Caracterização do patossistema goiabeira-serrana/Colletotrichum spp.

Abstract

Feijoa sellowiana (O. Berg) O. Berg popularly known as feijoa is a fruit species native to southern Brazil and northern Uruguay, with great economic and food potential. However, symptoms of anthracnose, a disease caused by fungi of the genus Colletotrichum, were observed in feijoas in the three states of southern Brazil and in the Salto Department in Uruguay. Because of this, studies in order to complement the knowledge about these pathogens are necessary, as they may provide subsidies for the development of strategies for disease control and prevention. Given this scenario, the objectives of the present study were: a) to verify if the mechanism of infection of Colletotrichum spp. in feijoa occurs systemically via floral structures; b) identify the anthracnose-causing species of Colletotrichum in feijoas from the three southern states of Brazil and from the Salto Department in Uruguay; c) verify the diversity and morphophysiological and genetic variability of isolates of Colletotrichum spp. from feijoas with anthracnose symptoms by sequencing the ITS, Actin and β-tubulin regions; d) confirm the pathogenicity of isolates of Colletotrichum spp., as well as quantify the incidence and evaluate the susceptibility/resistance reaction of the cultivars “Alcântara”, “Helena”, “Mattos” and “Nonante” to anthracnose; e) evaluate the diversity of endophytic fungi existing in feijoas of highland cultivars with different susceptibilities to anthracnose: “Mattos” (resistant) and “Alcântara” (susceptible), and select the isolates that present the highest antagonist activity against Colleotrichum spp.. Pathogen isolation was collected from symptomatic fruits in 33 municipalities, in the states of PR, SC, RS and in the Salto Department in Uruguay. The isolates were morphophysiologically characterized by mycelial growth, sporulation, conidia dimensions and shape and colony pigmentation. These variables were used in the UPGMA analysis in which the isolates were grouped in a dendrogram according to morphological similarity and established the characters that most contributed to the divergence. The incidence of the pathogen in feijoa flowers indicates that the pathogen infection occurs systemically via floral parts, since the fruit formation. Molecular analysis indicated that, in the states of RS, SC, PR and the Department of Salto in Uruguay, anthracnose of feijoa is caused by one species of the C. acutatum complex: C. nymphaeae, three species of the C. gloeosporioides complex: C. theobromicola, C. fructicola and C. siamense and by a species that does not belong to any complex due to their peculiar characteristics: C. pseudoacutatum. All species were pathogenic to feijoa, as they reproduced the original symptoms of anthracnose. The susceptibility of cvs. "Helena" and "Nonante" was influenced by the specific variability of the pathogen. The cv. "Alcantara" is susceptible and cv. “Mattos” is resistant to all Colletotrichum species tested. The cultivars “Mattos” and “Alcântara” presented similar endophytic fungal community in terms of diversity, however differing in abundance. Trichoderma harzianum, Trichoderma hamatum, Clonostachys rosea and Clonostachys rhizophaga occur exclusively in cv. “Mattos” and Clonostachys rosea, Trichoderma harzianum and Talaromyces amestolkiae are efficient in vitro control of Colletotrichum spp..