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fied QTLs for resistance to 1ECB and 2ECB. Schö n et al. (1991) identified four QTLs for resistance to 1ECB European corn borer (ECB), Ostrinia nubilalis (Hü bner), family on chromosomes 1, 4, 6, and 9 in F 3 families from the Crambidae, order Lepidoptera, is a serious insect pest of maize (Zea mays L.) in the USA. Understanding the genetic basis for ECB resis-cross of Mo17 (susceptible) and H99 (resistant). Schö n tance should increase the efficiency of breeding insect-resistant germ-et al. (1993) identified seven QTLs for resistance to plasm. The objectives of this study were to determine the number, 2ECB in an F 3 population derived from the cross of B73 genomic positions, and genetic effects of quantitative trait loci (QTL) (susceptible) ϫ B52 (resistant) on chromosomes 1 (two conferring resistance to leaf feeding damage cause by first-generation QTLs), 2 (two QTLs), 3, 7, and 10. Lee (1993) reported ECB (1ECB, defined as the trait of leaf feeding damage) and stalk 16 QTLs for resistance to 2ECB in three populations tunneling caused by second-generation ECB (2ECB, defined as the of F 3 families derived from crosses of B73 ϫ B52, B73 ϫ trait of stalk tunnel damage). The study included 244 F 2:3 families DE811 (resistant), and Mo17 (susceptible) ϫ B52. derived from the cross of B73Ht (susceptible) ϫ Mo47 (resistant). Beavis et al. (1994) identified QTLs for resistance to Inbred Mo47 represented a novel source of ECB resistance containing 2ECB on chromosomes 7, 8, and 9 from topcrosses and 50% tropical germplasm. The QTL analyses for three individual environments and combined across environments were performed by com-F 4 families from the cross of B73 ϫ Mo17. In the F 3 posite interval mapping using QTL Cartographer. Nine QTLs were families derived from the cross of two European maize identified for 1ECB on chromosomes 1 (three QTLs), 2, 4 (two QTLs), lines, D06 and D408, Bohn et al. (2000) identified six 5, 6, and 8, on the basis of data combined across environments. SevenQTLs for ECB tunnel length on chromosomes 1, 3, 5QTLs for 2ECB were found on chromosomes 2, 5 (two QTLs), 6 (two QTL), 9, and 10. Although some of the differences (two QTLs), 8, and 9. Several of the QTLs detected are located in in QTLs detected may be due to methods used in meagenomic regions reported for resistance to other stem borer pests of suring ECB damage, these results suggest that different maize. Inconsistency of QTLs across environments complicates use

European corn borer (ECB), Ostrinia nubilalis (Hübner), family Crambidae, order Lepidoptera, is a serious insect pest of maize (Zea mays L.) in the USA. Understanding the genetic basis for ECB resistance should increase the efficiency of breeding insect‐resistant germplasm. The objectives of this study were to determine the number, genomic positions, and genetic effects of quantitative trait loci (QTL) conferring resistance to leaf feeding damage cause by first‐generation ECB (1ECB, defined as the trait of leaf feeding damage) and stalk tunneling caused by second‐generation ECB (2ECB, defined as the trait of stalk tunnel damage). The study included 244 F2:3 families derived from the cross of B73Ht (susceptible) × Mo47 (resistant). Inbred Mo47 represented a novel source of ECB resistance containing 50% tropical germplasm. The QTL analyses for three individual environments and combined across environments were performed by composite interval mapping using QTL Cartographer. Nine QTLs were identified for 1ECB on chromosomes 1 (three QTLs), 2, 4 (two QTLs), 5, 6, and 8, on the basis of data combined across environments. Seven QTLs for 2ECB were found on chromosomes 2, 5 (two QTLs), 6 (two QTLs), 8, and 9. Several of the QTLs detected are located in genomic regions reported for resistance to other stem borer pests of maize. Inconsistency of QTLs across environments complicates use of Mo47 for marker‐assisted selection of ECB resistance.

rots in maize. High yielding cultivars, increased plant densities, and improvements in soil fertility are generally Stalk lodging in maize (Zea mays L.) causes yield losses estimated accepted to have also contributed to increased stalk to range from 5 to 20% annually worldwide. Selection for rind penetrometer resistance (RPR) has proven useful in enhancing germplasm lodging. for stalk strength, and therefore improving stalk lodging resistance. Stalk lodging counts are unreliable as a measure of We conducted quantitative trait locus (QTL) analysis for RPR in stalk lodging resistance because the expression of stalk four F 2:3 populations. The populations were constructed by means of lodging is affected by diseases, insects, and wind. Data combinations of MoSCSSS-High (selection for high RPR), MoSCSSSsummarized from the national white food corn perfor-Low (selection for low RPR), MoSQB-Low (selection for low stalk mance trials for the years 1986 to 2000 indicate that crushing strength), inbred line Mo47, and inbred line B73. Individuals visual counts of percentages of stalk lodging have coeffiin each population were genotyped for simple sequence repeat (SSR) cients of variation (CVs) in the range of 22 to 150% with or restriction fragment length polymorphism (RFLP) markers, and an average of 82% (L.L. Darrah, unpublished data). data were collected for RPR over multiple locations and replications. Several methods have been devised to measure stalk Means combined over environments were used as trait data for composite interval mapping by QTL Cartographer. Eight, 10, eight, and strength to improve stalk lodging resistance. Zuber and nine single-effect QTL and four, two, zero, and five epistatic interac-Grogan (1961) developed a stalk crushing strength tions were detected for RPR in the four populations. Multilocus mod-(SCS) technique whereby a 5.1-cm dried section of stalk els, including the single-effect QTL and epistatic interactions, accounted from the second or third internode above the ground for 33.4, 44.7, 48.4, and 58.7% of the total phenotypic variation. These was crushed vertically with a hydraulic press. The force data clearly indicate the complex nature of stalk strength. One chrorequired to "pop" the rind was significantly negatively mosomal region contained a QTL from all four populations, while correlated with stalk lodging in multiple studies (Zuber two QTL were in common among three of the four populations and and Grogan Thompson, 1963). The CVs for SCS five QTL were in common between two populations. Candidate genes ranged from 8 to 35%. However, because of the destructhat overlap QTL confidence intervals include those involved in lignin tive nature of sampling by SCS, an alternative method synthesis, the phenylpropanoid pathway, and the timing of vegetative phase change.S.A. Flint-Garcia, Genetics Department, North Carolina State Uni-date genes that might be associated with RPR. When versity,

In the present study, 122 maize local cultivars and adapted exotic germplasm from Thailand were used to develop open pollinate varieties (OPVs) using modified ear-to-row scheme, top-cross or test-cross programmes. Ten new maize OPVs with distinct characters were created based on the precise breeding objectives and directional design. The selection of breeding materials was based upon three factors: elite performance, broad adaptability, and genetic diversity. The synthesizing system provided four features: genetic mixing and recombination, equal comparable genetic contribution, mild selection pressure, and maximum intermating for genetic equilibrium (i.e., the female traits were close for the genetic com-positions). Subsequently, Suwan 1 composite and its deritives (Suwan 2, Suwan 3 composite, Suwan 5 and KS24 synthetics), KS6 and KS28 synthetics with the dent type of different origins, and Caripeno DMR composite, KS23, and KS27 synthetics with the dent type of Non-Suwan 1 origin were developed. These OPVs had been improved for 2~13 cycles using S1 recurrent selection method. About 50 inbred lines were developed from these OPVs, and 16 elite single (three-way) crosses were combined and released from these inbred lines. At present, at least one parental inbred line of all the tropical hybrids was derived from Suwan (KS) germplasm in Thailand. Based on the theory of the synthesizing OPVs and developing inbred lines, this paper discussed the genetic moderate diversity, relationship, heterotic group, and patterns for synthesizing OPVs, and inspiration for composed OPVs to heterosis breeding.