The Construction Of Two Potato (Solanum Tuberosum L.) Recurrent Populations With High Level Horizontal Resistance Against Phytophthora Infestans

Potato(Solarium tuberosum L) is 4th important crop both in the world and in China. Late blight caused by Phytophthora infestans (Mont.) de Bary is the biggest barrier in potato cultivation and also the 1st writings threat to China and even the whole world agricultural production and the food security. It has been proved that the resistant varieties are the most efficient way to overcome the disease. The resistance controlled by R genes seems to be easily overcome by the variation of the pathogens under high pressure of R genes. The horizontal resistance seems to be more stable, durable and reliable as it is polygenic inheritance with much less pressure against pathogens. In recent years, more attention and efforts have been shiftted to the utilization of horizontal resistance, and the core and ultimate goals were the assessment of the resistance and the selection of the materials with high level horizontal resistance against P. infestans. Yet the quiet narrow genetic basis of the cultivated potatoes is the bottleneck of the selection for the breakthrough materials.Here we report the construction of two recurrent populations based on 27 clones of population B3C1. The goal of these populations is to meet two requirements:1. maintaining the stable, durable and high level horizontal resistance as well as the widen heredity background of B3C1; simultaneously enhancing the frequency of good traits such as high level horizontal resistant, early maturity and good agronomic traits; and 2. crossing with the advanced cultivars/clones to improve the adaptability to the local conditions. The main results obtained are listed below:1. Seventeen B3C2 combinations with 11243 seeds and 19 modified B3C2 combinations were obtained through the bulk pollen fertilization. The hybrids were selected through the seedling stage and 2 following clonal generations.127 clones from the B3C2 combinations were selected as the candidate B3C2 clones while 68 clones from the modified B3C2 combinations. Considering the resistance against the late blight and the AFLP marker assisted selection,55 B3C2 clones and 50 modified B3C2 clones were selected to form the 2 goal populations. 2. The candidate clones for the goal population selected in the field were analyzed with the AFLP fragments. Based on the marker profiling, the 130 candidate B3C2 clones were clustered into 24 groups with 29 subgroups using the software "ClusterPrject", and the 78 candidate modified B3C2 clones were divided into 19 groups with 22 subgroups. The core samples of the 2 populations were selected with the method "Core Germplasm Materials" in the software "QGAStation" based on the markers and the performance of the resistance. These 2 samples were the skeletons of the final population.3. The percentage of plants with the mediate resistance to very high level resistance in the population B3C1 were 70.4% based on the 3 years’assessments, while in the candidate B3C2 population and modified population B3C2 based on the field selection were 68.9% and 85.2%, respectively. The core samples of B3C2 population selected by the software QGAStation have 61.5% plants with acceptable resistance against the late blight with 7.4% decrease compared to the entire candidate clones. In the core sample of modified population B3C2, the percentage was 85.5%. Here a little revision were applied to deal with the core samples of B3C2. Those clones with bad performance against the P. infestans were replaced by the clones belong to the same group with acceptable resistance based on the clustering figure. Thus, the percentage of the plants with acceptable resistance was increased to 75.5%, and the core samples were fixed as the goal populations.4. Based on the AFLP analysis, there were 148 fragments from the total 457 detached fragments were common fragments in the parental populations and domestic materials, and all of them could be found in the 2 goal populations, though some of them were not monomorphism in the goal populations. As to the rest 309 polymorphism fragments,272 and 267 of them could be found in the B3C2 population and modified population B3C2 with the percentage 88.0% and 86.4%, respectively. The percentage of the repetition rate in the goal population fits the expectation which were 85% repetition rate. While revision applied for the core samples were lead to the loss of 6 fragments in the population B3C2 with the percentage 1.94%. 5. Base on the main botany traits, the 2 goal populations have maintained the diversity from the population B3C1. Yet the plant shape and vigor have the tendency of the marketable need with a close-knit and mediate vigor plants. The tuber bearing traits has some improved with shorter stolons. The mean growing period of the 2 populations have shortened with 8 days and 10 days each. As to the yield trait, there is no improvement at all between the parental population and the offspring.6. The hybrids were obtained from the cross between the B3C1 clones and the domestic materials. The candidate population clones were also used to do the pair cross. The offspring were selected with pedigree method and some of them were chosen to be the high generation materials in the traditional breeding programs. These clones were need to do some more assessment and some of them were hopeful to be good breeding resources or even candidate varieties.