Identification and Mapping of Quantitative Trait Loci Conferring Disease and Insect Resistances in Maize

Abstract

Molecular markers were used to identify quantitative trait loci (QTLs) conferring resistance to three diseases and three insect pests in 110 maize recombinant inbred lines (RTLs). The markers included 116 restriction fragment length polymorphisms (RFLPs) and four simple sequence repeats (SSRs). The 110 RILs were derived from a cross between Hi34 (an Antigua 2D conversion) and TZi17 (a Nigerian inbred) by single seed descent (SSD) procedure. Significant differences among the parents and significant departures from normality with regard to these diseases and pests of the RIL populations served as the basis for further analysis and QTL mapping. The RTL data were analyzed to determine the chromosomal locations of QTLs by the use of QTL Cartographer version 1.12 and single factor analysis of variance (SAS GLM). The three corn diseases evaluated include maize streak virus (MSV), head smut (Sphacelotheca reiliafia (Kiihn) Clint), and common rust (Puccinia sorghi Schw.). The three insect pests studied were the corn leaf aphid (Rhopalosiphum maidis (Fitch)), fall armyworm {Spodoptera fnigiperda (J. E. Smith)), and sugarcane borer (Diatraea saccharalis (Fabricius)). Insect and disease nurseries of the RILs were planted or had been previously planted at International Institute of Tropical Agriculture (IITA) in Nigeria, International Corn and Wheat Improvement Center (CIMMYT) in Mexico, Pioneer Co. in South Africa, and Waimanalo, Hawaii from 1992 to 1998. Composite interval mapping located a major QTL conferring resistance to MSV, previous named msvl, and a major QTL conferring resistance to Sphacelotheca reiliana (Kiihn) Clint, designed as sprl, on the short arm of chromosome 1 between asgSO and nmcl67. The two genes were about 12 cM apart and both originated from Nigerian parent TZil7. Each explained 29.6% and 10.6% of the phenotypic variations, respectively. Two QTLs, designated as qrp1 and qrp2 with general resistance to Piiccinia sorghi Schw., were mapped to chromosomes 6 and 9, respectively. A major gene conferring resistance to corn leaf aphid, designated as aph2, was mapped on short arm of chromosome 2 with about 14.3% phenotypic variation explanation. Seven and three QTLs were identified for resistance to fall armyworm and sugarcane borer, respectively.