Bioactivity, biochemical and ultrastructural characteristics of Trichoderma atroviride conidia influenced by different culturing conditions: factors affecting biocontrol potential

Abstract

Identification of production and storage factors that affect conidial germination and bioactivity (fitness) will assist the success of biological control agents. Effects of abiotic factors (temperature, nutrients, water activity, pH) on conidial fitness of Trichoderma atroviride LU132 during production were studied. Conidia from the culturing regimes which resulted in greatest and least bioactivity against Rhizoctonia solani in dual culture were selected to assess effects of storage conditions on conidial fitness over time. Fitness of the test conidia was examined after storage at 30˚C and at 0 or 50% relative humidity (RH) over 6 months. Fitness declined over time, and the decline was greater for 50% RH than 0% RH. The greatest number of conidia and greatest germination resulted from growth at 25°C, but greatest bioactivity resulted from conidia produced at 30˚C. Different C to N ratios (5:1 or 160:1) did not affect these parameters. However, fewer conidia were produced at 30˚C, and the least germination and bioactivity resulted from conidia produced at 20°C. The different environmental factors were not independent. For example, conidial production at 30°C is probably accompanied by water stress, oxidation, and rapid pH change which may also affected fitness. Further study was performed based on temperature and hydrocarbon type. Biochemical and ultrastructural studies were carried out to determine relationships between quality variations and cellular characteristics for conidia produced in different culturing conditions. Results of fatty acid, and sugar (trehalose and polyols) analyses, and ultrastructural observations are presented in this paper.