Formulation of Trichoderma harzianum and its comparative storage stability in different substrates for the management of armillaria root rot of tea

Abstract

Armillaria root rot has been documented as one of the major diseases of tea (Camellia sinensis) that hinders successful establishment of tea when planted shortly after deforestation. Effective methods for managing the disease have not been fully developed. Trichoderma harzianum, a soil-borne fungus, has been demonstrated to be an effective antagonist to several species of Armillaria. In this study, formulation, stability in storage and viabilit y of T. harzianum in selected substrates was evaluated. Trichoderma harzianum isolate (T4) was multiplied by liquid fermentation and formulated in vermiculite, kaolin, wheat bran and talc substrates. Inocula of T. harzianum were prepared on potato dextrose agar and potato dextrose broth, and assessed for conidial yields over different time periods. The different substrates were then analyzed for compatibility with the fungal propagules by comparing dry weight, number of colony forming units and microscopic counts after one month of incubation. Stability of the formulations in storage was determined by assaying for viability of the inoculum; number of colony forming units, sporulation rates and microscopic counts every month. Effect of vegetative interaction between Armillaria isolate (8KA1) and T. harzianum isolated from the different formulations on the pathogen was also evaluated. Data on differences in the tested parameters was subjected to ANOVA with the help of SAS statistical software and the means separated using LSD (P=0.05). There was a positive correlation between conidial yield and incubation period in both PDA (R2=0.9274) and potato dextrose broth medium (R2=0.8954). Compatibility tests revealed that all the substrates supported multiplication and viability of T. harzianum at levels over 104 CFU/g and were thus considered to be compatible with the fungus. Most formulations retained viable propagules above 106 CFU/g by the sixth month of storage. Kaolin formulations had the highest mean counts (6 x106 CFU/g) followed by vermiculite (4.2x106 CFU/g), talc (2.1 x106 CFU/g) and wheat bran (3.4 x105 CFU/g). Mycelial formulations were more stable compared to conidio-mycelial and spore formulations. Vegetative interaction between Armillaria and T. harzianum revealed that T. harzianum taken from all the formulations antagonized Armillaria regardless of the period of storage. Attempts to re-isolate Armillaria after 20 days of interaction did not yield any viable pathogen, indicating stability of the antagonist in storage. Results from this study will enable formulation of T. harzianum based product whose use can be easily incorporated as a husbandry practice to manage Armillaria root rot in tea.