Genetic Diversity Evaluation Of Island Cotton And Genetics Analysis Of Segregation Distortion In Asian Cotton F₂ Population

1: Genetic diversity evaluation of island cottonQuantification and classification of diversity in germplasm collection and utilizationare important for both genetic researchers and plant breeders. Genetic diversity of 58island cotton (Gossypiumar barbadense L.) cultivars was assessed using SRAP markers,in which 19 were introduced from other countries. Of the 238 SRAP markers analyzed,132 primer pairs detected 419 polymorphic.Twnety-one accessions could be fingerprintedwith one or more SRAP markers. Jaccard's genetic similarity coefficients were calculatedand dendrograms were constructed by the unweighted pair group method of arithmeticaverage (UPGMA) using the NTSYS-pc version 2.10.The accessions were classified into six groups on the basis of the average similaritycoefficient (0.497) among the island cotton cultivars. The genetic similarity coefficientsamong all accessions ranged from 0.312 to 0.876, with an average of 0.497, indicatingthat there were highlevel of genetic variation in the G. barbadense collections.The average genetic similarity coefficient of domestic accessions (0.498) was lowerthan that of the introduced accessions (0.529).This suggesting that the civil materials hadhigher level in genetic diversity compared with the materials from foreign counties. Theseresults indicated that most of the germplasm introduced from other countries had beenselected and domesticated which had adapted to different ecotypic regions in our country,it would be enrich genetic resources of island cotton.The domestic accessions from different breeding periods were analyzed. The averagegenetic diversity coefficients of the SRAP markers for the domestic accessions of the firstand second breeding periods were 0.501 and 0.548, respectively. This implied that thegenomic difference among the modem accessions had gradually decreased compared tothat of the early accessions. The main reasons were that the germplasms of the latterbreeding periods were mostly derived from the first period. This was probably a result ofthe narrow breeding base as the breeders used a limited number of varieties with highquality and high yield.2: Genetics analysis of segregation distortion in intraspecific population ofAsian cottonFor molecular marker analysis, a total of 1025 pairs of SSR (BNL, CIR, and NAU)were screened for polymorphism between parents and generated 11, 1, and 8 polymorphicmarkers respectively; additionally, 153 SRAP primer combinations were screened forpolymorphism between parents and generated 11 polymorphic loci. The segregation ratioof markers in an F₂ population derived from Rudongjijiaoyaguo and Zhongmian971 wasstudied using three morphological markers, 20 SSR markers and 11 SRAP markers. Theresult indicated that totally, 24 markers (77.42%) showed distorted segregation and all ofthem skewed towards the female genotype, which were peculiar in recent cotton research.The normal segregation of morphological markers and the distorted segregation of molecular markers indicated that such a novel segregation distortion phenomenonresulted from interior genetic factors. Allele frequency (p=q) and the distribution ofdifferent genotype frequency (p²:2pq:q²) in the F₂ population were analyzed inco-dominant markers to find out factors attributed to distorted segregation. Most of themarkers showed distorted allele frequency but normal genotype frequency, which showedthat these markers were influenced at gamete level.