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。

‘华梨2号’是华中农业大学以‘二宫白’为母本，‘菊水’为父本杂交选育出的沙梨新品种，具有成熟期早、丰产、外观美、食用品质优等特点，适宜在我国土壤条件较好，管理水平较高的沙梨产区栽培。

以部分柿属（Diospyros）植物为材料，对ISSR-PCR反应体系的Mg2+、dNTPs、引物、模板DNA和TaqDNA聚合酶浓度，退火温度及扩增循环次数进行了探讨，确立了适合柿属植物ISSR分析技术体系：在25 uL反应体系中，含1×Buffer，Mg2+2.0或2.5mmol/L，dNTPs 0.2mmoI/L，引物0.6umol/L，TaqDNA聚合酶IU，甲酰胺2%，模板DNA 2.4ng/uL；PCR扩增程序：94℃变性3min；94℃30S，（Tm+2）℃（根据引物不同设定）45 S.72℃1.5min，35个循环；72℃延伸7min；2％琼脂糖电泳分离PCR产物。结果为柿属植物遗传多样性和分子系统学研究提供技术支持。

以‘罗田甜柿’试管苗离体叶片为材料，研究了秋水仙素浓度及处理时间对诱导染色体倍性变异的影响。结果表明： 013%秋水仙素处理4～6d，可诱导染色体加倍；与对照比较，再生变异植株的气孔孔径增大，密度降低，根尖染色体数2n=12x=180，叶片DNA含量为对照的两倍。L Ⅰ、L Ⅱ、L Ⅲ细胞层均加倍的证据表明，获得的倍性变异株为同质12倍体。

对柿（Diospyros kaki Thunb.）休眠芽茎尖进行了玻璃化法超低温保存及植株再生研究，结果表明，1.5～2.0mm 茎尖在含有0.3 、0.5 和0.7mol·L-1蔗糖的改良MS培养基（KNO3和NH4NO3减半）上预培养各1d，室温（20℃）下装载液（2mol·L-1甘油，0.4mol·L-1蔗糖）停留20min，0℃下玻璃化液（PVS2 或PVS3）处理30～40min，投入液氮保存1d后，40℃水浴化冻1min，含蔗糖1.2mol·L-1的改良MS培养基洗涤20min，接种于含0.2mg·L-1 CPPU、1mg·L-1 BA、0.05mg·L-1 IAA、500mg·L-1可溶性PVP、30g·L-1蔗糖和7g·L-1琼脂的改良MS培养基（再生培养基）表面的滤纸上，暗处理1d后转移到新鲜的上述再生培养基中，暗培养1周后转到正常光下，成活率高达70.2%，再生植株生长和分化正常。本研究结果为柿种质的长期保存提供了新途径。

研究了甜柿品种‘禅寺丸’2n花粉形成的细胞学机理，检测到导致2n花粉形成的异常减数分裂现象：（1）中期Ⅱ和后期Ⅱ的小孢子母细胞中发生异常的纺锤体定位，表现为平行（ps） 、融合（fs）和三极纺锤体（tps）；（2）末期Ⅱ4个子核呈两极分布，每极2核，或呈三极分布，其中一极2核，另两极单核；（3） 四分体时期观察到二分体和三分体。二分体最终发育成2个2n 配子，三分体则形成1个2n配子和2个n配子。经二分体和三分体的发生频率估算出的2n花粉频率与当年以花粉直径为指标测得的2n花粉的实际发生频率基本一致。因纺锤体定位异常而产生的2n配子遗传上等同于FDR（第1次分裂重组）型，因而在有性多倍化中具有重要的利用价值。