pH range and substrate organic matter levels modulate the sporulation of Fusarium oxysporum f. sp. passiflorae under controlled conditions

Fusarium wilt, caused by Fusarium oxysporum f. sp. passiflorae (FOP), stands out as an obstacle to the production of Passiflora edulis Sims. Little is known about the interaction of FOP with substrates and pH ranges that can be used in the development of management strategies or selection for resistance in Passiflora spp. Thus, the effect of different soil: manure or soil: coconut fiber ratios with pH ranging from acidic to alkaline on the production of FOP propagules was evaluated. The experiment was carried out in a completely randomized design, using four soil: manure or soil: coconut fiber ratios (5:0, 5:2, 5:4, 5:6 (v:v)). Each mixture’s pH was adjusted from 4.2 to 8.0 (soil: manure) or 4.2 to 9.7 (soil: coconut fiber). The production of microconidia, macroconidia, chlamydospores and colony forming units was evaluated at 3, 7, 14, 21 and 28 days after substrate infestation. The greatest number of propagules was registered in the groups treated with the highest proportions of manure or coconut fiber. The use of manure, regardless of the pH range, provided increases of 98%, 48%, and 13% in the number of colony forming units, microconidia and chlamydospores, respectively, in relation to the spores produced in substrates using coconut fiber. However, the production of macroconidia was 66% higher when fiber was used. Chlamydospore production was not affected by substrate pH, unlike other propagules with greater activity at slightly acidic, neutral or alkaline pH. The use of soil plus cattle manure in the ratios 5:4 or 5:6 with a pH between 5.1 and 8.0 was associated with the highest production of FOP propagules.