Studies On Identification And Detection Of Root Rot Pathogen In Protected Capsicum

With the development of capsicum production in greenhouse recently, rotation is more and more difficult. Root rot has been one of the limiting factors to capsicum growing in greenhouse in North China. Pesticides are often applied improperly due to the unidentified pathogens and resulted in invalid disease management. The objective of this study is to identify the pathogen and develop efficient methods to detect the pathogen.1. Capsicum rotten roots were collected from Beijing (Yangfang), Shandong (Shouguang) and Liaoning (Wafangdian). The pathogen was isolated and purified. According to the morphotype, culture characteristics, biochemical characteristics and pathogenicity test, it was identified as Phytophthora capsici Leonion. The pathogen has sporangia, which shape varies from elliptical, globose, ovoid to erose. The size of the sporangia is (11.8-46.6)×(11.2-24.5)μm, the ratio of its length to width is 1.4-1.8. The papillates are obvious and hemispheroidal. Most of the sporangia have only one papillate, few have two papillates. The length of the papillates is 1.7 - 5.9μm. The pathogen doesn't produce chlamydospores. Besides capsicum, the pathogen can infect cucumber, tomato and eggplant, but it can't infect Cole and cabbage. It is insensitive to malachite green and can utilize starch.2. Indirect ELISA (I-ELISA) and Dot-ELISA were established to detect P. capsici Leonion. Soluble protein of the fungus was first immunized to rabbit as antigen; antiserum with high titer was acquired, and IgG was isolated and purified. The process of I-ELISA and Dot-ELISA were established by optimizing sample dilution, incubation time and antibody concentration, incubation time and concentration of HRP conjugated goat anti-rabbit IgG and so on. The optimal I-ELISA blocking solution and blocking time were 0.5% and 2h at 37℃. The optimal concentration and incubation time of antibody and HRP conjugated goat anti-rabbit IgG were 16.67μg/mL and 1.5h at 37℃and 800×and 2h at 37℃, respectively. The optimal incubation time of substrate was 15min at 37℃. While in the process of Dot-ELISA, the optimal working concentration and incubation time of antibody and HRP conjugated goat anti-rabbit IgG were 8.69μg/mL and 1.5-2.0h at 37℃and 600×and 1.5h at 37℃, respectively. The two detection methods showed good stability, specificity and high sensitivity and could be used to detect the pathogen practically in field..In this study, we first identified the pathogen causing capsicum root rot in North China as Phytophthora capsici Leonion, providing information to protect and control of capsicum correctly. We also established two efficient methods for early disease diagnosis, pest control, monitoring and forecasting of capsicum root rot.