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Wisconsin Quality Synthetic (WQS) is a maize population that has undergone four cycles of S2–topcross selection for increased silage yield and feed quality. This study evaluated forage yield and quality for each cycle of WQS per se as well as testcrosses to two Stiff Stalk‐type testers. Linear improvement was seen in whole‐plant yield, stover yield, and whole‐plant quality both in the population per se and in testcrosses. Stover quality has not improved through selection. Starch content has increased while crude protein has decreased. Milk yields on a Mg dry matter and hectare basis have increased with selection. Changes in silage dry matter yield have been greater on a percent basis than changes in silage quality, suggesting that the current selection protocol of selecting S2–topcrosses first for yield then for quality may be more efficient at improving yield than quality. Selection directly focused on stover quality may be necessary if more rapid improvement in stover composition is desired.

Maize hybrids with improved stover yield and quality are needed to support the emerging cellulosic biofuels industry. Knowledge of the genetic variation, covariation, and genetic architecture of agronomic and cell wall traits will help maize breeders improve relevant traits through selective breeding and genetic engineering. We utilized the maize intermated B73 × Mo17 (IBM) recombinant inbred line (RIL) population to map quantitative trait loci (QTL) and to evaluate the genetic relationships among traits relevant for cellulosic biofuel production, including grain yield, stover yield, neutral detergent fiber digestibility (NDFD), and glucan, xylan, and lignin concentration. Intermated B73 × Mo17 RIL were evaluated per se and as testcrosses to W604S to assess how well performance and QTL effects correspond between inbreds and hybrids. There were no unfavorable correlations between agronomic and cell wall traits within the testcross progeny. Polysaccharide content was either positively correlated to, or not correlated to, NDFD, indicating that increasing both carbohydrate content and convertibility is feasible. Quantitative trait loci were identified for all traits evaluated, but few QTL were in common between inbred per se and testcross evaluations despite moderate to high genotypic correlations between progeny types. This study provides information that will support the development of dual‐purpose maize hybrids that are high in grain yield and also high in yield of digestible cellulosic feedstock.

The use of maize (Zea maysL.) stover as a feedstock for cellulosic biofuels production will create demand for maize hybrids with greater stover yield. It is expected that grain yield will remain the most critical trait and continue to drive hybrid sales, requiring that any increases in stover yield be made without sacrificing grain yield potential. The objective of this review was to determine the relationship between grain yield, harvest index, and stover yield to illuminate the potential for increasing both grain and stover yield through breeding. In contrast to what has been observed in other crops, gains in maize grain yield over time in the U.S. Corn Belt have been accompanied by increases in stover yield. Where recurrent selection on grain yield has been most successful, stover yield also increased while harvest index has been relatively stable. The opposite situation has been observed in tropical germplasm, where gains in grain yield have been associated with increasing harvest index and relatively constant biomass yield. We expect that stover yield of Corn Belt hybrids will continue to increase along with grain yield, resulting in future hybrids capable of producing both more food and biofeedstock for energy production. If maize breeders pursue selection for increased stover yield, we found no evidence to suggest that breeding for stover yield will necessarily reduce rate of gain in grain yield.

Maize (Zea maysL.) stover has been identified as an important feedstock for the production of cellulosic ethanol. Our objectives were to measure hybrid effect and combining ability patterns of traits related to cellulosic ethanol production, determine if germplasm and mutations used for silage production would also be beneficial for feedstock production, and examine relationships between traits that are relevant to selective breeding. We evaluated grain hybrids, germplasm bred for silage production, brown‐midrib hybrids, and a leafy hybrid. Yield and composition traits were measured in four environments. There was a 53% difference in stover yield between commercial grain hybrids that were equivalent for other production‐related traits. Silage germplasm may be useful for increasing stover yield and reducing lignin concentration. We found much more variation among hybrids than either in vitro ruminal fermentability or polysaccharide concentration. Correlations between traits were mostly favorable or nonexistent. Our results suggest that utilizing standing genetic variation of maize in breeding programs could substantially increase the amount of biofuels produced from stover per unit area of land.

The open‐pollinated maize (Zea mayssubsp. mays) population Golden Glow [GG(MP)] provides excellent material for the study of morphological and genetic changes associated with selection for prolificacy. Late generations of the GG(MP), when planted at low densities, resemble the architecture of teosinte (Z. mayssubsp. parviglumis), the ancestor of maize. Our objectives were (i) to identify molecular markers linked to chromosomal regions that influenced prolificacy and related morphological traits, (ii) to determine whether genes previously shown to influence branching patterns in maize were associated with quantitative trait loci (QTLs) influencing these traits, and (iii) to determine whether epistatic interactions among putative QTLs influenced prolificacy and correlated traits. A mapping population was developed from the cross of inbred A679 and a highly prolific S1plant from Cycle 23 of GG(MP). Simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers were combined for the linkage map construction. Thirty‐three QTLs were found for 14 of the 16 traits analyzed. A region located on Linkage Group 1 (LG 1) shared similarities with the pattern of development suggested for the teosinte branched1(tb1) mutant. This suggests that genetic control of prolificacy and associated traits in GG(MP) may resemble the genetic changes underlying branching morphology that occurred during maize domestication. No evidence for additive‐by‐additive epistatic interactions was found.

Prolificacy (the potential to produce ear shoots at multiple nodes on the main stalk) has been under selection since the early domestication of maize (Zea mayssubsp. mays) from teosinte (Z. mayssubsp. parviglumis). Until the early part of the 20th century, before mechanization, human selection may have favored single‐eared maize because it facilitated hand‐harvesting. Prolificacy, however, has the potential to increase stress tolerance under intensive management. Our objectives were (i) to assess variation for prolificacy and 15 related morphological traits in a population of 194 F3families derived from inbred line A679 and a highly prolific S1plant from the cultivar Golden Glow after 23 cycles of mass selection for prolificacy; and (ii) to determine relationships among traits and to infer which ones appear to be controlled by similar genetic factors. Traits were evaluated with two replications in three field environments. The population varied significantly for all traits and most traits had relatively high heritabilities (>0.80). Some traits were highly correlated, and two main groups were identified. These groups involved traits mostly associated with either the activity of axillary meristems, or intercalary meristems. In general, the correlations of traits across these two groups were insignificant or of lesser magnitude than within groups, suggesting that common genetic factors might be influencing some of these morphological traits.

Maize (Zea maysL.) silage is a high‐quality forage for ruminants, but there have been few significant breeding efforts specifically dedicated to improving maize forage yield or quality by breeders in the USA. The objective of this study was to evaluate the forage yield and quality of the Wisconsin Quality Synthetic (WQS) and related populations developed by the University of Wisconsin Maize Breeding Program for agronomic and nutritional attributes. Three cycles of divergent S1recurrent selection have been completed for stover fiber, silica, and lignin concentration for populations WFISIHI (Wisconsin‐fiber‐silica‐high) and WFISILO (Wisconsin‐fiber‐silica‐low). The third cycle (C3) of WFISILO was crossed to two high‐quality inbred lines, Mo17 and H99, to create WQS C0, which then underwent two cycles of S2–topcross selection for improved forage yield and quality. All cycles of selection for WFISIHI, WFISILO, and WQS were evaluated for forage yield and quality at two field locations in Wisconsin in 2000 and 2001. Results for WFISIHI and WFISILO demonstrated that S1selection for stover composition altered both stover and whole‐plant composition in the anticipated directions. Selection for whole‐plant yield and composition of S2–topcrosses was also effective for WQS, especially when using selection indices incorporating whole‐plant yield, neutral detergent fiber (NDF), neutral detergent fiber digestibility (NDFD), crude protein (CP), and starch. WQS C2 whole‐plant and stover in vitro true digestibility (IVTD), whole‐plant and stover acid detergent lignin, and milk yield per megagram dry matter (DM) were similar to the brown‐midrib check hybrid, F657. WQS C2 whole‐plant and stover NDFD were lower than F657 but higher than other commercial check hybrids. In addition, WQS population testcrosses improved over cycles of selection for whole‐plant yield and most quality attributes. Our results indicate that it is feasible to develop silage maize germplasm with both high whole‐plant yield and excellent nutritional quality.

Maize (Zea maysL.) has the potential to produce an ear primordium at several nodes, and selection for increased prolificacy often increases grain yield. We have previously demonstrated the effectiveness of mass selection for increasing the number of active ear shoots in the ‘Golden Glow’ maize population. The objective of our research was to evaluate associated changes in ear and plant morphology after 24 cycles of mass selection for prolificacy in Golden Glow. Cycles 0, 6, 12, 18, 23, and 24 were grown in 1997 at two locations (Madison and Arlington, WI) at two planting densities (15 070 and 73 197 plants ha−1). At the lower planting density, the mean number of ears per plant increased from 1.61 at C0 to 4.93 at C24, and the response rate increased over the more recent cycles, mainly from C18 to C24. At C24, tiller number has increased, and lateral branches (terminating in ears) were located at approximately one node higher and two nodes lower on the main stalk compared with the original population. Total node number on the main stalk increased, and the internode length decreased over the 24 cycles, but the opposite occurred for lateral branches. At the lower planting density, ear diameter, ear length, and kernel size decreased by 0.03, 0.10, and 0.01 cm cycle−1, respectively, but total number of kernels per plant and dry kernel weight per plant increased significantly at a rate of 36.69 kernels cycle−1and 5.60 g cycle−1over the 24 cycles. Similar trends, but of lesser magnitude, were observed at the higher planting density. The changes in plant morphology observed across cycles of selection for prolificacy represent a general derepression of axillary meristematic growth in both main stalks and lateral branches.

Gains in corn (Zea maysL.) grain yield over time are well documented, but corresponding changes in forage and stover yield and quality have received less attention. Our objective was to describe yield and quality changes of representative cultivars used by farmers in the northern Corn Belt. Six open‐pollinated cultivars used prior to 1930, 24 cultivars representing four 15‐yr eras between 1931 and 1990, and six modern cultivars, for a total of 36 cultivars, were divided into early‐ and late‐maturity trials. Each trial was grown at three locations in Wisconsin during 1997 and 1998. Since 1930, corn forage dry matter yield has increased at the rate of 0.128 to 0.164 Mg ha−1yr−1with stover dry matter yields increasing at the rate of 0.043 to 0.054 Mg ha−1yr−1Forage crude protein has not changed significantly with time. Forage neutral detergent fiber concentration has decreased 0.825 to 0.948 g kg−1yr−1, while forage in vitro digestibility increased 0.538 to 0.612 g kg−1yr−1Stover neutral detergent fiber concentration and in vitro digestibility have not changed over time. Since 1930 forage, stover, and ear yield have increased 1.4, 0.7, and 2.4% yr−1, respectively. This trend will no doubt continue, but greater progress might be made if corn forage breeding improvement concentrates on yield and quality changes in stover.

Feeding activities of herbivorous insects are influenced by host plant nutritional quality. Improved insect resistance resulting from either natural or artificial selection may be due, in part, to changes in nutritive constituents of plants. The first objective of this study was to measure changes in detergent fiber, lignin, ash, and N concentrations in whorls, leaf‐sheaths, and stalks of the BS9 maize (Zea maysL.) population across five cycles of selection for resistance to the European corn borer (ECB) [Ostrinia nubilalis(Hübner)]. The second objective was to evaluate ECB resistance in the WFISIHI and WFISILO maize populations, which were developed for high and low concentrations, respectively, of indigestible plant constituents (acid detergent fiber, lignin, and silica) in the leaf sheath. Leafsheath composition for all five cycles of BS9 was measured in three environments in Iowa. Whorl, leaf‐sheath and stalk composition, as well as first‐ and second‐generation ECB resistance of populations WFISIHI, WFISILO and Cycles 0, 2, 4, and 5 of BS9 were evaluated in two environments in Wisconsin. Whorl composition was not related to changes in ECB resistance in anypopulation. In BS9, leaf‐sheath and stalk concentrations of neutral and acid detergent fiber, cellulose, and lignin increased linearly over selection cycles. In contrast, WFISIHI was as susceptible to second‐generation ECB as WFISILO, suggesting that the responses in BS9 may be due to linkage or unintentional selection. Populations BS9, WFISIHI, and WFISILO, however, were derived from diverse sources, and it is likely that mechanisms for resistance differ for the three populations.

Resistant genotypes are the best means of control for Goss's wilt (Corynebacterium micMganensessp. nebraskenseSchuster, Hoff, Mandel, and Lazar) of maize (Zea maysL.). The purpose of this study was to identify susceptible and resistant genotypes and to determine the inheritance of resistance to Goss's wilt using generation means analysis and diallel experiments. Thirty‐nine inbred lines were screened for resistance to Goss's wilt. Sixteen were susceptible, 15 intermediate, and 8 resistant. Four experiments, two generation mean analyses (GMA), and two diallels were used to investigate the inheritance of Goss's wilt. One GMA experiment consisted of the resistant inbred Mol7Ht, the susceptible inbred A634Ht, the F1, F2, and the F1backcrossed to both parents. A second GMA experiment involved resistant MolTHt, susceptible CM105, the F1, F2, and the F1backcrossed to both parents. One diallel had five parents and one six. Additive gene action was important in the generation mean analyses for resistance to Goss's wilt. Year effects and the generations × years interaction were highly significant. In the diallel experiments, general combining ability was highly significant for both, demonstrating the importance of additive gene effects. General combining ability and specific combining ability sums of squares accounted for 97.7 and 2.3% of the variation among crosses, respectively, in the first diallel, and for 91.0 and 9.0% in the secondiallel. The results suggest that recurrent selection should be effective among the maize lines tested for resistance to Goss's wilt in maize.

Selection for prolificacy in maize, Zea maysL., has been recommended as an effective method to improve grain yield. The objective of this study was to evaluate selection response from 12 cycles of biparental mass selection for prolificacy in the Golden Glow maize population as measured under different plant densities and fertility levels. Genotypes evaluated were Cycles 0, 3, 6, 9, and 12, along with testcrosses of Cycles 0, 6, and 12 with three inbred lines, A632, W64A, and W9. The evaluation was conducted in 1985 in low‐fertility plots at two locations and three plant densities (38 271, 53 597, and 68 887 plants ha−1). The evaluation was repeated in 1986 at two fertility levels (no added fertilizer and 168 kg N ha−1with 37 kg K ha−1). Number of ears plant−1in the cycles per se increased by 2.4 and 3.3% cycle−1in 1985 and 1986, respectively. Corresponding increases in grain yield plant−1were 2.0 and 3.0% cycle−1, and increases in grain yield ha−1were 2.0 and 2.8% cycle−1. Grain moisture, flowering dates, and the period between silk emergence and anthesis decreased with selection for cycles per se. Testcross responses were approximately one‐half those of cycles per se for ears plant−1and either measure of grain yield. Grain moisture did not change with selection, and days to flowering increased by 1 to 2 d in the testcrosses. The correlations between ears plant−1and grain yield plant−1were 0.90 and 0.79 for cycles per se and testcrosses, respectively (both significant at P≤ 0.05). Response to selection for ears plant−1, as reflected in the regression of ears plant−1on cycle of selection, was greater under optimum fertility (b= 0.032 ± 0.002) than low fertility (b= 0.022 ± 0.003). Selection response for ears plant−1was progressively greater as plant density decreased (b= 0.016 ± 0.003, 0.027 ± 0.003, and 0.036 ± 0.003 for 68 887, 53 597, and 38 271 plants ha−1, respectively).

Four diverse alfalfa (Medicagospp.) populations were screened in the field for nutritional quality. Acid detergent fiber of composite samples from first and second harvests was used to select for dry matter digestibility. First‐harvest percent transmittance, a Udy dyebinding procedure, was used to estimate crude protein concentration. Comparisons with standard cultivars showed that one cycle of selection was effective in reducing total cell wall, lignin, and amount of cell wall lignification and in increasing crude protein, hemicellulose (when expressed as a fraction of cell wall), in vitro dry matter digestibility, and in vitro cell wall digestibility in three of the four populations. Improved digestibility was associated with an increase in hemicellulose and a decrease in lignin fractions of the cell wall. Cellulose (when expressed as a fraction of the cell wall) did not change with selection. The mean crude protein concentration of the most improved population was 208 g kg−1, and total digestible dry matter was 775 g kg−1as compared to 199 and 756 g kg−1, respectively, measured for the mean of standard cultivars. These differences correspond to an increased crude protein yield of approximately 200 kg ha−1yr−1and an increased digestible dry matter yield of approximately 525 kg ha−1yr−1.

Alfalfa (Medicago sativaL.) is low in soluble carbohydrates, which are required for successful silage preservation. Storing alfalfa as silage could reduce quality losses due to weathering, however. Adding grain high in soluble carbohydrates, such as sugary‐Brawn2 (su‐Bn2) endosperm maize (Zea maysL.), improves silage preservation, and results in higher quality feed. However, certain endosperm mutants, including alleles at the sugary locus, have been shown to reduce grain yields, dry matter production, and possibly photosynthetic rates. Our objective was to determine if su‐Bn2maize hybrids have acceptable yield, ear moisture levels, and stalk and root quality for on‐farm grain production in the northern Corn Belt. Twenty su‐Bn2hybrids and two adapted dent hybrids were grown at three locations in Wisconsin in 1986 and 1987. Data were collected on ear yield, ear moisture, heat units to midpollen and midsilk, plant and ear height, and root and stalk lodging. Yield of the su‐Bn2hybrids ranged from 7.26 to 9.41 Mg ha−1, as compared with 7.96 and 9.40 Mg ha−1, for the two checks. Ear moisture of the su‐Bn2hybrids was higher than that of the checks, although a number of su‐Bn2hybrids had acceptable moisture levels. The su‐Bn2hybrids compared favorably with the checks for plant and ear height, and stalk and root lodging. Maize with su‐Bn2endosperm can be grown successfully in the northern Corn Belt for use as an additive in the ensiling of alfalfa. Management practices and economic aspects need to be further investigated.

Sugary-Brawn2(su-Bn2) corn endosperm contains higher concentrations of water-soluble polysaccharides than dent corn. Eight multiparous Holstein cows averaging 48 d in milk and 667 kg BW at trial initiation were in a replicated 4×4 Latin square design with 28-d periods. Only cows in one square were ruminally cannulated. Treatments were su-Bn2or dent corn and 45 or 60% of ration DM as alfalfa silage arranged as a 2 × 2 factorial within each square. Diets, formulated to contain 19% CP, were fed as total mixed rations twice daily. Intake of DM and milk yield averaged 26.8 and 39.9 kg/d, respectively, and were not affected by treatment (P> .10). Sugary-Brawn2corn decreased milkfat percentage (3.27 vs 3.45%), particularly for the low-forage diet (3.15 vs 3.40%). Milk protein percentage was higher (3.15 vs 3.10%) for low-forage diets but was not affected (P> .10) by corn type. Ruminal pH was lower for low-forage diets. Feeding su-Bn2corn decreased ruminal pH only at 4 h after feeding. Total VFA in ruminal fluid (millimolar) 6 h after feeding were higher, whereas acetate molar percentage and acetate:propionate ratio were lower for su-Bn2corn. Ruminal in situ evaluation of su-Bn2and dent corn revealed a larger soluble fraction, a faster rate of degradation, and higher availabilities of both DM and starch for su-Bn2corn. Ruminal in situ rate of degradation and availability of alfalfa hay DM were reduced by su-Bn2corn. Total tract apparent digestibilities of DM, CP, and starch were greater for su-Bn2diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Effective recurrent selection for intrapopulation improvement in maize (Zea maysL.) should be most effective when both inbred and noninbred progenies are evaluated. The objective of this study was to examine the effectiveness of evaluating both half‐sib (HS) and selfed (S1) families during selection to improve population per performance and inbred productivity. Four cycles of combined HS and S1selection for increased grain yield and reduced grain moisture were completed in a narrow‐based maize population derived from inbred lines; A635, W182E, and W64A. For each cycle, both HS and S1progenies were produced on prolific plants by selfing the bottom ear and exposing the upper ear to random pollen from the population. Half‐sib and S1progenies were then evaluated in separate trials. Plants with superior HS and S1progeny performance, i.e., above average yield and below average grain moisture in both trials, were selected. Half‐sib progeny were used for recombination through the first two cycles. In the third cycle, S1progeny were recombined. Both progeny types were recombined to form two subpopulations in the fourth cycle. Over four selection cycles, yield of the population increased by 3.5% cycle−1, and grain moisture decreased by 1.5% cycle−1. Corresponding increases in yield were not detected in testcrosses with inbred lines A554 and Wl17, but cycle four testcrosses had significantly lower grain moisture than corresponding testcrosses with the initial population. The yield of bulked composites from random, selfpollinated plants increased by 20 g plant‐1 over four cycles. Broad‐sense heritability estimates were 0.34 and 0.76 for HS and S1families, respectively, for yield, and 0.68 and 0.88 for moisture. The genetic covariance of HS and Sa progenies was compared to the variance among HS progenies for grain yield and moisture in order to estimate D1, the covariance of additive and homozygous dominance effects. A large negative value for D̂1for yield, −309±126 g2plant−2, indicated that simultaneous improvement of both inbred and testcross performance may be difficult. However, the magnitude of D̂1may have been affected by linkage disequilibrium in the initial population.

An interactive microcomputer program was developed to provide plant breeders and graduate students in quantitative genetics the opportunity to devise selection strategies and review expected gains for eight intrapopulation selection methods. Selection methods include uniparental and biparental mass selection, three forms of half‐sib selection, full‐sib selection, and S1and S2selection. Users provide estimates of genetic and environmental components of variance, selection intensities, and an array of possible experimental designs including number of environments, number of replicates within environments, and plot size. Expected gains can be expressed as either gain cycle−1, gain year−1, or gain season−1. Help screens are included that explain selection methods and the calculation of expected gains. The program is designed so the user can easily move within it, reenter values for individual variables, and rapidly redisplay results.

Maize (Zea maysL.) hybrids with good yields of grain and wholeplant dry matter are recommended for silage production. The stover can comprise more than 50% of the whole‐plant dry matter and, therefore, can influence dry matter yield and nutritive value of the whole plant. The objective of this study was to determine relationships between agronomic characteristics (stover and whole‐plant forage yield and moisture, grain yield and moisture, lodging, maturity, and ear percentage) and nutritional quality of maize forage in three populations. Twenty‐four S0.1families (S0‐derived families in S1) exhibiting a range in neutral detergent fiber (NDF) and lignin at mid‐flower, were testcrossed to two commercial inbred lines (FR23 and LH74) to form two groups of F1hybrids. A third experimental group was created by self‐pollinating the S0.1families to form S0.2families. This germplasm was evaluated at three environments in Wisconsin. for FR23 testcrosses, grain yield had a correlation coefficient of 0.53 with stover dry matter yield, 0.65 with whole‐plant dry matter yield, and −0.03 with whole‐plant in vitro true digestibility. For LH74 testcrosses, the similar correlation coefficients were 0.46, 0.54, and −0.02, respectively. Also for FR23 testcrosses correlation coefficients of stover yield with whole‐plant yield, NDF, and in vitro true digestibility were 0.89, 0.53, and −0.28, respectively. For LH74 testcrosses the coefficients were, 0.85, 0.40, and −0.48, respectively. The results of this study demonstrate that stover yield and nutritional quality are important factors influencing whole‐plant yield and nutritional quality of maize forage.

An understanding of the factors and relationships affecting wholeplant digestibility is needed to improve the nutritional quality of maize (Zea maysL.) forage. The objectives of this study were to: (i) determine the ranges among 24 maize genotypes for fiber composition and digestibility of stover and whole‐plant forage, and (ii) determine the relationships between fiber composition and digestibility. Twenty‐four S0.1families (S0‐derived families in S1) exhibiting a range in neutral detergent fiber (NDF) and lignin at mid‐flower, were testcrossed to two commercial inbred lines (FR23 and LH74) to form two groups of F1hybrids. A third experimental group was created by self‐pollinating the S0.1families to form S0.2families. These germplasms were evaluated in three Wisconsin environments. Ranges in S0.2family means for fiber and digestibility were: NDF, 439 to 582 g kg−1for the whole plant and 579 to 654 g kg−1for the stover; and in vitro true digestibility (IVTD), 714 to 820 g kg‐1 for the whole plant and 689 to 757 g kg−1for the stover. Narrower ranges were observed among LH74 and FR23 testcrosses. For S0.2families, correlation coefficients for stover IVTD with stover NDF and lignin were −0.76 and −0.85, respectively. Correlation coefficients for whole‐plant IVTD with stover IVTD and lignin of S0.2families were 0.44 and −0.49, respectively. The results of this study show that (i) significant variation exists for nutritional quality traits of the stover and whole‐plant forage and (ii) stover quality is an important factor influencing whole‐plant nutritional quality within the germplasm studied.

Selection for increased ears per plant may be an effective method for increasing grain yield in maize (Zea maysL.). Since 1970, biparental mass selection for prolificacy has been carried out in the open‐pollinated maize population Golden Glow. The objectives of this study were to (i) evaluate the direct and correlated responses to 20 cycles of mass selection for prolificacy in Golden Glow, and (ii) relate changes prolificacy to the population's performance at different plant population densities. Yield trials were conducted in 1993 at Madison and Arlington, WI, and in 1994 at Madison, Arlington, and Hancock, WI. In each location and year, the trials were grown at four plant population densities: 28 889 plants ha−1; 44 444 plants ha−1; 57 778 plants ha−1; and 73 333 plants ha−1. Ears per plant increased by 3.3% per cycle, from an average of 0.98 ears plant−1for C0 to 1.63 ears plant−1for C20. Grain yield per plant and grain yield per hectare both increased by 1% per cycle, from 126.5 g plant−1and 5.91 Mg ha−1for C0 to 151.9 g plant−1and 7.16 Mg ha−1for C20. Days to midpollen, days to midsilk, silk delay, and grain moisture decreased across cycles of selection. Root lodging decreased while stalk lodging did not change. Number of ears per plant was significantly and positively correlated with both grain yield per plant (r= 0.71) and grain yield per hectare (r= 0.76). The later, more prolific cycles yielded more than the initial population at high plant population density. The principal benefit of prolificacy for Golden Glow is that it may contribute to the population's ability to produce grain under competitive stress.

An understanding of the genetic nature underlying tolerance to low-phosphorus (low-P) stress could aid in the efficient development of tolerant plant strains. The objective of this study was to identify the number of loci in a maize (Zea mays L.) population segregating for tolerance to low-P stress, their approximate location, and the magnitude of their effect.

Two maize (Zea mays L.) populations, AS1(S) and ECR-A, were evaluated for allozyme frequency changes associated with selection for improved seedling emergence, early season vigor and early maturity. Eleven marker loci were examined and four loci were used for indirect selection in an attempt to modify cold tolerance and maturity. Allozyme-selected divergent subpopulations were produced by compositing selected S1 progeny from cycle one (C1) of AS1(S) and from C2 of ECR-A. These subpopulations and S1 generations from all cycles resulting from phenotypic selection, ECR-A C1 through C7 and AS1(S) CO through C6, were tested in cold tolerance and agronomic performance trials over five environments in 1986. Seedling emergence and seedling dry weight did not improve with phenotypic selection in ECR-A, while plant height, ear height, grain yield, grain moisture, days to mid-silk and days to mid-pollen were reduced significantly. Contrasts between divergent allozyme-selected subpopulations from ECR-A were significant for grain moisture and mid-pollen date. For AS1(S), seeding emergence increased, while plant and ear height decreased with phenotypic selection. Contrasts between allozyme-selected subpopulations were significant for plant and ear height. Changes associated with marker-based selection for AS1(S) were not in the same direction as with phenotypic selection. Selection for favorable allozyme genotypes may be effective in changing certain traits in populations that have been modified by direct selection, however results may not be predictable.

The relationship between yield and forage quality of corn (Zea maysL.) is influenced by maturity and strength of reproductive sink. Our objective was to isolate the effect of ear fill alone on stover and whole‐plant quality. Three hybrids (Pioneer Brand 3394, 3417, and 3504) were evaluated in Wisconsin during 1992 and 1993. Developing ear shoots were covered, partially covered, or left uncovered before pollen shed to create three levels of ear fill: 0, 50, and 100%. Wholeplant and stover samples were collected from plants harvested at approximately 300 g kg−1dry matter concentration and evaluated for dry matter yield, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and in vitro true digestibility (VTD). As ear fill increased from 0 to 100%, wholeplant CP decreased by 10 g kg−1, NDF decreased by 86 g kg−1, ADF decreased by 42 g kg−1, ADL decreased by 1 g kg−1, and IVTD increased by 37 g kg−1. For stover, CP decreased by 18 g kg−1, NDF increased by 136 g kg−1, ADF increased by 94 g kg−1, ADL increased by 6 g kg−1, and IVTD decreased by 55 g kg−1. Digestibility of stover NDF increased by 15 g kg−1. An effective ear was clearly necessary to realize maximumto tal dry matter yield and quality.

Breeders have selected for European corn borer [Ostrinia nubilalis(Hubner)] (ECB) resistance for manyears and this may have led to higher concentrations of cell wall carbohydrates and lignin in stalks and leaf sheaths of maize (Zea maysL.). 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 S1family selection for increased first‐ and second‐generation ECB resistance. Cycle 2 of BS9(CB) also underwent one cycle of divergent S1selection for neutral detergent fiber (NDF) and lignin concentrations in the stalk and leaf sheath. Populations WFISILO and WFISIHI underwent two cycles of S1family 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.