Detection and Actinobacteria-based biological suppression of leaf necrosis in tea (Camellia sinensis) caused by Lasiodiplodia theobromae in India.

Fungal diseases are a common threat to the cultivation of tea [Camellia sinensis (L.)] in India, with Lasiodiplodia theobromae found recently to be a major cause of leaf necrosis. The objective of this work was to isolate and identify fungal pathogens from diseased tea plants and to assess the biocontrol effectiveness of Streptomyces sp. strains OR02 and PTS59 against L. theobromae strain KF16. Four fungal isolates were isolated, among which KF16 was identified as L. theobromae. Antagonistic analysis found that OR02 showed the maximum inhibition zone (24 ± 0.8 mm) and mycelial suppression (91.11%) against KF16, outperforming commercial fungicides, Mancozeb and Hexaconazole. In vitro and In vivo studies revealed that OR02 and PTS59 substantially decreased the formation of necrotic lesions and enhanced plant growth without causing any harmful effects. Improved height, leaf count, and branches were observed in OR02 treated plants, suggesting that it serves as both a biocontrol and growth-promoting agent. The study also revealed that KF16 could systematically infect newly growing leaves, emphasizing its virulence and the pressing need for sustainable control measures. These results highlight Streptomyces sp. OR02 potential as an eco-friendly substitute to chemical fungicides in the treatment of tea diseases, particularly against L. theobromae, and encourages its further development into a bioformulation for field use.