| The quite narrow genetic basis of the cultivated potato {Solarium tuberosum L.) and the difficulty in breakthrough of germplasms segregation entail the enlargement of Solamum gene pool. Many wild species and primordial cultivated types of potato exhibit comprehensive resistance or tolerance to pathogens, virus, pests, frost and drought, which are highly attractive to breeders. The application of these desirable genes is confined, however, as differences in ploidy level or endosperm balance numbers that cause sexual incompatibility or low fertility of the progenies. Somatic hybridization, however, provides a new approach to make use of these wild recourses, bypassing sexual incompatibilities to widen the germplasms scope and recombine the cytoplasmic DNAs.Bacterial wilt, a severe and devastating plant disease caused by Ralstonia solanacearum, occurs widely in tropical, subtropical, warm temperate areas and even in some cool regions. It affects more than 200 plant species distributed over 50 families, particularly potatoes and tomatoes. Currently, resistant or tolerant cultivars are mainly utilized for disease management since chemicals are not always effective to diseases control and most of them have negative effects on ecological environments. Therefore, the worldwide strategy of potato bacterial wilt control has been consisted on development of new resistant varieties. Fortunately, some wild or related cultivated species are known to be resistant or highly tolerant to bacterial wilt, such as Solunum chacoense and S. phureja, and thus are potential sources for resistance. However, cross incompitibility with cultivated species provents their use in potato breeding. The purpose of the present research was to incorporate resistance against bacterial wilt from ?chacoense or 5. phureja into cultivated potato by somatic hybridization. The major results are as following:1. Establishment of a high efficient fusing system of potato mesophyll protoplasts. This study was primarily attempted to optimize the fusion parameters using mesophyll protoplasts isolated from potato clones 3# and 8# (2n = 4x = 48), which were derived from c.v. Zhongshu 2 by pollination inducing, and diploid species S. chacoense (2n = 2x = 24). It was shown that binuclear fusion frequency reached up to 45.0 % with the following electrofusion parameters: alternate current (AC) 100 V/cm, AC duration 10 s, directcurrent (DC) 1 100 V/cm, 1 DC pulse with 60 us. The frequency of PEG induced fusion reached 42.7 %, as FA solution treated for 15 min and FB 10 min respectively. The PEG and electrofusion methods were employed to look into their effects on the protoplast fusion. The results showed that no much difference existed in the fusion efficiency between these two methods, except that higher cell plating frequency and stronger plant differentiation ability of callus were accompanied with electrofusion. From four different fusion combinations we have isolated 1 212 vigorously growing calli, from 128 calli of which (10.6 %) shoots regenerated and developed into intact plants. The regeneration frequency ranged between 9.2 %~16.8 % depending on the fusion combination.2. There were 154 somatic hybrids derived from the two fusion combinations were obtained, of which nearly half had a ploidy level summed to the parental materials and about 90 % performed either one of the parents' chloroplast DNA type. Total 160 plants differentiated and regenerated earlier were subjected to RAPD analysis. The results revealed that 154 plants (96.3 %) were true somatic hybrids with a combination range between 94.4 -100 %. Further analysis of ploidy level using flow cytometry demonstrated that 47.1 % were hexaploids, 10.7 % octoploids, 17.1 % amphiploids and 25.0 % mixoploids. The identification of chloroplast types of the somatic hybrids was conducted with chloroplast SSR marker, NTCP-9. The results indicated that only 11.0 % of the hybrids combined the two parental chloroplasts while the majority contained the chloroplast from either of the fusion parents. It w... |
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