Abstract:
BACKGROUND: Gray 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.
RESULTS: A 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.
CONCLUSIONS: QTL 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.
