Lack of Population Structure and Mixed Reproduction Modes inExserohilum turcicumfrom South Africa

Abstract

Exserohilum turcicum is the causal agent of northern corn leaf blight, a destructive foliar disease of maize that results in yield losses worldwide. In South Africa, typical yield losses range from 15 to 30%. Previous studies found high haplotypic diversity with evidence for sexual recombination in E. turcicum populations from tropical climates such as Kenya. However, the population genetic structure and method of reproduction of E. turcicum in South Africa is unknown and, therefore, was investigated. Twelve polymorphic microsatellite markers were screened on 258 E. turcicum isolates from maize collected during 2012 and 2013 from three maize fields in South Africa. A multiplex polymerase chain reaction assay amplifying both mating type idiomorphs was applied to investigate the distribution of mating types. No distinct genetic clusters were observed. Shared haplotypes were identified between isolates separated by distances of up to 762 km, which provided evidence of migration. High haplotypic diversity indicated that sexual reproduction is occurring among E. turcicum isolates, although mating type ratios and linkage disequilibrium analyses did not support the hypothesis of random mating. The population genetic structure of E. turcicum in South Africa is likely due to the direct movement and spread of isolates undergoing a mixed reproductive lifecycle.

Genetic Differentiation and Mixed Reproductive Strategies in the Northern Corn Leaf Blight Pathogen Setosphaeria turcica From Sweet Corn in Fujian Province, China

“…Furthermore, for both full and clone-corrected (with the exception of NJ) datasets, we detected significant differences in linkage disequilibrium (I A and−r d ) (P < 0.05), and thus obtained no convincing evidence in support of the occurrence of random mating in Fujian S. turcica populations. Collectively, the low haplotypic diversities, skewed mating type distribution, and conspicuous linkage disequilibrium (I A and−r d ) tend to be indicative of a clonal or mixed reproductive strategy within the S. turcica populations distributed throughout Fujian, which is consistent with finding reported by Human et al (2016). In addition, although we successfully identified the mating types of 117 field S. turcica isolates along with those of a further 48 single leaf isolates based on multiple PCR analyses using two mating type-specific primer pairs, we failed to detect any S. turcica isolate with both MAT1-1 and MAT1-2 mating types in these populations.…”

“…For most of the S. turcica collection sites in Fujian Province, we detected shared multi-locus haplotypes among isolates (Supplementary Table 3), thereby implying that either largescale population migration has occurred or that the pathogen been spread via natural agents such as wind or through the long-distance transportation of fresh corn materials (Robert and Findley, 1952;Human et al, 2016), particularly fresh corn stalks, which are a frequently used to prepare silage for livestock.…”

“…Accordingly, these observations indicate that sexual reproduction may be an important source of genetic diversity in S. turcica . With numerous new physiological races continually appearing in the main corn-growing countries ( Welz et al, 1993 ; Ferguson and Carson, 2007 ; Muiru et al, 2010b ; Zhang et al, 2011 , 2012 ; Weems and Bradley, 2018 ; Jindal et al, 2019 ), an increasing number of studies have focused on investigating the distribution of mating types, genetic diversity, and population structure of S. turcica ( Borchardt et al, 1998b ; Ferguson and Carson, 2004 ; Haasbroek et al, 2014 ; Tang et al, 2015 ; Human et al, 2016 ; Nieuwoudt et al, 2018 ; Ma et al, 2020 ).…”

Genetic analysis of grain yield and resistance of extra‐early‐maturing maize inbreds to northern corn leaf blight

“…The need for significant increase in maize production and productivity in SSA is inevitable due to the increasing need for food for the burgeoning population and raw materials for existing and emerging feed and brewing industries. Yield reduction (as reported in the present study) due to emerging NCLB disease in regions that were known to be free from this disease is a major challenge that needs rapid response by seeking appropriate management strategies (Human et al., 2016; Hooda et al., 2017). White and yellow EEM maize hybrids responded differently to NCLB infection across the contrasting environments where the experiments were conducted as revealed by significant entry (genotype), environment, and the genotype × environment (G × E, partitioned into GCA‐male and GCA‐female) interaction for almost all measured traits, particularly GYLD and NCLB disease severity.…”

“…In recent years, however, the emergence of NCLB in areas traditionally free of the disease has been a major concern in West and Central Africa (WCA) (Akinwale & Oyelakin, 2018). Northern corn leaf blight causes grain yield (GYLD) losses ranging from 50% when infection occurs at the grain‐filling stage (Human et al., 2016), to 100% when infected at the seedling stage (Hooda et al., 2017). These losses have serious economic implications for farmers in SSA.…”