Study On The Biocontrol Effect Of Yeast Strain 0939-5 Fumigation On Postharvest Grape Gray Mold

Grape gray mold is one of the common diseases during postharvest storage of grapes and is also a devastating disease caused by Botrytis cinerea.The disease is easy to cause large-scale rot of grapes after harvesting,resulting in a decline in their quality and seriously affecting the economic benefits of fruits.Based on the previous research work,a yeast strain 0939-5 with significant inhibitory effect on B.cinerea was successfully screened,the objectives of this study were to further explore the optimal solid-state fermentation medium and culture conditions for producing volatile antimicrobial substances by yeast strain0939-5,and to evaluate the effect of fumigation treatment with volatile antifungal substances produced by solid-state fermentation on the biocontrol of B.cinerea and quality of postharvest grapes.It is expected to provide theoretical basis and practical reference value for the biological control of B.cinerea and the development an application of fumigation biocontrol agents of antagonistic yeasts.Objective:Using yeast strain 0939-5 as the test material,the best solid fermentation matrix and culture conditions for the production of volatile bacteriostatic substances were clarified;To evaluate the effect of fumigation of volatile substances produced by yeast strain 0939-5 on the biocontrol and freshness preservation effect of grape postharvest gray mold;At the same time,the effect of fumigation treatment on grape quality was also explored.Methods:The one-way method was used to optimize the nutrient composition and culture conditions of the solid fermentation matrix of yeast strain 0939-5 to produce volatile substances;At the same time,fumigation treatment was carried out under different inoculation methods,application amounts,treatment temperature and time conditions to evaluate the effect of prevention and control of postharvest gray mold in grapes;The effect of fumigation on grape quality was explored by sodium hydroxide titration and ultraviolet rapid method.Result:（1）The optimal solid fermentation matrix for volatile substances produced by yeast strain 0939-5 is corn flour,the optimal carbon source and concentration is glucose 2%,and the optimal inorganic salt and concentration is Mg SO₄0.1%;The solid fermentation conditions of strain 0939-5 are:yeast inoculation concentration 1×10⁸CFU/m L,inoculation amount of 10%,initial p H4,and initial moisture content of40%.（2）After fumigation of volatile substances produced by solid fermentation of yeast strain 0939-5,when stored at 25°C for 25 days,the grape fruit disease index of the control group in the injured inoculation group was 40.30 and 6.94 in the treatment group,and the prevention effectiveness is 82.78%.The disease index of the control group in the non-injury inoculation group was 33.62 and the treatment group was 4.99,and the prevention effectiveness is 85.16%.The disease index of each treatment group was significantly lower than that of the control group,and there was no significant difference between the injured and non-injury inoculation.After the solid fermentation fumigation treatment of yeast strain 0939-5,the application amount,temperature,storage time,etc.were optimized and selected.The result showed that the fumigation treatment of yeast strain 0939-5 had the best disease prevention effect when the application amount was 20 g,the temperature was 5℃,and the storage period was 15 days.（3）After fumigating grape berries with yeast strain 0939-5 by solid-state fermentation,the titratable acid increased slowly with the increase of storage time,while the reducing sugar,Vc and hardness decreased,the content of soluble solid had no obvious change trend.The treatment of postharvest grape berries with VOCs produced by yeast strain 0939-5 solid-state fermentation could not only delay the decomposition and loss of hardness,reducing sugar and VC,but also effectively maintain the quality of grape berries,moreover,the speed of ripening and senescence of grape fruit was reduced,and the storage life was prolonged.Conclusion:After adding 2%glucose and 0.1%Mg SO₄to corn flour as solid-state fermentation,10%1×10⁸CFU/m L yeast suspension were introduced according to the mass ratio,and the initial p H value and initial water content of the fermentation substrate were adjusted to 4 and 40%,respectively,25°C for 3days,the inhibitory activity of the volatiles produced by yeast 0939-5 against B.cinerea was the strongest.The best effect of disease control was obtained by taking 20g of fermented material with yeast and fumigating the grape berries at 5℃for 15 days,and can better maintain the freshness and quality of grape berries after harvest.