Inhibitive Effect Of Allium Sativum L. Extract On Pepper Blight And Mechanism Of Inhibition

At present the main method for controlling Phytophthora capsici is by chemicals, but the chemicals are harmful for human health and environment,with the development of nuisance free vegetable cultivation, people have higher request of chemicals, recently, the pesticides made from plant in the plant disease, which became hot research topic. By the research of inhibitive effect,protective effect and mechanism on garlic extracts to Phytophthora capsici, the purpose is to lay the foundation for protective measure of nuisance free vegetable on garlic extract to Phytophthora capsici. The mian reacerch is as follows:1. Inhibitive effect on garlic extract to pathogen and sporeBy the methods of pathogen mycelia growth and spore germination, the result show that inhibitive effects on pathogen mycelia growth and spore germination were increasing as the increase of garlic extracts concentration. Total inhibition of growth of the mycelia of Phytophthora capsici was observed at a concentration of 150.0 mg/mL of garlic.The extract also total inhibited zoospore germination with a concentration 100.0 mg/mL. The extract had significant inhibitive effect than 58% Metalaxyl 500×solution. The results indicated that the effective concentration (EC50) values of garlic extract against mycelium growth and zoospore germination were 64.23 mg/mL and 25.85 mg/mL respectively. The minimal inhibitory concentration (MIC) and minimal anti-microbial concentration (MAC) of garlic extract were 100.0 mg/mL and 150.0 mg/mL, respectively.2. The significant effect of preventing and controlling on garlic extract to Phytophthora capsiciBy the inoculation of P. capsici disc on the leaf and the pot trial of the resistant chili pepper (cv. Shijihong) and sweet pepper (cv. Tedaqiemen) seedlings at the four-leaf,six-leaf and eight-leaf growth stages. Significant protective and curative effects with the concentration of garlic extract increased. In the pot trial, at the six-leaf stage, 200mg/mL garlic had most protecting and curative effect to two cultivars. To the resistant chili pepper (cv. Shijihong), the protective effect and curative effects was 91.1%, 81.5%, respectively, and the the protective effect and curative effects was 90.18%, 78.97% for sweet pepper (cv. Tedaqiemen) seedlings. In the inoculation of P. capsici disc on the leaf, garlic concentration of 150mg/mL had significant protective effect (100%) and curative effects (89.74%) to chili pepper. The protective and curative effects on he resistant chili pepper (cv. Shijihong) were better than sweet pepper (cv. Tedaqiemen). 58% Metalaxyl 500×solution had better protective and curative effects than the garlic extract.3. The inhibition of garlic extract with high concentration to the germination of host vegetable seed and the growth of the seedlings on physiological index By physiological measuring, the result show that garlic extracts inhibited on the range of concentration, the inhibitive effect is the most and difference is remarkable with control, but difference is unremarkable among the other treatment and control. The most inhibiton to germination of the resistant chili pepper (cv. Shijihong) and sweet pepper (cv. Tedaqiemen) seeds when the concentration of garlic extract was 150mg/mL. Garlic extract had more inhibitive effect on the root length and weight than the top with the high concentration of garlic extract. 58% Metalaxyl 500×solution had not significant inhibition on the seeds and seedlings.4. Inhibited mechanism of garlic extracts to pathogen and sporeThe pathogen and spore were observed by microscope and find that the pathogen are abnormal, short and wide, more branches, expand in the middle of pathogen; bud tube of spore is abnormal and shortened, germination volume of spore decreased and the relative membrane permeability rate raised and soluble protein content decreased in mycelia of P. capsici when the concentration of garlic extract was increased. With the treatment time increased, the protective enzyme activities increased and then dropped. High concentration of garlic extract inhibited the protective enzyme activities.