POPULATION DYNAMICS OF F. graminearum SPECIES COMPLEX IN A FIELD WITH SOYBEAN/WHEAT ROTATION

CHIOTTA, M.L.; PALAZZINI, J.M.; ALBERIONE, E.; BARROS, G.; CHULZE, S.

Congreso; XI Congreso Argentino de Microbiología General SAMIGE; 2015

Soybean crop in Argentina is one of the more relevant economic activities and it is commonly grown in rotation with wheat. Infection by Fusarium graminearum has been observed in wheat causing yield and quality losses. Recently, this species and others within the F. graminearum species complex (FGSC) were identified as soybean pathogens in South America, producing pod discoloration, seed decay and root rot beside trichothecene contamination. However, the dynamic of FGSC population in a mixed cropping system of soybean/wheat has not yet been evaluated. Thus, to determine whether the wheat crop is an important primary inoculum source of FGSC in the soybean agro-ecosystem, a study in a field with soybean/wheat rotation during 2012/13 and 2013/14 harvest season was carried out. The FGSC population was monitored evaluating wheat debris, implanted seed and different vegetative and reproductive developmental stages of the soybean. In the vegetative stage, root at V1 was analyzed while in the reproductive stage, pods and seeds at R6 (fully developed seed) and R8 (total maturity) were analyzed. The isolation in roots was performed on internal tissues and rhizoplane. Samples of wheat debris were collected during the V1, R2 (total flowering), R6 and R8 stages. FGSC spores in the air surrounding the soybean lot evaluated were collected during R6 stage in Petri plates containing Nash-Snyder selective medium. The plates were placed exposed to wind on the soil surface and others on the plant canopies. Contamination with deoxynivalenol (DON) was evaluated according to Barros et al. (2008). The results showed that the infection percentages of FGSC in debris varied from 4 to 21% during two years evaluated. In the internal tissues of roots were not observed infection and only during the second year in the rhizoplane were detected low levels (8%). Seed contamination was higher in R6 stage than R8 in two harvest seasons, 7 and 0% in 2012/13 and 26 and 4% in 2013/14 respectively. Regardless DON contamination, in 2012/13 harvest only one seed sample at R6 stage showed contamination at level of 0.3 ppm while in 2013/14 harvest a higher number of samples both R6 and R8 stages showed contamination with DON at levels ranging from 0.7 to 4.3 ppm. In air samples, the infection percentage was higher in samples placed on the soil surface ranged from 5 to 12%. The data demonstrate that FGSC inoculum is higher in debris than air surrounding the soybean. The declination in seed infection rates from their maximum development to maturity could be due to decrease of the water availability in seeds. Higher moisture levels recorded during the 2013/14 harvest could explain the higher levels of DON contamination in seeds. Therefore, environmental conditions predisposing could indicate a higher potential risk of DON contamination, mainly at R6 stage.