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White maize (Zea mays L.) is preferred for human consumption, but little is known about the genetic regulation of flour quality, and the potential value of genotypes adapted to temperate areas has not been reported. The objectives of this work were to assess the potential value of flint white maize inbreds from northwestern Spain and to determine the genetic effects of quality. A diallel among flint and dent white inbred lines was evaluated in northwestern Spain, and generation mean analyses were performed for three crosses representing flint by flint, dent by dent, and flint by dent combinations. Dent x dent hybrids had Iow density. Considering grain yield and density together, the best hybrids were EP64 x K301, EP71 x K301, and EC22 x Mo20W, which had poor milling test values, and high proportions of whole kernels. Considering the relative importance of nonadditive genetic effects, the final goal of breeding programs should be to obtain hybrids. Both additive and nonadditive genetic effects have to be otaken into account to improve any of these traits in the flint genetic background. Moreover, it will be difficult to improve kernel density and proportion of whole kernels in any genetic background.

Selection against pink stem borer (Sesamia non-agrioides Lef) (PSB) attack was performed in the maize (Zea mays L.) synthetic EPS12. The direct response of the EPS12 population to three cycles of selection to reduce tunnel length damage by PSB while maintaining yield was evaluated. [S.sub.0] (cycles of selection) and [S.sub.1] (selfed cycles of selection) generations and testcrosses to three testers were evaluated under artificial infestation with two corn borers, PSB and European corn borer (Ostrinia nubilalis Hubner) (ECB). Genotypes and the genotype x environment interaction were significant for tunnel length and yield. Differences among cycles of selection were significant for tunnel length, and the linear decrease for this trait (-1.80 cm [cycle.sup.1]) achieved during selection accounted for most of these differences. Yield was not significantly reduced with selection. Inbreeding for yield significantly increased due to selection. EPS12 crossed to EP42 showed a significant increase in yield with selection, while crosses to other testers showed a nonsignificant reduction in yield. Although crosses to EP42 were not significantly different for tunnel length, the high heterosis between EPS12 and EP42 and the increased yield of EPS12 x EP42 during selection suggest that inbred lines developed from advanced cycles of EPS12 could be crossed to EP42 to generate promising hybrids. In general, resistance to PSB and ECB was improved, while yield was maintained, inbreeding was increased, and yield of the cross EP42 x EPS12 was improved.

Low spring temperatures are one of the main limiting factors for maize (Zea mays L.) growth along the European Atlantic coast. Several breeding programs have been performed to obtain cold-tolerant maize genotypes, but the few cold-tolerant inbreds and hybrids available need further improvements for cold tolerance and agronomic performance. The objective of this study was to identify cold-tolerant maize populations with favorable alleles to improve cold tolerance and agronomic performance in early sowing of two cold-tolerant hybrids. The parental inbred lines of two cold-tolerant hybrids were crossed to nine cold-tolerant populations. Tests were performed in a cold chamber and in the field for 2 yr at two locations. The populations Rojo de Tolosa and Puenteareas were the most promising sources of new favorable alleles for transferring cold tolerance to the hybrids EP80 x F7 and EP80 x Z78007, respectively. The populations Puenteareas and Silver King were the most outstanding donors to improve the agronomic performance of EP80 x F7 and EP80 x Z78007, respectively. Some improved versions of the cold-tolerant inbred parents could be developed from crosses between F7 or Z78007 and Puenteareas; alternatively, Rojo de Tolosa or Silver King could be used as donors of favorable alleles, but the simultaneous improvement of yield and cold tolerance is not straightforward.

Heterotic patterns among European maize (Zea mays L.) populations are strongly affected by genotype x environment (GE) interactions and no single heterntic pattern has been identified so far that is not influenced by GE interaction. The objectives of this work were to study (i) the mean performance and stability of the heterotic patterns 'Humid Spain x Southern France' and 'Dry Spain x Humid Spain' and (ii) the influence of some environmental and genotypic covariates on G and E main effects and their interaction. We studied the GE interaction for grain yield in eight environments using Sites Regression (SREG) and factorial regression models. The biplot obtained from the SREG model allowed visual cultivar evaluation. The factorial regression model incorporated genotypic and environmental covariates that enhanced biological interpretation of GE interaction. The heterotic patterns Humid Spain x Southern France and Dry Spain x Humid Spain had similar mean performance across environments, but the former, represented by the cross Lazcano x Millette du Lauragais, was more stable. Effects of G, E, and GE for grain yield were mainly due to earliness, vigor effects, and/or environmental factors related to cold stress. An adequately long vegetative cycle along with early vigor had a great influence on the mean grain yield performance of Lazcano x Millette du Lanragais. Additionally, its intermediate number of days to silking and tolerance to temperature stresses could be related to its stability. Breeding for tolerance to temperature stresses could render more stable maize genotypes., MOST MAIZE HYBRIDS grown in Europe correspond to the U.S. heterotic pattern Reid x Lancaster, or the heterotic pattern European flint x U.S. dent (Moreno-Gonzalez, 1988; Misevic, 1989; Ordas, 1991; [...]

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 [...]

Variability for the timing of transition from juvenile to adult vegetative phases in maize (Zea mays L.) is genetically regulated and has been associated with disease and pest tolerance. Epicuticular wax is present in juvenile leaves and absent in adult leaves. The objective of this work was to assess the potential modification through selection of the timing of vegetative phase transition. Three cycles of divergent phenotypic selection for early and late vegetative phase transition performed on a synthetic population were evaluated by means of a randomized complete block design with two replications, in two locations of northwestern Spain across two years. Selection for early transition was made by recombining plants with fewer leaves with epicuticular wax, while, for late transition, plants with more leaves with epicuticular wax were recombined. Selection response was significant and more efficient for late phase transition than for early phase transition. Other changes observed cannot be considered correlated responses to selection because they changed in the same way for both directions of selection. We conclude that selection for the timing of vegetative phase transition was efficient and there was no detrimental correlated responses on any agronomic trait., MAIZE HAS TWO VEGETATIVE PHASES, juvenile and adult. Juvenile and adult leaves, internodes, and axillary buds differ in anatomy and physiology (Lawson and Poethig, 1995; Poethig, 1988, 1990). The traits [...]

The pink stem borer (Sesamia nonagrioides Lef.) is the most important pest of maize (Zea mays L.) in northwestern Spain. The objective of this work was to evaluate defense mechanisms against Sesamia in 10 inbred lines and the 10-parent diailel among these inbreds. Hybrids and inbred lines were tested over 2 yr in northwestern Spain under natural and artificial infestations. Yield of infested and non infested plants per plot were computed to calculate yield loss caused by the pink stem borer attack. Principal component analyses for stem damage traits and for ear damage traits were made for each infestation condition. From the principal component analysis, an index was computed to measure stem damage and ear damage. Damage index under artificial infestation was used to evaluate antibiosis while antixenosis was detected when damage index of each genotype was compared under artificial and natural infestation. The regressions of yield loss on the damage index were used to separate the genotypes into four groups according to the possession of antibiosis and/or tolerance mechanisms. A509, A661, EP31, F7, PB60, and Z77016 showed stem antibiosis. A637, A661, EP31, F7, and PB60 exhibited stem tolerance. A509, A661, and EP31 stood out by their ear antibiosis. A637, A661, F7, and PB60 were tolerant to ear damage. We conclude that the three mechanisms of defense to the pink stem borer attack (antixenosis, antibiosis, and tolerance) were found among inbred lines and hybrids. A multitrait selection scheme using damage traits and yield could improve the defense level against pink stem borer., The most important maize pest in North America as well as in Central Europe is the European corn borer (Ostrinia nubilalis Hubner). However, in the South of Europe the pink [...]

Elite American and European field corn inbreds (Zea mays L.) could improve the agronomic value of sweet corn for European conditions. The choice of field corn inbreds for improving sweet corn performance can be accomplished by a variety of methods. Our objectives were to identify American and European field corn inbreds adapted to European conditions as potential donors for improving yield and agronomic performance of sweet corn hybrids, and to provide additional information on the relationships among different estimators of favorable alleles when the donor fines show better performance than the inbred lines to be improved. Eleven field corn inbreds were crossed to seven sweet corn inbreds that were parents of seven sweet corn hybrids. The field x sweet corn hybrids and inbreds were evaluated separately in field trials at two locations in northwestern Spain in 1993 and 1994. Yield and four agronomic traits were recorded. Estimates of the relative number of alleles at six classes of loci (B, C, D, E, F, and G) were computed, and the methods for identifying field corn inbreds with favorable alleles were an estimate of favorable dominant alleles present in the donor but not in the hybrid (μG′), predicted three-way cross (PTC), minimum upper bound (UBND), net improvement (N!), probability of net gain of favorable alleles given complete dominance (PN[G.sub.g]) and given partial dominance or complementary epistasis (PN[G.sub.ceg]), and general combining ability (GCA). Correlations between ΜG′, UBND, PTC, NI, and GCA were very high for all traits. The field corn inbreds A632, EP42, and EP29 were identified as the best potential donors for improving yield and several yield components of sweet corn hybrids. European flint inbreds offer new possibilities for improving the agronomic value of sweet corn and its adaptation to cold areas with short growing seasons., Sweet corn has a poor agronomic value compared with field corn. Field corn has been used to improve the agronomic performance of sweet corn in the USA (Tracy, 1994) and [...]

Sweet corn (Zea mays L.) has been intensively selected for quality and appearance, whereas less effort has gone into improving yield. Acceptance of sweet corn in Europe has increased in the last 10 yr. However, in regions with cool and humid springs and short growing seasons, sweet corn planting is still limited. Identification of donor parents useful for improving sweet corn hybrids would be greatly beneficial for sweet corn breeding programs. The objectives of this study were to identify field corn populations to increase yield in four sweet corn hybrids and to compare different methods for identifying populations with the greatest number of favorable alleles for yield and its components. Ten maize populations were crossed to five sweet corn inbreds. The 50 crosses along with five inbred parents, four sweet corn hybrids, and ten populations were evaluated in two locations in northwestern Spain in 1992 and 1993. Six estimators of relative number of favorable alleles [, predicted three-way cross (PTC), minimum upper bound (UBND), net improvement (NI), probabilities of net gain of favorable alleles given complete dominance, and probabilities of net gain of favorable alleles given partial dominance or complementary epistasis] and general combining ability were calculated. The U.S. synthetic AS-3(HT)C3 and the northwestern Spanish populations Tuy and Oroso could improve yield and other yield components in sweet corn hybrids. However, European flint corn populations, such as Tuy and Oroso, should have less detrimental effect on kernel quality than U.S. dent populations. Moreover, European flint corn should be better adapted to cool and wet springs and short growing seasons. The , PTC, UBND, and NI statistics identified the same populations as the best donors., ---------- Please note: Some tables or figures were omitted from this [...]

Reports of estimates of components of genetic variance in open pollinated populations of maize (Zea mays L.) have been mostly on U.S. Corn Belt germplasm, whereas few studies have been conducted using European germplasm. This study was undertaken to obtain estimates of genetic parameters for important agronomic traits in two populations (Ribadumia and Tuy) from northwestern Spain. Full-sib within half-sib groups were developed by the Design I mating system and evaluated at two locations in Spain in 1987 and 1988. The populations showed a similar genetic structure with very small differences. Moreover, the pattern of genetic variability was similar to other germplasm because the greatest proportion of total genetic variance was attributed to additive effects for most traits. In contrast, estimates of dominance variance were large for yield, ear, and plant height and ear length. In general, additive x environment interaction variances were significant while dominance x environment interaction variances were not significant for either population. The large range of variation and the high values of heritability for lodging and ear and kernels traits, as well as values of expected gain from selection for these traits, suggested good potential for improvement through an intrapopulation selection program. However, the large dominance effects and the small additive effects for grain yield indicated that an interpopulation selection program would be effective if the large intrapopulation dominance variance is expressed in population crosses. Yield did not show significant additive variance so estimates of additive correlation with any trait were not calculated. Correlated response between yield and any trait is not expected and improved grain yield based on indirect selection of yield components is not recommended.

The most important insect pest of maize (Zea mays L.) in southern Europe is the pink stem borer (Sesamia nonagrioides Lef.). The objective of this work was to identify sources of resistance to stem and ear damage by the pink stem borer. One hundred twenty-one inbreds from seven germplasm groups (American, Argentine, European, Lancaster, Northern Flint, Reid, and Other), divided according to their maturity grouping (very early, early, midseason, and late), were evaluated for several years under artificial infestation at Pontevedra (northwestern Spain). Twelve traits were recorded to measure stem and ear damage. Stem and ear damage resistance traits were not correlated, therefore simultaneous selection for the two types of resistance within the same population should be carried out. Eight very early, two early, seven midseason, and four late inbreds were resistant to stem-damage. The Reid germplasm group was more resistant to stem attack than the other groups. Therefore, the best Reid inbreds could be used to form a stem-damage resistant Reid synthetic, which could be a source of new stem-damage resistant varieties. Simultaneously, the best non-Reid inbreds could be used for making a non-Reid stem-damage resistant synthetic. Thirteen very early, 10 early, two midseason, and three late inbreds performed better than the others against ear attack. Only seven inbreds (A509, A635, CO125, EA2024, EP39, Oh43, and PB130) were resistant to both stem and ear damage. These inbreds could be used as sources of resistance to pink stem borer in a breeding program., In Southern Europe, the pink stem borer causes significant maize damage and, under the environmental conditions of northwestern Spain, this insect is the major borer pest (Anglade, 1972; Malvar et [...]

Investigates the inheritance of cold tolerance at emergence and during early season growth in corn in Spain. Lack of relation of percentage emergence to other traits; Conformation of the genetic regulation to the additive-dominance model; Possibility of combining high percent emergence and vigorous seedling growth.

Estimates the general combining ability (GCA), specific combining ability and reciprocal effects for stem damage traits, yield and yield loss by a complete diallel of 10 inbreds to determine the most useful trait for evaluating the resistance of corn to pink stem borer. Effects important to stem antibiosis; Significance of GCA for all stem damage traits.