Espécies de fungos e bactérias associados à cultura da pitaia e avaliação de estádios de maturação na qualidade do fruto

Abstract

Pitaya is a promising fruit for cultivation. However, its cultivation is being affected by several diseases caused by fungi and bacteria, as well as the short post-harvest life of the fruits. It was aimed at this work; (i) identifying the diversity of fungi species associated with Pitaya culture; (ii) isolating and identifying bacteria present in the pulp of symptomatic Pitaya fruits; (iii) evaluating the fruits quality harvested at three exocarp staining levels. In the first experiment, for the fungi isolation, fragments of plant material were used disinfested, incubated in petri dishes with malt (MA2%). Forty-five fungi isolates obtained were grouped into morphotypes and identified up to the level of genus and species. Eight monosporic isolates from the Fusarium fujikuroi (FFSC) species were identified by morphotype. Crosses were performed with testers isolated of species. Molecular phylogeny analysis was performed on isolates Bipolaris cactivora (CML 4000) and Alternaria alternata (CML 4001 and CML 4062). Five isolates from the Fusarium, Bipolaris and Alternaria genus were tested for pathogenicity in fruits and cladodes. The morphological characters of the asexual and sexed phases from FFSC isolates were according to the literature. For the Fusarium proliferatum morphotype isolate there were no fertile crosses, and it was not possible to identify the mating type and confirm its identity. For all seven Fusarium verticillioides isolates were identified as MAT-2 idiomorph. By phylogenetic analysis, isolates CML 4001 and CML 4062 were identified as Alternaria alternata and CML 4000 as Bipolaris cactivora. Bipolaris cactivora, Fusarium proliferatum, Fusarium verticillioides and Alternaria alternata species are pathogenic to cladodes and pitaya fruits. It was described for the first time in Brazil, the Bipolaris cactivora occurrence in cladodes and ripe pitaya fruits. It was found the association of the Alternaria, Cladosporium, Colletotrichum, Nigrospora, Curvularia, Botryosphaeria, Bipolaris and Fusarium genera in association with the pitaya. In the second experiment, for the bacteria isolation and identification, aliquots were used, 10 g of the pitaya pulp fruit with and without symptoms diluted in 90 mL of sterile peptone water and homogenized in Stomacher® for 2 minutes. The microorganisms counting were carried out in YEPG agar and the identification by the protein profile of the isolates in MALDI-TOF MS. By mineral chemical analysis it was observed that fruits with symptoms of gelatinous spot had a higher mineral composition for micronutrients boron, copper and manganese. Sphingobacterium multivorum, Microbacterium testaceum, Pseudomonas rhodesiae, Microbacterium arborescens, Enterobacter asburiae, Microbacterium imperiale and Kocuria kristinae bacteria were identified in pitaya pulps with gelatinous spot symptoms. In the third experiment, fruits were collected at three levels of exocarp staining (25%, 50% and 75%, respectively) to determine the harvest point. For the interaction exocarp coloration levels x species had significant effect for fruit mass, pulp firmness, pH, soluble solids and acidity. For the levels of exocarp staining, significant effects were verified for all the variables, excepting the fruit mass. Regarding the species, a significant effect was verified for exocarp thickness, transverse diameter and fruit shape. Important differences in fruit mass characteristics; pulp firmness, pH, soluble solids and acidity are found when comparing red and white fruits of pulp species. It is indicated that the fruits are harvested at level 3 of exocarp staining, with 75% exocarp pink staining.