Southern rust, caused by Puccinia polysora Underw, is a foliar disease that can severely reduce grain yield in maize (Zea mays L.). Major resistance genes exist, but their effectiveness can be limited in areas where P. polysora is multi-racial. General resistance could be achieved by combining quantitative and race-specific resistances. This would be desirable if the resistance alleles maintained resistance across environments while not increasing plant maturity. Recombinant inbred (RI) lines were derived from a cross between NC300, a temperate-adapted all-tropical line, and B104, an Iowa Stiff Stalk Synthetic line. The RI lines were topcrossed to the tester FR615 x FR697. The 143 topcrosses were scored for Southern rust in four environments. Time to flowering was measured in two environments. The RI lines were genotyped at 113 simple sequence repeat markers and quantitative trait loci (QTL) were mapped for both traits. The entry mean heritability estimate for Southern rust resistance was 0.93. A multiple interval mapping model, including four QTL, accounted for 88% of the variation among average disease ratings. A major QTL located on the short arm of chromosome 10, explained 83% of the phenotypic variation, with the NC300 allele carrying the resistance. Significant (P < 0.001), but relatively minor, topcross-by-environment interaction occurred for Southern rust, and resulted from the interaction of the major QTL with the environment. Maturity and Southern rust rating were slightly correlated, but QTL for the two traits did not co-localize. Resistance was simply inherited in this population and the major QTL is likely a dominant resistant gene that is independent of plant maturity.

The races of southern and eastern South America are described in several of the Races of Maize Bulletins, as well as in a pioneering work by Hugh Cutler. Basically, there appear to be eight essentially distinct types of maize that have contributed to the diversity that has been collected there. These include: (1) a wide assortment of commercial races and some of the more productive Indigenous races that can be subdivided into six subgroups: (a) the commercial dent and semi-dent races of Brazil, Caingang, Moroti, the Brazilian Catetos and Cristals; (b) the Cateto and Cristal Sulinos; (c) Cristalino and Dentado, Comercial from Chile (d) Camelia, the lowland Bolivian Flints and Flours, and the Cateto Nortistas; (e) Canario de Ocho of Uruguay, Cateto Grande, and Moroti Precoce; (f) Tuson from Brazil. Many races of this group appear to be the most valuable for breeding programs. Seven other groups include: (2) Lenha, the Cravos, Cateto Sulino Grosso, and Choclero; (3) the introduced, commercial races, Argentino and Hickory King; (4) Cristalino Norteno, Canario de ocho from Argentina, Dulce Golden Bantam, and Dulce Evergreen from Chile, all apparently related to U.S. Northern Flints such as Longfellow; (5) the races of the highlands of northwestern Argentina, including the Capias, Chulpi, Culli, Oke, Morocho and Harinoso Tarapaqueno from Chile; (6) Curagua and Curagua Grande from Chile; (7) Pororo and the Guarani popcorns, Avati Pichinga and Avati Pichinga Ihu; (8) The interlocked races from the interior lowlands, Entrelacado, Piricinco, and the Coroicos. Araucano from Chile and Cateto Sulino Precoce from Argentina do not show clear relationships to the other races studied. This report uses morphological data, geographic data, and isozyme-allele-frequency data to characterize the relationships among previously-described races of maize from the region. Allelic variation among and within races and racial groups is utilized to attempt to infer historical relationships among maize types throughout the region.

Crop ScienceVolume 46, Issue 2 p. 996-998 Registrations of Germplasm Registration of 20 GEM Maize Breeding Germplasm Lines Adapted to the Southern USA P.J. Balint-Kurti, Corresponding Author P.J. Balint-Kurti [email protected] USDA-ARS, Plant Science Research Unit, North Carolina State University, Raleigh, N.C., 27695-7616Author for correspondence ([email protected])Search for more papers by this authorM. Blanco, M. Blanco USDA-ARS, Iowa State University, Ames, IA, 50011Search for more papers by this authorM. Millard, M. Millard North Central Regional Plant Introduction Station (NC7), USDA-ARS & Iowa State University, Ames, IA, 50011Search for more papers by this authorS. Duvick, S. Duvick USDA-ARS, Iowa State University, Ames, IA, 50011Search for more papers by this authorJ. Holland, J. Holland USDA-ARS, Plant Science Research Unit, North Carolina State University, Raleigh, N.C., 27695-7616Search for more papers by this authorM. Clements, M. Clements USDA-ARS Corn Host Plant Resistance Research Unit, Mississippi State, MS, 39762Search for more papers by this authorR. Holley, R. Holley Syngenta Seeds, Inc., Henderson, KY, 42420Search for more papers by this authorM.L. Carson, M.L. Carson USDA-ARS Cereal Disease Lab, Univ. of Minnesota, Saint Paul, MN, 55108Search for more papers by this authorM.M. Goodman, M.M. Goodman Department of Crop Science, North Carolina State University, Raleigh, NC, 27695 Pioneer Hibred, DuPont Agriculture and Nutrition, RR1, Box 90a, Princeton, IN, 47670Search for more papers by this author P.J. Balint-Kurti, Corresponding Author P.J. Balint-Kurti [email protected] USDA-ARS, Plant Science Research Unit, North Carolina State University, Raleigh, N.C., 27695-7616Author for correspondence ([email protected])Search for more papers by this authorM. Blanco, M. Blanco USDA-ARS, Iowa State University, Ames, IA, 50011Search for more papers by this authorM. Millard, M. Millard North Central Regional Plant Introduction Station (NC7), USDA-ARS & Iowa State University, Ames, IA, 50011Search for more papers by this authorS. Duvick, S. Duvick USDA-ARS, Iowa State University, Ames, IA, 50011Search for more papers by this authorJ. Holland, J. Holland USDA-ARS, Plant Science Research Unit, North Carolina State University, Raleigh, N.C., 27695-7616Search for more papers by this authorM. Clements, M. Clements USDA-ARS Corn Host Plant Resistance Research Unit, Mississippi State, MS, 39762Search for more papers by this authorR. Holley, R. Holley Syngenta Seeds, Inc., Henderson, KY, 42420Search for more papers by this authorM.L. Carson, M.L. Carson USDA-ARS Cereal Disease Lab, Univ. of Minnesota, Saint Paul, MN, 55108Search for more papers by this authorM.M. Goodman, M.M. Goodman Department of Crop Science, North Carolina State University, Raleigh, NC, 27695 Pioneer Hibred, DuPont Agriculture and Nutrition, RR1, Box 90a, Princeton, IN, 47670Search for more papers by this author First published: 01 March 2006 https://doi.org/10.2135/cropsci2005.04-0013Citations: 24 Registration by CSSA. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article.Citing Literature Volume46, Issue2March–April 2006Pages 996-998 RelatedInformation

ABSTRACT A recombinant inbred line population derived from a cross between the maize lines NC300 (resistant) and B104 (susceptible) was evaluated for resistance to southern leaf blight (SLB) disease caused by Cochliobolus heterostrophus race O and for days to anthesis in four environments (Clayton, NC, and Tifton, GA, in both 2004 and 2005). Entry mean and average genetic correlations between disease ratings in different environments were high (0.78 to 0.89 and 0.9, respectively) and the overall entry mean heritability for SLB resistance was 0.89. When weighted mean disease ratings were fitted to a model using multiple interval mapping, seven potential quantitative trait loci (QTL) were identified, the two strongest being on chromosomes 3 (bin 3.04) and 9 (bin 9.03-9.04). These QTL explained a combined 80% of the phenotypic variation for SLB resistance. Some time-point-specific SLB resistance QTL were also identified. There was no significant correlation between disease resistance and days to anthesis. Six putative QTL for time to anthesis were identified, none of which coincided with any SLB resistance QTL.

Crop ScienceVolume 46, Issue 4 p. 1825-1826 Registrations of Germplasm Registration of Nine High-Yielding Tropical by Temperate Maize Germplasm Lines Adapted for the Southern USA M.L. Carson, M.L. Carson USDA-ARS Cereal Disease Lab, Univ. of Minnesota, Saint Paul, MN, 55108Search for more papers by this authorP.J. Balint-Kurti, Corresponding Author P.J. Balint-Kurti peter_balintkurti@ncsu.edu USDA-ARS, North Carolina State Univ., Dep. of Plant Pathology, Raleigh, NC, 27695-7616Corresponding author (peter_balintkurti@ncsu.edu)Search for more papers by this authorM. Blanco, M. Blanco USDA-ARS, Iowa State Univ., Ames, IA, 50011Search for more papers by this authorM. Millard, M. Millard USDA-ARS, North Central Regional Plant Introduction Station, Iowa State Univ., Ames, IA, 50011Search for more papers by this authorS. Duvick, S. Duvick USDA-ARS, Iowa State Univ., Ames, IA, 50011Search for more papers by this authorR. Holley, R. Holley Syngenta Seeds, Inc., Henderson, KY, 42420 Pioneer Hi-bred, DuPont Agriculture and Nutrition, RR1, Box 90a, Princeton, IN, 47670Search for more papers by this authorJ. Hudyncia, J. Hudyncia USDA-ARS, North Carolina State Univ., Dep. of Plant Pathology, Raleigh, NC, 27695-7616Search for more papers by this authorM.M. Goodman, M.M. Goodman Dep. of Crop Science, North Carolina State Univ., Raleigh, NC, 27695Search for more papers by this author M.L. Carson, M.L. Carson USDA-ARS Cereal Disease Lab, Univ. of Minnesota, Saint Paul, MN, 55108Search for more papers by this authorP.J. Balint-Kurti, Corresponding Author P.J. Balint-Kurti peter_balintkurti@ncsu.edu USDA-ARS, North Carolina State Univ., Dep. of Plant Pathology, Raleigh, NC, 27695-7616Corresponding author (peter_balintkurti@ncsu.edu)Search for more papers by this authorM. Blanco, M. Blanco USDA-ARS, Iowa State Univ., Ames, IA, 50011Search for more papers by this authorM. Millard, M. Millard USDA-ARS, North Central Regional Plant Introduction Station, Iowa State Univ., Ames, IA, 50011Search for more papers by this authorS. Duvick, S. Duvick USDA-ARS, Iowa State Univ., Ames, IA, 50011Search for more papers by this authorR. Holley, R. Holley Syngenta Seeds, Inc., Henderson, KY, 42420 Pioneer Hi-bred, DuPont Agriculture and Nutrition, RR1, Box 90a, Princeton, IN, 47670Search for more papers by this authorJ. Hudyncia, J. Hudyncia USDA-ARS, North Carolina State Univ., Dep. of Plant Pathology, Raleigh, NC, 27695-7616Search for more papers by this authorM.M. Goodman, M.M. Goodman Dep. of Crop Science, North Carolina State Univ., Raleigh, NC, 27695Search for more papers by this author First published: 01 July 2006 https://doi.org/10.2135/cropsci2005.08-0283Citations: 8 Registration by CSSA. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume46, Issue4July–August 2006Pages 1825-1826 RelatedInformation

Los agricultores tradicionales practican la conservacion in situ de la diversidad genetica del maiz (Zea mays L.) mediante la siembra de variantes criollas. Para mejorar dicha practica es necesario conocer la diversidad del maiz en las condiciones de la agricultura tradicional, y tener un diagnostico del material a conservar. El objetivo del presente estudio fue evaluar la diversidad genetica de poblaciones de maiz de la raza Chalqueno que se cultivan en el oriente del Estado de Mexico, con base en caracteres morfologicos y agronomicos. Se evaluaron 104 poblaciones en cuatro ambientes y se registraron 11 caracteres morfologicos para evaluar la diversidad entre poblaciones de maiz en la region. Los resultados de un analisis de componentes principales, y otro de conglomerados, indican que las poblaciones presentan traslapes en caracteristicas entre los grupos taxonomicos Palomero Toluqueno, Conico, Conico Norteno, Chalqueno-Conico, Chalqueno cremoso, Elotes Chalquenos, Palomo, Chalqueno-Ancho, Cacahuacintle y Ancho, dentro del complejo de mazorca piramidal. Las poblaciones de la Sierra Norte de Puebla, semejantes en mazorca a Chalqueno y Mushito en Oaxaca y Michoacan, fueron diferentes del resto. La diversidad del maiz es dinamica porque, aunque predomina el Chalqueno, el Cacahuacintle se encuentra en baja frecuencia, el Ancho se distribuye de una altitud intermedia al Altiplano, y el Chalqueno amarillo presenta una fuerte reduccion en su frecuencia.

Genetic diversity of elite maize germplasm in the United States is narrow relative to the species worldwide. Tropical maize represents the most diverse source of germplasm. To incorporate germplasm from tropical maize landraces into the temperate gene pool, 23 Latin American maize accessions were crossed to temperate inbred line Mo44. During inbred line development, selection was practiced in temperate environments, potentially resulting in the loss of substantial proportions of tropical alleles. Genotyping 161 semiexotic inbreds at 51 simple sequence repeat (SSR) loci permitted the classification of their alleles as either Mo44 or tropical and allowed estimation of the proportion of detectable tropical alleles retained in these lines. On average, the percentage of detectable tropical alleles ranged among lines from 15% to 56%, with a mean of 31%. These are conservative, lower-bound estimates of the proportion of tropical germplasm within lines, because it is not known how frequently Mo44 and the tropical maize accession parental populations shared SSR alleles. These results suggest that substantial proportions of exotic germplasm were recovered in the semiexotic lines, despite their selection in temperate environments. The percent of tropical germplasm in semiexotic lines was not correlated to grain yield or moisture of lines testcrossed to a Corn Belt Dent tester, indicating that the incorporation of a substantial percentage of tropical germplasm in an inbred line does not necessarily negatively impact its combining ability. Thus, tropical maize accessions represent a good source of exotic germplasm to broaden the genetic base of temperate maize without hindering agronomic performance.

Exotic maize (Zea mays L.) germplasm may allow for increased flexibility and greater long-term progress from selection if it can be incorporated at high rates into U.S. breeding programs. Crosses were made between a temperate line, NC262A, and each of eight different lines consisting of 100% temperate-adapted tropical germplasm. Pedigree selection was used to generate a set of 148 F5S2 lines that were evaluated in testcrosses with FR992/FR1064 in nine North Carolina environments. Several entries had grain yield, grain moisture content and standability that were comparable to three commercial checks. The best testcrosses outyielded the cross NC262A × FR992/FR1064 by 9.5 to 10.9%, suggesting that a significant amount of tropical germplasm was retained in these lines and that this germplasm combined well with the Stiff Stalk tester. Previous researchers had suggested that tropical alleles could be rapidly lost during inbreeding in populations derived from tropical × temperate bi-parental crosses, leading to the development of lines that possess significantly less than 50% tropical germplasm. F5S5 sub-lines corresponding to the 14 best testcrosses were genotyped at 47 to 49 polymorphic simple sequence repeat (SSR) loci across all ten chromosomes to estimate the amount of tropical germplasm that was retained. The estimated genetic contribution from the tropical parent ranged from 32 to 70%, with the average being 49%. Only two of the 14 lines deviated significantly from a 50%-tropical/50%-temperate ratio, suggesting limited overall selection against germplasm from the tropical parents. These experiments collectively demonstrated that tropical maize germplasm can be incorporated at high rates into a temperate line via pedigree breeding methods in order to derive new inbred lines with acceptable agronomic performance.

Tropical maize (Zea mays L.) represents the most diverse readily available source of germplasm to broaden the limited genetic base of temperate maize in the USA. One objective of this study was to determine if exotic‐derived alleles contributing to enhanced testcross agronomic performance were maintained in semiexotic lines created by inbreeding and pedigree selection. A second objective was to determine if first‐generation semiexotic lines could produce hybrids with agronomic performance comparable to commercial U.S. hybrids. One hundred sixty‐four semiexotic inbred lines were developed from crosses between temperate‐adapted inbred line Mo44 and 23 Latin American maize accessions. Mo44 and each semiexotic line were testcrossed to temperate hybrid LH132 × LH51 for evaluations. In first‐stage replicated yield trials, testcrosses of 18 semiexotic lines, representing six different races, had significantly greater grain yields than the Mo44 testcross. Advanced yield evaluations were performed on check entries and 33 selected semiexotic line testcrosses in three additional environments. Across 10 environments, 12 semiexotic line testcrosses exhibited significantly greater grain yield than the Mo44 testcross, indicating recovery of favorable exotic alleles. Semiexotic testcrosses were not competitive with commercial hybrids for grain yield but were similar to or better than commercial hybrids for grain moisture and lodging resistance. Many superior accessions represent relatively recent introductions into regions from which they were collected. Tropical landraces seem to be a good source of exotic germplasm that can be used to broaden the genetic base of modern U.S. maize production and improve productivity.

Commercial maize (Zea mays L.) in the USA has a restricted genetic base as newer hybrids are largely produced from crosses among elite inbred lines representing a small sample (predominantly about 6- to 8-base inbreds) of the Stiff stalk and Lancaster genetic backgrounds. Thus, expansion of genetic diversity in maize has been a continuous challenge to breeders. Tropical germplasm has been viewed as a useable source of diversity, although the integration of tropical germplasm into existing inbred line and hybrid development is laborious. The present study is an evaluation of the potential of tropical germplasm for temperate maize improvement. All possible single-, three-way-, and double-cross hybrids among three largely temperate and three temperate-adapted, all-tropical inbred lines were evaluated in yield-trial tests. Single-cross hybrids containing as much as 50–60% tropical germplasm produced 8.0 t ha-1 of grain yield, equivalent to the mean yield of the commercial check hybrids. On the other hand, three-way and double-cross hybrids with the highest mean yield contained lower amounts of tropical germplasm, 10–19% and 34–44%, respectively. Overall, hybrids containing 10–60% tropical germplasm yielded within the range of the commercial hybrid checks. Hybrids with more than 60% tropical germplasm had significantly lower yields, and 100% tropical hybrids yielded the least among all hybrids evaluated. The results indicate that inbred lines containing tropical germplasm are not only a useful source to expand the genetic diversity of commercial maize hybrids, but they, also are competitive in crosses with temperate materials, producing high-yielding hybrids. These experimental hybrids exhibited good standability (comparable to the commercial check hybrids) but contained 1–2% higher grain moisture, leading to delayed maturity. Recurrent selection procedures are being conducted on derivatives of these materials to extract lines with superior yield, good standability, and reduced grain moisture which can be used for commercial exploitation.

The inheritance of resistance to southern rust (caused by Puccinia polysora Underw.) was investigated in two F 2:3 populations derived from crossing two temperate-adapted, 100% tropical maize ( Zea mays L.) inbred lines (1416-1 and 1497-2) to a susceptible Corn Belt Dent hybrid, B73 Ht ×Mo17 Ht . The inbred lines possess high levels of resistance to southern rust and may be unique sources of resistance genes. Heritability for resistance was estimated as 30% and 50% in the two populations from regression of F 2:3 family mean scores on F 2 parent scores, and as 65% and 75% from variances among F 2:3 families on a single-plot basis. RFLP loci on three chromosomal regions previously known to possess genes for resistance to either southern rust or common rust ( P. sorghi Schw.) were used to localize genes affecting resistance to southern rust in selected genotypes of both populations, and to estimate their genetic effects. A single locus on 10S, bnl3.04 , was associated with 82–83% of the variation among field resistance scores of selected F 2:3 families in the two populations. Loci on chromosomes 3 ( umc26 ) and 4 ( umc31 ) were significantly associated with resistance in the 1497-2 population, each accounting for 13–15% of the phenotypic variation for F 2:3 field scores. Multiple-marker locus models, including loci from chromosomes 3, 4, and 10 and their epistatic interactions, accounted for 96–99% of the variation in F 2:3 field scores. Similar results were obtained for resistance measured by counting pustules on juvenile plants in the greenhouse. An attempt was made to determine if the major gene for resistance from 1416-1 was allelic to Rpp9 , which is also located on 10S. Testcross families from the cross (1416-1×B37 Rpp9 )×B14A Ht were evaluated for resistance to southern rust in Mexico. Neither source of resistance was completely effective in this environment, preventing determination of allelism of the two genes; however, both sources of resistance had better partial resistance to southern rust than did B14A Ht .

Late maturity and high grain moisture content at harvest have been major limitations to the use of tropical maize (Zea mays L.) germplasm in temperate regions. The objective of this study was to determine if selection for reduced grain moisture content at harvest in a tropical maize population indirectly influenced grain yield potential. Two hundred sixteen temperately‐adapted S4 lines were derived in 1991 at Raleigh, NC, from Cycle 9 of recurrent phenotypic selection for reduced grain moisture at harvest in the tropical maize population TROPHY, and these were testcrossed in 1992 at Raleigh, NC, to the temperate hybrid B73Ht × Mo17Ht. Selected subsets of these testcrosses were evaluated for their agronomic potential in seven environments over two years, and their performance was compared with that of Cycle 0 S0 testcrosses as well as three public and three commercial F1 hybrids. Selected Cycle 9 S4 testcrosses had higher mean grain yield (7.14 Mg ha‒1) and lower mean grain moisture at harvest (184 g kg−1) than the Cycle 0 So testcrosses (6.77 Mg ha−1, and 189 g kg−1 respectively). The highest yielding Cycle 9 S4 testcrosses were comparable to the commercial hybrid LH132 × LH51. This study supported the conclusion that ergonomically competitive inbred lines with acceptable grain moisture content at harvest can be derived from 100% tropical germplasm.

Few data exist regarding the agronomic utility of tens of thousands of available tropical maize (Zea mays L.) racial accessions. A long‐term, multi‐stage evaluation project has been developed at North Carolina State University to evaluate the breeding potentials in the temperate USA of typical Latin American maize germplasm collections. Agronomic evaluations of accessions per se were performed in daylength neutral environments. Superior accessions were crossed to a temperate‐adapted inbred line and converted to photoperiod‐insensitive 50%‐exotic and 75%‐exotic populations by selection during 1986 to 1990. These semi‐exotic populations were evaluated as testcrosses to Corn Belt testers in North Carolina during 1993 and 1994. Testcrosses of many 75%‐exotic families were higher‐yielding than the hybrid tester, B73Ht × Mo17Ht, providing evidence that agronomically superior Latin American maize accessions possess favorable genes for yield that apparently are absent from Corn Belt germplasm. Yields of accessions evaluated as 100%‐exotic and 50%‐exotic populations were significantly correlated (r = 0.62, P = 0.005) with each other, but not with yields of 75%‐exotic populations. Some accessions exhibited extreme ranking changes across different testing stages. Multi‐stage evaluations of maize racial accessions successfully identified superior germplasm for use by U.S. breeders, but there is no guarantee that all of the most valuable accessions were advanced to later testing stages. Evaluations in many environments and minimal culling levels at each stage could be used to improve the probabilities of successfully identifying useful accessions in future multi‐stage evaluation procedures.

To supplement minimal information regarding the utility of tropical maize (Zea mays L.) germplasm to temperate maize breeding programs, agronomic evaluations of typical accessions of the Latin American races were made. Based on data from previous evaluation stages, 40 accessions exhibiting superior agronomic performance in tropical environments were chosen for photoperiod conversion and combining ability evaluations with U.S. germplasm in temperate environments. Accessions were converted to photoperiod insensitive semiexotic populations by crossing each to Mo44, a temperate‐adapted inbred unrelated to either of two major U.S. heterotic groups. Four families from each semiexotic population were crossed to two U.S. testers. Testcrosses were evaluated in three North Carolina locations for 2 yr. Based on these results, 29 agronomically superior semiexotic testcrosses were tested a third year. The variation for combining ability for yield was estimated to be two times greater among vs. within accessions, suggesting that sampling among accessions be given priority compared with sampling within to maximize genetic diversity for combining ability. Family yields were highly correlated across testers (r = 0.78), suggesting that a single temperate tester would be sufficient for evaluating large samples of Latin American accessions. Grain yields, resistance to gray leaf spot disease (incited by Cercospora zeae‐maydis Tehon & E.Y. Daniels), and other agronomic traits of superior semiexotic testcrosses were competitive with the public U.S. hybrid Mo17 × B73. The best accessions should be a promising source of useful genes for commercial U.S. maize breeding programs.

The present study was designed to advance the classification of the Mexican races of maize as part of the process of revising the Razas de Maíz en México by Wellhausen et al. The interrelationships among the races are examined by numerical taxonomy of morphological characters and the comparison of classifications with previous studies. Forty-nine Mexican races, represented by 148 collections, were grown in several locations and seasons in México from 1982 to 1984; 47 characters were measured directly. For the analysis using numerical taxonomy, characters with the ratio\(r = [\hat \sigma ^2 _r /(\hat \sigma ^2 _{re} + \hat \sigma ^2 _e )] \geqslant 3.0\) were chosen. Classifications of Mexican races indicate general agreement with the relationships found in previous studies which were based on conventional taxonomic methods and numerical taxonomy. In addition, poorly described races and new types may now be assigned to well defined groups.

An average of 14(7-34) plants each for 61 different collections of Zea (maize and its wild relatives, the teosintes) were studied for 12 enzyme systems coded for by 21 loci. Principal component and cluster analyses based on allele frequencies showed Zea can be divided into two major groups: 1) sect. Luxuriantes, including Z. perennis, Z. diploperennis, and Z. luxurians; and 2) sect. Zea (in part), including Z. mays subsp. mays, var. parviglumis, and subsp. mexicana. Zea mays var. huehuetenangensis (Huehuetenango teosinte) is isoenzymatically distinct from both sections, but shows its closest relationship to Z. mays var. parviglumis of sect. Zea. Populations of Z. mays subsp. mexicana and var. parviglumis grade isoenzymatically from one into the other without any clear break, but without any overlap either. Five populations of Z. mays subsp. mays are all isoenzymat- ically very similar to Z. mays var. parviglumis. The isozyme data are consistent with the theory that Mexican annual teosinte is the ancestor of maize. With the exception of the unusual isoenzymatic nature of Z. mays var. huehuetenangensis, the isoenzymatic data agree with previous studies of tassel morphology and cytoplasm DNAs. A comparison of sympatric populations of maize and teosinte suggests that teosintes are not greatly affected by introgression from maize. Zea mays var. parviglumis and Z. diploperennis have considerable within and among population variation; Z. luxurians has much less. Race Central Plateau of Z. mays subsp. mexicana has greater among population variation than any other taxon in Zea. Zea tends to show greater within population heterozygosity and more variance within species and subspecies than most other plants that have been studied isoenzymat- ically.

Mitochondrial DNAs (mtDNAs) were isolated from 93 diverse races of maize from Latin America. DNAs were examined by agarose gel electrophoresis of undigested DNA and by BamHI and EcoRI cleavage fragment analysis. Eighteen races contained plasmid-like mtDNAs. One race contained the S-1 and S-2 molecules associated with the S cytoplasmic male-sterile, and 17 were found to have the R-1 and R-2 plasmid-like DNAs. BamHI digestion of mtDNAs generated ten distinct electrophoretograms, and Eco RI digestion produced eight different fragment patterns. Races were assigned to one of 18 groups according to EcoRI and BamHI fragment patterns and whether or not they contained plasmid-like DNAs. Eight races produced restriction patterns similar to one of the characterized cytoplasmic male-steriles C, T, or S. Races from Meso-America and some from South America with Meso-American affinities were separated from other South American races. South American races were placed in three general classes of related groups. There was considerable agreement among the groupings here and those based on morphological and cytological affinities.