Fusariores do maracujazeiro: etiologia e sintomatologia

Abstract

Brazil is the world’s largest producer of passion fruit and it has been cultivated in many different regions of the country. The occurrence of diseases has severely damaged its production, and among these diseases, the worst are those which affect its root system caused by Fusarium spp. These diseases have different nomenclatures, such as wilt, stem rot and root rot, or also premature plant mortality, andit has also been associated to Fusarium oxysporum f. sp. passiflorae and F. solani species. These fungi of the soil can be symptomatologically mistaken due to symptom reflections caused on the plant. In the north of the Minas Gerais State, the symptoms associated with the diseases caused by that species of fungus have been reported frequently, though there is no report of which species predominates in this region. The present work aimed to: assess the patogenicity and morphologically characterize the isolates from Fusarium spp. and to identify them by species level; characterize the symptoms of the disease in the plants according to the species; assess the variability of the isolates of Fusarium spp. associated to the premature mortality of the passion fruit plant. Plants with symptoms of wilt, found in the principal regions of production of the North of Minas Gerais and in the county from Sebastião Laranjeira – Bahia State, were collected and their infected tissues were submitted to procedures of fungi isolation. After isolation in an Agar – Agar medium (AA) and stored in a Synthetic Nutrient-poor Agar medium (SNA), the isolates were then transferred for Potato Dextrose Agar (BDA) and SNA and the characteristics of the colonies and their morphologic structures were then assessed as for morpho-physiologic variability, allowing the species identification by means of the classification key. The isolates were submitted to pathogenicity tests, where passion fruit plantlets were inoculated by dipping method with a suspension of spores containing 105 conidia / mL. These plants were assessed as for incidence of the disease and the roots of the diseased plants were again submitted to isolation to confirm the presence of the pathogen. The symptoms observed on the field and in inoculated plants were described and photo documented and then related to the isolated pathogen species. For the assessment of genetic variability of the isolates, their DNA was extracted and submitted to RAPD and ISSR analysis. Through accounting of the polymorphic bands, the genetic distances were calculated between the isolates ones and a grouping analysis was performed from these genetic distances in a dendrogram using the Average Connection Method between groups (UPGMA). All of the 50 obtained isolates were pathogenic to passion fruit, being 13 of them identified as F. oxysporum f. sp. passiflorae and 37 identified as F. solani. It was possible to relate some of the symptoms observed in collected plants as well as in inoculated plants with one of the respective pathogen species. The ISSR and RAPD analysis revealed a population with high intra-specific genetic variability and the dendrograms formed from the two analyses generated distinct clusters for F. oxysporum f. sp. passiflorae and F. solani.