The collection, conservation, and assessment of genetic resources of Pyrus pyrifolia, as well as the utilization in the bud sport selection and the cross breeding of those in China are reviewed based mainly on the present data from Chinese literature.

Persimmon (Diospyros kaki Thunb.) is one of the most popular fruit crops in China mainland. According to the FAOSTAT in 2003, the acreage and production are 293,000 ha and 1, 737, 747 tons respectively, both of which ranked first in the world and 9th in China mainland comparing with other fruits. At the National Fruits Germplasm Repository for Persimmon located at Northwest Sci-Tech University of Agriculture and Forestry, Yangling, Shaanxi province, more than 550 accessions are being preserved in vivo. Fruit de-astringency mechanism and rootstock selection for non-astringent persimmon were conducted at Institute of Subtropical Forestry of Chinese Academy of Forestry Science, Fuyang, Zhejiang province. Physiology, ecology and cultivation were mostly studied at Jiangxi Agricultural University, Nanchang, Jiangxi province and Nanjing Agricultural University, Nanjing, Jiangsu province. In addition, ecological adaptability was tested and non-astringent Japanese persimmons were introduced by Institute of Fruit Trees of Shandong, Tai'an, Shangdong. More than 110 accessions, including some local cultivars (land race) and all pollination constant and non-astringent (PCNA) types of Chinese persimmon, were preserved in vitro and in vivo in Huazhong Agricultural University, Wuhan, Hubei province. The PCNA types were collected, preserved, identified for genetic diversity and evaluated for economic traits, along with the studies on their origin and evolution. It has been affirmed that non-astringent cultivars including Luotiantianshiexist in Dabieshan Mountains, and so do the rare male resources and the new other types. The cryopreservation techniques by vitrification have been established. In order to improve' Luotiantianshi', which bears small fruit with many seeds, nonaploid production from 2n pollen is now being pursued.

Pollination constant non-astringent (PCNA) type persimmons are unique in that they originate in Japan in recent era. The development of the PCNA type cultivars is not so advanced, since only six PCNA type cultivars were reported among more than 1,000 cultivars by a nationwide survey in Japan in 1912. The PCNA type cultivars are known to have very narrow genetic variability, and it causes a serious problem for breeding of new cultivars because of inbreeding depression in breeding population. On the other hand, in 1982, a new PCNA type cultivar, 'Luotian tianshi', was reported to be found in Luotian county in Hubei province. This PCNA type cultivar has a different genetic background from Japanese PCNA cultivars, since a cross between 'Luotian tianshi' and Japanese PCNA 'Taishu' yielded astringent type offspring in addition to PCNA type offspring. This means that the Chinese PCNA cultivar may provide a new strategy for persimmon breeding in the future. In addition to 'Luotian tianshi', it is believed that several non-astringent type persimmons exist in the same area of Luotian county in Hubei province where 'Luotian tianshi' was found. In this study, we have collected the fruits from several cultivars assumed to be a non-astringent type in Luotian county and determined whether or not those are true non-astringent cultivars of PCNA type by measuring tannin cell sizes of the fruits, which is a good criterion for distinguishing a PCNA type from a non-PCNA type. As a consequence, we could demonstrate that several PCNA type persimmons exist in Luotian county. These cultivars should be an important addition to persimmon germplasm and should have a potential role for breeding in the future.

A procedure was established for cryopreservation of dormant vegetative buds of persimmon (Diospyros kaki Thunb.). Intact buds, attached to shoot segments and subjected to preliminary stepwise freezing down to -20℃ (12h at each of 0, -5, -10 and -20℃), were immersed in liquid nitrogen for storage. After thawing in agitated water at 40℃, shoot-tips of 1.5-2.0mm in size were excised from shoot segments surface-sterilized with 0.1% HgCl2. The shoot-tips were then plated on the modified MS medium with a half-strength nitrate supplemented with 0.2mg L-1 CPPU, 1.0mg L-1BA, 0.05 mg L-1 IAA and 500mg L-1 soluble PVP. They were grown for one week in darkness before exposure to light. The survival of shoot-tips was higher than 60%. The genetic stability of regenerated plantlets from cryopreserved shoot-tips of dormant buds was assessed by cytological and AFLP analysis. The results showed that there were no variations in chromosome number and AFLP patterns. This simple and reliable protocol provided a new strategy for long-term preservation of persimmon germplasm.

取‘罗田甜柿’自然授粉后约70 d 的胚乳，采用不同细胞分裂素和生长素组合进行离体培养。结果表明：以1/2MS （1/2N ）+ZT（玉米素）111mg/L+2042D 110mg/L+CH（水解酪蛋白）1000mg/L 诱导产生的愈伤组织易获得再生植株；形态学和细胞学检测确认再生植株中存在2n=12x=180的个体。该十二倍体植株对中国原产甜柿的遗传改良可能具有潜在的应用价值。