| Pepper (Capsicum annuum L.) is an annual herb plant. Its fruit is berries with hot or sweet taste. Pepper is full rich in nutrition. It has the maximum content of vitamin C compared with other vegetables. It is regarded as a kind of special aromatic condiment. Pepper, which is widely planted around the world, is an important economic vegetable crop in our country. While the pepper blight caused by phytophthora capsici Leon has been an epidemic in many provinces and areas and has become a major limiting factor on pepper production. The pepper blight is a kind of disease which has a very wide spread distribution. In1918, it was reported in State of Mexico that the blight had very serious harm in pepper in United States for the first time. Then, in the south of Latin American Argentina, north to North America Colorado and New York and large areas of Europe, Asia, all of those places have been reported to find the disease. In our country it was in the1960s that phytophthora blight was found; Since the1970s, the disease was epidemic in China’s Jilin Province, Liaoning Province, Qinghai Province, Hebei Province, Beijing city, Yunnan Province, Gansu Province, Shanxi Province, Shanghai city, Zhejiang Province, Hunan Province,Jiangsu Province, Jiangxi Province. It has serious threat and is harmful to the pepper production and the degree is increasing year by year. In addition, pepper hybrid advantage is very obvious. The hybrid combination is higher than the traditional main variety in yield by30%-40%. Pepper hybrid generation have been widely used in production, and have obtained the obvious economic benefits. But at present, a large number of pepper hybrid seeds used are produced by artificial castration, pollination. It costs high in seed production and the seed price is high. The application of male sterility is the most effective way to reduce the pepper seed costs by far. We have chosen three pepper varieties in this research. First of all, we identified the resistance to phytophthora blight in those three varieties. Then, according to the evaluation results, based on a pair of them as parents, we chosed the F2group. This F2group was irrigated by zoospores of phytophthora capsict Leon in root. According to the pepper epidemic grading standards, the pepper seedlings were classified after eight days inculation. Then we extracted the leaf DNA from the pepper seedlings. Then those DNA were used to construct the resistance gene pool and susceptible gene pool. The primers were designed in order to screen the molecular markers for resistance to phytophthora blight. Thus we try to provide theoretical foundation for breeding. Also in this study we used the male sterile line as material. Taking the different pepper floral bud, through the paraffin section of pepper male sterile line and its maintainer line in different anther developmental period of cytological characteristics were observed. We aim to clarify the period of abortion, to find the cause of male sterile abortion, to clarify the mechanism of abortion for pepper cytoplasm male sterility, thus to provide the theoretical basis for application of pepper male sterile line in cross-breeding.The main research results are as follows:1) Three pepper varieties, Jm, ASC0503, NSC0501, were chosed as the material. In pepper seedling period with6～8leaves, the pepper was irrigated by zoospores of phytophthora capsici Leon in root. After inoculation, three surveys were conducted. The first time (72h after inoculation) was to understand the speed of disease development in different materials; The Second time (8d after inoculation) was to classify the pepper seedling according to the resistance to pepper blight; The third time (15days after inoculation) is to screen resistance of each individual material. According to the grading standards, we calculated the disease index in pepper, so as to determine the degree of resistance to pepper blight. The results showed that Jm, ASC0503, NSC0501had disease index with60.14,29.34,27.36, respectively. Thus we concluded that Jm is a susceptible variety, while ASC0503and NSC0501are resistant varieties.2) Based on the testing results, we chosed the Jm and NSC0501as parents, used the F2group of them, the group was irrigated by zoospores of phytophthora capsici Leon in root during seedling stage. Seven days after inoculation, according to the grading standards, pepper seedlings were classified. Then the DNA of pepper leaves were extrated, the resistance gene pool and susceptible gene pool were constructed. Then we designed SSR primers for PCR and the PCR products were loaded and electrophoresised on PAGE gels. We screened related specific bands. Totally,229pairs of primers were used to screen polymorphic bands with a ratio of88.21%. Finally, we identified two possible bands which related to the character of resistance to phytophthora blight.3) In our study we observed the morphology between pepper male sterile line and maintainer line. The results showed that the morphology between sterile line and maintainer line were significantly different. The plant height was higher in maintainer line. The flower in maintainer line was bigger. The anther was wizened in male sterle line while plump in maintiner line. The fruite shape was similar in those two groups, but the fruit was smaller in male sterile line. The fruit in male sterile line was filled with seeds while the other was without any seeds.4) Observations of different size of anther paraffin transverse sections showed that no structural difference existed between male sterility line and maintainer line in pollen mother cell stages. In maintainer line the tetrads disintegrated and released the individual uni-nucleate microspores. The tapetum underwent lysis normaly and microspores could further develop into mature pollen grains. However, in male sterility line, the anther locule was pressed by the abnormally swollen tapetum. The microspores could not absorb the nutrition and collapsed because of the irregular and abnormal tapetum, leading to male sterility. Based on our reaserch, we concluded that the abortion of male sterility line happened at the tetrad stage. |
PDF Full Text Request