Lancaster Sure Research Articles

Solid-state fermentation of corn to make Chinese liquor: Effect of corn variety and dynamic microbial community variation

This study aims to evaluate the impact of different corn varieties (Lancaster Sure Crop-LSC, Hickory King White-HKW, and Yellow Dent Corn-YDC) on baijiu fermentation especially focusing on ethanol yield and flavor compounds) and characteristics of dried distillers grains (DDG); and reveal the relationship between flavor compounds and the microbial community in baijiu fermentation. The results showed that LSC generated the highest ethanol (14.73%, v/v) and least methanol (6.6 g/L) concentrations in zaopei (fermented grains before distillation) among the three studied varieties. The DDG from the LSC variety had higher protein (21.14%) and fat (12.20%) contents (dry weight basis) compared to the other two varieties. The results of High-throughput sequencing indicated that both Bacillus and Weissella were dominant bacteria, while Saccharomyces, Saccharmycopsis, and Rhizopus were predominant fungi in all zaopei. In addition, 17 different flavor compounds were found in zaopei, including esters, alcohols, acids, and phenolics. Based on the Pearson correlation analysis, Bacillus, Pediococcus, Leuconostoc, Enterococcus, Weissella, and Pseudomonas, along with Saccharomyces, Saccharmycopsis, Rhizopus, and Mucor fungi, played significant roles in the formation of flavor compounds. These findings deepen our understanding of the microbial contribution to flavor compounds and will help improve baijiu quality.

Temperate testers’ efficiency in the screening of tropical and subtropical maize germplasm

Despite much effort, little exotic germplasm has been introduced in temperate maize breeding programs. Tropical and subtropical maize germplasm from CIMMYT is the most genetically diverse in the world and should be useful in widening the genetic base of temperate maize germplasm. Extracting the most suitable material from exotic germplasm is a tough challenge for plant breeding programs. This study aimed to determine the optimal number of testers to screen a maize line derived from tropical and subtropical CIMMYT germplasm. For this purpose, four temperate maize testers (MO17, B73, K47/3, and K18) and nine lines from CIMMYT were crossed. The 36 crosses along with two hybrid checks were assessed in a randomized complete block design with three replications at four maize growing regions in Iran. The GGE biplot procedure and methodology proposed by Fan et al. (2010) were used to analyze the results indicating a possibility of direct use of 2, 3, 4, and 9 CIMMYT lines to improve grain yield in temperate environments. Temperate maize testers B73 and K47/3, which belong to the Reid Yellow Dent heterotic group, were very efficient in selecting superior tropical and subtropical CIMMYT germplasm, whereas testers MO17 and K18 from the Lancaster Sure Crop heterotic group were fairly good and weak, respectively. Actually just one temperate tester could select most, if not all, of the top exotic tropical and subtropical lines, and a second tester would provide backup.

Comparing the efficiency of the three heterotic-group and traditional two heterotic-group classifications for the hybrid maize breeding

Increasing the efficiency of the hybrid-based maize breeding program has highly contributed to the heterotic group classification. The present study was aimed to compare the breeding efficiency of the three heterotic-group (TriHG) classification [Lancaster Sure Crop (LSC), Reid Yellow Dent (RYD), CIMMYT] system and usual two heterotic-group (DiHG) classification (RYD, LSC) system. To accomplish this, specific breeding efficiency (SBE) and general breeding efficiency (GBE) were estimated for the grain yield. The mating design was a line × tester scheme in which seven adapted tropical and subtropical lines were crossed to four testers. GBE increased by 128% in the TriHG classification system as compared to the DiHG system while no significant loss was observed in SBE. It seems that the TriHG system was advantageous over the DiHG system by improving the maize breeding efficiency. Therefore, using one tester from each of the three heterotic groups (RYD, LSC, CIMMYT) could be more efficient in hybrid-based maize breeding programs in temperate regions, including Iran.

Arbuscular mycorrhiza improved drought tolerance of maize seedlings by altering photosystem II efficiency and the levels of key metabolites

BackgroundWater shortage can limit plant growth, which can be ameliorated by arbuscular mycorrhizal (AM) symbiosis through physiological and metabolic regulations. Deciphering which physiological and metabolic processes are central for AM-mediated regulations is essential for applications of mycorrhizal biotechnology in dryland agriculture.MethodologyIn this study, the influence of AM symbiosis on growth performance, photosynthesis, and organ accumulation of key C and N metabolites were assessed by growing maize (Mo17, Lancaster Sure Crop) seedlings inoculated with or without AM fungus (Rhizophagus irregularis Schenck & Smith BGC AH01) under different water regimes in greenhouse.ResultsDrought stress reduced shoot growth, while AM symbiosis significantly improved growth performances, with significant changes of photochemical processes and organ concentration of the key metabolites. AM symbiosis increased root levels of the metabolites in ornithine cycle and unsaturation of fatty acids regardless of water conditions. Root putrescine (Put) concentration was higher in AM than non-inoculated (NM) plants under well-watered conditions; the conversion of Put via diamine oxidase to γ-aminobutyric acid (GABA) occurred in roots of AM plants under drought stress. Leaf concentration of Put, the tricarboxylic acids, and soluble sugars significantly increased in AM plants under drought stress, showing higher values compared to that of NM plants. Moreover, photosystem II efficiency and chlorophyll concentration were higher in AM than NM plants regardless of water status.ConclusionFatty acid- and ornithine cycle-related metabolites along with soluble sugars, Put, and GABA were the key metabolites of AM-mediated regulations in response to drought stress.

Association analysis of agronomic traits with microsatellites in maize inbred lines

Association analysis or linkage disequilibrium mapping is a method for identification of quantitative trait loci (QTLs) in a panel of divergent unrelated individuals based on historical recombinations during a crop?s domestication and selection. It should account for the population structure, which can be the result of adaptation to local conditions or selection, to reduce the possibility of declaring false-positive associations. The aim of this study was to determine potentially significant and consistent associations between markers and agronomic important maize (Zea mays L.) traits using association analysis in a diverse breeding material that can be ultimately implemented in maize selection. To this end, 96 maize inbred lines were evaluated in field trials at three locations in Serbia for eleven agronomic traits and analysed with microsatellite markers. Twenty five microsatellites were used to assess the population structure using Bayesian model-based clustering method and to test the significance of associations between the markers and the traits with general (GLM) and mixed linear (MLM) models. The cluster analysis divided maize inbred lines in four subpopulations, corresponding to the BSSS (Iowa Stiff Stalk Synthetic), LSC (Lancaster Sure Crop), Iodent heterotic groups and exotic and independent germplasm. The models identified associations between twenty five microsatellite markers and eleven agronomic traits, resulting in 133 and 71 associations across the environments for GLM and MLM, respectively. Some of the identified marker-trait associations were significant and consistent in several environments. The associations stable in several environments were identified between the markers bnlg1067 and two flowering traits; nc005 and bnlg434 and plant height, bnlg434 and ear height; bnlg1643 and umc1127 and leaf number, bnlg1360 and ear diameter; umc1019 and umc1506 and number of rows per ear; bnlg2305 and bnlg1451 and ear length, and between bnlg1175 and thousand-kernel weight. The results of this study indicate that these microsatellites could be used in marker-assisted selection of inbred lines, after validation of the marker-trait associations and testing combining abilities of the inbreds during hybrid development.

Array-based genotyping and genetic dissimilarity analysis of a set of maize inbred lines belonging to different heterotic groups

Here we describe the results of the detailed array-based genotyping obtained by using the Illumina MaizeSNP50 BeadChip of eleven inbred lines belonging to different heterotic groups relevant for maize breeding in Southeast Europe - European Corn Belt. The objectives of this study were to assess the utility of the MaizeSNP50 BeadChip platform by determining its descriptive power and to assess genetic dissimilarity of the inbred lines. The distribution of the SNPs was found not completely uniform among chromosomes, but average call rate was very high (97.9%) and number of polymorphic loci was 33200 out of 50074 SNPs with known mapping position indicating descriptive power of the MaizeSNP50 BeadChip. The dendrogram obtained from UPGMA cluster analysis as well as principal component analysis (PCA) confirmed pedigree information, undoubtedly distinguishing lines according to their background in two population varieties of Reid Yellow Dent and Lancaster Sure Crop. Dissimilarity analysis showed that all of the inbred lines could be distinguished from each other. Whereas cluster analysis did not definitely differentiate Mo17 and Ohio inbred lines, PCA revealed clear genetic differences between them. The studied inbred lines were confirmed to be genetically diverse, representing a large proportion of the genetic variation occurring in two maize heterotic groups.

Fine genetic characterization of elite maize germplasm using high-throughput SNP genotyping

To investigate the genetic structure of Chinese maize germplasm, the MaizeSNP50 BeadChip with 56,110 single nucleotide polymorphisms (SNPs) was used to genotype a collection of 367 inbred lines widely used in maize breeding of China. A total of 41,819 informative SNPs with minor allele number of more than 0.05 were used to estimate the genetic diversity, relatedness, and linkage disequilibrium (LD) decay. Totally 1,015 SNPs evenly distributed in the genome were selected randomly to evaluate the population structure of these accessions. Results showed that two main groups could be determined i.e., the introduced germplasm and the local germplasm. Further, five subgroups corresponding to different heterotic groups, that is, Reid Yellow Dent (Reid), Lancaster Sure Crop (Lancaster), P group (P), Tang Sipingtou (TSPT), and Tem-tropic I group (Tem-tropic I), were determined. The genetic diversity of within subgroups was highest in the Tem-Tropic I and lowest in the P. Most lines in this panel showed limited relatedness with each other. Comparisons of gene diversity showed that there existed some conservative genetic regions in specific subgroups across the ten chromosomes, i.e., seven in the Lancaster, seven in the Reid, six in the TSPT, five in the P, and two in the Tem-Tropical I. In addition, the results also revealed that there existed fifteen conservative regions transmitted from Huangzaosi, an important foundation parent, to its descendants. These are important for further studies since the outcomes may provide clues to understand why Huangzaosi could become a foundation parent in Chinese maize breeding. For the panel of 367 elite lines, average LD distance was 391 kb and varied among different chromosomes as well as in different genomic regions of one chromosome. This analysis uncovered a high natural genetic diversity in the elite maize inbred set, suggesting that the panel can be used in association study, esp. for temperate regions.

Identification of Heterotic Pairs by Full-Sib Reciprocal Recurrent Selection in Maize Synthetic Populations on Turda CompositeA(B)(2) x Turda CompositeB(A)(2)

In the last 40 years, pre-breeding works induced, in more and more centers of maize breeding, full-sib reciprocal recurrent selection programmes to identify some heterotic pairs which can be sources for obtaining performance inbred lines. The aim is to identify the heterotic pairs with the best results according to the yield potential of maize, the breaking and falling resistance, and the grains moisture at the harvesting time. The creation programme of A and B composite population started at ARDS Turda in 1985. Inside of A composite came the next inbred lines: B73, A632, M117, TC209, T291, being from the B SSS heterotic group, and inside of B composite came the inbred lines Mo17, C103, TC 208, T248, W633, appreciated by us or being related to Lancaster Sure Crop heterotic group. The experimentation was done in two orientation comparative cultures, each one with 49 variants, in 4 repetitions; the comparative culture was a balanced quadratic grid of 7x7 type. From each culture were chosen the first six variants, which were evaluated according to the next characters: production potential, breaking and falling resistance, grains moisture at harvest. The presented results are a part from the second cycle of full-sib reciprocal recurrent selection. Test crosses and self-pollinations were made on plants from the two composites which had two cobs; on the first cob from A Composite realised the cross with the corresponding plant from the B Composite, and from the plant panicle of the B Composite was collected pollen to pollinate the chosen plant from the A Composite. At the both plants from the crossing, the second cob was self-pollinated and kept in reserve until 2010, when the test crosses was experimented and were selected the pairs with the best results according to the above characters. Using the full-sib reciprocal recurrent selection, we can successfully harnessing, simultaneously, the additive and non-additive gene effects.

Broadening the Genetic Base of Chinese Maize Heterotic Pools with Exotic Germplasm

ABSTRACTIntrogression of elite exotic maize (Zea mays L.) germplasm into breeding programs would increase genetic variation within heterotic groups and counter the narrowing of the Chinese germplasm base. This study measured the performance of exotic populations in northern China to allow use of elite germplasm to broaden the genetic base of Chinese germplasm. Fifteen International Maize and Wheat Improvement Center (CIMMYT) and U.S. populations were testcrossed with Csyn 5, Cpop.11, and Cpop.12, which represent Chinese Sipingtou, Lancaster Sure crop, and Reid Yellow Dent subgroups, respectively. Forty‐five testcrosses and 18 populations were evaluated using Miranda Filho and Geraldi's analysis for variety effects and combining ability for grain yield, stalk lodging, ear height, and days to silking in northern China. The results indicated that additive genetic effects were more important than nonadditive genetic effects for all traits measured. Pop28 and BS29 were most adapted to northern China for grain yield and other adaptation traits, and Pool 26, Pop32, Tuxpeño, and Suwan 1 exhibited more favorable alleles for stalk lodging tolerance and high yield potential. We propose to introgress Pool 26 and Suwan 1 into Sipingtou, BS29 and Pop32 into Lancaster, and Pop28 and Tuxpeño into Reid to enrich the genetic base of Chinese heterotic pools.

Breeding Potential of Elite Maize Landraces to Improve Forage Yield and Quality of Two Heterotic Patterns

Breeders recognize that the maize (Zea mays L.) germplasm base is narrow and consequently, it should be extended by the introgression of exotic germplasm. Several studies have explored the potential of open‐pollinated populations to improve grain yield, disease resistances, and other traits, but few have considered traits related to forage yield and quality. In the present study, a group of elite landraces were evaluated as sources of favorable alleles to improve two target hybrids representing two heterotic patterns, Stiff Stalk Synthetic × Lancaster Sure Crop (B73 × Mo17) and Stiff Stalk Synthetic × Argentine Orange Flint (B73 × LP122‐2). Inbred lines B73, Mo17, and LP122‐2, single crosses B73 × Mo17 and B73 × LP122‐2, and 24 inbred × landrace crosses were evaluated in four environments for stover dry matter yield (SY), ear dry matter yield (EY), in vitro digestibility of stover dry matter (iDS), and in vitro digestibility of ear dry matter (iDE). Several landraces are a potential source of favorable alleles not present in the parent inbred lines of both target hybrids for SY, EY, and iDE. ARZM17035 is the most promising landrace since it has favorable alleles for all traits not present in both target hybrids. The results indicate that landraces represent a potential source of useful genetic variability to improve forage maize.

Breeding potential of early-maturing flint maize germplasm adapted to temperate conditions

Early-maturing flint maize germplasm could be an important alternative for the development of new early-maturing commercial hybrids adapted to cooler summer regions. Our objective was to evaluate the performance of flint populations in crosses with four testers from different heterotic groups, as sources of new potential inbred lines. Ten flint maize populations were crossed to four inbred testers representing Reid Yellow Dent, Lancaster Sure Crop and two Spanish flint heterotic groups. Topcrosses were evaluated in four environments in north eastern Spain in 2001 and 2002. The main type of gene action expressed was additive. All populations except Enano Norteño/Vasco and Hembrilla Norteño/Vasco, had a higher specific combining ability in crosses with Reid Yellow Dent or Lancaster Sure Crop testers. Average yields were better when populations were crossed with dent lines rather than with the flint inbred line EP42. These results could be useful in the development of new inbred lines that would increase genetic variability present in commercial European flint maize.

High congruency of QTL positions for heterosis of grain yield in three crosses of maize

The genetic basis of heterosis in maize has been investigated in a number of studies but results have not been conclusive. Here, we compare quantitative trait loci (QTL) mapping results for grain yield, grain moisture, and plant height from three populations derived from crosses of the heterotic pattern Iowa Stiff Stalk Synthetic x Lancaster Sure Crop, investigated with the Design III, and analyzed with advanced statistical methods specifically developed to examine the genetic basis of mid-parent heterosis (MPH). In two populations, QTL analyses were conducted with a joint fit of linear transformations Z (1) (trait mean across pairs of backcross progenies) and Z (2) (half the trait difference between pairs of backcross progenies) to estimate augmented additive and augmented dominance effects of each QTL, as well as their ratio. QTL results for the third population were obtained from the literature. For Z (2) of grain yield, congruency of QTL positions was high across populations, and a large proportion of the genetic variance (~70%) was accounted for by QTL. This was not the case for Z (1) or the other two traits. Further, almost all congruent grain yield QTL were located in the same or an adjacent bin encompassing the centromere. We conclude that different alleles have been fixed in each heterotic pool, which in combination with allele(s) from the opposite heterotic pool lead to high MPH for grain yield. Their positive interactions very likely form the base line for the superior performance of the heterotic pattern under study.

Inferring Genome Ancestry and Estimating Molecular Relatedness Among 187 Chinese Maize Inbred Lines

The inference of genome ancestry and the estimation of molecular relatedness are of great importance for breeding efficiency and association studies. Seventy SSR loci, evenly distributed in 10 chromosomes, were assayed for polymorphism among 187 commonly used maize ( Zea mays L.) inbreds which represent the genetic diversity in China. The identified 290 alleles served as raw data for estimating population structure using the coalescent linked loci, based on the ADMIXTURE model. Population number, K, has been inferred to be between five and seven. Specifying five subpopulations ( K = 5) led to a distinct decrease and specifying K to be greater than six resulted in only minimal increases in the likelihood value. Therefore, population number, K, has been inferred into six subpopulations, which are PA, BSSS (includes Reid), PB, Lan (Lancaster Sure Crop), LRC (Luda Reb Cob, a Chinese landrace, and its derivatives), and SPT (Si-ping-tou, a Chinese landrace and its derivatives). The Kullback-Leibler distance of pairwise subpopulation was also inferred as n × p (187 × 6) Q matrices, which gave a detailed percentage of genetic composition of six subpopulations and molecular relatedness of each line. The genome-wide linkage disequilibrium (LD) indicated that the association studies in QTLs and/or candidate genes might avoid nonfunctional and spurious associations, as most of the LD blocks were broken among diverse germplasm. The defined population structure has given us a clear genetic structure of these lines for breeding practice and established a good basis for association analysis.

Classification of North Dakota maize inbred lines into heterotic groups based on molecular and testcross data

Establishment of the best combination among heterotic groups, heterotic patterns, is crucial to the development of successful maize (Zea Mays L.) hybrids. The use of molecular markers in maize-breeding programs might or might not increase the efficiency of heterosis prediction by classifying diverse inbred lines into heterotic groups. The objectives of present research were to classify elite North Dakota (ND) maize inbred lines into heterotic groups and evaluate the consistency between simple sequence repeat (SSR) grouping and testcross data. Thirteen ND inbred lines representing diverse genetic background were crossed in a diallel mating design in 2000. The crosses and 12 checks were evaluated across four ND environments in 2001 and 2002. In addition, these lines were crossed to commercial inbred testers representing known heterotic groups in 2002. Hybrids between public and private lines were evaluated across three ND environments in 2003. Inbred lines representing Lancaster Sure Crop, Iowa Stiff Stalk Synthetic (BSSS), Minnesota #13, Northwestern Dent, Golden Glow pedigrees and ND inbred lines were screened with 49 SSR markers. Inbred lines ND246, ND278, ND280, ND281, ND282 and ND284 were clustered within the BSSS heterotic group. Inbreds ND277, ND285, ND286, ND290, and ND291 grouped closer to the Lancaster Sure Crop heterotic group. Inbred lines ND257 and ND288 grouped within Minnesota #13. Data from ND278 and ND290 testcrosses showed good combining ability with testers representing more than one heterotic group. Our research shows that groups of genetically similar germplasm could not be identified accurately and reliably with molecular markers even when the available germplasm was diverse contrary what has been suggested. Therefore, extensive field evaluation is recommended to classify unrelated inbred lines of maize.

Alternative Maize Heterotic Patterns for the Northern Corn Belt

Development of maize (Zea mays L.) inbred lines is based on the identification and utilization of heterotic groups and patterns. The objective of this research was to identify alternative heterotic patterns for the northern Corn Belt. Ten maize populations [BS5, BS21(R)C7, BS22(R)C7, CGL(S1–S2)C5, CGSS(S1–S2)C5, LEAMING(S)C4, NDSAB(MER)C12, NDSCD(M)C10, NDSG(M)C15, and NDSM(M)C7] were crossed in a diallel mating design. The 45 F1 crosses along with nine checks were evaluated in experiments with two replicates at each of four North Dakota and three Iowa locations in 2002. Data were collected for grain yield, harvest grain moisture, and root and stalk lodging. Analyses of variance were performed following the Gardner and Eberhart Analysis III model. Differences among genotypes existed for all of the traits, and the general combining ability (GCA) sums of squares were larger than the specific combining ability (SCA) sums of squares, indicating the predominance of additive genetic effects. Alternative heterotic patterns to ‘Iowa Stiff Stalk Synthetic’ (BSSS) × ‘Lancaster Sure Crop’ (LSC) were found for grain yield among early‐maturing populations. The most promising crosses were those in which BS21(R)C7 was combined with CGL(S1–S2)C5, BS22(R)C7, NDSG(M)C15, LEAMING(S)C4, CGSS(S1–S2)C5, and NDSAB(MER)C12, and the heterotic pattern formed by BS22(R)C7 and LEAMING(S)C4. A strong association was found between the grain yield of populations per se and their GCA for harvest grain moisture. The population CGSS(S1–S2)C5 was the earliest among the 10 populations studied and had the best GCA value for grain moisture.

Use of SSR data to determine relationships and potential heterotic groupings within medium to late maturing Iranian maize inbred lines

Information on germplasm diversity and relationships among elite materials is fundamentally important in crop improvement. The main objectives of our study were to: (1) determine the level of genetic diversity within and relationships among the most commonly used medium to late maturing Iranian maize inbred lines using simple sequence repeat (SSR) markers, and to (2) suggest heterotic groups among the lines using genetic distance as measured by the SSR markers. Fifty-six inbred lines, which are the most commonly used in maize breeding programs in Iran, and two lines from CIMMYT, Mexico (used as checks) were fingerprinted with 46 SSR markers. A total of 225 alleles were detected. The UPGMA clustering grouped the Iranian inbreds into four clusters (in addition to one group which included only the CIMMYT control lines), which were consistent with the pedigrees or known information about source materials. The highest distance was found between the cluster of Reid Yellow Dent related lines and the cluster of Lancaster Sure Crop related lines, and this pattern has produced some of the highest yielding hybrids in Iran. Other heterotic patterns based on the SSR markers are suggested, but must be field tested to confirm what appears to be promising alternative heterotic patterns.

Improvement Of The M017 Family Of The Lancaster Heterotic Group of Maize

All maize inbreds have been classified into heterotic groups based on pedigree information or combining ability. The Lancaster Sure Crop and BSSS heterotic groups are the most commonly used heterotic pair to developing commercial maize hybrids in central and southern Europe. One of the best middle late hybrids was that between B73 (BSSS) and Mol7 (Lancaster). In the present study, we analyzed the means of test cross grain yield, grain yield per se, ear length, number of grain rows, grain mass, cob diameter, kernal length, kernal width and stem rot of 19 maize inbreds derived from Mo 17 family. The Mo 17 derivative inbreds are characterized by divergence of all the above traits. Two of the 19 inbreds crossed with the B73-type inbred tester 568 had significantly higher grain yield (P<0.05) than the standard hybrid B73×SMol7. Germplasm unrelated to Mo 17 one, namely that originating from the domestic populations Vukovarski Zuti zuban and Zuti zuban, as well as that from the public-domain line N152 brought to the Mo 17 family a longer ear, a larger number of grain rows per ear and a higher potential for grain yield per se and in test crosses with B73 inbred line relative to Mol7.

Background of U.S. Hybrid Corn II

Understanding the history of a crop helps plant breeders select. This paper supplements and corrects Background of U.S. Hybrid Corn (Zea mays L., Crop Sci. 39:601–626). I explain which open‐pollinated cultivars and landmark inbreds persisted into today's hybrids and attempt to explain how and why. I briefly discuss human (artificial) selection, natural selection, and food production. Pedigree background frequencies from 33 elite, 1990s era inbreds directly estimate about 40% of U.S. hybrid corn hectarage and indirectly estimate the rest. I've searched historical records to trace the succession of cultivars and inbreds. Reid Yellow Dent is 51% of the documented U.S. hybrid corn background (Iodent Reid, 13%; Troyer Reid, 12%; Osterland Reid, 11%; Stiff Stalk Synthetic, 8%; Reid per se, 4%; and Funk Reid, 3%). Minnesota 13 is 13%, Lancaster Sure Crop is 13%, Northwestern Dent is 5%, and Leaming Corn is 5%. Five widely adapted, century‐old, open‐pollinated cultivars surpassed in use tens of thousands of genetically divergent cultivars to account for 87% of the known background of today's U.S. hybrid corn. Adaptedness mattered; U.S. corn breeders are adapting a tropical crop to a temperate climate. New, diverse background sources will probably be better adapted to longer daylengths, cooler minimum temperatures, drought, shorter seasons, and improved crop production practices. Selecting for adaptation to these conditions and to improved agronomic production practices will continue to increase yield. Traditional corn breeding methods will continue to accommodate climate change. Plant breeding and crop production research provides plentiful food in the USA.

Background of U.S. Hybrid Corn

Understanding the history of a crop helps plant breeders select. This historical narrative discusses the background of hybrid corn (Zea mays L.) in the USA. It attempts to explain why certain open-pollinated cultivars persisted into today's hybrids. Domesticated corn originated by selecting larger, non-shattering ears in tropical, southern Mexico. Corn moved to temperate areas requiring adaptation to more variable, more stressful conditions. Flint corn arrived in the USA about 1000 BC and dent corn arrived after Columbus 2500 yr later. The first southern Corn Belt of the 1830s (Tennessee, Kentucky, and Virginia) moved northwest (Iowa, Illinois, and Missouri) by 1880; shorter-season, more drought tolerant cultivars were developed. About 1000 open-pollinated cultivars resulted from natural and artificial selection in flint × dent backgrounds. A few cultivars were widely adapted and became popular. Virtually all 1000 cultivars became parents of inbred lines. Yellow corn (containing vitamin A) proved better for feeding; white corn production diminished from 50% in 1920 to 1% of total in 1970. Earlier planting, higher plant densities, more nitrogen application, and wider adaptation affected hybrid selection. Pedigree background frequencies of 33 Pioneer Hi-Bred International Inc. proprietary, elite inbred lines directly estimate background Of >40% of U.S. hybrid corn hectarage and indirectly estimate the rest. Forms of ‘Reid Yellow Dent’(‘Iodent Reid’, ‘Troyer Reid’, ‘Osterland Reid’, ‘Stiff Stalk Synthetic’, Reid Yellow Dent per se, and ‘Funk Yellow Dent Reid’) are 50%. ‘Minnesota 13’ is 13%. ‘Northwestern-Dent’ is 5%. ‘Lancaster Sure Crop’ is 4%. ‘Learning Corn’ is 4%. These cultivars were widely adapted and popular. The results are consistent with evolutionary (adaptation) expectations. Genes for adaptedness to the temperate, U.S. Corn Belt (longer days, cooler minimum temperatures, and shorter, drier, more stressful seasons) were naturally and artificially selected; first, in widely adapted, open-pollinated cultivars then, in widely adapted hybrids. Old cultivar and inbred line background sources, few in number, indicate adaptedness is more important than diversity to increase yield.

Organization of RFLP Diversity among Inbred Lines of Maize Representing the Most Significant Heterotic Groups

One hundred‐sixteen inbred lines of maize (Zea mays L.) from significant heterotic groups (i.e., European flint, Lancaster Sure Crop, Minnesota 13, and Reid Yellow Dent) and miscellaneous origins were assayed for restriction fragment length polymorphism (RFLP). Our goals were to investigate (i) genetic variability and its structure among and within heterotic groups and (ii) the use of RFLP markers to assign miscellaneous lines to heterotic groups by means of probes selected for locus specificity, clear patterns, and reproducibility. Among the 63 single copy probe‐enzyme combinations used, 372 variants were scored with a mean of 5.9 variants per combination. Principal component and cluster analyses performed on lines from established heterotic groups clearly separated flint lines from dent lines. Loci that contributed the most to the genetic differentiation between European flint and northern U.S. dent lines were determined. Within U.S. germplasm, classification showed an association of inbreds that closely matched associations based on pedigree relationships. Correlation between pedigree distance and molecular Rogers' distance was significant (r = 0.77, P &lt; 0.001). Based on these results, classification by molecular distance was convenient (i) for identifying heterotic groups and (ii) for assigning origins to unknown or broadly based inbreds. This information should prove useful for choosing (i) combinations of inbreds to be evaluated in hybrid trials and (ii) parents for breeding programs.