Inheritance of superoxide dismutase (<Emphasis Type="Italic">Sod-1</Emphasis>) in a perennial × annual ryegrass cross and its allelic distribution among cultivars

Identifying annual ryegrass contamination in perennial ryegrass seed lots has been of major interest in seed-testing laboratories and for seed regulatory agencies in the USA for many years. This study was conducted to characterize a superoxide dismutase locus (Sod-1) and determine its potential to distinguish cultivated ryegrass species. The inheritance of Sod-1 was evaluated in a three-generation annual 2 perennial ryegrass mapping population and segregation fitted an expected 1:2:1 ratio for a single locus with two alleles. The molecular form of the Sod-1 locus was determined by H₂O₂ and KCN inhibitor assays which indicated that the Sod-1, and a second independently segregating Sod-2, locus were both Cu/ZnSod enzymes. The common alleles at the Sod-1 locus were scored in 13 annual and 24 perennial ryegrass cultivars to determine the potential of using this locus for species separation. The Sod-1b allele was homozygous in 98% of perennial ryegrass individuals from 24 cultivars, but those not 100% homozygous for Sod-1b were seed lots with unknown contamination from annual ryegrass. These results indicate that the Sod-1b allele in the homozygous condition is a good indicator of perenniality. All eight annual ryegrass cultivars originating in Europe or Asia had a low frequency of Sod-1b homozygous individuals or none at all. The five cultivars originating in the Western Hemisphere, however, had genotype frequencies for homozygous Sod-1b of up to 56%. The potential of the Sod-1 locus to serve as a test to separate the two growth forms depends on the source of the annual-type contamination.     

Isozyme gene markers in Vicia faba L.

Summary This study was conducted to assess the genetic basis of the variability observed for the glutamate oxaloacetate transaminase (GOT), Superoxide dismutase (SOD), esterase (EST), and malate dehydrogenase (MDH) isozyme systems in different open-pollinated Vicia faba varieties. Individual plants showing contrasting zymogram patterns were simultaneously selfed and cross-combined. Crossing was unsuccessful in producing progeny, and only selfed progenies were suitable for genetical analysis of isozyme variability. Three zones of GOT activity were made visible. The isozyme of GOT-2 and GOT-3 zones were dimeric and under the control of three alleles at the Got-2 locus and two alleles at the Got-3 locus, respectively. The isozymes of the GOT-1 zone did not show any variability. Three zones of SOD isozyme activity were made visible. The isozymes occurring in the SOD-1 (chloroplastic isozyme form) and SOD-2 (cytosol isozyme form) zones were dimeric and under the control of two alleles at the Sod-1 and Sod-2 loci. The isozyme visualized in the SOD-3 zone (mitochondrial isozyme form) were tetrameric and under the control of two alleles at the Sod-3 locus. Apparently the isozymes made visible in the most anodal esterase zones EST-1, EST-2, and EST-3 were monomeric, and the occurrence of two alleles at each of two different loci explained the variability observed in the EST-2 and EST-3 zones. For MDH, only two five-banded zymogram pattern types were found, and every selfed progeny showed only one of the two zymogram type, indicating that each individual possessed fixed alleles at the loci controlling MDH isozyme. Got-2, Got-3, Sod-1, Sod-2, and Sod-3 appear to be five new isozyme gene markers that can be useful in Vicia faba breeding for linkage study, varietal fingerprinting, outcrossing rate estimate, and indirect selection for quantitative characters.     

Associations of genes encoding allozymes peroxidase and superoxide dismutase in poplar and spruce species

Summary Isozymes of peroxidase (PER) and superoxide dismutase (SOD) were analyzed in vegetative buds or very young leaves of seven species and two interspecific hybrids of Populus, in progenies of seven controlled crosses of three Populus species, and in needles of five Picea species and one putative hybrid. One to three PER, and one or two SOD zones of activity were observed. Electrophoretic mobility (EM) and banding phenotypes of isozymes of one PER locus were identical to those of one SOD locus in vegetative buds of five Populus species and hybrid. In leaves of the four Populus species and hybrid and progenies of controlled crosses, EM and phenotypes of isozymes of two PER loci were identical to those of two SOD loci. In Picea species, EM of isozymes of the only SOD locus was somewhat similar but not identical to that of one PER locus, and isozyme phenotypes of all individuals at the SOD locus were not identical to those at a PER locus. Chi-square tests verified the single-gene Mendelian control of the segregating allozyme variants at each of Per-L1 and Sod-1 in the three Populus species. The results of joint two-locus segregation tests indicated a very tight linkage and no recombination between Per-L1 and Sod-1 in three Populus species. Genes coding for isozymes of one or two PER loci are either presumably the same as, or very tightly linked to, the genes coding for isozymes of one or two SOD loci in the Populus species.     

Tight linkage between a nuclear male-sterile locus and an enzyme marker in tomato

Summary The linkage relationship of a nuclear male sterile locus, ms-10, was tested with two enzyme marker loci known to be on the same chromosome (long arm of chromosome 2). The results indicate the gene order is Est-1 — 18 cM — Prx-2 — 1.5 cM — ms-10. The linkage intensity of ms-10 and Prx-2 (1.5 cM) suggests that Prx-2 might provide a selectable marker for male-sterility. In accordance with this idea, the ms-10 allele was placed in cis with a rare-allele of Prx-2 (Prx-2 ¹). Selection on the basis of the codominant Prx-2 ¹ allele should allow for more rapid and efficient transfer of the recessive male sterile allele into an array of genetic backgrounds, thus promoting its use in hybrid seed production.     

Genetics of esterase isoenzymes in Malus

Summary Three main zones of esterase activity (EST-I, EST-III, EST-IV) identified in leaf extracts of cultivated apple and Malus species were determined by the genes EST-1, EST-3 and EST-4, respectively. In addition to earlier reported alleles of EST-1 (a, b) three further bands c, d and f were identified in the EST-I zone of which c was found to be determined by an allele, c. Two alleles, a, b, and a null allele were found for both the genes EST-3 and EST-4. Differences in allelic frequency were observed between cultivars, rootstocks and Malus species. Allele EST-1a was rare amongst the rootstocks. The examination of Malus species and derivatives showed a geographical relationship. Allele EST-1c was confined to species of Asian origin, and EST-1d was confined to American species.     

Genetics and mapping of new isozyme loci in Vicia faba L using trisomics

Polymorphism in ten enzyme systems (ACO, ACP, AAT, EST, FK, ME, NAG, PRX, 6PGD, and SOD) in Vicia faba L. was analyzed, revealing 13 loci, six of which have not been reported before. Inheritance, genetics, possible location, and linkage analysis were studied in 13 different F² populations trisomic for four of the six chromosomes (nos. 3, 4, 5, and 6) of the species. Each of these loci exhibited typical Mendelian inheritance except for those involved in the trisomic chromosome. Five loci have been assigned to a specific chromosome: Est-2 to chromosome 3, Fk-2 to chromosome 4, Prx-1 to chromosome 5, and Sod-1 and Pgd-p to chromosome 6. Nag-1 and Pgd-c displayed a linkage of 22.8 cM indicating a clear homology with chromosome 5 of garden pea on which both markers are syntenic.     

Genetic analysis of disease resistance to all strains of BaYMV in a Chinese barley landrace, Mokusekko 3

 A Chinese landrace of barley, Mokusekko 3, is unique in being completely resistant against all strains of barley yellow mosaic virus (BaYMV). The present investigation revealed that the resistance of Mokusekko 3 is governed by two recessive genes. As one of the resistance genes was known to be tightly linked with alleles at the Est complex locus, consisting of the Est1, Est2 and Est4 loci for esterase isozymes, each of the resistance genes could be separated by means of marker-assisted selection using an isozyme allelic combination as a marker. One of the resistance genes, ym1, is linked to K (hooded lemma) and gl3 (glossy leaf 3) with recombination values of 25.3% and 9.7% respectively, and these three genes are located in the order K-gl3-ym1 on chromosome 4. Another newly designated resistance gene, ym5, is linked to alleles at the Est complex locus and cu2 (curly growth 2), with recombination values of 1.9% and 19.5% respectively, in the order cu2-Est-ym5 from proximal to distal on the long arm of chromosome 3. The complete resistance of Mokusekko 3 is caused by combining two resistance genes, ym1 and ym5. However, almost all the “resistant” cultivars derived from crosses with Mokusekko 3 are susceptible to the recently detected strain BaYMV-III in Japan, since they contain only one resistance gene, ym5. Marker-assisted selection to combine resistance genes into a cultivar is discussed for the breeding of stabilizing resistance to BaYMV. Received: 23 September 1996 / Accepted: 8 November 1996     

Linkage map positions and allelic diversity of two Mal d 3 (non-specific lipid transfer protein) genes in the cultivated apple (Malus domestica)

Non-specific lipid transfer proteins (nsLTPs) of Rosaceae fruits, such as peach, apricot, cherry, plum and apple, represent major allergens for Mediterranean atopic populations. As a first step in elucidating the genetics of nsLTPs, we directed the research reported here towards identifying the number and location of nsLTP (Mal d 3) genes in the apple genome and determining their allelic diversity. PCR cloning was initially performed on two cultivars, Prima and Fiesta, parents of a core apple mapping progeny in Europe, based on two Mal d 3 sequences (AF221502 and AJ277164) in the GenBank. This resulted in the identification of two distinct sequences (representing two genes) encoding the mature nsLTP proteins. One is identical to accession AF221502 and has been named Mal d 3.01, and the other is new and has been named Mal d 3.02. Subsequent genome walking in the upstream direction and DNA polymorphism analysis revealed that these two genes are intronless and that they could be mapped on two homoeologous segments of linkage groups 12 and 4, respectively. Further cloning and sequencing of the coding and upstream region of both Mal d 3 genes in eight cultivars was performed to identify allelic variation. Assessment of the deduced nsLTP amino acid sequences gave a total of two variants at the protein level for Mal d 3.01 and three for Mal d 3.02. The consequences of our results for allergen nomenclature and the breeding of low allergenic apple cultivars are discussed.     

Linkage relationships of 19 protein coding genes in watermelon

Summary Segregation of seed proteins and isozymes was analysed in two Citrullus crosses. In the first cross an F1 hybrid between C. lanatus and the wild species C. colocynthis was used as a female parent in a backcross to C. lanatus. In this interspecific cross the segregation of 17 markers was analysed. Four linkage groups were identified: linkage group 1 includes the genes Est-2, Skdh-2, Tpi-1, Fdp-1, Sod-1 and Prx-1; linkage group 2 — Got-1, Got-2 and Sp-4; linkage group 3 — Pgm-1 and Gdh-2; linkage group 4 with Pgi-1 and Pgi-2. In the second cross an F1 hybrid between two C. colocynthis accessions was backcrossed to one of its parents. Seven loci were scored and no new linkages were found.     

Trisomic analysis of isozymic loci in tomato species: Segregation and dosage effects

Five isozymic loci were localized in the tomato (Lycopersicon esculentum) genome by trisomic analysis. Results revealed the following locations: Aps-1 on chromosome 6, Est-1 and Prx-2 on chromosome 2, Prx-4 on chromosome 10, and Prx-7 on chromosome 3. Three genes—Aps-1, Prx-2, and Prx-4—showed an arithmetic increase in allozyme concentration in direct proportion to the increase of gene dosage in respective primary trisomics. In contrast, no increase in relative Est-1 isozyme concentration was observed for any primary trisomic type. The phenotypes of the Aps-1, Prx-2, and Est-1 genes showed a pattern of banding intensity proportional to the allelic ratio (+/+/a vs. + /a/a) in primary trisomics; zymotypes of these differential trisomic heterozygotes appeared as converse images of each other.This research was performed under the auspices of NSF Grants BMS75-03024 and DEB77-02248 to C. M. Rick.     

Characteristics associated with Woolly Apple Aphid Eriosoma lanigerum, resistance of three apple rootstocks

The resistance characteristics of the apple resistance genes (Er1, Er2, and Er3) to the woolly apple aphid, Eriosoma lanigerum (Hausmann) (Homoptera: Aphididae) were studied according to the performance measured on apple cultivars containing these resistance genes. The resistance characteristics of Northern Spy (Er1), Robusta 5 (Er2), and Aotea (Er3) were compared to the susceptible cultivar Royal Gala, by measuring the aphid settlement, development, and survival rates correlated with electronically monitored probing behaviour. Er1 and Er2 had a higher level of resistance with a significantly shorter period of phloem feeding, suggesting that the resistance factors were present in the phloem tissue. Phenological measurements indicated that the aphids showed poor settlement, development, and survival on Er2. Er1 also showed low settlement and survival, although not as low as Er2. Aphid performance and feeding on Aotea (Er3) were similar to Royal Gala, suggesting that some woolly apple aphids in New Zealand may have recently overcome Er3 resistance. The differences in resistance mechanisms of Er1, Er2, and Er3 are discussed in relation to the strategy of pyramiding these genes to give a durable resistance to woolly apple aphid.     

Application of High-Throughput Sequencing to Evaluate the Genetic Diversity Among Wild Apple Species Indigenous to Shandong,China, and Introduced Cultivars

The Taiyi mountainous region of Shandong province in eastern China has an abundance of wild Malus species. We evaluated the genetic diversity of 88 Malus accessions (45 Asian apple cultivars, 10 American apple cultivars, 12 European apple cultivars, 19 Chinese wild apples, and two apple cultivars with unknown origins) based on single-nucleotide polymorphism (SNP) markers. A total of 38,364 SNPs were obtained with an average of 2256 SNPs per chromosome. The average of the polymorphism information content (PIC), gene diversity, and allele frequency for SNPs was 0.268, 0.306, and 0.364, respectively. A circular phylogenetic tree constructed based on SNP data revealed that the 88 Malus accessions could be divided into three groups. However, a population structure analysis suggested the 88 Malus accessions could be divided into four groups. A principal component analysis (PCA) revealed some population stratification. The first three PCs accounted for 41.62% of the population-wide SNP variation, with PC1 accounting for 33.9%. Moreover, the kinship values of the 88 Malus accessions ranged from 0 to 2.36, with 96.42% of the kinship values between 0 and 0.2. A phylogenetic tree and a PCA indicated the Chinese wild apples widely distributed among the cultivated apples had a diverse genetic background. Characterizing the genetic relationships between cultivated apples and Chinese wild apples is essential for increasing the genetic diversity of the germplasms used by apple breeders.

     

Response to potyvirus infection and genetic mapping of resistance loci to potyvirus infection in Lactuca

 We have investigated the interaction between two different potyviruses and resistant cultivars of Lactuca sativa. Turnip mosaic virus (TuMV) and lettuce mosaic virus (LMV) were used to inoculate several cultivars under different temperature regimes to characterize the resistance reaction. Resistance conferred by the recessive mo locus against LMV infection did not provide immunity. Virus accumulated in plant tissues to different levels depending on the genetic background of the cultivar, suggesting that several genes were involved in the resistance phenotype. Under temperature regimes that enhanced the hypersensitive reaction, resistant cultivars produced necrotic reactions. In contrast, resistance to TuMV infection conferred by the dominant Tu locus resulted in complete immunity in the plant. No virus accumulated in inoculated leaves nor was any necrotic reaction observed. The resistance loci were characterized at the genetic level by mapping them relative to molecular markers. Only weak linkages could be identified to mo, again supporting the hypothesis that several genes are involved. The Tu locus was mapped in two different crosses relative to several markers, the closest two linked at less than 1 cM. A high-resolution genetic map of the Tu locus was constructed by screening 500 F₂ individuals for recombinants around that locus. Received: 4 June 1996/Accepted: 15 November 1996     

Resistance to Phytophthora fragariae var. fragariae in strawberry: the Rpf2 gene

  Phytophthora fragariae var. fragariae is the causal agent of red stele (red core) root rot in strawberry (Fragaria spp.). The inheritance of resistance to one isolate of this fungus was studied in 12 segregating populations of F.×ananassa derived from crosses between four resistant cultivars (‘Climax’, ‘Redgauntlet’, ‘Siletz’, and ‘Sparkle’) and three susceptible cultivars (‘Blakemore’, ‘Glasa’, and ‘Senga’ Sengana’). The analysis clearly supports the hypothesis of a single segregating dominant resistance gene. It is proposed that this gene be designated Rpf2. Received 12 November 1996 / Accepted: 22 November 1996     

Characterization of three new S-alleles and development of an S-allele-specific PCR system for rapidly identifying the S-genotype in apple cultivars

Apple (Malus domestica Borkh), a member of the Rosaceae, shows gametophytic self-incompatibility (GSI) controlled by polymorphic S-alleles. Identifying the S-genotypes of apple cultivars can be applied on correct assignment of apple cultivars to cross-compatibility groups, which is important for the efficient production of apple fruit. This study characterized three new S-alleles (designated S ₄₄ , S ₄₅ , and S ₄₆ ) in apple and developed an efficient analysis method that can be used to characterize S-genotypes by utilizing allele-specific polymerase chain reaction rapidly. Nineteen allele-specific primers were selectively designed to identify different alleles. Using this method, S-genotypes of 157 apple cultivars were identified.     

Evidence for single gene resistance in apple to brownheaded leafroller, Ctenopseustis obliquana, and implications for resistance to other New Zealand leafrollers

The survival and development rate of Ctenopseustis obliquana (Walker) (Lepidoptera: Tortricidae) larvae, and weight of pupae were measured on detached mature leaves of two apple (Malus domestica Borkh.) progenies derived from the resistant (R) parent ‘Prima’ crossed with the susceptible (S) cultivars ‘Liberty’ (n = 44) and ‘Red Delicious’ (n = 35). The R:S ratio in both these modified backcross families did not differ significantly from the 1:1 expected in the case of monogenic resistance, carried in a heterozygous condition in the resistant parent. The survival to pupation on the individual seedlings was either zero/very low (R) or high (S). With all resistant seedlings being heterozygous, this indicates that the resistance allele shows complete dominance over the susceptible allele. We have named this putative gene Cob1. The expression of the resistance was found to be influenced by both the colony of C. obliquana used and the time of the season when resistance was assessed. In a separate experiment with another tortricid, there was no survival of Planotortrix octoDugdale larvae on the apple cultivar ‘Prima’ and high survival on the cultivars ‘Liberty’ and ‘Red Delicious’. The similarity of the responses of the two leafroller species to these cultivars, and other published evidence concerning Planotortrix excessana (Walker) and Ctenopseustis herana(Felder and Rogerhofer), suggest that the resistance discovered to C. obliquana may be effective against all four endemic tortricid species. The implications of these findings for apple breeding and leafroller control in New Zealand are discussed.     

Genome mapping of three major resistance genes to woolly apple aphid (Eriosoma lanigerum Hausm.)

Woolly apple aphid (WAA; Eriosoma lanigerum Hausm.) can be a major economic problem to apple growers in most parts of the world, and resistance breeding provides a sustainable means to control this pest. We report molecular markers for three genes conferring WAA resistance and placing them on two linkage groups (LG) on the genetic map of apple. The Er1 and Er2 genes derived from ‘Northern Spy’ and ‘Robusta 5,’ respectively, are the two major genes that breeders have used to date to improve the resistance of apple rootstocks to this pest. The gene Er3, from ‘Aotea 1’ (an accession classified as Malus sieboldii), is a new major gene for WAA resistance. Genetic markers linked to the Er1 and Er3 genes were identified by screening random amplification of polymorphic deoxyribonucleic acid (DNA; RAPD) markers across DNA bulks from resistant and susceptible plants from populations segregating for these genes. The closest RAPD markers were converted into sequence-characterized amplified region markers and the genome location of these two genes was assigned to LG 08 by aligning the maps around the genes with a reference map of ‘Discovery’ using microsatellite markers. The Er2 gene was located on LG 17 of ‘Robusta 5’ using a genetic map developed in a M.9 × ‘Robusta 5’ progeny. Markers for each of the genes were validated for their usefulness for marker-assisted selection in separate populations. The potential use of the genetic markers for these genes in the breeding of apple cultivars with durable resistance to WAA is discussed.