Evidence that the fungus Rhizoctonia solani AG-1 IA adapted to Urochloa in Colombia keeps a broad host range including maize

Palavras-chave

The fungus Rhizoctonia solani anastomosis group AG-1 IA has emerged as an important pathogen associated with foliar blight, collar rot and death of Urochloa (Brachiaria) forage pastures in South America. This study aimed to determine whether the adaptation of R. solani AG-1 IA to Urochloa spp. in Colombia promoted phenotypic differences in aggressiveness to distinct hosts. Our hypothesis was that the pathogen populations adapted to Urochloa spp. are not host-specialized and hence are not genetically isolated, thereby maintaining a broad host range, including the fabaceous plants cowpea and soybeans. We also determined whether two groups of isolates from populations of R. solani AG-1 IA sampled from Urochloa in Colombia have adaptive potential to emerge as maize pathogens. Besides the levels of disease severity in different hosts, we also determined the components of evolvability, such as the coefficient of genotypic variance (I_G), the environmental variance (I_E) and the heritability (h²). We concluded that: i) The adaptation of R. solani AG-1 IA to Urochloa spp. did not cause any phenotypic differences in aggressiveness to distinct hosts and therefore the pathogen maintains a broad host range. ii) The population of R. solani AG-1 IA from Urochloa hybrid Mulato in Colombia has adaptive potential to emerge as a maize pathogen.

Keywords
emerging pathogens in agriculture; pathogenic adaptability; genetic divergence; Urochloa foliar blight; forage diseases