Morphological aspects and effect of carbon sources in the physiology of Fusarium oxysporum f. sp. passiflorae

Abstract

The objective of this study was to evaluate the morphological and physiological characteristics of F. oxysporum f. sp. passiflorae. Isolates were obtained from yellow passion fruit plants with fusariosis symptoms grown in four production poles. The pathogenicity test was carried out on seedlings of this crop, under greenhouse conditions. The morphological characters evaluated were the size of macroconidia and microconidia in single conidiophores or in false heads; number of septa, presence of basal cell in the macroconidia and chlamydospores, and the aspects of the colonies of the isolates cultivated in potato dextrose agar (PDA) culture medium for aerial mycelium formation and colony coloration. The carbon sources: starch, lactose, maltose and sucrose were tested for the three most virulent isolates obtained in the pathogenicity test. The mycelial growth was obtained through readings every 24 hours of the diameter of the colony in two diametrically opposite directions. Sporulation determination was performed by counting spores in a Neubauer chamber. The isolate Fusarium oxysporum f. sp. passiflorae 4 (FOP 4) was the most virulent. There was variation in the morphological characteristics of all the isolates. The starch provided the highest mycelial growth and the isolates showed preferences for a particular carbon source in the sporulation test.