Chromosomal regions associated with green plant regeneration in wheat (Triticum aestivum L.) anther culture

Genetic capacity for green plant regeneration in anther culture were mapped in a population comprising 50 doubled haploid lines from a cross between two wheat varieties ‘Ciano’ and ‘Walter’ with widely different capacity for green plant regeneration. Bulked segregant analysis with AFLP markers and composite interval mapping detected four QTLs for green plant percentage on chromosomes 2AL (QGpp.kvl-2A), 2BL (QGpp.kvl-2B.1 and QGpp.kvl-2B.2) and 5BL (QGpp.kvl-5B).The three QTLs detected on chromosome 2AL and 2BL all derived their alleles favouring green plant formation from the responsive parent ‘Ciano’.The remaining QTL on chromosome 5BL had the allele favouring green plants from the low responding parent ‘Walter’. In a multiple regression analysis the four QTLs could explain a total of 80% of the genotypic variation for green plant percentage. None of the chromosomal regions with QTLs for green plant percentage showed significant influence on either embryo formation or regeneration frequencies from the anther culture. The three major QTLs located on group two chromosomes were fixed in a second DH population derived from two parents ‘Ciano’ and ‘Benoist’,both with high capacity to produce green plants. A QTL explaining31.5% of the genetic variation for green plant formation were detected on chromosome 5BL in this cross as well. This revised version was published online in July 2006 with corrections to the Cover Date.     

A practical method for apple cultivar identification and parent-offspring analysis using simple sequence repeat markers

Differentiation of cultivars with simple sequence repeat (SSR) markers is a very useful technique for the true-to-type characterization of cultivars and clarification of parent-offspring relationships. We developed an SSR marker set for cultivar identification comprising 15 markers that were screened from 46 previously published SSRs. This marker set could be used for apple varieties including Malus × domestica and/or other Malus species. These SSRs successfully characterized 95 apples, including the leading and major founding cultivars used worldwide for modern apple breeding. Therefore, this marker set could be applied to almost all apple cultivars. We also analyzed the parent-offspring relationships of 69 cultivars by considering allele transmissions. This analysis revealed the true parentage of the following seven cultivars: ‘Kizashi’, ‘Chinatsu’, ‘Honey Queen’, ‘Haruka’, ‘Seirin’, ‘Ozenokurenai’, and Morioka #48. This analysis also revealed a parentage discrepancy for ‘Hacnine’. From the parent-offspring analysis, two microsatellite mutation events at alleles inherited from pollen parents were observed.     

More precise map position and origin of a durable non-specific adult plant disease resistance against stripe rust (Puccinia striiformis) in wheat

Recently a major gene determining non-specific adult plant disease resistance against stripe rust (Puccinia striiformis) designated Yrns-B1 was mapped in wheat Triticum aestivum L. by using a cross between ‘Lgst. 79-74’ (resistant) and ‘Winzi’ (susceptible). Linkage to five Gatersleben wheat microsatellite (GWM) markers was discovered, previously mapped on chromosome arm 3BS. In the present study this map was improved by the incorporation of four additional GWM markers. QTL-analysis revealed high LOD values for the resistance at all nine loci, whereas the largest LOD (20.76) was found for the newly mapped marker Xgwm1329. Microsatellite analysis and resistance tests of a collection of old German/UK wheat varieties, including probable ancestors of ‘Lgst.79-74’ were carried out. A high coincidence of non-specific adult plant disease resistance against stripe rust and the presence of ‘Lgst. 79-74’ allele (117 bp) of the marker Xgwm533 was observed among the varieties tested. Linkage during the inheritance of both the resistance and the 117 bp allele of Xgwm533 was demonstrated. The probable origin of Yrns-B1 is discussed. Carriers of this resistance gene were grown on large areas since more than 100 years. To estimate the capability of Xgwm533 as a diagnostic marker for non-specific adult plant disease resistance against stripe rust, microsatellite analysis and resistance tests of a collection of Russian spring wheat varieties were performed. The 117 bp allele of Xgwm533 was found in about 35% of the Russian cultivars analysed, however, none of them possessed the expected disease resistance. Thus, the utilisation of Xgwm533 as diagnostic marker seems to be restricted to certain genepools.     

The self-incompatible RNase S-alleles of Brazilian apple cultivars

Apple plants are self-incompatible because a genetic mechanism allows the female reproductive organ to recognize and reject self-pollen or pollen from genetic related individuals and allows non-self pollen to effect fertilization. Thus, there are implications to both breeding strategies and orchard management for fruit production. The purpose of this study was to identify and to characterize the S-RNase alleles of the gametophytic incompatibility among apple cultivars developed in Brazil, seeking to give support for choosing right combinations of parent in the apple breeding programs. It also sought to identify correct combinations of scion/pollinator cultivars of commercial apple orchards. A total of 16 specific S-RNase alleles primers were tested against DNA extracted from 12 Brazilian cultivars and their parents. The molecular analysis confronted to the reference cultivars, showed that the cultivars Daiane, Imperatriz and Princesa have the same incompatibility S3 and S5 alleles, while ‘Lisgala’ showed the alleles S2 and S5; ‘Suprema’, S1 and S9; ‘Catarina’, S1 and S19; ‘Joaquina’ and ‘Fred Hough’, S5 and S19; ‘Baronesa’, S3 and S9; ‘Duquesa’, S2 and S3. For ‘Primícia’ and ‘Condessa’ it was only possible to identify one of the S-alleles, namely S24 and S2, respectively, with the second allele remaining to be identified. Progeny test indicated the Mendelian inheritance for RNase alleles. Results of this study will be helpful to judiciously choose parents in apple breeding programs to improve compatibility.     

Development and application of molecular marker linkage maps in woody fruit crops

Summary Extensive linkage maps, consisting primarily of molecular markers, are being developed for apple, pear, and grape varieties. The intrinsically high heterozygosity of outcrossing perennial species is utilized to produce segregating populations directly from a cross between varieties. Nearly complete linkage maps have been generated for the apple varieties ‘Rome Beauty’ and ‘White Angel’. The map for ‘Rome Beauty’ contains 161 molecular markers, while that for ‘White Angel’ has 251 markers. Maps for the pear varieties, ‘Bartlett’ and NY10353, also are being developed. Linkages conserved between the pear and apple genomes have been identified. In grapes, maps for four varieties are available, the most extensive being those for ‘Cayuga White’ and ‘Aurore’. The apple maps have been used to investigate the genetic basis of morphological and physiological characters. A gene controlling the presence of anthocyanins in the skin of the fruit is located on linkage group 3. Genes controlling early bud break, branching habit, and production of root suckers have also been identified and mapped.     

Assessment of the uniformity and stability of grapevine cultivars using a set of microsatellite markers

Solidity of microsatellite markers is a key issue for varietal identification, especially when they are used for legal purposes, what includes their probable future use in the distinctness, uniformity and stability testing of new varieties needed for the granting of Plant Breeders’ Rights. Nine grapevine microsatellites (VVS2, VVMD5, VVMD27, VVMD28, ssrVrZAG29, ssrVrZAG62, ssrVrZAG67, ssrVrZAG83 and ssrVrZAG112), which had previously demonstrated its capacity to discriminate any grapevine variety, have been assessed to evaluate its uniformity and stability. 19 varieties were selected, representative of a high diversity for morphological, agronomical, cultural and historical aspects, as well as for microsatellite allele variability. Then, for each variety, uniformity and stability were evaluated through the analysis of 50 plants from each of three different plots, and five plants from each of seven additional plots. Material from 4,137 plants of 229 plots of the 19 varieties was sampled in seven countries. Of 3,654 plants analyzed with the set of nine microsatellites, 3,299 were of the right variety and used for the survey. An average of 172 individual values was studied for each allele of each microsatellite of each variety, and none differences were detected that could not be explained as technical variations, with the exception of several putative chimeras in two varieties. Of the total of 171 variety x microsatellite combinations, only in one combination (‘Merlot’ x VVMD27) the number of off-types exceeded the threshold allowed. The remaining 170 combinations have been found uniform and stable according to internationally accepted rules.     

Marker selection for <Emphasis Type="Italic">Fusarium</Emphasis> head blight resistance based on quantitative trait loci (QTL) from two European sources compared to phenotypic selection in winter wheat

Fusarium head blight (FHB) infects all cereals including maize and is considered a major wheat disease, causing yield losses and mycotoxin contamination. This study aimed to compare the realized selection gain from marker and phenotypic selection in European winter wheat. A double cross (DC) combined three FHB resistance donor-QTL alleles (Qfhs.lfl-6AL and Qfhs.lfl-7BS from ‘Dream’, and one QTL on chromosome 2BL from ‘G16-92’) with two high yielding, susceptible winter wheats, ‘Brando’ and ‘LP235.1’. The base population of 600 DC derived F₁ lines was on one hand selected for the respective QTLs by SSR markers (marker-selected cycle, CM), resulting in 35 progeny possessing different combinations of beneficial donor-QTL alleles. On the other hand it was selected phenotypically, only by FHB rating, and the best 20 lines were recombined and selfed (phenotypically selected cycle, CP). The variants CP, CM, and an unselected variant (C0) were tested at four locations by inoculation of Fusarium culmorum. Resistance was measured as the mean of multiple FHB ratings (0–100%). FHB severity was reduced through both phenotypic and marker selection by 6.2 vs. 5.0%, respectively. On a per-year basis, marker selection by 2.5% was slightly superior to phenotypic selection with 2.1%, because the first variant saved 1 year. Marker-selected lines were on average 8.6 cm taller than phenotypically selected lines. A high genetic variation within the marker-selected variant for FHB resistance and the high effect of a resistance-QTL allele on straw length indicate that additional phenotypic selection will further enhance selection gain.     

Cultivar identification and genetic map of mango (Mangifera indica)

Amplified Fragment Length Polymorphism (AFLP) information was used for identification of mango (Mangifera indica L.) cultivars, for studying the genetic relationship among 16 mango cultivars and seven mango rootstocks and for the construction of a genetic linkage map. Six AFLP primer combinations produced 204 clear bands and on the average 34 bands for each combination. The average Band-Sharing between cultivars and rootstocks was 83% and 80%, respectively. The average Band-Sharing for mango is 81%. The probability of obtaining a similar pattern for two different mango cultivars and rootstocks is 6 × 10⁻³and 2 × 10⁻³, respectively. A preliminary genetic linkage map of the mango genome was constructed, based on the progeny of a cross between ‘Keitt’ and ‘Tommy-Atkins’. This linkage map consists of 13 linkage groups and covers 161.5 cm defined by 34 AFLP markers. This revised version was published online in August 2006 with corrections to the Cover Date.     

Comparison of molecular markers and coefficients of parentage for the analysis of genetic diversity among spring bread wheat accessions

The comparison of different methods of estimating genetic diversity could define their usefulness in plant breeding and genetic improvement programs. This study evaluates and compares the genetic diversity of 70 spring wheat accessions representing a broad genetic pool based on molecular markers and parentage relationships. The sample was composed of 32 accessions from the International Maize and Wheat Improvement Center (CIMMYT) and 38 from other breeding programs worldwide. Eight AFLP-primer combinations and 37 pairs of SSR primers were used to characterize the accessions and the Coefficients of Parentage (COP) were calculated from registered pedigrees. The average genealogical (COP) similarity (0.09 with a range of 0.0–1.0) was low in comparison to similarity calculated using SSR markers (0.41 with a range of 0.15–0.88) and AFLP markers (0.70 with a range of 0.33–0.98). Correlation between the genealogical similarity matrix (excluding accessions with COPs = 0) and the matrices of genetic similarity based on molecular markers was 0.34≤r≤0.46 (p <0.05). It is concluded that AFLP and SSR markers are generally in agreement with estimates of diversity measured using COPs, especially when complete pedigree data are available. However, markers may provide a more correct estimate due to some unrealistic assumptions made when calculating COPs, such as absence of selection. Furthermore, both COP and marker distances indicate that CIMMYT accessions are different from the worldwide group of accessions. This revised version was published online in July 2006 with corrections to the Cover Date.     

A genetic map of macadamia based on randomly amplified DNA fingerprinting (RAF) markers

The first genetic linkage map of macadamia (Macadamia integrifolia and M. tetraphylla) is presented. The map is based on 56 F₁ progeny of cultivars ‘Keauhou’ and ‘A16’. Eighty-four percent of the 382 markers analysed segregated as Mendelian loci. The two-way pseudo-testcross mapping strategy allowed construction of separate parental cultivar maps. Ninety bridging loci enabled merging of these maps to produce a detailed genetic map of macadamia, 1100 cm in length and spanning 70–80% of the genome. The combined map comprised 24 linkage groups with 265 framework markers: 259 markers from randomly amplified DNA fingerprinting (RAF), five random amplified polymorphic DNA (RAPD), and one sequence-tagged microsatellite site (STMS). The RAF marker system unexpectedly revealed 16 codominant markers, one of them a putative microsatellite locus and exhibiting four distinct alleles in the cross. This molecular study is the most comprehensive examination to date of genetic loci of macadamia, and is a major step towards developing marker-assisted selection for this crop. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phenotypic and genotypic analysis of a commercial cultivar and wild populations of Anemone coronaria

Seven wild populations of Anemonecoronaria were assessed for 11 phenotypic traits, most of them having economic value for the flower industry. The wild populations were sampled to represent the diversity in habitats, climates, rock and soil types, terrains, and elevations in Israel. AFLP analysis was carried out on 12 individuals from each of six out of the seven wild populations and for six individuals from the commercial cultivar ‘Mona-Lisa’. It was found that the Dorot population, which is located in the area bordering the semi-arid zone at the very end of the species distribution, exhibits extreme and different phenotypes with relatively low variability compared withthe other wild populations. The other six wild populations, that grow in more favorable geographic and climatic conditions exhibit phenotypes with larger plants, larger numbers of flowers and less dissected leaves. These populations were less uniform than that of Dorot. Genetic characterization by AFLP markers revealed a total of 165 bands. The wild populations exhibit wide variation within-population, with about 80% polymorphic bands and average gene diversity between pairs of about 30%. The Dorot population has the lowest genetic variation and the Megido population the highest. Thus, the phenotypic variation reflects the genetic variation. The cultivar ‘Mona-Lisa’, as expected, has much lower genetic variation. The Dorot population and the ‘Mona-Lisa’ cultivar were found to have the largest genetic distances from the other wild populations, and the highest genetic variation between themselves. Phenetic analysis yielded a dendrogram describing the genetic relatedness of these populations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Molecular mapping of genes involved in root hair formation in barley

In the presented study, the existing AFLP and SSR maps of barley were used to find chromosomal position of four genes controlling different stages of root hair development. Four barley mutants were used in the analysis: the root hairless mutant rhl1.b, mutant rhp1.b with root hair development blocked at the initial bulge formation, mutant rhi1.a with irregular pattern of sparsely located root hairs and mutant rhs1.a with very short root hairs. Each mutant was crossed with parents of ‘Steptoe’/‘Morex’ mapping population and F₂ progenies of crosses: mutant × ‘Steptoe’ and mutant × ‘Morex’ were analyzed for segregation of root hair phenotype and polymorphic AFLP and SSR markers. It was possible to map all the analyzed genes on barley chromosomes: rhl1 gene on the short arm of chromosome 7H, rhp1 gene on chromosome 1H, rhs1 locus in the pericentromeric region of chromosome 5H and rhi1 gene on the long arm of chromosome 6H. Subsequently, the Bulk Segregant Analysis and AFLP technique were used for saturation of the identified regions with new markers. The joint maps were constructed using as common points the SSR markers located in the target regions. Linkage maps of the regions around the four genes involved in the root hair formation in barley were composed of 8–11 markers and spanned over 16.1–49.0 cM. The distances between localized genes and the closest markers ranged from 1.0 to 3.8 cM. The identified chromosomal locations of genes can be used for their fine mapping and future map-based cloning.     

Leaf proteins as markers useful in the genetic improvement of coconut palms

There is a need to identify genetic markers that can assist coconut (Cocos nucifera L.) breeding programs. With that objective, electrophoretic patterns of leaf peroxidases, endopeptidases and coomassie blue stained proteins were analysed in four cultivars (‘West African Tall’, ‘Rennell Tall’, ‘Malayan Yellow Dwarf’, ‘Cameroon Red Dwarf’), and in the hybrids PB121 (‘Malayan Yellow Dwarf’ × ‘West African Tall’) and PB111 (‘Cameroon Red Dwarf’ × ‘West African Tall’). The polymorphisms detected fit the expression of two alleles of a dimeric peroxidase, two alleles of a monomeric endopeptidase, and a pair of active and null alleles of a coomassie blue stained protein. Four distinctive genotypes were identified. One for each of the tall cultivars, another for both of the dwarf cultivars, and the last for both of the hybrids. Applications of the markers in breeding programs, and in research concerning reproductive biology and phylogeny, are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular diversity of Egyptian cotton (<Emphasis Type="Italic">Gossypium barbadense</Emphasis> L.) and its relation to varietal development

Twenty-eight Egyptian cotton (Gossypium barbadense L.) genotypes (varieties and hybrids) were used for analysis of genetic diversity using DNA based markers (ISSR, SSR, and EST) and to study varietal development of cotton. The ISSR markers gave the highest percentage of polymorphic bands as well as polymorphic information content compared with the other molecular markers (i.e. EST and SSR markers). Using clustering analysis, no general clustering according to the pedigree history of the genotypes was observed. Using principal coordinate analysis (PCOORDA), cotton genotypes were separated by the first three principal coordinates (PC1, PC2, and PC3) accounting for 11.5, 8.6, and 7.2% of the total genetic variance, respectively. The cotton genotypes were distributed into three parts based on the first PC, each part containing a group of varieties having a common ancestor. ‘Giza 12’ variety was the common ancestor for the varieties included in the first part and ‘Ashmouni’ variety was the common ancestor for the varieties included in the second part, while both ‘Sakha 3’ and ‘Sakha 4’ varieties were common ancestors for the varieties included in the third part. The results of the PCOORDA also showed better resolution of the genetic diversity than cluster analysis especially in the illustration of the varietal development of cotton. That means that principal coordinate analysis can be strongly used either alone or in combination with cluster analysis to discuss both genetic diversity and varietal development in the cotton genotypes.     

Genetic characterization and identification of new accessions from Syria in an olive germplasm bank by means of RAPD markers

Thirty-two olive cultivar accessions from Syria, most of them obtained from collecting expeditions, were characterized by means of RAPD markers before being introduced in the World Germplasm Bank of Cordoba. A total of 79 polymorphic bands(6.1 polymorphisms per primer) out of 93(7.1 bands per primer) were scored for the13 primers used, corresponding to 84.9% of the amplification products. Thirty-one different genotypes were clearly discriminated. Differences were not found among the amplification profiles from different individuals of the same cultivar. Only two cases of mislabeling or errors of planting were found. Fourteen accessions corresponding to 6 homonyms were discriminated by RAPDs as different genotypes. The dendrogram obtained by RAPD analysis included three major groups. Some evidence of relationships of the Syrian accessions studied according to their geographic origin and/or diffusion was found. For instance, cultivars from the Central Syria (Tadmur/Palmyra)such as Toffahi', ‘Abbadi Abo Gabra’-1033,‘Abo Kanani’, ‘Shami’-1041, ‘Abbadi Shalal’ ‘Adgam’-844 and ‘Majhol’-1013 clustered in Group 1 and 2. Six cultivars from Northern Syria clustered in Group 2. But it was not found a geographic structure for the cultivars from South and West of Syria. These results agree with the hypothesis of autochthonous origin of most of the olive cultivars. Some associations between cultivars from Central Syria and their fruit size were observed. This suggests that fruit size was a criterion of local selection in olive cultivars of this area. This revised version was published online in July 2006 with corrections to the Cover Date.     

Penetrance of creeping-rootedness in clonal progenies of lucerne and observations on underground morphology of plants differing for this character

Elaeis oleifera or ‘caiaué’, a close relative of oil palm (E. guineensis), has some agronomic traits of great interest for the oil palm genetic breeding such as slow growth, oil quality (mostly unsaturated) and disease resistance. An analysis of a Brazilian oil palm germplasm collection was carried out using RAPD (Random Amplified Polymorphic DNA) markers with the objective of understanding the genetic variation of ‘caiaué’ accessions collected in the Amazon Forest in the last two decades. A sample of 175 accessions obtained along the Amazon River Basin was analyzed and compared to 17 accessions of oil palm from Africa. Ninety-six RAPD markers were used in the analysis, of which fourteen were shown to be specific to oil palm, while twelve were specific to ‘caiaué’. Results showed that the Brazilian ‘caiaué’ accessions studied have moderate levels of genetic diversity as compared to oil palm accessions. The data allowed the establishment of similarity groups for ‘caiaué’ accessions, which is useful for selecting parental plants for population breeding. Cluster analysis showed that, in general, genetic similarities are not correlated to geographical distances, but consistent with geographical dispersal along the Amazon River network. AMOVA showed that most of the genetic variation is found within populations, as expected for anallogamous and long-lived perennial species. The study provides important information to define strategies for future collection expeditions, for germplasm conservation and for the use of E. oleifera in breeding programs. This revised version was published online in August 2006 with corrections to the Cover Date.     

Linkage mapping and genome analysis in a Saccharum interspecific cross using AFLP, SRAP and TRAP markers

Framework genetic linkage maps of two progenitor species of cultivated sugarcane, Saccharum officinarum ‘La Striped’ (2n = 80) and S. spontaneum ‘SES 147B’ (2n = 64) were constructed using amplified fragment length polymorphism (AFLP), sequence related amplified polymorphism (SRAP), and target region amplification polymorphism (TRAP) markers. The mapping population was comprised of 100 F₁ progeny derived from the interspecific cross. A total of 344 polymorphic markers were generated from the female (S. officinarum) parent, out of which 247 (72%) were single-dose (segregating in a 1:1 ratio) and 33 (9%) were double-dose (segregating in a 3.3:1 ratio) markers. Sixty-four (19%) markers deviated from Mendelian segregation ratios. In the S. spontaneum genome, out of a total of 306 markers, 221 (72%) were single-dose, 43 (14%) were double-dose, and 42 markers (14%) deviated from Mendelian segregation ratios. Linkage maps with Kosambi map distances were constructed using a LOD score ≥5.0 and a recombination threshold of 0.45. In Saccharum officinarum, 146 markers were linked to form 49 linkage groups (LG) spanning 1732 cM whereas, in S. spontaneum, 121 markers were linked to form 45 LG spanning 1491 cM. The estimated genome size of S. officinarum ‘La Striped’ was 2448 cM whereas that of S. spontaneum ‘SES 147B’ was 3232 cM. Based on the two maps, genome coverage was 69% in S. officinarum and 46% in S. spontaneum. The S. officinarum parent ‘La Striped’ behaved like an auto-allopolyploid whereas S. spontaneum ‘SES 147B’ behaved like a true autopolyploid. Although a large disparity exists between the two genomes, the existence of simple duplex markers, which are heterozygous in both parents and segregate 3:1 in the progeny, indicates that pairing and recombination can occur between the two genomes. The study also revealed that, compared with AFLP, the SRAP and TRAP markers appear less effective at generating a large number of genome-wide markers for linkage mapping in sugarcane. However, SRAP and TRAP markers can be useful for QTL mapping because of their ability to target gene-rich regions of the genome, which is a focus of our future research.     

Classification of cassava into ‘bitter’ and ‘cool’ in Malawi: From farmers' perception to characterisation by molecular markers

Cassava roots, a major food in Africa, contain cyanogenic glucosides that may cause toxic effects. Malawian women farmers considered fields of seemingly similar cassava plants to be mixes of both ‘cool’ and ‘bitter’ cultivars. They regard roots from ‘cool’ cultivars as non-toxic. Roots of ‘bitter’ were considered to require extensive traditional processing done by women to be safe for consumption. But curiously, these women farmers preferred ‘bitter’ cultivars since toxicity confers protection against theft, which was a serious threat to the food security of their families. We studied how well these farmers comprehend the effects of genetic variations in cassava when dealing with cyanogenesis in this complex system. Using molecular markers we show that most plants farmers identified as belonging to a particular named cultivar had a genotype typical of that cultivar. Farmers' ethno-classification into ‘cool’ and ‘bitter’ cultivars corresponded to a genetic sub-division of the typical genotypes of the most common cultivars, with four-fold higher cyanogenic glucoside levels in the bitter cultivars. Examining morphology, farmers distinguished genotypes better than did the investigators when using a standard botanical key. Undoubtedly, these women farmers grasp sufficiently the genetic diversity of cassava with regard to cyanogenesis to simultaneously benefit from it and avoid its dangers. Consequently, acyanogenic cassava – the breeding of which is an announced good of some cassava genetic improvement programmes – is not a priority to these farmers. Advances in molecular genetics can help improve food supply in Africa by rapid micropropagation, marker assisted breeding and introduction of transgenic varieties, but can also help to elucidate tropical small-scale farmers' needs and skills. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic diversity among elite varieties of the aromatic grasses, Cymbopogon martinii

The elite and popular cultivars of Cymbopogon martinii were examined for genomic and expressed molecular diversity through RAPD, enzyme and SDS-PAGE protein polymorphisms. The allelic score at each locus of the enzymes as well as presence and absence profiling in RAPDs, overall occurrence of band types etc. were subjected to computation of gene diversity, expected heterozygosity, allele number per locus, and similarity matrix. These, in turn, provide inputs to derive primary account of allelic variability, genetic bases of the cultivated germplasm, putative need for gene/trait introgression from the wild or geographically diverse habitat etc. in elite selections. ‘PRC1’ possessed highest number of unique bands based on RAPD polymorphism. In variety ‘IW31245E’, diaphorase and glutamate oxaloacetate transaminase isozymes generated two unique bands as dia-III ² and got-II ⁴. ‘RRL(B)77’ exhibited three unique bands; one produced by esterase as allele est-II ¹ and two by malic enzyme (me-III ^1,3). Only one unique band was generated by malic enzyme in variety ‘Trishna’. But sofia had three unique bands, two contributed by diaphorase (dia-II ³ and dia-II ⁴ and one by glutamate oxaloacetate transaminase (got-II ²). SDS-PAGE analysis revealed presence of unique polypeptide fragments (97.7 kDa to 31.6 kDa) in varieties ‘IW31245E’, ‘RRL(B)77’, ‘Tripta’, ‘Trishna’, ‘PRC1’ and var. sofia, generated as a diagnostic marker. In general, molecular distinctions associated with var. motia and var. sofia have been clearly noticed in C. martinii. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of segregation distortion on chromosome 3 induced in wide hybridization between indica and japonica type rice varieties

We previously surveyed chromosomal regions showing segregation distortion of RFLP markers in the F₂ population from the cross between a japonica type variety ‘Nipponbare’ and an indica type variety ‘Milyang23’, and showed that the most skewed segregation appeared on the short arm of chromosome 3. By comparison with the marker loci where distortion factors were previously identified, this region was assumed to be a gametophytic selection-2 (ga2) gene region. To evaluate this region, two near isogenic lines (NILs) were developed. One NIL had the ‘Nipponbare’ segment of this region on the genetic background of ‘Milyang23’ (NIL9-23), and the other NIL had the ‘Milyang23’ segment on the genetic background of ‘Nipponbare’ (NIL33-18). NIL9-23 and ‘Milyang23’, NIL33-18 and ‘Nipponbare’, and ‘Nipponbare’ and ‘Milyang23’ were respectively crossed to produce F₁ and F₂ populations. The F₁ plants of NIL9-23 × ‘Milyang23’ and NIL33-18 × ‘Nipponbare’ showed high seed fertility and the same pollen fertility as their parental cultivars, indicating that ga2 does not reduce seed and pollen fertility. Segregation ratio of a molecular marker on the ga2 region in the three F₂ populations was investigated to clarify whether segregation distortion occurred on the different genetic backgrounds. Segregation distortion of the ga2 region appeared in the both F₂ populations from the NIL9-23 and ‘Milyang23’ cross (background was ‘Milyang23’ homozygote) and the ‘Nipponbare’ and ‘Milyang23’ cross (background was heterozygote), but did notin the F₂ population from the NIL33-18 and ‘Nipponbare’ cross (background was ‘Nipponbare’ homozygote). This result indicates that ga2 interacts with a ‘Milyang23’ allele(s) on the different chromosomal region(s) to cause skewed segregation of the ga2 region. In addition, segregation ratio was the same between the F₂ populations from NIL9-23 × ‘Milyang23’ and ‘Nipponbare’ × ‘Milyang23’ crosses, suggesting that the both genotypes, ‘Milyang23’ homozygote and heterozygote, of gene(s) located on the different chromosomal region(s) have the same effect on the segregation distortion. This revised version was published online in July 2006 with corrections to the Cover Date.