Bud Sport Mutants Research Articles

Clone identification in Japanese flowering cherry (<i>Prunus</i> subgenus <i>Cerasus</i>) cultivars using nuclear SSR markers

Numerous cultivars of Japanese flowering cherry (Prunus subgenus Cerasus) are recognized, but in many cases they are difficult to distinguish morphologically. Therefore, we evaluated the clonal status of 215 designated cultivars using 17 SSR markers. More than half the cultivars were morphologically distinct and had unique genotypes. However, 22 cultivars were found to consist of multiple clones, which probably originate from the chance seedlings, suggesting that their unique characteristics have not been maintained through propagation by grafting alone. We also identified 23 groups consisting of two or more cultivars with identical genotypes. Most members of these groups were putatively synonymously related and morphologically identical. However, some of them were probably derived from bud sport mutants and had distinct morphologies. SSR marker analysis provided useful insights into the clonal status of the examined Japanese flowering cherry cultivars and proved to be a useful tool for cultivar characterization.

Growth Characteristics of a Small-fruit Dwarf Mutant Arising from Bud Sport Mutation in Japanese Persimmon (Diospyros kaki Thunb.)

Fruit size is one of the most important traits that affect the economic value of fruit. In persimmon (Diospyros kaki Thunb.), somatic and bud-sport mutations that affect the fruit traits are frequently observed. Recently, a small-fruit mutant, ‘Totsutanenashi’ (TTN), was discovered in Japan as a bud-sport mutant of the leading cultivar Hiratanenashi (HTN). In this study, we investigated the morphological and physiological characteristics of TTN and HTN focusing on the tree architecture, fruit size, and the fruit flesh chemical composition. The objectives of the study were to evaluate the potential horticultural use of TTN and to characterize the differences between HTN and TTN. Both TTN and HTN are nonaploid plants, indicating that a difference in ploidy is not the cause of the small-fruit mutation. The vegetative growth of trees and tissue-cultured shoots of TTN was more compact than that of HTN. The floral organs of TTN appeared similar to those of HTN before flowering, but the TTN flowers opened earlier, resulting in smaller ovaries than in HTN flowers. The fruit size of TTN was consistently lower than that of HTN at all fruit developmental stages. TTN fruit had a higher sugar content and a higher proportion of sucrose to total sugars than HTN fruit. TTN fruits contained lower levels of secondary metabolites such as soluble tannins and ascorbate than HTN fruits. These results suggest that the fruit size mutation also affects the fruit biochemistry, leading to alterations in the fruit flesh composition. TTN may be a valuable genetic resource because compact trees require less labor and maintenance, and small, sweeter fruits may meet the various needs of consumers. The use of TTN in studies of the genetic control of fruit size is also discussed.

Identification of Parent-offspring Relationships in 55 Japanese Pear Cultivars Using S-RNase Allele and SSR markers

S-RNase alleles and 18 simple sequence repeats (SSR) markers were used to analyze 55 Japanese pear cultivars, including 47 hybrid cultivars, 6 bud sport mutants, and 2 derived from open pollinations. Fifteen cultivars used in the breeding of some of the hybrid cultivars were also examined. Each cultivar was genotyped at the S-locus and SSR loci. Parent-offspring relationships were analyzed by comparing genotypes among the cultivars. Of the 47 crossbreeding cultivars and selections, parent-offspring relationships of 37 were re-confirmed because the hybrids inherited S-RNase and SSR alleles from both parents without any discrepancies. Discrepancies at 3 or more SSR loci were found between 10 hybrid cultivars (‘Kisui’, ‘Tanzawa’, ‘Niitaka’, ‘Seiryu’, ‘Akemizu’, ‘Atago’, ‘Echigonishiki’, ‘Ishiiwase’, ‘Shusui’, and ‘Yachiyo’) and their previously reported parents, suggesting that these hybrid cultivars have different parents than reported. Furthermore, ‘Momoeduki’ and ‘Sanko’, which were previously reported as bud sports of ‘Niitaka’ and ‘Kosui’, respectively, exhibited SSR genotypes that were different from their reported parents. Paternal cultivars were previously unknown in ‘Shinko’ and ‘Yoshikaori’, which are open-pollinated seedlings of ‘Nijisseiki’. SSR genotypes revealed that their paternal cultivars are ‘Amanogawa’ and ‘Chojuro’, respectively.

Analysis of Bud Sport Cultivars of Peach (Prunus persica (L.) Batsch) by Simple Sequence Repeats (SSR) and Restriction Landmark Genomic Scanning (RLGS)

To detect genetic mutations in bud sport cultivars of peach, RLGS (restriction landmark genomic scanning) analysis was performed on 7 putative bud sport mutant cultivars after SSR (simple sequence repeats) analysis for identifying false-mutants. Three cultivars, ‘Yawata Hakuho’, ‘Odoroki’, and ‘Kanoiwa Hakuto’, postulated to be bud sport mutants, were confirmed as false-mutant cultivars. This suggests that other false-mutant strains of peach are also likely to be registered with the Plant Variety Authority as bud mutant cultivars. A stable RLGS profile of peach, obtained using NotI as a landmark enzyme, showed about 400 spots in a single experiment. Comparing the profiles between mutant and original cultivars, polymorphic spots were discovered in 2 mutatnt cultivars, ‘Gyosei’ and ‘Nagasawa Hakuho’, but were not detected by SSR analysis. RLGS was thus considered to be an effective method to detect very small genomic variations in mutant strains.

Parentage Analysis in Japanese Peaches using SSR Markers.

Parentage of 16 peach cultivars, including 9 cultivars bred by controlled hybridization, 2 from bud sport mutations and 5 from chance seedlings, was analyzed using 17 SSR markers. The parent-offspring relationships of 9 crossbreeding cultivars were confirmed because SSR alleles were transmitted to offspring cultivars from their parents without discrepancy at all the used loci. ‘Akatsuki’ and ‘Gyousei’ showed identical SSR genotypes, which suggested that ‘Gyousei’ was derived from a bud sport mutation. In contrast, another bud sport cultivar, ‘Hikawa Hakuhou’, showed different SSR genotypes from those of the original cultivar ‘Hakuhou’ at 12 SSR loci, indicating that ‘Hikawa Hakuhou’ was not a bud sport mutant of ‘Hakuhou’. Four cultivars that presumably originated from chance seedlings, i.e., ‘Abe Hakutou’, ‘Kawanakajima Hakutou’, ‘Kouyou Hakutou’ and ‘Shimizu Hakutou’, shared one allele with their putative parent ‘Hakutou’ at each SSR locus. SSR analysis suggested that these 4 cultivars were not bud sport mutants, but offsprings of ‘Hakutou’. It was concluded that SSR markers could be effectively utilized for parentage analysis in Japanese cultivated peaches.