AGGRESSIVENESS OF Fusarium graminearum SPECIES COMPLEX ISOLATES ON ROOT INFECTION OF SOYBEAN VARIETIES FROM DIFFERENT MATURITY GROUPS

CHIOTTA MARIA LAURA; BONACCI MARTIN; CHULZE SOFIA; BARROS GERMAN

Córdoba

Congreso; XI Congreso de Microbiología General; 2015

Samige

Members of Fusarium graminearum species complex (FGSC) are recognized as a primary pathogen of soybean in several countries in the American continents. The presence of species belonging to Fg complex in soybean may be attributable to the increase of the conservation tillage system in Argentina. The no-tillage cultivation must leave at least 30% of the crop residues on the soil surface and members of Fg complex has been shown to readily colonize crop debris left behind wheat, corn and soybean. The objective of this study was to compare the aggressiveness of crop residues isolates within the FGSC on root infection of soybean varieties from different maturity groups under controlled conditions. The evaluation of seedlings height and disease severity was performed in a rolled-towel assay described by Xue et al. (2007). Soybean seeds of three varieties from maturity group IV (planting late, medium and early-maturing varieties) were used in this study. Ten isolates characterized morphologically as strains belonging to the FGSC were included. These isolates were collected in a previous study during the 2012/2013 harvest season from an experimental field at EEA INTA Marcos Juarez, Córdoba. Ten days after inoculation, plants were removed from the growth unit and visually assessed for root-rot severity. Symptoms were rated using a 0-4 scale: 0, no visible disease symptoms; 1, lesion visible, but infection confined to the inoculation site, with normal seedling growth; 2, lesion size extended and the plant growth retarded; 3, infection of the entire root, and the plant growth halted; and 4, massive infection of the entire root resulting in plant death. In therolled-towel assays the seedling height of the inoculated seedlings was reduced by all isolates in the three cultivars relative to the control seedlings. All isolates caused root rot and there were significant differences in disease severity among isolates were observed in both experiments. The mean disease severity averaged across all isolates ranged between 1 and 2 in a 0-4 rating scale where 0 = healthy seedling and 4 = dead seedling. Analysis of variance demonstrated significant differences for genotype?isolate interactions for disease severity. Based on contrast analysis, no significant differences were detected in the susceptibility of three of soybean varieties from different maturity groups.