Infecção latente de Colletotrichum truncatum e Cercospora kikuchii em soja

Diseases are the major constraints for higher yields and annual losses in Brazil are estimated at 15-20%, amounting to US$1.3 billion. This work was aimed at studying the latent infection between pathogens and the above ground parts of the soybean plants and the effect of fungicide sprays at the pod filling stages. The soybean (Glycine max) cultivar BR-37 was sown in a randomized complete block design, with four treatments (check and diphenoconazole fungicide sprays at R5.3, R5.4 and R5.5.) and five replicates each. The fungicide was sprayed at the rate of 75 g a.i. at growth stages. For the latent infection studies, six plants were randomly collected from each plot at growth stages R5.2, R5.4 and R7.2. From each plant the central leaflet of the leaf at the seventh node and segments of 5cm were collected from the lower, middle and top portions of the stem. The leaflets and stem pieces were surface disinfested, treated with 11.64% paraquat solution, incubated in moist chamber for 3-4 days and rated for fungal development based on the area of leaflet or stem piece colonized and frequency of leaflets or stem pieces with individual fungus. Late season disease severity (lsd) (brown spot and Cercospora leaf blight), percent defoliation, yield and 1.000 seed weight (tsw) were also determined. Latent infection by Colletotrichum truncatum had already occurred at R5.2. Cercospora kikuchii occurred at R5.2 and at R5.4. There were no effects of the fungicide or timing of sprays on the latent infections. There were no yield differences among the fungicide treatments but disease severity and percent defoliation were lowest and tsw was highest on fungicide treatment at R5.4.