Clonality, spatial structure, and pathogenic variation in Fusarium fujikuroi from rain-fed rice in southern Laos

Abstract

Bakanae disease, caused by the fungal phytopathogen Fusarium fujikuroi, can be detected in most rice (Oryza sativa L.) growing areas worldwide. In this study, we investigated the population structure of this fungus in southern Lao PDR, a country located near the geographic origin of rice domestication. Microsatellites (SSRs) and mating type (MAT) analyses, pathogenicity and fungicide sensitivity tests were integrated in the study. The first key finding is that the population genetic structure of F. fujikuroi in Lao PDR is consistent with high clonal reproduction. Indeed, (i) “true” clones were identified; (ii) within populations, MAT types were frequently skewed from 1:1 ratio, (iii) linkage disequilibrium (among SSRs as also among SSRs and MAT) was present, and (iv) gene-flow between opposite MAT types within the same population is restricted. The presence of genetic divergence among areas and populations and the occurrence of positive spatial autocorrelation of genetic variation, indicate that migration is restricted, and that genetic drift plays an important role in the evolution of this fungus. Two main well-defined groups of isolates were detected (FST = 0.213) that display a non-random spatial distribution. They differ in the ability to induce seedlings death but not seedlings elongation (the typical Bakanae symptom) suggesting that the pathogen’s ability to induce the two symptoms is under different genetic control. Finally, we compared two agroecosystems with contrasting characteristics: low-input and traditional (Lao PDR) vs high-input and modern (Italy). We found differences in the level of population structuring and of spatial autocorrelation. This suggests that the evolutionary potential of the fungus not only depends on its intrinsic characteristics, but is strongly influenced by other external factors, most likely by the dynamics of infested seed exchange. Thus, quarantine and chemical treatments are a way to reduce population connectivity and hence the evolutionary potential of this pathogen.

Variations in Morpho-Cultural Characteristics and Pathogenicity of Fusarium moniliforme of Bakanae Disease of Rice and Evaluation of In Vitro Growth Suppression Potential of Some Bioagents

“…Disease assessment (Table 2) was done following the scale reported by Scherm et al [27] Table 2. The disease intensity of bakanae is rated using a 0-4 scale.…”

Imaging the invasion of rice roots by the bakanae agent Fusarium fujikuroi using a GFP-tagged isolate

“…One or more of the described symptoms, for each class, could be present on the infected plants. Evaluation of virulence of the isolates was performed as described in Scherm et al (2019)…”

Map-Based Cloning and Characterization of a Major QTL Gene, FfR1, Which Confers Resistance to Rice Bakanae Disease

“…Bakanae disease (BD), also called “foot rot disease”, is an important disease of rice ( Oryza sativa ), causing yield losses of 3.0–95.4% [ 1 ], and has been reported in almost all rice-growing regions worldwide [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. BD is caused by the fungal pathogen Fusarium fujikuroi , which can thrive in temperatures as high as 35 °C [ 1 ], allowing this disease to reproduce more rapidly and spread as temperatures increase due to climate change.…”