基于桔梅奇酵母冻干粉制备可湿性粉剂及其在柑橘上的应用

确保生防制剂的贮藏稳定性是保证微生物种群数量和生物防治效果不受影响的关键因素。为开发货架期较长且防治效果稳定的拮抗酵母生物制剂，该研究通过助剂的单因素筛选试验和混料试验研制出一种基于桔梅奇酵母冻干粉制备得到可湿性粉剂，经过升温加速贮藏试验预测制剂的贮藏稳定性，同时评价了制剂在离体和活体条件下对柑橘采后主要病害的控制效果。试验结果表明：试验筛选得到制剂优化配方的质量分数分别为皂角粉5.69%、亚甲基二萘磺酸钠8.74%、母粉85.57%。冻干制剂中酵母活菌数可达到4.72×108 CFU/g，贮藏稳定性试验表明，冻干制剂的贮藏稳定性较好，预测在4℃贮藏后制剂中酵母活菌数约为4.6×108 CFU/g。适当降低贮藏温度可延长冻干制剂贮藏期。离体试验发现，与新鲜酵母相比，液体制剂对柑橘采后病原菌的抑制作用无显著变化，抑菌圈可达到9 mm以上。在柑橘果实上能够有效控制柑橘果实采后青霉病、绿霉病、酸腐病和炭疽病，可将发病率降低约40%～70%。综上，对桔梅奇酵母进行制剂化能够延长其货架期并维持其对柑橘果实采后病害防治效果。

Preparation of wettable powder and its application on citrus fruits based on Metschnikowia citriensis freeze-dried powder

Microbial preparation refers to the living microorganism as the main component, including inert carrier materials, nutrients, and other accessory ingredients. It is necessary to maintain the vitality and effectiveness of microorganisms in the biocontrol preparations for a long time, particularly in the development of biocontrol products. The storage stability of biocontrol agents can be a key factor to ensure the number of microorganisms and the biological control. Metschnikowia citriensis can be expected to efficiently control the postharvest green mold and sour rot caused by Penicillium digitatum and Geotrichum citri-aurantii on the citrus fruit, indicating its great application and development value. This study aims to develop antagonistic yeast biocontrol agents with a long shelf life and stable biocontrol effect. The wettable powder was also prepared with the M. citriensis as the main active ingredient. The single factor and mixing tests were carried out to optimize the accessory ingredient for the wettable powder. Then, the wettable powder was applied to the citrus fruits. An accelerated storage test was conducted to predict the storage stability of the preparation, and evaluate the control effect of the preparation on the main postharvest diseases of citrus under in vitro and in vivo conditions. The results showed that the carriers, wetting powder, and suspending agent were screened by the single factor test with the mixing test. An optimal combination of the preparation was achieved with the honeylocust powder of 5.69%, dispersing agent NNO of 8.74%, and freeze-dried powder of 85.57%. The number of viable yeast in the freeze-dried preparation reached 4.72×108 CFU/g, and the wetting time was (7.82±1.02) s, while the suspensibility was up to 71.56%±0.06%. The accelerated storage test demonstrated that better storage performance was achieved in the freeze-dried bioformulation. Among them, the wettable powder was stored at four temperatures. The deactivation rate constant of yeast gradually increased in the wettable powder, whereas, the death rate of yeast accelerated with the increase in storage temperature. The viable yeast population in the preparation was estimated to be 4.6×108 CFU/g, when the storage at 4℃ for one year. Therefore, there was an appropriate reduction of storage temperature for better storage ability. In vitro tests and fruit tests were carried out to learn the application effect of the preparation. The experiments showed that the wettable powder effectively controlled the occurrence of postharvest citrus fruit diseases. It was found that there was no significant change in the inhibitory effect of wettable powder on the postharvest pathogen and pigment production capacity of M. citriensis, compared with fresh yeast. Specifically, the inhibition zone reached more than 9 mm. Fresh yeast presented a remarkable control effect on the blue and green mold, and sour rot on the citrus fruits. The formulation reduced the incidence of three citrus postharvest diseases by 40%-70%. To sum up, the preparation treatment of M. citriensis can be expected to effectively retain cell viability and biocontrol efficacy. The wettable powder with the M. citriensis as the main active ingredient indicated a significant decrease in the incidence of postharvest disease on the citrus fruits. The finding can provide the theoretical and practical basis for the application of M. citriensis in the biological control of postharvest citrus diseases.