The Etiology And Disease Control On Cherry Black Fruit Rot

Cherry (Cerasus pseudocerasus) which belongs to the plant family Rosaceae has became an important economic fruit as introduced in the1990s in China. Some diseases have happened and become more and more serious as the increasing commercial cultivation. Black spot disease on cherry fruits which was found in Dalian City, Liaoning Province was a new disease and has occurred seriously in recent years. Disease incidence was approximately75%of the plants during growing seasons in June and July, and the disease reduced yield and affected fruit quality.This article has conducted systematic research on pathogen of cherry black spot, including pathogen identification, biological characteristics, infection cycle, pathogenesis and the inhibition effect of fungicides and so on, in order to offer the theoretical basis of disease control. The results are as follows:1. Identification of the pathogen of black rot on cherry fruitsThe samples of cherry black rot were collected from cherry orchard in Dalian, Liaoning Province. Pathogenicity of fungal isolates obtained from these samples was tested according to the Koch’s Postulation. The pathogen was identified as Alternaria alternata (Fr:Fr.) Keissler, which belongs to Hyphomycetes, Hyphomycetales, Dematiaceae, Alternaria(Nees)(Zhang,2003). The ITS and EF-la sequence had99%identity with Alternaria alternata (GenBank Accession No. JF835834and DQ677927.1).2. Biological characteristics of Alternaria alternataThe test revealed that the light condition was good for mycelia growth and the optimal temperature was30℃, the optimal pH was6.0. Oat media was the best culture media for mycelia growth, carrot-agar was the best for sporulation. The carbon sources of fructose and sucrose were best for mycelia growth, among nitrogen sources, KNO3was the best. For spore germination, the optimal temperature was30℃, the optimal pH was7.0, xylose was the best carbon source, NH4H2PO4was the best nitrogen source. The lethal temperature for mycelia growth was56℃for10min. The pathogen had a broad condition for live and a high capacity for spore germination which were consistent with the occurrence of the disease in field.3. The pathogenesis of A. alternataThe test revealed the pathogen had a high pathogenic activity, and had varying degree pathogenicity on fruit, leaf, seedling and seed. The toxic filtrate treating on cherry fruit lead concave and black brown spots and the leaf appeared colour fading; It was also indicated obviously that toxin treating on seedling and seed caused seedling withered and germination of seeds downtrod. The best nutrient solution was PS, the optimal pH was8.0, and toxin activity enhanced as the culture time increased; The optimal temperature was25℃, sustained oscillation was best for toxin production. The toxin had a very strong pathogenicity on pear, apricot and plum, while had a slight pathogenicity on nectarine and hawthorn.The pathogen produced PG、PMG、Cx and β-glucosidase both in vivo and vitro, and the enzymatic activity was higher in vitro than that in vivo. The enzymatic activity of Cx and β-glucosidase in vitro was higher than that of PG、PMG, which testified that Cx and β-glucosidase played a important role in disease infection process, in the contrary, enzymatic activity of PG and PMG was higher in vitro. All of them reached a top of enzymatic activity in30℃, Cx and β-glucosidase reached a top activity in9d, while PG and PMG got a top activity in12d.4. Infection cycles characteristics of A. alternataAccording to the survey results between2010and2012in Dalian, the disease has occurred more and more seriously in recent years. Disease incidence was approximately75%to95%of the plants during growing seasons in June and July. The late-maturing varieties have higher disease incidence than early-maturing varieties.The pathogen of cherry black spot had a survival ability which could live in the field surface, underground10cm, indoor20℃, indoor-frozen4℃and minus20℃. It showed that the survival rates of pathogen treated in the field and indoor were above70%during12months, and the survival rates were above62.5%even after18months.The test revealed the pathogen infected host by natural ostiole or wound, and disease morbidity was higher by cut. The pathogen infected host by mycelium directly, disease was heavier in carpopodium depression, the incubation period was3d, the disease symptoms became obviously after7d.The test of host range showed A. alternata had strong pathogenicity on strawberry, pear and apple, next were peach, nectarine, apricot and plum, but had no effect or hardly infected on hawthorn. The pathogen caused the leaves of pear and plum appearing ring spot, but had little effect on leaves of strawberry and hawthorn.5. The inhibition effect of fungicide to A. alternataThe results of indoor inhibition experiment showed significant differences among eight kinds of fungicides in inhibitory effect on mycelial growth and spore germination. The fungicides of best inhibitory effect on mycelial growth were flusilazole and prochloraz, and the inhibition rate reached100%; Mancozeb, prochloraz and myclobutanil had strongest effect on spore germination, and the inhibition rates were above85%. In conclusion, prochloraz, difenoconazole and myclobutanil had good inhibition effect both on mycelial growth and spore germination.