| Cotton is a global cash crop, which has an important role in national economics of China. Fusarium wilt and Verticillium wilt are not only two kinds of diseases which do serious harm to cotton, but also the most factors which influence high and stable production of cotton all over the world. It is confirmed that the most effective and economical method for controlling two diseases should be obtained through selection and utilization of highly resistant varieties. To study and understand genetic information of germplasm is the important basis of breeding and utilizing resistant cultivars.In the study, 143 China-bred cultivars and 14 foreign cultivars have been used to identify disease resistance in disease nursery of Agricultural University of Hebei, Baoding. Based on the identification results, 117 cultivars including 105 Chinese cultivars and 12 exotic cultivars were selected for AFLP fingerprinting establishment. Parents, first and second self-pollinated generations were used for AFLP fingerprinting stability determination. The main results were as follows:1. The results in the field disease nursery showed that for Fusarium wilt there were 43 highly resistant cultivars, 61 resistant cultivars, 41 tolerant cultivars and 12 susceptible cotton, accounted for 27.4%, 38.9%, 26.1% and 7.6% of the total cottons tested, respectively, indicating that the progress were made in Fusarium wilt breeding. For Verticillium wilt, 2 foreign cultivars showed high resistance (accounted for 1.3%), 67 cottons with resistance (42.7%), 73 cultivars with tolerance (46.5%) and 15 with susceptibility (9.5%). The evolvement of disease resistance from different years breedingcottons was conducted. The disease index (DI) of Fusarium wilt resistance showed a down trend from 1960's to 1990's. There was a down trend of Verticillium wilt'DIfrom 1960's to 1980's, but an up trend from 1990's.2. Different cultivars showed different patterns of DI. The patterns of DI could be divided into 3 types. The first pattern meant DI was low from the end of June to late July, but increased rapidly in August. The second pattern of DI was a smooth trend from the late of June to end of August. The third pattern was there were two peaks of DI in the end of June and late of August, but DI was low from the middle of July to early August.3. AFLP procedure used for cotton DNA fingerprinting was established by analyzing some critical factors. Some improved factors were below: (1)the usage of template DNA 450ng; (2)Msel and EcoRI each 3 units, digestion time 2 hours; (3)the products of ligation were diluted to 10 times for preamplification; (4)the products of preamplification were diluted to 10 times for selective amplification.4. From 100 primer combinations, 20 polymorphic primer combinations were selected to perform the AFLP fingerprinting. 49 cultivars had specific bands, accounted for 41.88%. The Sea Island cotton Pima90-53 had specific bands in 18 primer combinations except for E38/M50 and E40/M62. Every primer combination was different in the identification efficiency of cultivars. No primer combination could distinguish all the cultivars. Ninty-four cultivars could be identified by 20 primers. Far genetic relationships between Gossypium hirsutum and Gossypium barbadense were found, but genetic relationships among Gossypium hirsutum were close based on dendrogram of AFLPs. Groups and subgroups of tested cultivars could not be determined according to their pedigrees and geographic regions. Similar genetic diversity of resistant cultivars was detected between the cottons of Changjiang and Huanghe cotton-producing areas.5. AFLP fingerprintings' stability was tested by parent, first and second self-pollinated generations of parent. The results showed AFLP fingerprintings were stable.6. Core collection including 26 cultivars was constructed based on AFLPs.
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