Divergence Between Sympatric Rice- and Maize-Infecting Populations of Rhizoctonia solani AG-1 IA from Latin America

Abstract

The basidiomycetous fungus Rhizoctonia solani anastomosis group (AG)-1 IA is a major pathogen in Latin America causing sheath blight (SB) of rice. Particularly in Venezuela, the fungus also causes banded leaf and sheath blight (BLSB) on maize, which is considered an emerging disease problem where maize replaced traditional rice-cropping areas or is now planted in adjacent fields. Our goals in this study were to elucidate (i) the effects of host specialization on gene flow between sympatric and allopatric rice and maize-infecting fungal populations and (ii) the reproductive mode of the fungus, looking for evidence of recombination. In total, 375 isolates of R. solani AG1 IA sampled from three sympatric rice and maize fields in Venezuela (Portuguesa State) and two allopatric rice fields from Colombia (Meta State) and Panama (Chiriquí State) were genotyped using 10 microsatellite loci. Allopatric populations from Venezuela, Colombia, and Panama were significantly differentiated (Phi(ST) of 0.16 to 0.34). Partitioning of the genetic diversity indicated differentiation between sympatric populations from different host species, with 17% of the total genetic variation distributed between hosts while only 3 to 6% was distributed geographically among the sympatric Venezuelan fields. We detected symmetrical historical migration between the rice-and the maize-infecting populations from Venezuela. Rice-and maize-derived isolates were able to infect both rice and maize but were more aggressive on their original hosts, consistent with host specialization. Because the maize-and rice-infecting populations are still cross-pathogenic, we postulate that the genetic differentiation was relatively recent and mediated via a host shift. An isolation with migration analysis indicated that the maize-infecting population diverged from the rice-infecting population between 40 and 240 years ago. Our findings also suggest that maize-infecting populations have a mainly recombining reproductive system whereas the rice-infecting populations have a mixed reproductive system in Latin America.

Virulence and molecular characterization of Costa Rican isolates of Rhizoctonia solani from common bean

“…Godoy-Lutz et al (2003) mention that AG 1 macrosclerotia producing isolates were the most virulent, and AG 4 no if you read well is AG 2-2 the least virulent. Similar results have been observed in Latin America and the Caribbean, where virulence patterns vary between regions and genotypes (González-Vera et al, 2010).…”

Assessing genetic diversity in the web blight pathogen Thanatephorus cucumeris (anamorph = Rhizoctonia solani) subgroups AG-1-IE and AG-1-IF with molecular markers

“…The development of co-dominant microsatellite markers would facilitate studies attempting to understand population structure and dynamics. Recently, the population structure of R. solani subgroup AG-1-IA, causal agent of sheath blight of rice and other blights of maize and soybean from South America, United States, China and India has been studied by employing subgroup specific DNA co-dominant microsatellite simple sequence repeat (SSR) markers (Bernardesde-Assis et al 2009;Ciampi et al 2008;González-Vera et al 2010). Host specialization was shown to affect selection and the pattern of populations with different reproductive modes, leading the authors to propose a recombining reproductive mode for maize-infecting populations and a mixed reproductive mode (asexual and sexual) for the rice-infecting populations that includes recombination events followed by clonal expansion during the growing season (González-Vera et al 2010).…”

“…Recently, the population structure of R. solani subgroup AG-1-IA, causal agent of sheath blight of rice and other blights of maize and soybean from South America, United States, China and India has been studied by employing subgroup specific DNA co-dominant microsatellite simple sequence repeat (SSR) markers (Bernardesde-Assis et al 2009;Ciampi et al 2008;González-Vera et al 2010). Host specialization was shown to affect selection and the pattern of populations with different reproductive modes, leading the authors to propose a recombining reproductive mode for maize-infecting populations and a mixed reproductive mode (asexual and sexual) for the rice-infecting populations that includes recombination events followed by clonal expansion during the growing season (González-Vera et al 2010). These results supported the hypothesis that characterizing populations of AG-1-IA can optimize the deployment of major resistance genes or single-pathway target fungicides as well as agricultural practices that lead to minimizing gene flow by reducing the spread of propagules via irrigation systems or contaminated machinery (González-Vera et al 2010;McDonald and Linde 2002).…”

“…Host specialization was shown to affect selection and the pattern of populations with different reproductive modes, leading the authors to propose a recombining reproductive mode for maize-infecting populations and a mixed reproductive mode (asexual and sexual) for the rice-infecting populations that includes recombination events followed by clonal expansion during the growing season (González-Vera et al 2010). These results supported the hypothesis that characterizing populations of AG-1-IA can optimize the deployment of major resistance genes or single-pathway target fungicides as well as agricultural practices that lead to minimizing gene flow by reducing the spread of propagules via irrigation systems or contaminated machinery (González-Vera et al 2010;McDonald and Linde 2002).…”

Rhizoctonia solani AG-1 IA infects both rice and signalgrass in the Colombian Llanos

“…most likely originated from a population that originally infected rice via host shift (Chavarro Mesa et al 2015). Similar examples are known to have occurred, such as host jump (from rice to soybean) or host shift (from rice to maize) of R. solani AG-1 IA populations in the southern United States (Assis et al 2008) and Venezuela (González-Vera et al 2010).…”