Development of Pre-breeding Materials in Capsicum spp. and Map-based Cloning of a Male Sterile Gene, ms1035 in Tomato

Abstract

Tomato and pepper belong to the Solanaceae family and economically important vegetable crops worldwide. The main objectives of tomato and pepper breeding are developing high yield, pest resistant, and quality cultivars. Narrowed genetic diversity in commercial lines due to under-utilization of germlasm is a serious problem in tomato and pepper breeding. Therefore, discovering of allelic diversity and characterization of useful traits are essential for breeding. In the first chapter, species identification markers for Capsicum spp. were developed. Identification of Capsicum species has always been controversial because of ambiguous morphological behaviors. Moreover, most previous studies for species identification using molecular markers also had disadvantages that were low reproducibility and unsuitability for handling large quantities of samples. Here, SNP markers derivd from conserved ortholog set II (COS II) and the Waxy gene were developed as candidate maker set for species identification. Furthermore, phylogenetic analysis supported that C. annuum, C. baccatum, and C. pubescens clades were clearly separated. Closely related species C. chinense and C. frutescens were divided into subclades, indicating that the two species are apparently different. C. chacoense, the most controversial species, was belonged to C. baccatum clade. These results provide the information of genetic relationship of Capsicum species and reliable species classification method. In the second chapter, allele mining was performed to find useful allelic variation of a virus resistance gene in natural germplasm pool and ethyl methanesulfonate (EMS) mutagenized population to enhance the genetic diversity of Capsicum species. A fast and accurate method was developed to mine the useful alleles in significant number of germplasm using high resolution melting (HRM) analysis. Of 248 pepper germplasm, 13 newly obtained allelic variations of eIF4E were identified and one accession of them, C03946 (pvrHRM113) from C. baccatum was shown to carry strong resistance to TEV-HAT virus. Furthremore, five more allelic variations from EMS-mutageneized M1 population were also identified. Therefore, this result provides the strength of genetic diversity in Capsicum spp. and a useful tool for mining novel alleles. In the third chapter, a male sterile gene of tomato was characterized. Male sterility is the one of the most important characteristics for plant breeding. Here, the map-based cloning of the ms1035 mutant of tomato was performed and a responsible gene encoding a bHLH transcription factor was discovered. With morphological defects and molecular evidence, Ms1035 played a pivotal role for pollen development after meiotic stage. ms1035 was firstly isolated gene in tomato discovered by map-based cloning among the pollen development related genes at early stage. This provides that the insight of molecular evidence for tomato pollen development and utilization of male sterility line to improve tomato breeding.