| In order to furtherly improve heterosis of wheat, it is necessary to establish new heterotic group. In this study, ISSR (inter-simple sequence repeat) marker was used to measure the genetic diversity within and among common wheat (Triticum aestivum L), spelt (Triticum spelta L.), compactum (Triticum cumpactum Host.) and progeny of foreign wheat-based recurrent selection, In addition, relationship between regulation of GA metabolism and molecular basis of wheat and maize heterosis was also analyzed. The main results were as follows:1) Forty seven genotypes were used for ISSR analysis, which include 14 common wheat, 10 spelt wheat, 11 compactum and 12 progeny of recurrent selection. Eleven of 33 ISSR primers that can produce distinguishable bands were selected for PCR amplification. A total of 238 bands were amplified, among which 207 (87%) bands were polymorphic. The polymorphic bands amplified by each primer ranged from 11 to 38, with an averaged of 18.8. The percentage of polymorphic band (80.3%) in common wheat was higher than that in progeny of recurrent selection (78.7%), spelt (75.0%) and compactum (74.9%). The 238 polymorphic products were used to calculate Nei's similarity index (GS) and the genetic distance (GD). It was found that the mean genetic distance between different wheat types (0.3115 ~ 0.3442) was obviously higher than that within common wheat (0.2743), spelt (0.2351), compactum (0.2622). In addition, progeny of recurrent selection also showed much higher genetic distance with other three wheat types (0.3217, 0.3256, 0.3198). The cluster analysis was performed based on the genetic distance (GD) matrix by using UPGMA method. Common wheat, spelt, compactum and progeny of recurrent selection were classified into four different groups. In this study, ISSR marker was firstly used to assess genetic diversity among common wheat, spelt, compactum and progeny of recurrent selection, and can differentiate the wheat cultivars (lines) that selected from the same cross combination. It was concluded that spelt, compactum and progeny of recurrent selection can be used to diversify the genetic basis for hybrid wheat breeding and improve heterosis.2) Although hybrids between common wheat and the other three different wheat types have higher heterosis, no significant correlation was observed between ISSR-marker based genetic distance and heterosis. Therefore, genetic distance revealed by ISSR molecular marker can't be used to accurately predict the high heterotic combination, but it is possible to establish the wheat heterotic group, and four heterotic groups, namely common wheat, spelt wheat, compactum and progeny of recurrent selection, were preliminarily suggested.3) To give an insight into the relationship between regulation of hormonal metabolism and the molecular basis of heterosis, we analyzed hormonal content between 20 intra-specific hybrids and their parents in a wheat diallel cross of vigorous tillering stage. The results showed that ZR content in tiller node was significantly related to the tiller number. In addition, significant correlation was also observed between heterosis of ZR and IAA content and that of tillering number. At the same time, one GA 20-oxidase gene with complete ORF was isolated and characterized. RT-PCR results showed that, with little exceptions, this gene was up-regulated in hybrid in most developmental stages and tissues that wetested.4) To further investigate the possible role of GA in heterosis, highly heterotic hybrids and their parental inbred lines was also used for analysis. Exogenous GA can accelerate the growth rate per day, and one amazing feature we found is that, hybrids was less insensitive to exogenous GA than their parents. Moreover, one GA 20-oxidase gene with complete ORF, names as GA20M, was isolated in maize, and its expression pattern between hybrid NongdalOS and its parentai inbred lines was also characterized. To our knowledge, GA20M is the first GA 20-oxidase gene that was cloned in maize. RT-PCR results indicated that, in most...
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