Fusarium basal rot: characterization of a Fusarium spp. collection in Argentina

CALIGIORE GEI, P; VALDEZ, J.; PICCOLO, R.; GALMARINI, C.R.

Nidge

Simposio; Seventh International Symposium on Edible Alliaceae.; 2015

ISHS

Onion basal rot is one of the most important diseases for this crop in Argentina. The probable presence of more aggressive Fusarium isolates in Argentina fields might cause a more inductive environment and lead to greater development of the disease. These isolates can produce phytotoxic compounds, affecting seed germination, seedling establishment and facilitating the further development of the infection. The virulence of five Fusarium isolates was studied in pathogenicity trials. The incidence of FBR in seedlings was tested in greenhouse, using four onion cultivars and four inoculum concentrations. All onion cultivars were susceptible and non-specific interactions were observed. A foreign variety previously reported as tolerant was susceptible, especially when challenged with local isolates. The isolates showed differences in virulence among them and there was positive correlation between the inoculum concentration and disease expression. A similar assay was carried out with onion field soil samples, where colony forming units (CFU) were quantified using selective media and the incidence in seedlings was recorded. CFUs showed no pattern of distribution in the soil, and there was no correlation between CFUs density and FBR incidence. The fungal production of fusaric acid was measured for nineteen isolates and the influence of this compound on germination of onion seeds was evaluated, establishing the LD50 = 97.4 mg / mL. The results showed great variability in fusaric acid production amongst the isolates (16,5-186,8 mg/g), while high correlation (0,952 Pearson) were found between fusaric acid concentration and abnormality values in germinating seedlings.