The effect of Trichoderma harzianum on seedling growth and seed-borne fungi in sunflower

In this study, the antagonistic effect of Trichoderma harzianum isolate TRIC8 against Alternaria alternata, Bipolaris cynodontis, Fusarium culmorum and F. oxysporum, which cause seedling rot in sunflower genotypes that are highly tolerant to downy mildew was determined under in vitro conditions. TRIC8 isolate is a candidate antagonist that has been found effective against many fungal agents in vitro, pot and field conditions. In the experiments, the isolates, which were isolated from sunflower seeds and were pathogenic more than 30% were used. During the study, the effect of seed treatments with the antagonist isolate at different times (2, 4 and 6 hours) on seedling growth was first investigated. The root length increased, shoot length and seedling vigour decreased at the lowest rate when the seeds were treated with antagonist for 6 hours. Evaluation of the antagonistic effect included the criteria such as dual culture, conidia germination, conidia germ tube length, alterations in hyphae and seed colonization. Dual culture tests were carried out in two inoculation assays, such as inoculation of antagonist at the same time with pathogen and its inoculation at 48 hour before pathogen. In both types of inoculation, TRIC8 inhibited the colony development of F. culmorum at the highest rate (%75.69% and 76.87%, respectively). TRIC8 was found to be effective on other pathogens between 70.67% and 74.40%, when it was inoculated at 48 hours before pathogen. Conidial germination of F. culmorum was inhibited at the highest rate. There were not significant differences among the germ tube length of the pathogens after TRIC8 treatment. However, alterations in hypha (coagulation and empty hypha.) were observed. The seed death (ungerminated seed) was controlled by the TRIC8 between 76% and 91% when the antagonist was treated to the seeds together with the pathogens for 6 hours. In the same treatment, A. alternata, B. cynodontis and F. culmorum could not colonize the seeds. This study shows that TRIC8 has the potential to be used against some seed-borne fungi in sunflower.