Studies on the recent advances and future trends in Asian pear in Japan

Compared with Pyrus spp. in the world, the one in Japan shows some unique features. As pears in Japan have been diffused from the original place of genus Pyrus to the eastern margin of the Eurasian continent, some growing characters and disease resistance are different from those of pears in the western part. Although hybridization between these two has been tried to introduce disease resistance of western species into Asian pears, unfortunately, no success has been obtained. In Japan, over 1,200 names of cultivars have been recorded, and escaped and wild trees are still preserved. Among them, wide genetic diversities are observed. These facts indicate the ancient introduction of pears from continental China and Korean peninsula and complex hybridization among domestic and introduced ones. Recent results from DNA analysis and discovery of a new S-genotype of self-incompatibility strongly support these diversities. In the near future, genetic relationship among pear sps. in Asia should be clarified. In addition, almost all-recent commercial cultivars are genetically derived from cv. Nijisseiki and some local cultivars originated in the Southern Kanto districts. Consequently, they seem to be genetically close to each other. From the recent breeding program to introduce the distant gene from a different gene group, some cultivars have been released. As the growing area in Japan is located under a typhoon course, trellis training system is indispensable to prevent strong wind damage. That is why dwarf rootstock is not studied. Under humid climate conditions, chemicals are sprayed frequently to control insects and diseases. Fruit have been bagged to control this damage way back from the end of the Edo era. Three serious diseases as rust (Gymnosporangium asiaticum), black spot (Alternaria alternata) and scab (Venturia nashicola) are recorded. However, rust has been overcome by emasculating the intermediate host plants and the use of effective chemicals. Black spot is also controlled by newly bred resistant cultivars. Scab is left as a difficult disease to control. In orchards developed in the forestry region, fruit are attacked by birds, fruit-piercing stinkbugs and piercing moths. To control them, the use of yellow fluorescent lamps for piercing moths and netting over the orchard for birds and stinkbugs are practiced. For Nashi, Japanese consumers ask sweetness, juiciness and soft and non-gritty texture as well as cheap price. Therefore, practical orchard management has to be improved to obtain high quality fruit with low management cost. Recent progress on fruit maturation revealed sugar-related enzymes and their related genes, and cultivar differences in shelf life and their related enzymes and genes. In the future, gene modifying of Nashi quality should succeed after successful induction of redifferentiated explants. For reducing production costs and intensive work, a new breeding program has been started to introduce self-compatibility for non-artificial pollination, self-thinning ability for non-fruit thinning one and scab resistance. In addition, to reduce chemicals, pheromones for moths are now in practice. In the 21st century, four important changes should be pointed out for Nashi cultivation in Japan. First, the population of Japan is estimated to decrease from the year 2008. Unless the consumption of fresh fruit by consumers increases, severe competitive condition of imported fresh fruit, beverages and sweets will occur, and the growers should be limitedly selected. Second, growers' age will be older than before because the rate of aged people will increase. Therefore, hard and intensive work on managing trees and handling fruit should be improved. Third, global warming may induce the transfer of the growing area to the north, and film-protected cultivation and oil heating should be controlled to decrease carbon dioxide release. In the future, a new type of Nashi, having a low level of dormancy, should be bred. Fourth, consumers' concern about the preservation of earth environment should be strictly changed. So to conclude, decreasing chemical applications as well as oil products may develop more friendly management of cultivation.