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Yield under infestation by the pink stem borer [Sesamia nonagrioides (Lefebvre)] has been proposed as the best estimator of maize (Zea mays L.) performance under pink stem borer attack. Yield is a complex trait that greatly interacts with the environment. Several methods could be used to study the genotype X environment (GE) interaction. The objective of this work was to study the GE interaction for yield of 49 maize hybrids in five different environments by the Site Regression (SREG) and factorial regression methods. Locations presented different levels of natural infestation by the pink stem borer. The biplot obtained by applying the SREG method allowed visual cultivar evaluation. The factorial regression method incorporated genotypic and environmental covariates that enhanced biological interpretation of GE interaction. Hybrid A637 x EP42 would be recommended in northwestern Spain under medium and high natural infestation by the pink stem borer because it showed high and stable yielding ability. Genotypic and environmental covariates explained approximately 75% of the GE interaction variation, but other genotypic covariates could be introduced in the model to reduce GE residual variation to a nonsignificant level. In general, GE effects for grain yield were mainly due to earliness, vigor effects, and environmental yield limiting factors such as the mean of minimum temperature and percentage of air humidity., THE MOST IMPORTANT PEST of maize in the temperate areas of the northern hemisphere is the European corn borer [Ostrinia nubilalis (Hubner)] (Dicke and Guthrie, 1988), but, in the Mediterranean [...]

Corn (Zea mays L.) grain yield is affected by a number of factors, including stalk lodging and pests such as the European corn borer (Ostrinia nubilalis Hubner; ECB). European corn borers contribute to stalk lodging and also cause a direct grain yield reduction through physiological effects that decrease the plant's ability to produce and translocate photosynthates. Although much progress has been made in improving standability, stalk lodging remains a major problem, and breeding for stalk lodging resistance continues to be important, especially if it also plays a role in ECB resistance. Missouri Second Cycle Stiff Stalk Synthetic (MoSCSSS) was selected for stalk strength by using a rind penetrometer. Twelve cycles of bidirectional selection have been completed, which has resulted in increased and decreased stalk strength in the high and low directions of selection, respectively. Selected cycles were evaluated for grain yield, stalk lodging, rind penetrometer resistance, first- and second-generation ECB damage, leaf penetrometer resistance at the whorl stage and anthesis, and stalk traits including crude fiber, cellulose, lignin, and silica. Evaluation showed a decrease in grain yield in both directions of selection. Selection for high rind penetrometer resistance was effective at providing resistance to second-generation ECB damage as well as resistance to stalk lodging. Leaf penetrometer resistance was higher in the high direction of selection at whorl stage, but reversed by anthesis where the low direction of selection had higher leaf penetrometer resistance. Crude fiber, cellulose, and lignin increased in the high direction of selection, but silica decreased in the high direction of selection. Significant correlations between the stalk traits analyzed demonstrated that stalk composition was important in providing rind penetrometer resistance, stalk lodging resistance, and second-generation ECB resistance., CORN GRAIN YIELD is affected by a number of factors, including stalk lodging and pests such as the ECB. Stalk lodging accounts for 5 to 25% annual grain yield losses [...]

Two maize (Zea mays L) lines, susceptible and resistant to first-generation southwestern corn borer (SWCB), Diatraea grandiosella Dyar, were hybridized then backcrossed to the susceptible parent to form a population that was selected over three backcross generations by either marker-assisted or conventional selection for resistance to first generation SWCB leaf feeding. Quantitative trait loci (QTL) mapping was done by B[C.sub.1][F.sub.1] genotyping and B[C.sub.1][F.sub.2] infestation with SWCB. Three putative QTL were identified on chromosomes 7, 9, and 10 accounting for 28% of the phenotypic variance. Marker-assisted selection (MAS) proceeded by selecting plants heterozygous at the QTL regions and homozygous for the recurrent parent genotype outside the QTL regions in the B[C.sub.1][F.sub.1] and B[C.sub.2][F.sub.1] generations. B[C.sub.2][F.sub.2] individuals were selected for the homozygous donor genotype in the QTL regions. Conventional selection initiated from the most resistant 30 B[C.sub.1][F.sub.2] lines. Conventional trials of B[C.sub.2][F.sub.2] and B[C.sub.2][F.sub.3] families were infested with SWCB and based on leaf damage ratings selected selfed progeny of the former generation formed the subsequent trial entries. A comparative trial of B[C.sub.2][F.sub.3] lines, selected by the two methods, was evaluated under SWCB infestation at three locations. Leaf damage ratings were taken at all locations and larvae weight was taken at one location. No significant differences for leaf damage ratings or larvae weight were found between lines selected by the two methods. Both methods produced lines significantly improved over the susceptible parent for SWCB leaf feeding damage indicating that the methods were equivalent as conducted in this experiment., SUBSTANTIAL RESOURCES have been invested in developing maize with host-plant resistance to tropical insects by the International Maize and Wheat Improvement Center (CIMMYT) (Mihm, 1985, 1997; Smith et al., 1989; [...]

In Mediterranean countries, the principal corn (Zea mays L.) pest is the pink stem borer (PSB) (Sesamia nonagrioides Lef.), followed in importance by the European corn borer (ECB) [Ostrinia nubilalis (Hubner)]. Our objective was to quantify injury by these pests in a set of inbreds that showed different levels of ear damage by the PSB in a previous study and in their hybrids. A diallel among seven sweet corn inbreds that varied for ear damage by PSB was evaluated in three environments under PSB and ECB infestations. The importance of general combining ability (GCA) and specific combining ability (SCA) for ear damage by corn borer was determined. Inbred parents were also tested under manual infestation conditions with both borers. There was variability for ear damage traits among sweet corn inbred lines, but none of them were completely resistant. General combining ability effects were significant for the general appearance of the ear, ears with damaged grain, and ears with damaged shanks under PSB infestation. Under PSB infestation, SCA was not significant for any trait. Most traits showed significant GCA effects under ECB infestation, although SCA effects were also important for some damage traits. The inbred EP61 could supply some favorable alleles because it showed negative and significant GCA effects for ear damage under infestation by both species. Inbreds EP59 and V7726 showed negative and significant GCA effects for ear damage by ECB. These inbreds could be included in a sweet corn synthetic population that would be improved to decrease ear damage by corn borers., IN SPAIN AND OTHER MEDITERRANEAN COUNTRIES, the principal corn pests are the PSB (Anglade, 1972) and the ECB. In Mediterranean countries, the PSB is more abundant than the ECB. The [...]

Southwestern corn borer (SWCB), Diatraea grandiosella (Dyar), and the sugar cane borer (SCB), Diatraea saccharalis (Fabricius), are serious insect pests in maize (Zea mays L.) production areas of Central America and the southern USA. We mapped and characterized quantitative trait loci (QTL) affecting resistance to the leaf feeding generation of SWCB (1SWCB), compared these QTL with those for resistance to the leaf feeding generation of SCB (1SCB) identified in the same mapping population, and assessed the consistency of QTL for 1SWCB across two populations. One hundred seventy-one [F.sub.2] genotypes from cross CML131 (susceptible) X CML67 (resistant) and 100 RFLP marker loci were used for the QTL analyses. 1SWCB and 1SCB resistance were assessed in [F.sub.2:3] lines by leaf damage ratings (LDR) after artificial infestation in field experiments with two replications at one subtropical environment in 2 yr. The method of composite interval mapping (CIM) was used for QTL detection. Estimates of genotypic ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) and genotype X year interaction variance ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) were highly significant for 1SWCB LDR and 1SCB LDR. phenotypic and genotypic correlations between both traits were 0.62 and 1.02, respectively. For 1SWCB LDR, six QTL were detected explaining 53.3% of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], with two QTL displaying significant QTL X year interactions. Ten QTL were detected for 1SCB LDR, accounting for 98.2% of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. The QTL showed predominantly additive or partially dominant gene action. Seven out of 10 QTL were pleiotropic to both Diatraea spp. Three genomic regions, on Chromosomes 5 and 9, were consistent with a second mapping population derived from cross Ki3 (susceptible) X CML139 (resistant), for which seven QTL for 1SWCB LDR were found. Marker-assisted `gene stacking' is recommended for transferring pleiotropic QTL into susceptible germplasm and for pyramiding QTL from different sources of insect resistance., The southwestern corn borer and the sugar cane borer are important insect pests in tropical and subtropical areas of maize production in Central America and the southern USA. Both insect [...]

Breeders have selected for European corn borer [Ostrinia nubilalis (Hubner)] (ECB) resistance for many years and this may have led to higher concentrations of cell wall carbohydrates and lignin in stalks and leaf sheaths of maize (Zea mays L.). Our objectives were to evaluate the compositional changes accompanying divergent selection for cell wall constituents in three maize populations and to determine whether these changes were associated with changes in ECB resistance. Population BS9(CB) had undergone five cycles of [S.sub.1] family selection for increased first- and second-generation ECB resistance. Cycle 2 of BS9(CB) also underwent one cycle of divergent [S.sub.1] selection for neutral detergent fiber (NDF) and lignin concentrations in the stalk and leaf sheath. Populations WFISILO and WFISIHI underwent two cycles of [S.sub.1] family selection, respectively, for low and high NDF, acid detergent fiber (ADF), and lignin. Whorl samples were collected at the time of first-generation infestation. Stalks, leaf sheaths, and leaf blades were sampled following second-generation infestation. Selection for increased ECB resistance in BS9(CB) increased NDF, ADF, and lignin concentrations in stalks and leaf sheaths. Selection for high NDF and lignin concentrations in BS9(CB) C2 produced materials with greater second-generation ECB resistance than did divergent selection for low concentrations. Selection for decreased NDF, ADF, and lignin in WFISILO decreased second-generation ECB resistance. Selection for increased NDF, ADF, and lignin in WFISIHI did not influence ECB resistance, however. In general, there was an association between plant cell wall composition and ECB resistance, but genetic background influenced the relationship., Maize grown in most of the USA is commonly exposed to two or more distinct ECB generations each growing season. Plants are at different growth stages during each attack and [...]

Southwestern corn borer (Diatraea grandiosella Dyar) is a serious pest of corn (Zea mays L.) in the southern USA. Lack of reliable techniques for evaluating resistance after anthesis is a major problem. The objective was to develop a laboratory bioassay for evaluating southwestern corn borer larval growth on diets comprised primarily of lyophilized husks of corn inbred lines. Diets were prepared by adding 15 g of lyophilized husk tissue collected within 3 d after silk emergence to a mixture of 250 mL distilled water, 2400 mg agar, 12.5 mg gentamicin sulfate, 132 mg sorbic acid, and 528 mg ascorbic acid. Larvae were weighed after feeding on the test diet for 21 d. Larvae fed diets containing husks of different inbred lines varied significantly. Because southwestern corn borer larvae that infest corn plants at or after anthesis feed initially on husks, this bioassay is a potentially useful technique for identifying resistant germplasm.

More than 30 crop species have been genetically engineered to express Bacillus thuringiensis endotoxins which are highly toxic to specific insect pests (1). However, several insect species have evolved resistance [...]

Southwestern corn borer, Diatraea grandiosella Dyar, is an important pest of corn, Zea mays L., in the southern USA and Mexico. Germplasm with resistance to attack by southwestern corn borer in the vegetative stages has been released; however, resistance to attack after anthems has not yet been identified. The objectives of this investigation were to evaluate a diallel cross among a group of inbred fines, some of which appeared to exhibit resistance in laboratory and preliminary field tests, and to evaluate the effectiveness of visual ratings of leaf sheath and husk damage in identifying resistant hybrids. The nine-parent diallel cross was grown for 2 yr and plants were infested with southwestern corn borer larvae 7 d after anthems. Leaf sheaths and husks were visually rated and larvae recovered, counted, and weighed 14 d after infestation. Husks were also collected from an additional planting of the diallel cross within 3 d after silk emergence, lyophilized, and used in preparation of laboratory diets. Larvae were fed on the diets for 21 d and then weighed. Leaf sheath and husk ratings were not significant among hybrids; however, differences in number of larvae, mean larval weight, and total weight of larvae collected from a plant in the field test and mean larval weight in the laboratory among hybrids were significant. General combining ability (GCA) was a significant source of variation among hybrids for all traits. Estimates of general combining ability effects indicated that the parental inbreds, Mp305 and SC213, contributed to resistance of their hybrids., Southwestern corn borer is an important pest of corn in the southern USA and Mexico. Corn is attacked in both the vegetative and reproductive stages of growth. When plants are [...]