Caracterização morfofisiológica e molecular de Fusarium spp., agente causal da murcha em Carya illinoinensis k.

Abstract

The production of pecan (Carya illinoinensis) contributes with the productive chain and economy of many regions from both the country and in Rio Grande do Sul state, cultivation has been established for quite some time, drawing greater attention in the last few years due to the profitability provided by the activity. However, one of the harmful factors in growing the species is the incidence of diseases, which are capable of severely damaging and devastating orchards. In this context, wilt occasioned by fungi of the Fusarium genus arises as a new threat to orchards from the southern region of the country, manifesting through symptoms such as wilt, shrouding and necrosis of leaves, as well as browning of vascular tissue. In this direction, the present work aimed to analyze the morphophisiological and molecular characteristics, as well as validate the pathogenicity from isolates of Fusarium spp. associated to pecan wilt in the southern region of Brasil. In order to do so, samples of symptomatic matter were collected in different towns from Rio Grande do Sul and Paraná. Subsequently, potentially pathogenic isolates were obtained and purified. After being obtained, the isolates were evaluated regarding the morphophisiological variability through measurement of mycelial growth, sporulation, colony pigmentation and coloring of the aerial mycelium as well as dimensioning of spores and further characteristics of reproductive structures. Molecular characterization was carried out through PCR (Polymerase Chain Reaction) to amplify the region of elongation factor 1-alpha and further sequencing. The pathogenicity test was carried out through immersion of pecan tree roots in suspension of spores from the Fusarium spp. isolates. Besides that, the severity of diseases has been evaluated through a scoring scale according to the symptoms indicated in the plants. Nineteen fungi isolates were obtained from plants distributed in different localities from Southern-region states. The analysed morphophisiological characteristics were enough to prove the existence of variability among isolates, with sporulation and macroconidium length being the highest contributing factors to such differentiation. Through dissimilarity analysis of morphophisiological traits, isolates could be separated in different groups. Sequencing of the region of elongation factor 1-alpha enabled proving difference among isolates as well as identifying five species, Fusarium oxysporum, F. fujikuroi, F. graminearum, F. incarnatum and F. solani. All isolates were considered pathogenic to the pecan tree, however, there was variability regarding their aggressiveness. Therefore, it can be concluded that different species of the Fusarium genus are responsible for pecan tree wilt in the southern region of Brazil.