EVALUATION OF VIRULENCE OF CASSAVA ROOT PATHOGENIC Fusarium SPP. STRAINS ISOLATED FROM AFFECTED FARM IN MISIONES

MARTÍNEZ SA; MADRASSI LM; MÓNACO CI; ZAPATA PD; ALVARENGA AE

Congreso; LVII SAIB Meeting - XVI SAMIGE Meeting; 2021

Cassava (Manihot esculenta Crantz) is a commonly cultivated and consumed vegetable in Misiones and its production is carried out by small farmer families. However, these crops can be affected by cassava root rot disease (CRRD) produced by phytopathogenic fungi, generating economic losses. Several species of the genus Fusarium are phytopathogenic and they can produce CRRD. Nonetheless, little is known about these fungi`s virulence in the Misiones province. The aim of this research is to determine in vitro the virulence of native Fusarium spp. strains. We assessed the virulence of four Fusarium spp. strains (1.1, 1.1A, 1.9A, and 1.12) isolated from plants with CRRD symptoms. Those plants were in a cassava crop near Gobernador Roca city (27°15'58.9"S-55°21'48.9"W). The assay was carried out using disinfected cassava tubers obtained from the local market. For disinfection, fresh roots were cleansed out of visible soil particles using tap water and then, submerged in a 10% commercial bleach solution for 1 hour. After that time, we took 4 mm-wide and 10 mm-depth punches along every tuber, with a 40 mm distance between each punch. The inoculation was performed utilizing 4 mm diameter punches taken from the edge of fungal colonies growing in potato dextrose agar and cultivated for 10 days at 28ºC ±2°C. After inoculation, tubers were placed in an incubation chamber at 25ºC ± 2°C for 10 days. Afterwards, the surface colonization (mm) and depth of the root rot (mm) were measured in each punch. With the obtained values, severity index was calculated as the percentage of colonized superficial root tissue and as the percentage of rotten root (depth of root rot / root diameter * 100). All the analyzed strains were capable of both, growing on the root's surface and producing rot symptoms in the pulp. Average surface colonization values varied between 11 - 14 mm (50 - 70% severity) and the depth of root rot varied between 10 - 17 mm (20 - 35% severity). A single strain (1.12) showed the highest severity values for both parameters. Present results indicate that evaluated Fusarium spp. strains may have the potential to cause root rot in cassava crops in Misiones, since they were all able to produce CRRD symptoms in vitro.