Interactions of Burkholderia glumae and B. gladioli in symptom development in rice seeds and seedlings

Burkholderia glumae and B. gladioli are major pathogens of rice that cause seedling rot, kernel rot and other related diseases in many countries worldwide. Despite the importance of both pathogens to rice production, the interactions between B. glumae and B. gladioli in seedling rot development as well as the effect of either pathogen on seed germination and growth is still poorly understood. Isolates of both pathogens were obtained from rice fields in Ecuador and the identification of each isolate was confirmed by PCR and sequencing of the 16s rDNA region. Rice seeds and seedlings were inoculated with each pathogen separately or in combination. Germination and development of roots and coleoptiles were evaluated in rice seeds, whereas progression of disease severity was assessed in seedlings. Burkholderia gladioli was isolated at significantly higher proportions than B. glumae in the rice fields sampled. Seed germination was not affected by any of the inoculation treatments but both pathogens significantly reduced root development. Only B. glumae significantly affected the growth of the coleoptile. Both pathogens produced similar seedling rot disease progression, but no significant interaction effect was observed in any of the seed or seedling treatments. Bacterial recovery from seedlings inoculated with the combination of both pathogens showed high levels of B. gladioli but almost negligible levels of B. glumae. Additionally, B. gladioli inhibited the growth of B. glumae in vitro, with average inhibition halos of 29.6 mm. This is the first report of B. glumae and B. gladioli interaction in planta.