Abstract
Head smut in maize (Zea mays) is a systemic disease caused by the phytopathogenic fungus Sporisorium reilianum. One of the most severely-affected regions in Mexico is Valle del Mezquital in the state of Hidalgo, a high production zone with irrigated agriculture that produces over 50% of maize supplies in the state. This study was designed to analyze the genetic diversity of this phytopathogen isolated from different zones of Valle del Mezquital using the following molecular markers: ITS, aspartyl protease, β-tubulin and the mitochondrial endonuclease LAGLIDADG. Our objective was to estimate the level of genetic variability in a regional space and understand the evolutionary processes to which non-model organisms are subjected. A total of 53 strains of S. reilianum were isolated from the sampling sites and then purified. A Bayesian Analysis of Population Structure (BAPS) analysis of the genetic structuring allowed us to recover three genetic groupings (K = 3), while molecular variance analysis showed a very low fixation index (FST = 0.0146), which was not statistically significant and indicated little between-group genetic differentiation. Also, the value determined for the coefficient of genetic differentiation (Gst) showed little variation among the genetic groups, while the gene flow number (Nm) was 8.25. The Tajima´s D estimator and haplotype network recently indicated a rapid population expansion. Together, these results suggest that reproduction and migration are key factors in the evolution and virulence of this fungus.
Highlights
Head smut in maize (Zea mays) is a systemic disease caused by the phytopathogenic fungus Sporisorium reilianum f. sp. zeae (Kühn)
There are reports of the use of Bacillus subtilis as a biological control, the methods traditionally utilized to reduce the incidence of this disease in this area are genetic: primarily planting resistant hybrid seeds coupled with chemical control using fungicides to combat the disease and obtain good yields (Mercado-Flores et al, 2014, 2016)
We identified haplotype 4 as ancestral, as it is distributed in Los Pinos Tezontepec (PITE) and Tlahuelilpan (TLAH), with five derived haplotypes with high genetic variability distributed in Tlahuelilpan (TLAH), Los Pinos Tezontepec (PITE), “Teñhé” Mixquiahuala (TNMX), and La Cañada, Mixquiahuala (CAMX)
Summary
Head smut in maize (Zea mays) is a systemic disease caused by the phytopathogenic fungus Sporisorium reilianum f. sp. zeae (Kühn). This process begins during the life cycle of S. reilianum, when temperature and humidity are optimal for the germination of mature uninucleate diploid teliospores in the soil, which produces a structure called promycelium, whose nucleus is divided by meiosis to generate four haploid nuclei that enter lateral cells to constitute four basidiospores of different sexual compatibility. This is considered the saprophytic yeast phase of the fungus that reproduces by gemmation. Despite efforts to solve this problem, studies have identified strains that are resistant to fungicides and hybrids that, as products of selection processes, have increased disease incidence (Pérez and Bobadilla, 2007; Mercado-Flores et al, 2016; Álvarez-Cervantes et al, 2016)
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