Estudos bioquímicos e moleculares de Ceratocystis spp. em Eucalyptus sp. e Arracacia xanthorhiza

Abstract

Pathogenic species of the Ceratocystis genus are widely distributed, especially in the tropics, causing damage to several hosts of economic importance. In Eucalyptus, the use of resistant clones is the main control strategy for Ceratocystis fimbriata. However, little is known about the defense responses involved in Eucalyptus resistance to fungal attack. We observed that C. fimbriata induced defensive responses of the eucalyptus clones, regardless of the resistant or susceptible phenotype. The amount of sugars and lignin produced by the resistant clone inoculated with the fungus (RC) was higher when compared with the inoculated susceptible clone (SC), but the activities of polyphenol oxidase and peroxidase enzymes were higher in the SC. As for the phenolic compounds, the concentration of hydroxycinnamic acid in RC was higher compared with CS. Singularly, it was observed that the RC had higher concentration of phenolic compounds catechin, chlorogenic acid and caffeic acid. In histochemical tests, the presence of lignin and phenolic compounds were observed in all treatments, with the greatest intensity detected in the RC sections. The alterations in the concentration of sugars and lignin, as well as some enzymes and phenolic compounds might help predicting phenotypes of eucalyptus clones resistant to this disease. The number of pathogen hosts has increased in Brazil. Already in Peruvian carrot (Arracacia xanthorhiza), on which fungus has recently been reported, there are no known resistant varieties control method for the pathogen in this culture, which still depends on other studies. Thus, in this study, we performed phylogenetic and morphological studies, as well as, interfertility and fungal pathogenicity tests on this culture and on taro (Colocasia esculenta), to which the fungus causes also the black rot. The trees of the ITS region, MAT1-1-2 and MAT1-2-1 of Ceratocystis isolates of the Peruvian carrot, were grouped in a clade separate from other Ceratocystis isolates. The MAT2-male tester strains from eucalyptus did not successfully cross with MAT1 tester strains of Ceratocystis isolates on Peruvian carrot. The result of the crossing was the occurrence of only a few malformed perithecia, with misshapen ostiolar hyphae without ascospore masses on the top of the perithecial neck. Pathogenicity tests indicated that the tested isolates were pathogenic to Peruvian carrot, but no symptoms were observed on taro plants, demonstrating host specificity. The inoculation performed on roots of Peruvian carrot and taro tubers, showed development and production of fungal structures. However, we observed the formation of a reddish halo on taro tubers when inoculated with isolates from Peruvian carrot, showing that host response may be present and blocking the pathogen attack. Based on the phylogenetic evidence, mating experiments, morphology and host specialization, a new species associated to Peruvian carrot was herein described as Ceratocystis arracacicola sp. nov.