Densidade populacional e germinação conidial de Trichoderma sp. submetidos a variações de fatores físicos

Abstract

Fungi of the genus Trichoderma stand out for their broad tolerance to environmental conditions and their relevance in agricultural applications, especially in the biocontrol of phytopathogens and in plant growth promotion. Among the physical factors influencing their development, temperature and light play a decisive role in conidial germination and population maintenance in the soil. This study aimed to evaluate the adaptability of Trichoderma sp. by estimating soil population density and conidial germination under different thermal and light regimes. Soil samples were collected at the Universidade Estadual de Goiás, Ipameri Campus, in an area free from previous applications of fungi or biological products. Inoculum densities were estimated before and after the application of the commercial strain T. harzianum IBLF 006 at temperatures of 16, 20, 24, 28, and 32°C, and conidial germination and germ tube growth of the strain Trichoderma sp. T-18-24 were evaluated under constant light and complete darkness at the same temperatures. The propagule density in the soil exhibited a negative polynomial behavior with temperature, with maximum estimated values at 22.5°C for soil inoculated with T. harzianum IBLF 006 and 23.4°C for non-inoculated soil, both decreasing significantly above 28°C, indicating reduced inoculum persistence at higher temperatures. Conidial germination of strain T-18-24 began between 8.0 and 17.5 h after incubation, predominantly unipolar. Higher temperatures anticipated germ tube emission but limited its subsequent growth. Linear and polynomial models adjusted for germ tube growth were statistically significant (P < 0.05) with high determination coefficients (R² = 0.73–0.99), demonstrating the strong influence of temperature. Under constant light, 24°C and 28°C sustained growth up to the fifth hour, whereas at 32°C a significant reduction occurred. In darkness, 24°C and 28°C also promoted superior growth, indicating this range as the optimal physiological zone of the strain. Light modulated germ tube growth according to temperature, enhancing development at 20°C and 32°C, inhibiting it at 16°C, and maintaining the highest growth between 24°C and 28°C. Light did not interfere with the onset of germination at higher temperatures.