| Phytophthora blight caused by Phytophthora capsici L. is one of the most economically destructive soil borne diseases of pepper (Capsicum annuum L.) throughout the world and can be a limiting factor for pepper production in tropical areas with hot and humid climates. Symptoms associated with the disease include damping-off, fruit rot, foliar blight, root and crown rot and stem lesion. The pathogen can survive in soil for a long time. The temperature and humidity suitable for the pepper growth is also for the pathogenic fungus. The use of resistant cultivars is the most promising method to control the disease, because the pathogen is easy to counteract the active site of currently used fungicides. However, most scientists believe that there is no pepper variety immune to Phytophthora capsici. Inheritance of the resistance, a quantitative trait, is very complex and controlled by polygenes. The attainment of pepper cultivars resistant to Phytophthora capsici is difficult because of the polygenic nature of this trait. It is an obstacle to earmark and map the related resistant gene to Phytophthora capsici in pepper for molecular marker-assisted selection.Qie-men, a native susceptible sweet pepper lines, and 93-100-17-1-0, a native resistant pungent line were used as main materials in this study. We analyzed constitutional resistance genes using PCR approach with degenerate primers designed from conserved motifs found in cloned resistant genes and inducible resistance genes by mRNA differential display technique, and mapped quantitative trait loci (QTL) based on AFLP technique-constructed genetic linkage map. The main results are as follows:1. Three different Phytophthora blight inoculation methods were compared on eight pepper varieties. In vitro inoculation of leaves can screen many varieties at short time in room without damage to plants. Stem cutting inoculation is easily exercisable and the length of necrotic part is can measurable. Zoospore inoculation of root simulates nature infection, reflecting the true resistance, but the operation is more complicated. All three-inoculation methods can be used to identify pepper resistance to Phytophthora capsici. Among eight pepper varieties,resistance of 93-100-17-1-0 is the most powerful. 93-100-1-1, perennial, SCM334showed high resistance and Deng-long-jiao mid-resistance. Qie-men, Fu-di-jian-jiao, Yolo Wonder are susceptible lines.2. Several fragments were cloned from 9 different pepper (Capsicum annuuni) varieties, using a PCR techniques with degenerate primers designed from conserved motifs found in a number of plant resistance genes. The sequences associated with known resistance gene or resistant gene analogs were used in BLAST searching from GeneBank. Amino acid sequences deduced from those pepper resistance gene analog (RGAs) had high identity to amino acid sequences encoded by known resistance genes by DNAMAN analysis. It showed that these amplified sequences were likely associated with disease resistance genes of pepper and could be regarded as candidate sequences of disease resistance genes in Capsicum annuum to study. Total 24 sequence were submitted to Genbank, the accession numbers are AY125911, AF492473, AF513548, AF513549, AF525124 -AF525153.3. Two differential expression fragments oligo(dT)15CD1 and oligo(dT)15AD1 were screened by mRNA DDRT-PCR using anchor primers oligo(dT)15A, oligo(dT)15C, oligo(dT)15G, and degenerate primers B1, C1, D1 combination. Out of them, oligo(dT)15CD1 had a high homology to a Lycopersicon esculentum BAC clone, a express sequence tag.4. We established F2 population derived from the intraspecific F1 hybrid obtained from a cross between 93-100-17-1-0 and Qie-men. Genetic analysis and chi-square test have not a fit of 3:1 ratio among F2 population, suggesting that the resistance is polygenically controlled. At that time, we constructed a genetic linkage map that included 11 linkage groups, 46 markers, and 1381.5 cM...
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