Serik Shaikhin1 , Akbota Satenova1,2*, Maira Urazova1*, Altynay Tuyakova1, Аrman Аbilkhadirov1 and Zinigul Sarmurzina1
1Laboratory of Genetics and Biochemistry of Microorganisms in the Republic Collection of Microorganisms of the Ministry of Healthcare of the Republic of Kazakhstan, Astana, Republic of Kazakhstan 2Department of General Biology and Genomics, L.N. Gumilyov Eurasian National University, Astana, Republic of Kazakhstan
*Corresponding author: amsatenova01@gmail.com (AS); urazova.maira01@gmail.com (MU)
Postharvest fungal pathogens cause substantial losses of fresh fruit, highlighting the need for sustainable biological alternatives to sulfur dioxide (SO₂)-based preservation. This study evaluated native epiphytic yeasts isolated from the Kazakh Aisulu table-grape cultivar using a two-stage screening framework followed by testing in two postharvest systems: artificially wounded berries (W system) and unwounded grape bunches (B system). Antagonistic activity was assessed against Botrytis cinerea F-RKM 1032, Aspergillus niger ATCC 6275, and Rhizopus stolonifer ATCC 6227b. Initially, 34 yeast isolates were screened for inhibition of fungal growth (PIRG: 23.76–71.76%; selection threshold >50%) and biofilm-forming capacity (OD₅₅₀ > 0.245), resulting in 11 candidates for further evaluation. In vivo screening identified five strains with high protective activity: Metschnikowia pulcherrima A2, Hanseniaspora uvarum HU15, Aureobasidium pullulans AP11 and AP13, and Clavispora lusitaniae CL03. Against B. cinerea, biocontrol efficacy in wounded berries (BEW) reached 77.47% for A2, 78.56% for HU15, 73.43% for AP11, 71.65% for AP13, and 65.06% for CL03. Importantly, M. pulcherrima A2 and H. uvarum HU15 retained high efficacy in the more restrictive unwounded-bunch system, with B-system biocontrol efficacy (BEB) of 78.02% and 72.83%, respectively. Their W-to-B efficacy ratios were close to 1 (0.99–1.20), indicating that their protective activity remained relatively stable between wounded berries and intact grape bunches. In contrast, A. pullulans AP11 and AP13 showed substantially reduced efficacy in the B system, with W-to-B efficacy ratios of 1.79–3.07. C. lusitaniae CL03 was excluded from further consideration because of biosafety concerns. Comparative evaluation indicated that A2 performed better than the previously reported Metschnikowia sp. 291 in the B system, whereas HU15 showed efficacy comparable to the previously reported H. uvarum P2. Overall, M. pulcherrima A2 and H. uvarum HU15 emerged as the most promising indigenous biocontrol candidates because they combined high antifungal efficacy with stable performance in both wounded and unwounded grape systems. These strains warrant further evaluation under cold-storage and commercial conditions, individually and as a defined microbial consortium, to develop sustainable postharvest grape-protection strategies.