First Report of Bipolaris micropus, Curvularia geniculata, Epicoccum sorghinum, and Fusarium incarnatum on Paspalum guenoarum Seeds in Rio Grande do Sul, Brazil

Abstract

Paspalum guenoarum Arechav. is a tropical forage species that occurs naturally in South America. In May 2015, P. guenoarum plants (virgule) showing a large number of lesions, ranging from elliptical to elongated, with brown coloration, covering more than 50% of the leaf area, were observed in the field plots located in Eldorado do Sul, RS, Brazil. Seeds from those plants showed a high incidence of various fungi. Subsamples of 100 seeds were submitted to the blotter test at 20°C with a 12-h photoperiod for 7 days (MAPA 2009). After isolation on potato dextrose agar (PDA) culture medium, structures of the following fungi were observed under a microscope: conidia (32 to 57 × 16 to 21 μm) of Bipolaris sp., conidia (17 to 25 × 12 to 19 μm) of Curvularia sp.; in carnation leaf agar (CLA) medium, canoe-shaped or banana-shaped mesoconidia (9 to 16 × 2 to 3 μm) of Fusarium sp., and pycnidia (100 to 250 × 105 to 240 μm in diam.) and conidia (8 to 12 × 5 to 7 μm) of Phoma sp. The isolates were deposited in the Mycological Collection of the Federal University of Lavras (UFLA), Lavras, MG, as CML 3600 (Bipolaris micropus), CML 3602 (Curvularia geniculata), CML 3599 (Epicoccum sorghinum), and CML 3601 (Fusarium incarnatum). The species were identified based on the rDNA internal transcribed spacer (ITS) (primers ITS1/ITS4; White et al. 1990). The RNA polymerase II (RPB2) gene (primers 5F2/7cR; O’Donnell et al. 2007) was used to identify Fusarium sp. The ITS region showed 99% identity to the isolate CML 3600 (GenBank accession no. KY20355) of B. micropus (HE792935.1), CML 3602 (KY120356) was 99% identical to Cochliobolus geniculatus (KF590040.1), which is the obsolete teleomorph name of Curvularia geniculata. Isolate CML 3599 (KY120357) was 100% identical to E. sorghinum (KY454467.1). Using the RPB2 gene, CML 3601 (KY120358) was found to be 99% identical to F. incarnatum (KF255542.1). A total of 60 seedlings were inoculated by spraying (1 ml/seedling) a spore suspension (1 × 105 CFU/ml) with each of the isolates over both the adaxial and abaxial leaf surfaces. Sixty additional plants were sprayed with water as the control. The plants were incubated at 22°C with a 12:12 h light/dark cycle. After 10 days, all inoculated seedlings developed necrotic lesions, except the controls. The pathogens were recovered from the infected tissues, fulfilling the Koch’s postulates. This is the first report of incidence of B. micropus, C. geniculata, E. sorghinum, and F. incarnatum associated with P. guenoarum seeds in Brazil. Further investigations are warranted to determine if one or more of these fungi are responsible for low seed germination rate (76%) of the P. guenoarum seeds.