Identification and inhibitory effect of two fungicides on the pathogen causing pomegranate dry rot of Coniella granati

Abstract：【Objective】Pomegranate dry rot is one of the most serious diseases on pomegranate in China. Pomegranate dry rot cause harm generally infected after pomegranate flowering and before bagging, attacking in the fruit mature period and storage period, causing rot and deterioration of the pomegranate, and bringing growers huge economic losses. According to the symptoms pomegranate fruit diseases are often called dry rot and rot disease and so on, disease name is inconsisten. Resulting in domestic and foreign reports on pomegranate dry rot pathogens are also quite different. However, in recent years, domestic and foreign research reports have favored that pomegranate dry rot is caused by Coniella granati. Identify pathogens is the basis of disease prevention, in order to investigate the pathogen causing pomegranate dry rot and the biological activity of fungicide against this pathogen, the isolated pathogen was purified and identified. Pomegranate dry rot currently lacks effective control fungicides, and there were very few reports on new fungicides. Carbendazim, thiophanate-methyl and other benzimidazole fungicides are frequently used, because using this type fungicides in a large amount for a long time in orchard, some fungicide has become fungicide resistance. The resistance control of pathogenic fungal is getting more and more attention from people, among several different resistance control measures, reasonable composite fungicides and alternate use of fungicides are the most conventional and effectivemethods. As a result, how to use the existing low-toxicity, high-efficiency and safe fungicides for formulation to delay resistance to pathogenic germs, selecting more and more fungicides to C. granati are very urgent and necessary. Triazole fungicides have inhibitive broad-spectrum that affects the formation of fungal cell wall by hindering the biosynthesis of the fungal ergosterol. This type fungicides have the characteristics of high bactericidal activity, wide spectrum of bactericidal activity and environmental friendliness. This type of fungicides has good prevention and treatment against diverse crops diseases. Tebuconazole and difenoconazole are two excellent triazole fungicides, have good effects on most fungal diseases conclued fruit tree diseases, and most of the pathogenic fungi have relatively low resistance to them at the present time. At the same time, tebuconazole has not been registered for use on pomegranates. We studied the identification and inhibitory effect of two fungicides on the pathogen causing pomegranate dry rot of C. granati, in order to provide theoretical basis for controlling this disease.【Methods】 The pathogen was obtained by tissue isolation from the infected C. granati pomegranate fruit, it was identified according to its morphological characters and ITS sequence; Under laboratory conditions, the toxicity testing of tebuconazole and difenoconazole against C. granati hypha was determined by using the mycelial growth rate method, the control effect and preservation effect of the two fungicides against C. granati were evaluated by the field experiments; In addition, the influence of tebuconazole on the growth of pomegranate tree was determined by the field experiment.【Results】According to the pathogen’s morphological charactes and ITS sequence, the pathogen was identified as Coniella granati; The activity in laboratory studies disclosed that tebuconazole and difenoconazole can primely inhibit mycelia growth of C. granati，their EC50 values were (1.784 4±0.129 9) mg·L^-1 and (1.793 4±0.219 5) mg·L^-1 separately; The results of safety test showed that the inhibition rates of growth rate were 4.77%, 4.27% and 2.89% respectively on red skin and red seed super soft pomegranate, were 4.50% , 3.92% and 2.66% respectively on green skin and red seed super soft pomegranate, were 4.61%, 4.03% and 2.91% respectively on Yicheng single-lobe pink acid pomegranate, under different concentrations treatments of tebuconazole (300, 150, 75 mg·L^-1 ). All of these test concentrations of tebuconazole on three pomegranate varieties had no significant differences in the inhibition rate of growth rate. The inhibition rate of growth rate is less than 10% within 21 days after application, so tebuconazole was safe for pomegranate branch length. The results of safety test also showed that the plant morphology, leaf morphology and color were normal under different concentration treatments. In the field tebuconazole and difenoconazole showed excellent control efficacy against pomegranate dry rot, 11 days after the 3rd round of application, the control effects of tebuconazole (125, 100 and 75 mg · L^-1 ) were 79.42% ,76.73% and 67.81% respectively, and the control effects of difenoconazole (125, 100 and 75 mg ·L^-1 ) were 77.78%, 70.45% and 65.74%, respectively. The two fungicides control effects have the same results of variance analysis, there was no significant difference between high concentration treatment and intermediate concentration treatment, intermediate concentration treatment and high concentration treatment, but there was significant difference between high concentration treatment and low concentration treatment. The field trials showed that the best effects of tebuconazole and difenoconazole against this disease were 79.42% and 77.78% respectively.【Conclusion】The study indicated that the pathogen causing pomegranate dry rot was identified as C. granati, and tebuconazole and difenoconazole had high virulence to C. granati, tebuconazole was safe for pomegranate, and the tow fungicides had significant control effects on the disease in field.