The genetic diversities of 4 species of subg. Lithocerasus (Prunus, Rosaceae) revealed by RAPD analysis

RAPD analysis was applied to reveal the genetic diversities of 4 speciesof subg. Lithocerasus within the genus Prunus using 40accessions representing the subgenera Prunophora, Amygdalus,Lithocerasus and Cerasus. The accession of subg. Lithocerasus are phenotypically similar to members of subgenus Cerasus but different with them in interspecific crossing tests and isozymeprofiles. Two major clusters, `Prunophora and Amygdalus group' and `Cerasus group' were constructed in the phenogram. We revealthat the examined 4 species of subg. Lithocerasus species; P.tomentosa Thunb., P. japonica Thunb., P. glandulosa Thunb.and P. besseyi Bailey, were genetically closer to the members ofsubgenera Prunophora and Amygdalus than to subg. Cerasus.     

Production and characterization of Raphanus sativus-Brassica rapa monosomic chromosome addition lines

Breeding of Raphanus sativus‐Brassica rapa monosomic chromosome addition lines (MALs, 2n = 19) was carried out by backcrossing the synthesized amphidiploid line, Raphanobrassica (R. sativus×B. rapa, 2n = 38, RRAA, line RA89) with R. sativus cv. ‘Shogoin’ (2n = 18, RR). In the first cross of Raphanobrassica× radish, four sesquidiploidal BC₁ plants (2n = 28, RRA, RA89‐36‐1, RA89‐31‐1, RA89‐31‐2, RA89‐31‐3) were successfully developed. In these plants, the chromosome configurations of 9II + 10I and 10II + 8I were observed frequently at first metaphase (MI) of meiosis in pollen mother cells (PMCs). The RA 89‐36‐1 plant produced many seeds in the reciprocal backcrosses with radish. About 50% of the BC₂ plants obtained from the cross of RA89‐36‐1 plant × radish were 2n = 19 plants, followed by 2n = 18 plants (24%) and 2n = 20 plants (19%). In the reciprocal cross, 2n = 19 plants were also developed at the rate of 40%. From analysis of specific morphological traits, 2n = 19 plants were classified into eight types (a‐h). When 25 selected primers were used in polyacrylamide gel electrophoresis, random amplified polymorphic DNA (RAPD) markers derived from B. rapa for each type of MAL were detected in numbers between three for e‐type and 16 for b‐type. RAPD markers specific for each type alone were from one (OPE 05‐344) for h‐type to nine for b‐type. In the g‐type, no marker specific to this type alone was observed. However, 19 bands were common between at least two types. These MAL plants exhibited predominantly the chromosome configuration of 9II + 1I at MI of PMCs, pollen and seed fertility being the same level as the radish cv. ‘Shogoin’. From the morphological traits and DNA markers, eight different MAL types among 10 expected were identified.     

Identification of RAPD markers linked to the rust (<Emphasis Type="Italic">Uromyces fabae</Emphasis>) resistance gene in pea (<Emphasis Type="Italic">Pisum sativum</Emphasis>)

Summary Two RAPD markers linked to gene for resistance (assayed as pustule number cm⁻² leaf area) to rust [Uromyces fabae (Pers.) de Bary] in pea (Pisum sativum L.) were identified using a mapping population of 31 BC₁F₁ [HUVP 1 (HUVP 1 × FC 1] plants, FC 1 being the resistant parent. The analysis of genetics of rust resistance was based on the parents, F₁, F₂, BC₁F₁ and BC₁F₂ generations. Rust resistance in pea is of non-hypersensitive type; it appeared to be governed by a single partially dominant gene for which symbol Ruf is proposed. Further, this trait seems to be affected by some polygenes in addition to the proposed oligogene Ruf. A total of 614 decamer primers were used to survey the parental polymorphism with regard to DNA amplification by polymerase chain reaction. The primers that amplified polymorphic bands present in the resistant parent (FC 1) were used for bulked segregant analysis. Those markers that amplified consistently and differentially in the resistant and susceptible bulks were separately tested with the 31 BC₁F₁ individuals. Two RAPD makers, viz., SC10-82₃₆₀ (primer, GCCGTGAAGT), and SCRI-71₁₀₀₀ (primer, GTGGCGTAGT), flanking the rust resistance gene (Ruf) with a distance of 10.8 cM (0.097 rF and LOD of 5.05) and 24.5 cM (0.194 rF and a LOD of 2.72), respectively, were identified. These RAPD markers were not close enough to Ruf to allow a dependable maker-assisted selection for rust resistance. However, if the two makers flanking Ruf were used together, the effectiveness of MAS would be improved considerably.     

Assessment of genetic variability in grapefruits (Citrus paradisi Macf.) and pummelos (C. maxima (Burm.) Merr.) using RAPD and SSR markers

The genetic variability of 38 grapefruit (Citrus paradisi Macf.) and three pummelos (C. maxima (Burm.) Merr..) accessions was evaluated using RAPD, and single sequence repeat (SSR) analyses. Approximately49% of the 198 RAPD were polymorphic, and 4.6 alleles per SSR loci were identified. PIC values changed from 0.093 to 0.450. A UPGMA phenetic tree was constructed and two main grapefruit groups were identified. The grapefruit accessions `do Cabo' and `Siamesa-Filipinas'clustered very close to the pummelos in Group A. The Group B consisted of three sub-groups, which comprised all of the other grapefruit accessions. The majority of grapefruit accessions showed a narrow genetic base suggesting that the observed morphological polymorphism within the group must be associated with somatic mutations, which were not detected by these molecular markers. This revised version was published online in August 2006 with corrections to the Cover Date.     

Identification of sex in Carica papaya L. using RAPD markers

Brazil is currently the worlds largest producer of papaya (Carica papayaL.), producing fruits for both the domestic market and export. Only fruits from hermaphrodite plants are marketed because they have the necessary commercial characteristics, i.e. they are pear-shaped and have thicker flesh and a smaller internal cavity. Increased papaya yield has been limited mainly by the ratio of female to hermaphrodite (1: 2) plants normally occurring in orchards. This ratio causes great losses to papaya producers and the identification of the sex of seedlings during the nursery stage would be an important advance. In our study random amplified polymorphic DNA (RAPD) analysis was used to differentiate between the sexual forms of three commercial C. papaya cultivars belonging to the Solo group. RAPD assays using the BC210 primer were able to detect hermaphrodites in all of the cultivars tested. The BC210₄₃₈molecular marker was much better at papaya sex differentiation than other markers described in the literature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Molecular diversity in Indian sugarcane cultivars as revealed by randomly amplified DNA polymorphisms

Genetic diversity in 28 prominent Indian sugarcane varieties cultivated under a wide range of agroclimatic conditions, was studied using 25 RAPD markers. The mean genetic distance among the 28 varieties was only 29.31%, implying that a large part of the genome is similar among the varieties. This probably arises from the lack of parental diversity, with few clones which are themselves related, contributing to the parentage of these varieties. The parentage of the varieties did not contribute significantly to the clustering pattern. Varieties belonging to the same parentage were grouped under different clusters while varieties from different parentages were grouped under the same cluster. The tropical and subtropical identities of the varieties also did not contribute to the clustering pattern as individual clusters included varieties from both tropics and subtropics. This shows that genetically similar varieties are present in both the regions. Among the varieties, Co 7717 was found to be totally distinct and divergent from rest of the varieties. The study reveals the limited genetic base of the current Indian commercial varieties and the need to diversify the genetic base by using new sources from the germplasm. This revised version was published online in August 2006 with corrections to the Cover Date.     

Monosomic addition lines of Beta corolliflora in sugar beet: plant morphology and leaf spot resistance

Monosomic addition lines in Beta vulgaris from Beta corolliflora were described morphologically and characterized for disease resistance. Monosomic addition plants (2n= 19) were selected among segregating offspring by a squash dot technique in combination with B. corolliflora‐specific probes. Plants carrying an added chromosome were characterized by leaf shape, plant size and plant vigour. In this way, most addition lines could be distinguished from diploid beets, however, to identify those plants unequivocally, molecular marker analysis was also necessary. Transmission frequencies of each addition line were determined to be in the range 13.9% (Cor‐4) to 60% (Cor‐9). High transmission rate of addition line Cor‐9 was assumed to be due to apomictic propagation because transmission rate after selfing cannot exceed 50%. Cercospora leaf spot resistance tests were performed on 167 monosomic plants from seven different addition lines, two fragment addition lines and 89 diploid controls. No line exhibited complete resistance, but the monosomic additions Cor‐3 and Cor‐4 showed significantly lower infection rates than their diploid sibling plants. The identification of monosomic addition lines with apomictic and disease resistance characters offers the possibility of transferring those genes to sugar beet.     

Effectiveness of Twenty-Four Barley Resistance Genes Against Powdery Mildew (Erysiphe graminis DC f. sp. hordei Em. Marchal) in Spain

Twenty-four near-isogenic barley lines, with a cv.‘Pallas’ background, carrying different mildew resistance genes were subjected in 1987, 1989 and 1990 to natural infection by the pathogen at several different and contrasting Spanish sites in order to study its virulence. The virulence genes proved to be geographically grouped into three regions: western (Valladolid), southern (Sevilla) and northern and northeastern (Navarra, Lleida and Girona). The mildew population of Lleida was more variable when compared with Navarra and Valladolid. Overall, the most effective resistance genes were: Ml-a13 + Ml-(Ru3), mlo and Ml-(1402).     

Geographical distribution of genetic variation in Stylosanthes scabra revealed by RAPD analysis

A large number of S. scabra accessions have been accumulated worldwide. The majority of them were collected from Brazil and most of the others came from either Colombia or Venezuela. One hundred of these accessions, selected to represent the geographical distribution of the S. scabra collection held at the Australian Tropical Forages Genetic Resource Centre, were analysed using RAPD as markers. Seven of these accessions were found not to be S. scabra. Of the S. scabra accessions, the average dissimilarity value among Brazilian accessions (0.053) was much lower than that among Colombian (0.074) or Venezuelan (0.088) accessions, with an overall dissimilarity value of 0.059 among all the S. scabra accessions. Based on their dissimilarity values, most of these accessions could be separated into five groups. Geographical distributions for most accessions in each of these groups were well defined. Limited long distance introductions/dispersions of S. scabra between these regions were detected and they were mainly confined to Brazilian genotypes. The clustering results based on RAPD were compared with those based on morphological-agronomical characters, and the groups produced by the two different methods did not always match. Possible reasons for this discrepancy are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

RAPD and SCAR markers linked to the sex expression locus M in asparagus

Bulk segregant analysis (BSA), random amplified polymorphic DNA (RAPD) and sequence characterized amplified region (SCAR) methods were used to map molecular markers to the sex locus M of asparagus. Two parents, A19 (male, Mm) and MW25 (female, mm), and 63 progeny were used for the study. Two DNA bulks, one male and one female, were made by pooling equal amounts of DNA from 10 randomly selected progeny of each sex type. A total of 760 arbitrary decamer oligonucleotide primers were used for RAPD analysis. Primer OPC15 produced two RAPD markers, OPC15-98 and OPC15-30, both of which were linked to the M locus at a distance of 1.6 cM. Subsequently, amplified RAPD fragment OPC15-98 was cloned and sequenced. The sequence was then used to design flanking 24-mer oligonucleotide SCAR primers SCC15-1 and SCC15-2. Both of these SCAR primers amplified a single 980 bp fragment; the same size as the cloned RAPD fragment. However, the SCAR marker was dominant as was the original OPC15-98 band from which it was derived. These RAPD and SCAR markers could be used for scoring male and female progeny in the mapping population, but were not found to be applicable to other asparagus germplasm studied. This revised version was published online in July 2006 with corrections to the Cover Date.