| Phytophthora blight of pepper, caused by Phytophthora capsici Leonian, is one of most destructive soil-borne disease in the world. P. capsici is also pathogenic on several solanaceous and cucubit hosts except for pepper. The incidence of Phytophthora blight on pepper occurs popularly in China due to the rapid commercial development of pepper production, improvement of cultivated measures and the extension of different cultivars. Meanwhile, this disease on severity has increased yearly and caused significant economic loss in Guizhou province. In order to control the disease effectively, some researches including field symptom, isolation, purification and identification of isolates, resistance of pepper cultivars currently available have been evaluated in this article. The major results are listed as follows.1. Symptoms of pepper phytophthora blight in fieldThe pathogen can infect pepper at different growth stages beginning with damping-off of seedlings in seed beds. Symptoms in adult plant include root decay; stem cankers on the main stem near the soil-stem interface cause blight, collar rot and wilt; cankers on branches cause partial or entire black spots of the plant and wilt of branches above the spots; leave spots are circular, grayish brown, and water-soaked, and fruit rot are typically covered with white sporangia of pathogen. Fruits are highly susceptible and, in certain environment, fruit rot implicates the most important sign of the disease.2. Isolation and identification of pathogenThe pathogen was isolated using selective medium RCA. Total 67 effective isolates were obtained and purified through cutting the top of mycelium of colony into slope media. The isolates were preserved in paraffin oil or sterile water. Inoculation in green house with pepper seedlings indicated that the isolate were able to infect pepper and cause similar symptom with plants in field.Morphology, physiology and biochemistry, and biological characters were tested on five isolates from different places. The results showed that the pathogen had better growth rate on CA and CMA. CA was best for producing sporangia in 2~3 days. Colony on CA was white and dense or sparsefluff-like. The diameter of hyphae was l~2.5m. Sporangia morphologies were different. The mean size of sporangia was 43.5~52.7 33.3~38.8m, and the ratio of length and breadth was 1.0~2.3. Sporangia have conspicuous papilla, usually single, sometimes double. Oospores were not produced when single cultured. All isolates could grow from 12, and showed little sensitivity to malachite green (1:8 106) .The capability of utilizing starch varied in different isolates. According to the characteristics of Phytophthora sp., these isolates were identified as Phytophthora capsici Leonian.3. Resistance of pepper varietiesPouring sporangia in soil was used to screen resistance to phytophthora blight among 21 pepper cultivars, which come from Guizhou province. The results showed that Bijiexianjiao, Leishanzhaotianjiao, Zunyichaotianjiao were highly resistant. Qianjiao-2, Suijiao-1, Suijiao-2, Wudang pepper, Zunyi pepper, Xiangla-1, Zaoza-2 were resistant varieties. 6 varieties were middle-resistance and 5 varieties were susceptible. The ratio was 14.3%, 33.3%, 28.6%, 23.8%, respectively.The results of 7 peppers on screening resistance to pepper phytophthora blight in field showed that serial varieties of Xiangyan were highly susceptible, and local varieties such as Zunyichaotianjiao, Xiangla-1 and Suiyanglajiao had better resistance, especially dried pepper varieties.4. Control techniquesGrowth rate method was used to test virulence to P. capsici of fungicides in vitro, such as Cymoxanil, Mancozeb, Kasumn-Bordeaux, Polyoxin A, Metalaxyl, Cymoxanil, Metalaxyl and Mancozeb had better inhibiting effect, the EC50 were 8.80 g/ml, 8.67g/ml and 8.84g/ml, respectively. Polyoxin A was ineffective to P. capsici.Plot test of three fungicides selected in vitro was carried out.The results showed that 58% Metalaxyl WP500X and 72% Cymoxanil WP500X could control disease effectively, and control effic... |
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