Initial vegetative growth and survival analysis for the assessment of Fusarium wilt resistance in Passiflora spp.

Abstract

In Brazil, diseases caused by soil-borne pathogens such as Fusarium oxysporum f. sp. passiflorae are major constraints to the yellow passion fruit crop. We report the use of the survival analysis technique to assess the resistance of Passiflora spp. to Fusarium wilt in field conditions in a coastal tableland region of Brazil. Fifty genotypes were evaluated comprising the species Passiflora edulis, P. alata, P. gibertii, P. nitida, P. setacea,P. cincinnata, and backcross [(P. edulis x P. cincinnata) x P. edulis] and three graft combinations of P. edulis onto P. nitida, P. gibertii or P. alata. Plant growth and Fusarium wilt incidence were evaluated using 30 plants of each genotype in a completely randomized design. The highest growth speed indexes (GSI) were observed in P. cincinnata (BGP077) and P. edulis (BRS-GA) grafted onto P. gibertii (BGP008) with 12.04 and 11.96, respectively. Conversely, P. nitida (BGP390) had the lowest growth rate (4.10). Plants of P. gibertii, P. nitida and P. setacea did not present Fusarium wilt symptoms until 15 months after planting and presented the same median survival time with 466 days. Among P. edulis genotypes, Fusarium wilt incidence varied within three reaction groups, with the highest median survival time of 286 days. P. alata and P. cincinnata plants had high Fusarium wilt incidence (median survival time 250 and 252, respectively), similar to P. edulis, with 80% of symptomatic plants at 15 months after planting and median survival time of 240 days. Interspecific backcross hybrids differed from genotypes and intraspecific hybrids of P. edulis despite the similar median survival time among all of them (239–252 days). Grafting P. edulis onto wild species did not decrease Fusarium wilt incidence in relation to the most resistant group of P. edulis genotypes.