The shelf life of Japanese pear fruit is determined by its level of ethylene production. Relatively high levels of ethylene reduce storage potential and fruit quality. We have identified RFLP markers tightly linked to the locus that determines the rate of ethylene evolution in ripening fruit of the Japanese pear. The study was carried out using sequences of two types of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase genes (PPACS1 and pPPACS2) and a ACC oxidase gene (PPAOX1) as probes on 35 Japanese pear cultivars expressing different levels of ethylene (0.0 to approximately 300 microl/kg fresh weight/h) in ripening fruit. When total DNA was digested with HindIII and probed with pPPACS1, we identified a band of 2.8 kb which was specific to cultivars having very high ethylene levels (> or = 10 microl/kg f.w./h) during fruit ripening. The probe pPPACS2 identified a band of 0.8 kb specific to cultivars with moderate ethylene levels (0.5 microl/kg f.w./h-10 microl/kg f.w./h) during fruit ripening. The cultivars that produce high levels of ethylene possess at least one additional copy of pPPACS1 and those producing moderate levels of ethylene have at least one additional copy of pPPACS2. These results suggest that RFLP analysis with different ACC synthase genes could be useful for predicting the maximum ethylene level during fruit ripening in Japanese pear.
We investigated the effects of applied gibberellin A 3 (GA 3 ) and uniconazole P (UCP), a GA biosynthesis inhibitor, on tillering in Welsh onion, also known as Japanese bunching onion 'Hangzhou', a cultivar with very high tillering capacity. The number of tillers was increased by GA 3 treatment and reduced by UCP treatment. The tillering-inhibitory effect of UCP was counteracted by GA 3 treatment. GAs were considered to be involved in not axillary bud outgrowth but its initiation for the following results: UCP treatment raised the leaf position with the first tiller, and the tillering-promoting effect of GA 3 treatment became apparent about 8 weeks after the treatment, which mostly corresponded to the period during which an axillary bud initiated near the shoot apex develops to become visible. To clarify the relationship between the diversity of tillering capacity in Welsh onion cultivars and GAs, we investigated the levels of endogenous GAs and the responsiveness to GA 3 treatment in several cultivars possessing different tillering capacities. There was a negative correlation between the tillering capacity and the level of GA 4 , a major bioactive GA in Welsh onion. On the other hand, there was a positive correlation between the tillering capacity and the responsiveness to GA 3 treatment; GA 3 treatment markedly promoted tillering in 'Hangzhou', but not in 'Raitei-Shimonita' and 'HanemidoriIpponbuto', cultivars with very low tillering capacity. These results suggest that the sensitivity to GAs is a factor causing the diversity of tillering capacity in Welsh onion.
To clarify the role of gibberellin (GA) in the growth of bunching onion (Allium fistulosum), identification of endogenous GAs and expression analysis of a putative gibberellin 3-oxidase (AfGA3ox1) were conducted. GA1, GA3, GA4, GA9, GA20, and GA34 were identified with levels of GA4 and GA9 being higher than those of GA1, GA3, and GA20. The young seedlings were clearly elongated by exogenous GA4 treatment but not by GA3. These results indicate that the 13-non-hydroxylation pathway of GA biosynthesis may be predominant in shoots with GA4 playing an important role in the growth of bunching onion. Expression of AfGA3ox1 was higher in leaf sheaths than leaf blades during vegetative growth. In reproductive organs, expression of AfGA3ox1 was higher at early and middle development stages in the stalks but was detected at a late development stage in the umbels. AfGA3ox1 was mapped on chromosome 7A from shallot, a bunching onion-related species.
We established a four-year management system that decreased the population of Meloidogyne incognita to avoid injury due to continuous cropping of Japanese bunching onion by combination with soil disinfection and an antagonistic plant. In the first year, chemical treatments (chloropicrin + 1,3-dichloropropene, dazomet and oxamyl) were added to the soil before cultivation, the population of root-knot nematodes decreased after these treatments, resulting in an increased yield of Japanese bunching onion. Soil disinfections (chloropicrin + 1,3-dichloropropene and dazomet) had a higher effect on decreasing the population of root-knot nematodes. Positive effects of soil disinfection persisted for two years. In the third year, a leguminous antagonistic plant Crotalaria spectabilis was planted. There after, the population of root-knot nematodes greatly decreased, so the yield of Japanese bunching onion recovered the next year. The four years management system with soil disinfection and growth of an antagonistic plant crop was shown to be effective for reducing economic loss and the times of soil disinfection. This system should contribute to maintaining stable production of Japanese bunching onions.
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