ارزیابی مهار‌زیستی کنه بنه زعفران Rhizoglyphus robini به کمک قارچ‌های بیمارگر جداشده از مزارع شهرستان تربت‌حیدریه

The saffron bulb mite (Rhizoglyphus robini Claparède) is one of the critical soilborne pests of this crop, which causes symptoms such as stunting, thin and weak leaves, false autumn, pale petals, shrinking of the stigma, and finally, destruction of bulbs. It is expected that with the expansion of saffron cultivation areas to northern latitudes, this pest will be transferred to new areas along with infected corms. Since chemical compounds in this strategic product are not allowed, this research investigated the possibility of managing this pest with pathogenic fungi as a promising approach. In 2022 and 2023, the soil of saffron fields in 32 regions of Torbat-Heydarieh County in Khorasan-Razavi province was sampled. Larvae of the yellow mealworm beetle (Tenebrio molitor L.) were used to trap pathogenic fungi. Fungi grown on mealworm larvae were cultured on potato dextrose agar (PDA) medium, and then a single spore was isolated on water agar medium. A concentration of 107 conidia per milliliter prepared from the ten-day-old fungal culture in Tween 80 solution with a concentration of 0.05% was used to investigate the pathogenicity of fungi. Among the 55 isolates obtained, 26 isolates could re-colonize mealworm larvae. The mortality rate of mites treated with these isolates was recorded daily for 10 days. Among these fungi, 19 potent isolates in killing and colonizing mites were statistically compared. Using identification keys, five isolates belonged to Metarhizium sp., 13 to Beauveria sp., and one to Cordyceps sp. The results showed that from the second to the eighth day, the mortality caused by the Cordyceps sp. Co-TZ isolate was more than other fungi (73.33 ± 4.4%). On the ninth day, its lethality was equal to the Beauveria sp. B-TJ, B-TZ1, and B-TZ2 isolates (83.33 ± 4.4%). On the tenth day, the mortality of mites treated with Metarhizium sp. M-Kh and Cordyceps sp. Co-TZ isolates reached 100% but did not show significant differences with some isolates of Beauveria and Metarhizium fungi. Mites treated with the M-Kh isolate were 100% colonized on the 10th day, significantly different from other fungi. Based on the available information, the pathogenicity of the mentioned fungal species against the saffron bulb mite was reported for the first time in Iran. According to the results, the selected fungal isolates can be used as biological control agents to protect the saffron bulbs against this pest and prepare certified and healthy corm.