CHARACTERIZATION OF Fusarium oxysporum ISOLATES AND RESISTANCE OF PASSION FRUIT GENOTYPES TO FUSARIOSIS
ABSTRACT Passion fruit wilt, caused by Fusarium spp., is one of the most severe diseases for this crop. Although yellow passion fruit is propagated mostly by seeds, the use of rootstocks tolerant to early death could be a management strategy for cultivation in areas with disease history. Thus, this study characterized Fusarium isolates obtained in Triângulo Mineiro and determined the most suitable genotype to use for grafting to reduce losses caused by this pathogen. Mycelial growth and sporulation of Fusarium isolates, in three different growth media, was quantified by measuring colony diameter and by counting the conidia in Neubauer chamber 10 days after growth in malt extract-agar 2%, PDA or CMA at 22 ± 3ºC and 12 hours lighting. Five days later the color of the colonies was evaluated. The experimental design was a 4x3 factorial completely randomized design, with five replications. Characterization of morphological structures of isolates was done with minimum cultivation in Malt extract-agar 2% amended with sterilized soil + sand (1:1). Three Passiflora species and two seedling types were used as rootstock to evaluate field resistance to fusariosis, in a randomized block design, as a 3x2 factorial, with three Passiflora species (P. alata, P. setacea and P. edulis) and two seedling types (ungrafted or grafted with P. edulis). The medium PDA was the least favorable for mycelial growth of the isolates. The best medium for conidium production was Malt extract and the most sporulating isolates were Fus-01 and Fus-02. Isolate color varied from white to pink to violet. Only Fus-02 and Fus-04 formed macro and microconidia. Shape, dimensions and septa number of macroconidia and microconidia, as well as the presence of characteristic monophyalides allowed the classification of all isolates as Fusarium oxysporum f.sp. passiflorae. Passiflora alata and P. setacea, used as rootstocks for P. edulis in the field, were resistant to fusariosis. Despite its low survival, P. edulis grafted on itsef, promoted similar growth of secondary branches as P. setacea in the field.
