Fusarium spp. Associado a sementes de girassol

Abstract

Fusarium wilt caused by Fusarium sp., is a threat to sunflower production. Correct identification and use of control methods are essential to avoid damages caused by this pathogen. The management of this disease can be carried out through preventive measures, such as the microbiolization of seeds with Trichoderma spp .The aim of the present work was to characterize Fusarium spp. associated with sunflower seeds by morphological and molecular methods, and the pathogenicity and biological control of Fusarium spp. Fifty isolates of Fusarium spp. were obtained from seed samples of eight sunflower cultivars. Molecular characterization of Fusarium spp. was done by sequencing of the elongation factor (tef1) gene and the β-tubulin 2 (tub2) gene. Morphological characterization of the colony pigmentation was based on the presence or absence of sporodochia; size, shape and segregation of microconidia and macroconidia; types of phialides (single-phial and / or polyphyllid); presence or absence of chlamydospores; microconidia and their arrangement in chains or false heads; mycelial growth; mycelial growth rate index and conidia production. The prevalence of Fusarium spp. species was also determined. by cultivar and the pathogenicity of the isolates. In transmission, the percentage of emerged seedlings, nongerminated seeds with and without Fusarium spp., symptomatic and asymptomatic seedlings, transmission rate and disease incidence were counted. For control, seven isolates of Trichoderma sp. (TCH01, TCH02, TCH03, TCH04, TCH05, TCH06 and TCH07) was used in antagonism to F. proliferatum (F32). The isolates were compared with the pathogen in vitro tests of paired culture, antibiosis and mycoparasitism. The blotter test was condcuted to evaluated seed health of inoculated seeds, with a pathogen and treated with antagonism. Germination and emergence after seed microbiolization was also evaluated. In the greenhouse, the incidence, severity, length of the aerial part, number of leaves, fresh and dry mass of the aerial part and roots and the activity of the enzymes peroxidase (POD), polyphenoloxidase (PPO) and phenylalanine ammonia lyase (FAL). The experimental design was completely randomized.. DNA sequencing allowed the identification of F. fabacearum, F. pseudocircinatum, F. verticillioides and F. proliferatum associated with sunflower seeds. Colony morphology, mycelial growth, mycelial growth rate index and conidia production showed wide variability between the isolates. Among the sunflowers cultivars tested, F.proliferatum was the most prevalent species. Pathogenicity test, showed that all species of Fusarium spp. founded were pathogenic to sunflower. All isolates of the four species were transmitted via seeds. All the isolates caused symptoms such as rotting of seeds in the germination phase, in addition to rot of the neck and roots, tipping, vascular darkening, underdevelopment and rot of cotyledonous leaves after emergence. Volatile metabolites and direct mycoparasitism were observed in isolates of Trichoderma sp. on F. proliferatum. Trichoderma sp. efficiently reduce incidence and severity of wilt by promoting growth and in increasing the activity of the enzymes peroxidase, polyphenoloxidase and phenylalanine ammonia lyase in sunflower plants via seed microbiolization.