Mapping QTL conferring resistance in maize to gray leaf spot disease caused by Cercospora zeina

Abstract

BackgroundGray leaf spot (GLS) is a globally important foliar disease of maize. Cercospora zeina, one of the two fungal species that cause the disease, is prevalent in southern Africa, China, Brazil and the eastern corn belt of the USA. Identification of QTL for GLS resistance in subtropical germplasm is important to support breeding programmes in developing countries where C. zeina limits production of this staple food crop.ResultsA maize RIL population (F7:S6) from a cross between CML444 and SC Malawi was field-tested under GLS disease pressure at five field sites over three seasons in KwaZulu-Natal, South Africa. Thirty QTL identified from eleven field trials (environments) were consolidated to seven QTL for GLS resistance based on their expression in at least two environments and location in the same core maize bins. Four GLS resistance alleles were derived from the more resistant parent CML444 (bin 1.10, 4.08, 9.04/9.05, 10.06/10.07), whereas the remainder were from SC Malawi (bin 6.06/6.07, 7.02/7.03, 9.06). QTLs in bin 4.08 and bin 6.06/6.07 were also detected as joint QTLs, each explained more than 11% of the phenotypic variation, and were identified in four and seven environments, respectively. Common markers were used to allocate GLS QTL from eleven previous studies to bins on the IBM2005 map, and GLS QTL “hotspots” were noted. Bin 4.08 and 7.02/7.03 GLS QTL from this study overlapped with hotspots, whereas the bin 6.06/6.07 and bin 9.06 QTLs appeared to be unique. QTL for flowering time (bin 1.07, 4.09) in this population did not correspond to QTL for GLS resistance.ConclusionsQTL mapping of a RIL population from the subtropical maize parents CML444 and SC Malawi identified seven QTL for resistance to gray leaf spot disease caused by C. zeina. These QTL together with QTL from eleven studies were allocated to bins on the IBM2005 map to provide a basis for comparison. Hotspots of GLS QTL were identified on chromosomes one, two, four, five and seven, with QTL in the current study overlapping with two of these. Two QTL from this study did not overlap with previously reported QTL.

Selinene Volatiles Are Essential Precursors for Maize Defense Promoting Fungal Pathogen Resistance

“…If this hypothesis is true, related studies on maize disease resistance should note biological roles for QTLs that include ZmTps21. Supportively, independent disease-related QTLs have been detected in broad regions spanning bin 9.05 (Baumgarten et al, 2007;Berger et al, 2014). More specifically, ZmTps21 (GRMZM2G011151) has been identified as uniquely present in transcriptome analyses of resistant inbred lines associated with enhanced antifungal defenses (Lanubile et al, 2014).…”

Cercospora zeinafrom Maize in South Africa Exhibits High Genetic Diversity and Lack of Regional Population Differentiation

“…Resistance of maize germplasm to GLS is quantitative in nature with many QTL identified in different maize growing countries, although very few studies have defined the causal species (Berger et al 2014). The pathosystem is not characterized by pathogen races that are recognised by cognate resistance genes (Balint-Kurti et al 2008), however the high diversity and evidence for sexual recombination reported in this study reveal a potential for differences in virulence between C. zeina isolates.…”

“…Widespread adoption of conservation tillage has allowed many fungal foliar pathogens to over-winter on maize debris, thus increasing the inoculum pressure in subsequent growing seasons (Ward et al 1999). Maize foliar disease resistance breeding is ongoing (Berger et al 2014), and this is particularly important for small-holder farmers in developing countries who currently have limited access to chemical control.…”

QTL mapping for resistance of maize to grey leaf spot

“…Berger et al. () used recombinant inbred line (RIL) populations constructed from CML444 × SC Malawi and detected seven QTLs that explained more than 11% of the phenotypic variation in 11 environments on chromosomes 1, 4, 7, 9, and 10. Liu et al.…”

“…() used meta‐analysis methods to integrate the QTL mapping results of five GLS resistance studies and identified 26 “real” QTLs and seven hotspots in bins 1.06, 2.06, 3.04, 4.06, 4.08, 5.03, and 8.06. In addition to directly locating maize GLS resistance QTLs, attempts were made to locate QTLs related to the control of flowering time, and a close connection was detected between the two traits (Berger et al., ; Liu et al., ).…”