@article{oai:repository.naro.go.jp:00001745,
 author = {小原, 隆由 and OHARA, Takayoshi},
 journal = {野菜茶業研究所研究報告, Bulletin of the National Institute of Vegetable and Tea Science},
 month = {Feb},
 note = {Reducing production costs by mechanization and labor saving has become very important in the production of bunching onion (Allium Jistulosum L.) in Japan. Machine-assisted transplanting of nursery plugs has recently become common because of its substantial saving of labor. However, bunching onion initially grows very slowly, and the nursery period is limited because of the small volume of the plug. Because very young and small seedlings are transplanted into the field, unfavorable weather such as drought or heavy rain can severely retard growth. Therefore, breeding of cultivars showing vigorous seedling growth using heterosis is anticipated. However, little is known about heterosis or the combining abilities in bunching onion. Furthermore, genetic and molecular studies in bunching onion are limited because of its severe inbreeding depression, long generation time, and huge genome size. We evaluated heterosis for seedling growth in 11 cultivars of bunching onions belonging to the Senju, Kaga, Kujo, and Okunegi groups and 40 of their intervarietal F_1 progeny. For fresh weight of seedlings at 4 weeks after transplanting, heterosis over the mid-parent (the mean of the parents) ranged from -3% to 70%, with an average of 21%, and heterosis over the better parent ranged from -10% to 46%, with an average of 10%. High heterosis among F_1 hybrids occurred most frequently in the inter-group crosses of Senju × Kujo, and high heterosis for practical use was also seen in some intra-group crosses within the Senju group. Root number, plant height, and relative growth rate also showed significant heterosis, but the response was less than that for fresh weight. The 11 parental cultivars were assayed for DNA polymorphism by using 128 amplified fragment length polymorphisms (AFLPs) to estimate genetic distances (GDs). Cluster analysis of the parents based on GDs accorded with the traditional classification based on morphological and ecological characteristics. The GDs were correlated significantly with heterosis over the mid-parent for each seedling trait at 4 weeks after transplant-ing, but not with heterosis over the better parent. Consequently, these correlations are not applicable for predicting heterosis. To gain information about the mode of inheritance of seedling growth rate in bunching onion, we conducted a diallel analysis using a 9 × 9 half-diallel cross involving various types of inbred lines. Fresh weight at the transplanting stage (7 weeks after sowing) showed a high broad-sense heritability (h_B^2) and a low narrow-sense heritability (h_N^2）.The average degree of dominance was 1.50, suggesting that fresh weight at the transplanting stage is controlled by overdominant genes. The correlation between Vr + Wr and Pr showed that dominant genes induced heavier weight. Fresh weight at 4 weeks after transplanting also showed a high h_B^2, alow h_N^2， and a very high average degree of dominance (3.10), indicating the presence of a higher level of overdominance. Plant height at both growth stages also showed overdominance. Dominant genes increased plant height. The value of h_N^2 was higher for plant height than for fresh weight, suggesting that the contribution of additive effects is larger for plant height than for fresh weight. The F_1 hybrids between the Senju and Kujo groups tended to show higher heterosis. The results suggest that the frequency of the dominant alleles that increased fresh weight was high in the Senju parental lines, whereas the frequency of those that induced an increase in plant height was high in the Kujo lines. This makes the Senju × Kujo combination appropriate for quantitative trait loci (QTL) analysis of seedling growth. We constructed the first genetic linkage map of bunching onion based on AFLP and simple sequence repeat (SSR) markers using a set of reciprocally backcrossed populations (BC_1) produced from two inbred lines, D (Senju) and J (Kujo). A linkage map of D constructed from the (J) BC_1 population comprises 186 markers-146 AFLPs, 3 cleaved amplified polymorphic sequences (CAPS), and 37 SSRs-in 15 linkage groups (LGs) covering 1104 centimorgans (cM). A linkage map of J constructed from the (D) BC_1 population comprises 157 loci-117 AFLPs, 2 CAPS, and 38 SSRs -in 16 LGs covering 1068 cM. Neither map is saturated, but both are considered to cover most of the genome. Fifteen LGs in the two maps were connected by using co-dominant anchor markers: 37 SSRs and 2 CAPS. QTLs for seedling weight were mapped on the reciprocal BC_1 maps to identify QTLs controlling seedling growth and to elucidate their modes of gene action. Fresh weights of seedlings of BC_1 S_1 families were measured in three seasons. Remarkable heterosis was observed in F_1 and many BC_1 S_1 families. Many QTLs for seedling weight were detected on the two maps by composite interval mapping. The phenotypic variation explained by a single QTL was <25%. We consider four QTLs on four LGs to be consistently effective across different environmental conditions, because they were detected in different years and seasons. We expect these QTLs to be targets of marker-assisted selection for rapid seedling growth. Most QTLs were detected on one map but not in the corresponding region on the other map. We calculated the degree of dominance at each locus and observed overdominance at some loci. The other loci showed additive or dominant effects. The results suggest that the remarkable heterosis for seedling weight in our breeding population is based on the accumulation of dominant and overdominant gene actions.},
 pages = {1--38},
 title = {ネギの初期生育におけるヘテロシスに関する研究},
 volume = {10},
 year = {2011},
 yomi = {オハラ, タカヨシ}
}