Study On Separation, Identification And Biological Characteristics Of Penicillium Spp Causing Diseases Of Citrus

Blue mold (Penicillium spp) is the principal cause of decay on citrus, and it also caused postharvest diseases on many varieties commodities. It is said that Penicillium spp mainly included P. italicum and P. digitatum. With the development of molecular biology, the identification of Penicillium spp was carried out by morphological characters and polymerase chain reaction (PCR) protocol. In addition, the research of Penicillium spp was only arrived at the qualitative description of temperature, humidity, pH, and other biological characteristics has been not reported. In this paper, we studied morphological characters, pathogenicity, part of biological Characteristics of different Isolates of Penicillium spp. Main conclusions were drawn as follows:1. Identification of penicillium sppThis article reported eight typical pathogenic strains of Penicillium spp (L, Q, PL, PQ, CL, CQ, PTY-1, PTY-2), which were isolated from the surface of citrus fruits in different areas. They were identified as P. digitatum, P. expansum, P. chrysogenus and P. polonicum by morphological characters and internal transcribed spacer (ITS) analysis.2. PathogenicityThe incidence and development of disease were determined by pathogen, host, environment and interaction of each other. Those facters (including pathogen capacity, the way and period of infection, resistance of host, temperature and humidity of environment and so on) influenced disease development. It showed that disease incidence and severity both increased when initial pathogen capacity increased during citrus storage. pathogenicity of P. digitatum was the best, the incidence disease could be whole rot only for 7～10d while in suitable conditions; secondly was P. expansum; sequentially was P. polonicum; P. chrysogenum was the worst. Wound and inoculation quantity of spores would increase succession of infection., and it's the key factors for the incidence and development of disease.3. Biological Characteristics1) The results indicated that there was significant difference in growth characteristics (including: growth rate, quantity of spore, color of colony and thickness of colony) in the same or different medias. It's beneficial for both growth of mycelium and product of conidia in potato dextrose culture medium.2) The growth temperature range from 5℃to 35℃the hyphal could survived, and the suitable temperature for mycelia growth and spores germination were 15-30℃. and the optimum for mycelia growth of P. digitatum was 20℃; the optimum temperature for spores germination was 25℃; the optimum of P. chrysogenus, P. expansum, P. polonicum were 25℃, 25℃, 20℃respectively. Anyway, during the same range of temperature, mycelia growth of each penicillium spp in accord with spores germination.3) The effect of different lighting condition for penicillium spp strains were not significance.4) Alternata could make use of many carbohydrates and nitrogen sources, the optimum carbon source of four strains (P. digitatum, P. polonicum, P. expansum, P. chrysogenus) were dextrose, mannose, sucrose and lactose respectively; the optimum nitrogen source were peptone and yeast extract, while (NH₄)₂SO₄ and NH₄CL could inhibitmycelia growth.5) The result showed that P. digitatum and P. expansum could absolutely die at 70℃respectively in the deadly temperature test. It's different from each other for the four isolates of P. polonicum in the deadly temperature test, the strains were died from 75℃to 85℃.6) Eight isolates of penicillium spp differed from one other in UV-protective ability. The result showed that the range of death rates of spores from eight isalates were 40.00%～80.00% by UV irradiation for 5 minutes. Among these pathogens, P. chrysogenum has the most excellent charater in UV irradiation resistance, rate of death was 71.43% by UV irradiation for 9 minutes; P. expansum was the weakest, 90%; the death rate of P. digitatum (PL, CL) were 88.00%, 84.44%; the death rate of P. polonicum (PQ, CQ, PTY-1, PTY-2)were85%.7) Meanwhile, testing with seven pesticides in vitro showed that, the inhibition effect of 20% imidazole EC is the best. Carbendazim, 2,4-D and so on alone could resist the growth of pathogens, but the efficacy were reduced when mixed together; There was nearly no inhibition effect between both sodium carbonate and calcium chloride which are considered safe to human being.