Joint-toxicity and storage control efficacy of difenoconazole-iprodione mixtures against Coniella granati

Abstract: 【Objective】Pomegranate dry rot is one of the most serious diseases during thestorage periodwhich casues harm, the disease is caused by Coniella granati, generally infected after pomegranate flower-ing and before bagging, attacking in the fruit mature period and storage period, causing rot and deteriora-tion of the pomegranate, and bringing growers huge economic losses. After fruit harvest, preservation withbactericide is an important measure to reduce the fruit rot during storage; carbendazim, thiophanate-meth-yl and other benzimidazole bactericides are frequently used, the phenomenon of the induction of resistantbacteria has become increasingly prominent, the resistance control of pathogenic bacteria is getting moreand more attention from people, among several different resistance control measures, reasonable compos-ite bactericides and alternate uses of bactericides are the most conventional and effective methods. As aresult, how to use the existing low-toxicity, high-efficiency and safe bactericides for formulation to delayresistance to pathogenic germs, selecting a combination of two or more bactericides with synergisms to C.granati and making applications are very urgent and necessary. Difenoconazole and iprodione are two ex-cellent fruit fresh-keeping agents, and most of the pathogenic bacteria have relatively low resistance tothem at the present time. To delay the production of drug resistance, and effectively extend the useful value and life of the above two good fresh-keeping bactericides in preservation of pomegranate and otherfruit crops, and exert its best effect on control of postharvest diseases of fruit, mixing the two agents has im-portant theoretical and practical significance. At the same time, there are no reports about determinationof the virulence of difenoconazole-iprodione mixture against C. granati. In order to clarify the control ef-fect of difenoconazole-iprodione mixtures against C. granati, select an effective fresh-keeping agent forcontrolling pomegranate dry rot during storage, and delaying the drug resistance to C. granati, this testwas carried out.【Methods】Under indoor conditions, the toxicity testing of difenoconazole, the iprodioneand their mixtures at different mixed ratios against C. granati hypha and spore was determined by usingthe mycelial growth rate method and the conidial germination observation method respectively, and the co-toxicity was assessed with using the Wadley formula, the control effect and preservation effect of the bestmixtures against C. granati were evaluated by comparative trials of several agents during pomegranatestorage; In addition, the influence of the difenoconazole-iprodione mixture synergism combination onmemberane permeability of C. granati was determined with using the conductivity method and a begin-ning exploration to the mechanism of increasing efficiency of the best mixture was carried out.【Results】All the mixtures of difenoconazole and iprodione at mass ratio of 1∶2, 1∶3 and 1∶4 had an increasing effi-ciency against the mycelia growth and the conidial germination, the synergistic effects of the 1∶3 mixturewas most distinct with a synergistic ratio (SR) of 3.979 3 and 3.350 9 respectively; The result of compara-tive trials of several agents during pomegranate storage showed that the 1∶3 mixture displayed a signifi-cantly higher efficacy in controlling pomegranate dry rot, the control effect was significantly higher thanthe single fungicide with the same dosage and the other often used agents, and the mixture had a lastingcontrol effect and ran up to as much as 71.53% in pomegranate stored for 120 days; Under the treatmentof the difenoconazole-iprodione mixture (mass ratio 1∶3) , the weight loss rate of pomegranate was 3.84%, the peel browning index was only 0.35, and the total soluble solids content and the total acidity contentwere 14.15% and 0.43% respectively after being stored for 120 days. At the same time, there was a signifi-cant difference above these indexes compared with the control group. All of these test concentrations of in-creasing efficiency combination (mass ratio 1:3) had no significant differences in the control effect andfresh-keeping effect, considering economic and environmental effects and other factors, we recommend toapply the concentration of 100 mg·L^-1in production. Relative electric conductivity is an important indexfor measuring memberane permeability, according to comparisons between different test agents, increas-ing efficiency combinations (mass ratio 1∶3) had the largest destructive effect on mycelial memberane, even under the minimum treatment concentration with 0.2 mg·L^-1, its electrical conductivity increase ratecould reach 9.91%, next was difenoconazole, and iprodione was the lowest, under this concentration, itselectrical conductivity increase rate was only 5.36% within 24 h, which showed that the difenoconazole-iprodione mixture greatly improved membrane permeability of C. granati.【Conclusion】Difenoconazole-iprodione mixture at a mass ratio of 1∶3 can be used as a fresh-keeping agent for controlling pomegranatedry rot during storage, and a concentration of 100 mg·L^-1is recommended.