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

Yuli Dai,Xiujuan Yang,Chengzhong Lan,Lin Gan,Zhimou Gao,Xuesong Lu

doi:10.3389/fmicb.2021.632575

Abstract

The northern corn leaf blight (NCLB) pathogen Setosphaeria turcica (Luttrell) Leonard and Suggs is one of the main biotic constraints on sweet corn (Zea mays L.) yield and quality in Fujian Province, China. Currently, however, there is comparatively little information available regarding the distribution of mating types, population genetics, and reproductive strategies of this pathogen in Fujian. In this study, we investigated the distribution of mating types and population genetics of 117 isolates of S. turcica collected from seven of the main sweet corn-growing regions in Fujian Province, based on multiple polymerase chain reaction analyses using two mating type-specific primer pairs and 11 inter-simple sequence repeat markers. Furthermore, we examined the mode of reproduction of Fujian S. turcica populations. Both MAT1-1 and MAT1-2 mating types were detected throughout all seven sampling locations. The majority of MAT1-2 isolates were detected from Dongyou, Jian’ou, Pingnan, Songxi, and Longyan, whereas a large proportion of the detected MAT1-1 isolates were among those collected from Dongfeng and Nanjing. Furthermore, we detected five shared multi-locus haplotypes among S. turcica isolates from Dongyou, Jian’ou, Pingnan, Nanjing, and Songxi, whereas no shared haplotypes were observed between the Dongfeng (or Longyan) population and these five populations. Pairwise comparisons of the indices ΦPT and Nm, and population structure and principal coordinate analyses indicated genetic differentiation between both the regional and the mating type populations of S. turcica in Fujian. The skewed mating type ratio associated with low a haplotypic diversity and evident linkage disequilibrium reveals a mixed reproductive strategy for S. turcica populations in Fujian Province. The findings of this study advance our current understanding of the genetic diversity, population structure, and reproductive strategies of S. turcica populations infecting sweet corn in Fujian Province, and will potentially contribute to further resistance breeding efforts.

Highlights

The heterothallic ascomycetous phytopathogen Setosphaeria turcica (Luttrell) Leonard and Suggs) [anamorph, Exserohilum turcicum (Pass.) Leonard and Suggs], the causal agent of northern corn leaf blight (NCLB), is a biotic constrain factor, which worldwide is responsible for substantial reductions in the yield and quality of corn (Zea mays L.), a vital basic human food source
More than 60% of S. turcica isolates from five sampling locations (DY, JO, PN, SX, and LY) were characterized as MAT1-2 (Figure 1), whereas at least 60% of those isolates from DF and NJ were identified as MAT1-1
We identified a skew in the ratios of mating type of S. turcica populations from the seven sampling locations, differences did not reach the level of statistical significance in populations from PN, SX, LY, DF, and NJ (Figure 1)

Summary

Introduction

The heterothallic ascomycetous phytopathogen Setosphaeria turcica (Luttrell) Leonard and Suggs) [anamorph, Exserohilum turcicum (Pass.) Leonard and Suggs], the causal agent of northern corn leaf blight (NCLB), is a biotic constrain factor, which worldwide is responsible for substantial reductions in the yield and quality of corn (Zea mays L.), a vital basic human food source. The typical NCLB symptoms manifest as gray-green, long fusiform, watersoaked lesions on young leaves and later developed into larger necrotic lesions (Vieira et al, 2014; Shi et al, 2017). These necrotic lesions expand and merge, causing extensive damage to the majority of leaves, thereby markedly weakening the photosynthetic capacity of corn plants (Saito et al, 2018; Kotze et al, 2019). Outbreaks of NCLB occur worldwide, and in susceptible corn cultivars can result in severe yield losses of more than 60%, these outbreaks tend to be most frequent in low latitude regions characterized by temperate and humid conditions (Dingerdissen et al, 1996; Tefferi et al, 1996; Ferguson and Carson, 2004)

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