| Potato (Solarium tuberosum L.) is the fourth biggest food crop in both world and China and has very significant economic importance. Bacterial wilt (BW), caused by Ralstonia solanacearum, is cosmopolitan, especially in worm regions like southwest China, where usually experiences about 20% loss of potato yield due to BW which is only the second to potato late blight.Under the conditions of Liupanshui of Guizhou Province where BW epidemics frequently, a survey on distribution of the pathogen racies/biovars was carried out and evaluation of the resistance to bacterial wilt of the somatic hybrids, which were derived in Huazhong Agricultural University from the protoplast fusion between dihaploid of S. tuberosum 81-15 and diploid cultivated species S. phureja and wild species S. chacoense, was conducted in addition to the investigation of their morphological and biological characteristics aiming at to approach the capability of the somatic fusion strategy in transferring BW resistance between species and potential use of the somatic hybrids in potato breeding programme. The main results gained include:1. It was found from the experiment of inoculation with mixed races of R. solanacearum in greenhouses that clones of somatic hybrids CHT-3 and CHT-5 performed high resistance to BW, Clones CHT-11, CHT-12, CHT-16, PHT-17, PHT-24 and PHT-33 had the mid-level resistance, Clone CHT-4 was susceptible to BW while the rest showed middle susceptibility.2. The field trial identified variance in the resistance level of the somatic hybrids. When they grew in a BW infected field, clones CHT-3, CHT-5 and CHT-16 were resistant to BW, CHT-10, CHT-11, CHT-12, CHT-17 and PHT-24 showed mid-level resistance, CHT-1, CHT-2, CHT-6, CHT-8, CHT-13, PHT-17 and PHT-23 were middle susceptible.3. With aid of the two molecular markers which were proved to bracket the BW resistance locus of potato, there were 8 clones (CHT-5, CHT-6, CHT-7, VHT-9, CHT-10, CHT-14, CHT-15 and CHT-18) possessed the specific bands of both the two markers indicating potential resistance resources.4. The integrated analysis showed that the somatic hybrids had vigor growth but late maturity. There were 12 clones formed tubers and all the hybrids flowered but with a decreased probability of active pollens when compared with the fusion parents. There were three clones set berries. Although CHT-3 and CHT-5 were high resistant to BW buttheir agronomic traits were undesirable. In contrast, CHT-11, CRT-12 and CHT-16 had a lower level of resistance than CHT-3 and CHT-5 but a better agronomic performance.5. Race 1 (Biovar 3) and Race 3 (Biovar 2) of R. solanacearum commonly existed in the region of Liupanshui with Race 3 as the dominant one. However, there was no difference between the two races in distribution either among sites or altitudes. It was expected that Race 1 might expand to more places in next few years and become another dominant race since the race was not found by 1995 and had developed quickly in recent years.6. It was consider from the synthetical utilize that clones of somatic hybrids CHT-3, CHT-5, CHT-6, CHT-7, CHT-9, CHT-10, CHT-14, CHT-15 and CHT-18 performed high resistance to BW and would be the resistance source for breeding. Clones CHT-11, CHT-12, CHT-16 and PHT-33 had the mid-level resistance and first three seemed to have potentials to adapt the local conditions if their adaptation would be confirmed further.7. The resistance to BW in potato is specific to the pathogen races and it is influenced much by the environment, especially temperature. Therefore, the resistance of a variety may vary with the regions where it grows. It is necessary to improve the adaptability and agronomic traits, to increase the frequency of the resistance genes and broaden the genetic background of the somatic hybrids through recurrent selection or backcrossing. The present results elucidated that combination of somatic fusion and conventional breeding techniques approached a novel and efficient strategy for using resistance genes of wild s...
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