 7H9F/AST-R were used for detecting the molecular markers A1 and A3, respectively, which link AST alleles. Complete agreement was found between the sequence-characterized amplified region (SCAR) marker genotype and fruit astringency phenotype of the 48 offspring. The result confirmed that the marker-assisted selection using those markers was highly practical. In a larger offspring population (522 offspring) from the same cross, offspring segregated into 100 with both markers, 162 with only A1, 179 with A3, and 81 with neither, and this segregation ratio was significantly different from 2:3:3:2, which is the segregation ratio of random chromosome assortment in autohexaploid. The percentage of offspring expected to be PCNA was 15.5% (81 of 522), which was slightly lower than 20%.