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

YAO Xin; QIN Wen

doi:10.13925/j.cnki.gsxb.20160403

Abstract：[Objective] Pomegranate dry rot is one of the most serious diseases during thestorage period which casues harm,the disease is caused by Coniella granati,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.After fruit harvest,preservation with bactericide 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 resistant bacteria has become increasingly prominent,the resistance control of pathogenic bacteria is getting more and more attention from people,among several different resistance control measures,reasonable composite bactericides and alternate uses of bactericides are the most conventional and effective methods.As a result,how to use the existing low-toxicity,high-efficiency and safe bactericides for formulation to delay resistance 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 excellent fruit fresh-keeping agents,and most of the pathogenic bacteria have relatively low resistance to them 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 other fruit 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 determination of the virulence of difenoconazole-iprodione mixture against C.granati.In order to clarify the control effect of difenoconazole-iprodione mixtures against C.granati,select an effective fresh-keeping agent for controlling pomegranate dry rot during storage,and delaying the drug resistance to C.granati,this test was carried out.[Methods] Under indoor conditions,the toxicity testing of difenoconazole,the iprodione and their mixtures at different mixed ratios against C.granati hypha and spore was determined by using the mycelial growth rate method and the conidial germination observation method respectively,and the cotoxicity was assessed with using the Wadley formula,the control effect and preservation effect of the best mixtures against C.granati were evaluated by comparative trials of several agents during pomegranate storage;In addition,the influence of the difenoconazole-iprodione mixture synergism combination on memberane permeability of C.granati was determined with using the conductivity method and a beginning 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 efficiency against the mycelia growth and the conidial germination,the synergistic effects of the 1:3 mixture was most distinct with a synergistic ratio (SR) of 3.979 3 and 3.350 9 respectively;The result of comparative trials of several agents during pomegranate storage showed that the 1:3 mixture displayed a significantly higher efficacy in controlling pomegranate dry rot,the control effect was significantly higher than the single fungicide with the same dosage and the other often used agents,and the mixture had a lasting control effect and ran up to as much as 71.53％ in pomegranate stored for 120 days;Under the treatment of 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 content were 14.15％ and 0.43％ respectively after being stored for 120 days.At the same time,there was a significant difference above these indexes compared with the control group.All of these test concentrations of increasing efficiency combination (mass ratio 1:3) had no significant differences in the control effect and fresh-keeping effect,considering economic and environmental effects and other factors,we recommend to apply the concentration of 100 mg· L-1 in production.Relative electric conductivity is an important index for measuring memberane permeability,according to comparisons between different test agents,increasing 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 rate could reach 9.91％,next was difenoconazole,and iprodione was the lowest,under this concentration,its electrical conductivity increase rate was only 5.36％ within 24 h,which showed that the difenoconazoleiprodione mixture greatly improved membrane permeability of C.granati.[Conclusion] Difenoconazoleiprodione mixture at a mass ratio of 1:3 can be used as a fresh-keeping agent for controlling pomegranate dry rot during storage,and a concentration of 100 mg· L-1 is recommended.