Associations among widely used French and U.S. maize hybrids as revealed by restriction fragment length polymorphisms

Summary Eighty DNA Restriction Fragment Length Polymorphism (RFLP) clones were used as probes to profile 47 hybrids of maize (Zea mays L.) that are of widespread usage in France and 49 hybrids that are either in common usage or are new releases in the U.S. The objectives were to 1) investigate the degree to which RFLPs provide unique characterization of hybrids; 2) show associations among hybrids using both cluster and principal coordinate analyses; 3) measure the ability of RFLPs to show associations among hybrids that reflect those to be expected on the basis of pedigree; and 4) compare the patterns and extent of genetic diversity among French hybrids with that found among a set of widely used U.S. hybrids.RFLPs showed all French hybrids to have different profiles, however, 3 hybrids were very similar with more than 90% of their profiles in common. Twenty-seven U.S. hybrids showed this level of similarity with one or more U.S. hybrids. High correlations (r=0.93, 0.94) were found for pedigree distance versus RFLP distance between pairs of French and of French and U.S. hybrids, respectively. Similar levels of correspondence for rank correlations between RFLP and pedigree data were also found. Similar groupings of hybrids were shown by two cluster analysis methods and by principal coordinate analysis. Inclusion of hybrids in cluster groupings was supported by observation of raw distance data for selected hybrids and their nearest neighbors. Most hectarage in France is planted to hybrids that fall within 2 related groups of germplasm on the basis of RFLP data. Minimum distance standards could promote breeders to surmount the challenge of introducing elite yet diverse germplasm into agriculture.     

Adaptation of tropical maize germplasm to temperate environments

Maize (Zea mays L.) is one of few crops that can offer significant genetic gains with the utilization of genetic diversity. Genetically broad-based germplasm has the potential to contribute useful and unique alleles to U.S. Corn Belt breeding programs not present in current U.S. genome sequences (e.g. B73, NAM, etc.). Our objectives were to determine if unique tropical genetic materials have been effectively adapted to temperate environments and how their agronomic performance was relative to adapted populations. An important long-term objective of the Iowa and North Dakota maize breeding programs has been, in addition to the typical elite by elite line pedigree selection cultivar development process, to adapt exotic and unique germplasm, maximize their genetic improvement, and develop unique products for breeding and commercial uses. Stratified mass selection methodology for earliness has been utilized for the adaptation of tropical and temperate populations to Iowa and North Dakota environments. This method has allowed screening of up to 25,000 genotypes per population cycle at a rate of one cycle per year. In addition, the estimated cost per year our programs had for the adaptation of each population was less than $2,000 which could successfully be applied in any breeding program across the globe. This cost has been less than 1 % of the total cost for finding minor genes on the same trait. Our results showed the successful adaptation of exotic populations was independent from genetic background. We can speculate there are a few major genes responsible for most of flowering date expression. We encourage the use of technology to target traits according to their genetic complexity. Stratified mass selection at the phenotypic level has been successful. Each of the populations with either 25 of 100 % tropical germplasm are available for anyone who may desire to expand the germplasm base of their breeding programs with tropical germplasm adapted to temperate mid- and short-season U.S. Corn Belt environments.     

Genetic diversity for RAPD markers between cultivated and wild accessions of Coffea arabica

Summary Random amplified polymorphic DNA (RAPD) markers have been successfully employed to analyse the genetic diversity among cultivated and subspontaneous accessions of Coffea arabica. The narrow genetic base of commercial cultivars was confirmed. On the other hand, a relatively large genetic diversity was observed within the germplasm collection demonstrating the importance of collecting missions. Results suggested an East-West differentiation in Ethiopia, the primary centre of diversification of C. arabica. The large heterosis effect reported in intergroup hybrids could be related to such genetic differentiation. RAPD method appeared to be effective in resolving genetic variations and in grouping germplasm in C. arabica.     

Challenges and opportunities for developing maize cultivars in the public sector

Maize (Zea mays L.) breeding programs integrating pre-breeding with cultivar development are needed. The objectives of the North Dakota corn breeding program are to adapt exotic and unique germplasm, maximize the genetic improvement of adapted germplasm, and develop unique short-season products for breeding and commercial use. This applied program has significant support from state maize grower organizations, farmers, food and fuel processors, and industry. As a result 25 inbred lines and 17 improved populations, carrying unique alleles not present in the B73 line and the Nested Association Mapping population (NAM) genomes, were released in the past 10 years and six hybrids were identified for commercial purposes. These included the first releases from our NDSU EarlyGEM program to increase the genetic diversity of U.S. northern hybrids and break environmental margins. These are not registered nationally due to exclusive agreements with industry. The strategic location of this research program allows the exploitation of challenging environmental conditions making evolution toward desirable goals faster, discarding unstable and weak maize varieties effectively. There are still several challenges to be addressed though. Retailer companies offer fewer products with more events making maize more vulnerable due to similar genetics. The confidential nature of the maize business limits breeding rights to develop better industry products, which currently reduces the breeding efficiency to identify the most outstanding hybrids for farmers across regions. Maize research, development, and production in marginal regions can be uniquely positioned to lead breeding research for climate changes and the development of the next generation of genetically broad-based elite products. Improvements in intellectual property and re-thinking of breeding rights access are encouraged.     

Isozyme variation in a number of populations of Theobroma cacao L. obtained through various sampling regimes

Summary Isozyme polymorphism in four enzyme systems was used to estimate the genetic diversity in nine populations of Theobroma cacao L. The distribution of allelic variation observed in this study was inconsistent with the currently held view that the Upper Amazon region of Peru is the centre of cacao genetic diversity. All the populations analysed from this area of Peru were genetically similar, and contained a low level of isozyme polymorphism. It is argued that this is a result of genuine low diversity in the region rather than a sampling artifact. If a centre of diversity of wild cacao truly exists, this work indicates that it lies further north in Ecuador and Colombia.Although they are morphologically highly variable, Trinitario cacao populations derived from cultivation are currently accorded low priority for conservation. This phenotypic variation was observed to be reflected in high levels of isozyme polymorphism. It is suggested that the present strategy for the conservation of cacao germplasm, which accords priority to the Upper Amazon region of Peru while neglecting the Carribbean should be reconsidered.     

Creation of new maize germplasm using alien introgression from <Emphasis Type="Italic">Zea mays</Emphasis> ssp. <Emphasis Type="Italic">mexicana</Emphasis>

Zea mays ssp. mexicana, an annual wild relative of maize, has many desirable characteristics for maize improvement. To transfer alien genetic germplasm into maize background, F₁ hybrids were generated by using Z. mays ssp. mexicana as the female parent and cultivated maize inbred line Ye515 as the male parent. Alien introgression lines, with a large range of genetic diversity, were produced by backcross and successive self-pollinations. A number of alien introgression lines with the predominant traits of cultivated maize were selected. Genomic in situ hybridization (GISH) proved that small chromosome segments of Z. mays ssp. mexicana had been integrated into the maize genome. Some outstanding alien introgression lines were evaluated in performance trials which showed 54.6% hybrids had grain yield greater than that of hybrid check Yedan12 which possessed 50% Ye515 parentage, and 17.1, 9.9% hybrids had grain yield competitive or greater than those of Nongda108 and Zheng958, which were elite commercial hybrids in China, respectively. The results indicated that some of the introgression lines had excellent agronomic traits and combining ability for maize cultivar, and demonstrated that Z. mays ssp. mexicana was a valuable source for maize breeding, and could be used to broaden and enrich the maize germplasm.     

Assessment of genetic variation among asparagus (Asparagus officinalis L.) populations and cultivars: agromorphological and isozymic data

Summary The morphological variation and the isozymic polymorphism in 19 asparagus accessions currently used in cultivation and breeding are described. Moreover 2 wild populations from Turkey were added in the isozymic study. Characters of ramification height permit to separate accessions usually cultivated for white asparagus and accessions usually cultivated for green asparagus. Starch and polyacrylamide gel electrophoresis was realized to assay 7 enzyme systems. 29 polymorphic bands were taken into account in the study. Four accessions show specific bands for glutamate oxaloacetate transaminase, shikimate dehydrogenase and alcohol dehydrogenase. In particular, the two populations from Turkey and one population traditionally cultivated in local area of Spain are well differentiated from the remaining accessions. Accessions from the United States representing different selections are relatively well separated from each other.     

Genomic variation and genetic relationships in Ipomoea spp.

Random amplified polymorphic DNA (RAPD) markers were used to develop genetic fingerprints and analyse genetic relationships among 29 Ipomoea accessions from different geographical locations around the world, including unique wild species, and reproducible profiles were obtained for all accessions using random decamer primers. The primers generated 46 polymorphic markers, one primer alone having 10 products, enabling the discrimination of all 29 accessions. A high level of genetic variability in sweet potato collections was suggested by the degree of polymorphism. Half of the Japanese land races were closely related while accessions from Papua New Guinea and The Philippines were distinct and exhibited the greatest genetic diversity. The wild species Ipomoea gracilis and Ipomoea tiliacea formed a group distinct from the cultivated sweet potato. The wild tetraploid accession K233 and the species Ipomoea trifida were progressively more related genetically to the cultivated sweet potato and are the probable progenitors of Ipomoea batatas, and may be suitable as germplasm for genetic enhancement. RAPDs proved to be useful for sweet potato systematics and should be valuable for germplasm management, gene tagging and efficient choice of parents in breeding programmes.     

Patterns of RFLP-based genetic diversity in germplasm pools of common wheat with different geographical or breeding program origins

A set of 292 accessions of common wheat (Triticum aestivum L.) representing 21 germplasm pools based on geographical or breeding program origins was assayed for RFLP diversity. Thirty cDNA and genomic DNA probes and the HindIII restriction enzyme were employed for RFLP analysis. About 61% of all 233 scored bands were present in 75% or more of the accessions. All but one of the 30 probes revealed polymorphism, and the average number of distinct patterns per probe over all accessions was 9.5.Polymorphic Information Content (PIC) values within a pool varied from 0 to 0.9 and depended on the identities of both the germplasm pool and the probe. Rare banding patterns with a relative frequency of ≤0.2 within a pool were detected. These rare patterns were more likely to occur in pools exhibiting high levels of heterogeneity. The highest level of polymorphism was observed in the Turkish landraces from Southwest Asia. The Eastern U.S. soft red winter wheat germplasm pool was more genetically diverse than the other advanced germplasm pools, and nearly as diverse as the Turkish landrace pool. RFLP-based genetic relationships between germplasm pools generally tracked expectations based on common geographical origin, breeding history and/or shared parentages. The Chinese wheat landraces from Sichuan, Tibet, and Yunnan provinces were distinct from other pools. Similarity matrices for among-pool genetic distance estimates based on either band frequencies or banding pattern frequencies showed good correlation with matrices derived from Nei and Li's mean genetic similarity estimates (r=−0.82^** and r=−0.73^**, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Conservation of diversity in bulk populations of barley (hordeum vulgare L.)

Summary A series of experiments was conducted to investigate the effectiveness of mass propagated heterogeneous populations (bulk populations) in preserving genetic and phenotypic diversity. Five genetically broad-based bulk populations of cultivated barley (Hordeum vulgare L.) were employed. All of them were produced originally through mass hybridization that was facilitated by male sterility. Four of these populations had a common origin, but were subsequently propagated in different North American locations. Comparisons between early and advanced generations of these bulk populations revealed loss of variability in all populations for morphological and agronomic characters and very little to none for eight isozyme characters. Populations propagated in different locations differed in levels of residual diversity. The bulk populations were less variable than a random sample of parental accessions. The rapid loss of diversity in bulk populations was considered detrimental to genetic conservation.     

Genetic Divergence and Molecular Characterization of Sorghum Hybrids and their Parents for Reaction to Atherigona Soccata (Rondani)

Summary Simple sequence repeat (SSR) markers linked to quantitative trait loci (QTL) associated with resistance to sorghum shoot fly, Atherigona soccata resistance were used to characterize the genetic and phenotypic diversity of 12 cytoplasmic male-sterile (CMS) and maintainers, 12 restorer lines, and 144 F₁ hybrids. The genetic diversity was quite high among the shoot fly-susceptible parents and the hybrids based on them, as indicated by high polymorphic information content (PIC) values, while limited genetic diversity was observed among shoot fly-resistant lines. The phenotypic and genotypic dissimilarity analysis indicated that the shoot fly-resistant and -susceptible parents were 73.2 and 38.5% distinct from each other, and the morphological and genetic distances of certain resistant and susceptible cross combinations was more than their resistant or susceptible parents. Genetic variability among the groups was low (10.8%), but high within groups (89.2%). The genetic and morphological distances suggested that the F₁ hybrids were closer to CMS (5 to 12% dissimilar) than the restorer (11 to 87% dissimilar), suggesting that CMS influences the expression of resistance to sorghum shoot fly. The SSR markers can be used to characterize the homologous traits in sorghum germplasm.     

Characterization and evaluation of two genetic groups and value of intergroup hybrids of <Emphasis Type="Italic">Cola nitida</Emphasis> (Vent.) Schott and Endlicher

The collection of Cola nitida in Côte d’Ivoire was previously classified, based on isozyme markers, into three groups named A, B and C, based on isozymic differences. In this study, morphological traits and several yield components as well as genotypic and phenotypic variabilities for vigour were investigated in groups A and B. We found that group A was characterized by a low vigour and high yield components. In contrast, group B expressed high vigour and low yield components. Intergroup hybrids were more vigorous and high yielder than intragroup hybrids. The vigour of intergroup hybrids was comparable to that of half sib commercial hybrids. Value of heterosis obtained for the yield of intergroup hybrids was 350%. It was concluded, based on our findings, that reciprocal recurrent selection in Cola nitida using plant materials of groups A and B should lead to significant improvement.     

贵州大樱桃种质资源亲缘关系ISSR分析

探讨贵州大樱桃种质资源的遗传背景和亲缘关系,为大樱桃种质鉴定、品种登记和遗传育种提供参考。利用ISSR分子标记技术,研究贵州栽培的23份大樱桃种质的亲缘关系,并构建DNA指纹图谱。结果表明,筛选出的20条ISSR引物在供试种质中共扩增出132个标记,其中多态性标记106个,多态性比率达80.3%。遗传相似系数为0.26~0.92,平均达0.61。通过UPGMA聚类,ISSR标记能将供试种质完全区分。     

Assessing the breeding potential of day-neutral converted racestock germplasm in the Pee Dee cotton germplasm enhancement program

The primitive, upland cotton landrace collection represents one of the untapped genetic resources in cotton breeding programs. Efforts to utilize these resources have been slow, but the development of day-neutral converted germplasm lines offers tremendous potential for broadening the genetic base in upland cotton. Using topcross hybrids involving elite germplasm from the unique Pee Dee germplasm enhancement program, we evaluated the breeding potential of a select number of day-neutral converted racestocks. The mean performance of parental lines and F₂ topcross hybrids along with genetic effect estimates indicate that day-neutral converted germplasm lines decreased agronomic performance while increasing fiber quality performance. Results suggest that crosses between day-neutral converted racestocks and elite Pee Dee germplasm lines result in new allelic combinations associated with improved fiber quality performance that interact in a non-additive way. However, it appears that converted racestocks transmit negatively correlated alleles for agronomic performance and fiber quality. These negatively correlated allelic combinations present a major challenge for cotton breeding programs. Future efforts that incorporate DNA based selection methods to identify and fix introgressed segments from converted racestocks and their offspring should enhance the use of the genetic variation present in the primitive racestock germplasm accessions.     

Seed quality attributes of food-grade soybeans from the U.S. and Asia

Diversity of food-grade soybeans is critical for utilization of genetic resources in cultivar development, germplasm enhancement, and end-product commercialization. The objective of this study was to assess seed quality attributes and phenotypic variability among 54 U.S. and 51 Asian food-grade cultivars and breeding lines. The results showed greater genetic diversity of protein content, calcium content, seed hardness, and seed size uniformity than other quality traits in both small- and large-seeded genotypes evaluated in this study. Among the small-seeded soybeans, the U.S. genotypes were more diverse and exhibited higher swell ratio and oil content but lower stone seed ratio and protein content than Asian accessions. Among the large-seeded accessions, U.S. genotypes had higher stone seed ratio and oil content but lower swell ratio and protein content, and were less diverse than Asian genotypes. The characterization of diverse food-grade soybeans will facilitate parent selection in specialty soybean breeding.     

2个玉米人工合成群体部分S1株系SSR分析与产量配合力研究

以39002和39007群体不同基本株的S166个单株及其与3个测验种按不完全双列杂交试验设计组配198个组合为供试材料,对单株产量的配合力和供试群体S1的多态位点数,基因杂合度等参数进行了分析,并利用遗传相似系数进行聚类。结果表明,39002S1单株产量GCA的表现明显优于39007S1,39002S1的多态位点数、多态位点比例、基因型数、变异系数、基因杂合度等均大于39007S1,说明39002S1的遗传组成较丰富,同时表明39002S1自交后代的纯合速率可能比39007S1慢。此外,39002S1部分株系与39002S1部分株系聚在同一亚类,说明它们之间可能有相似的遗传背景。     

Exotic barley germplasm: variation and effects on agronomic traits in complex crosses

Summary Utilization of exotic germplasm offers an approach to broaden genetic variability in breeding populations. This study was conducted in order to 1) compare germplasm of exotic origin with adapted Swedish barleys with respect to genetic differences and 2) to evaluate how exotic material affected agronomic performance in complex crosses. Allozyme studies showed the following Nei's gene diversities among parents: 0.13 (adapted parents), 0.16 (landraces) and 0.25 (H. spontaneum). Cluster analysis indicated that parental groups were genetically divergent. Earliness, straw length, number of ears per plant and thousand kernel weight (TKW) were studied. Variation in agronomic traits showed the following pattern: landraces > H. spontaneum > adapted lines. The best sources for earliness were adapted parents and landraces. Mean straw length was greatest in H. spontaneum lines. Number of ears per plant was quite similar in all groups. The highest TKW was among landraces and adapted parents. Hybrids from the complex crossing programme exceeded parents in earliness and TKW. An index composed from the four traits showed the most favorable frequency distributions for adapted parents and hybrids. Both genetic and agronomic studies indicate that new valuable variation from exotic germplasm may be introduced into barley breeding material.     

抗黑胫病烟草种质的遗传多样性分析

为了从分子水平上了解种质库抗黑胫病种质的遗传多样性,为拓宽黑胫病种质的遗传多样性、提高黑胫病抗性种质的利用率提供理论和技术支持,利用筛选出来的34对烟草多态性引物,对取自国家烟草种质资源库的73份抗黑胫病烟草种质进行遗传多样性分析,根据材料类型将其中的68份普通烟草种质分为烤烟和晾晒烟2个群体。结果表明：这34对引物共扩增出88多态性条带,每对引物平均扩增出2.6个变异位点,其中有效变异占94.12%。遗传多样性指数(Nei’s)为0.4200,Shanno’s指数为0.6803,种质间遗传相似系数变异范围在0.5140~0.9818的占63.57%,表明烟草抗黑胫病种质遗传多样性较差,其遗传多样性与栽培类型没有必然联系。加大对抗性野生烟的利用,对拓宽烟草抗黑胫病种质资源的遗传多样性有重要意义。     

Morphological and molecular characterization of Italian emmer wheat accessions

Summary The characterization of 39 Italian ecotypes and cultivars of Triticum turgidum L. spp. dicoccum Shrank ex Schübler (emmer wheat) was performed utilizing agro-morphological and molecular tools. Emmer wheat is a hulled species which grows wild in the Near East and is still cultivated in the Mediterranean Basin. Due to its characteristics, in Italy it is cultivated mainly in marginal lands of central and southern Italy, where local varieties, adapted to the natural environment where they originated, are used. Emmer wheat cultivation has been drastically reduced during the last century as a consequence of its low yield. Nevertheless, more recently, its agronomic and nutritive values, together with its use in health food products, made its cultivation economically viable in the marginal lands with a parallel increase of the cultivated area which is now more than 2000 ha. In the present paper the results of morphological evaluation, carried out in an experimental field in central Italy using a randomized block design with three replications, and molecular characterization are reported. The analysed material showed distinctive molecular traits and the existence of a huge amount of diversity not only between varieties, but also within them. When the accessions were clustered utilizing their genetic distance, the clusters were not always in agreement with the accessions origins. The obtained results gave information that can be useful for: (i) future registration of material, (ii) germplasm conservation and (iii) use of this valuable source of emmer germplasm for future breeding programmes.