Bacteriosis in a diverse maize germplasm in south Córdoba, Argentina

LOPEZ RAMIREZ, V; PRINCIPE, A; RUIZ, M; ROSSI, E; FERNANDEZ, M; BONAMICO, N; FISCHER, S

Mendoza

Congreso; XXXVI Scientific Meeting of the Cuyo Biology Society; 2018

Sociedad de Biología de Cuyo

The maize is one of the most important crops of the Argentinian pampa region. Plant pathogens, such as fungi, bacteria, and virus can cause serious damage to agriculture and significantly reduce the yield and quality of crops. Diseases caused by bacteria,however, are the few studied. The objective of this work was to identify bacterial pathogens based on symptoms observed in a diverse maize germplasm. Therefore, a population of 200 maize inbred lines developed and provided by the International Maize and Wheat Improvement Center (CIMMYT) were evaluated at Río Cuarto location during the summer cycle of 2017/2018. Light-colored necrotic streaks or yellow irregular blotches were observed on leaves from symptomatic maize inbred lines. The leaves with symptoms were rinsed with sterile distilled water and cut into small bits. These pieces were immersed in 0.85% (w/v) NaCl (physiological solution) and macerated. The samples were serially diluted and plated onto Luria-Bertani (LB) medium, containing dicloran (to prevent fungal growth). Plates were incubated at 30 °C. A total of twenty isolates were obtained from symptomatic maize inbred lines. Gram staining, pigment production in LB medium and catalase reaction were tested in all isolates. In addition, β-galactosidase production was assessed by X-Gal test. Most of the strains were Gram-negative and five isolates were catalase positive. The isolates were distinguished by their different colonial morphologies. Light yellow, orange, red or white convex colonies were observed on LB medium. Moreover, three strains produced blue color colonies on X-Gal containing plates, indicating the presence of β-galactosidase enzyme in those bacteria. Representative isolates were chosen for further identification through the use of phylogenetic analysis of 16S rRNA gene sequences. A single product of about 1.5 kb was amplified by PCR with the primers fD1 and rD1 from each of strains analyzed. The purified PCR products were sent to Macrogen Inc. (Seoul, South Korea) for the sequencing of the gene encoding 16S rRNA. The identification of bacterial pathogenic strains in maize is relevant. Since the study of these emerging diseases in the maize region of Argentina is yet little explored.