Black spot in roses caused by the hemibiotrophic ascomycete Diplocarpon rosae (Wolf) (anamorph Marssonina rosae) is the most devastating disease of field grown roses and, therefore, affects both ...consumers of ornamental roses and commercial production. Chemical control of the disease is restricted by regulations, and consumers increasingly demand resistant varieties. As breeding black spot resistant rose varieties is complicated by its polyploid nature and the regular emergence of new pathogenic races of the pathogen, a deeper understanding of the biological characteristics of the interaction between the fungal parasite and its host is urgently needed. This review summarizes some investigations of the parasite and its interactions from early descriptions of the pathogen to recent molecular analyses of the fungus.
Amplified fragment length polymorphism (AFLP) markers and multilocus sequence analysis (MLSA) were used to analyse 63 bacterial strains, including 30 soft‐rot‐causing bacterial strains collected from ...Syrian potato fields and 33 reference strains. For the MLSA, additional sequences of 41 strains of Pectobacterium and Dickeya, available from the NCBI GenBank, were included to produce a single alignment of the 104 taxa for the seven concatenated genes (acnA, gapA, proA, icd, mtlD, mdh and pgi). The results indicate the need for a revision of the previously classified strains, as some potato‐derived Pectobacterium carotovorum strains were re‐identified as P. wasabiae. The strains that were classified as P. carotovorum during the analyses demonstrated high heterogeneity and grouped into five P. carotovorum highly supported clusters (PcI to PcV). The strains represented a wide range of host plants including potatoes, cabbage, avocados, arum lilies, sugar cane and more. Host specificity was detected in PcV, in which four of the six strains were isolated from monocotyledonous plants. The PcV strains formed a clearly distinct group in all the constructed phylogenetic trees. The number of strains phylogenetically classified as subspecies ‘P. c. subsp. brasiliensis’ in PcIV dramatically increased in size as a result of the characterization of new isolates or re‐identification of previous P. carotovorum and P. atrosepticum strains. The P. carotovorum strains from Syria were grouped into PcI, PcII and PcIV. This grouping indicates a lack of correlation between the geographical origin and classification of these pathogens.
Flower color is one of the most important traits of ornamental roses. Anthocyanins are the major secondary metabolites responsible for the red and pink colors found among rose cultivars. Color varies ...depending on the combination of particular anthocyanins, their co-factors and their concentrations. Several genetic investigations have indicated that variation in flower color is dependent on monogenic factors and quantitative trait loci (QTL). Here, we analyze quantitative variation of total anthocyanins in diploid rose progeny. We demonstrate that the environment produces relatively small effects; the main causes of variation in anthocyanin content are the genetic differences between individuals. Two major QTLs were detected in all six tested environments. Four additional QTLs were found only in a subset of the environments. Some of the QTLs either co-segregate or are located close to the map positions of known structural genes of the anthocyanin biosynthesis pathway or transcriptional regulators of anthocyanin biosynthesis. This information might be used to characterize tetraploid parental genotypes for their potential to pass on higher anthocyanin contents to their progeny.
Black spot disease caused by the hemibiotrophic ascomycete Diplocarpon rosae is the most devastating disease of field‐grown roses. Although resistance to black spot is an important trait for rose ...breeding, little information on the diversity of the pathogen is currently available. To date, a number of single‐spore isolates have been characterized based on a set of test genotypes of the host. In this study, six polymorphic simple sequence repeat (SSR) markers for D. rosae were developed and their potential application to single‐spore isolates collected from a wide range of geographic locations within and outside Europe discussed. Populations of the fungus were then analysed in different German rose collections/populations. Gene diversity was highest in older rose collections managed without fungicide application, and lowest in the two‐ to three‐year‐old testing sites of German rose breeders. Additional analyses of a global collection of single samples and populations revealed no unique alleles from any of the locations, indicating that global trading of rose varieties has led to an admixture of the pathogen.
Roses produced or grown in the field, as well as pot‐grown and cut roses, are attacked by different fungal pathogens causing leaf spot diseases. The incorrect identification and scoring of these ...pathogens and the lack of information about their genetic and pathotype diversity hamper resistance breeding. This is especially true for the hemibiotrophic ascomycete Sphaceloma rosarum, which is often confused with other fungi. Here for the first time, the genetic variability between isolates at both the molecular and morphological level is analysed. Eighty leaf spot samples were collected from different rose genotypes at five different locations, and 15 single conidial isolates established. All of the samples showed high morphological similarities to the reference isolate CBS 213.33 that was obtained from a public repository. By sequencing a part of the large subunit (LSU) of the 28S ribosomal RNA and phylogenetic analysis, high sequence similarities were shown to other Sphaceloma species for 13 of the isolates and the CBS reference. One of the isolates clustered with Septoria species and another clustered with Seimatosporium species. UPGMA clustering with 145 polymorphic AFLP markers resulted in five distinct groups in the majority rule consensus tree for the 14 S. rosarum isolates, including the CBS reference. Jaccard similarities ranged from 0·31 to 0·91. A detached leaf assay using a differential set of five rose genotypes led to the classification of the five tested isolates as five distinct pathotypes. Therefore, grouping depending on the avirulence gene diversity was clearly different from clustering using selectively neutral AFLP markers that were evenly distributed throughout the genome.
The objective of this study was to determine quantitative trait loci (QTL) underlying ten floral and related traits in Aquilegia. The traits assessed were calyx diameter, corolla diameter, petal ...length, petal blade length, sepal length, sepal width, spur length, spur width, plant height and flower number. These are important traits for ornamental value and reproductive isolation of Aquilegia. QTL analysis of these traits was conducted using single‐marker analysis and composite interval mapping (CIM). We used an F₂ population consisting of 148 individuals derived from a cross between the Chinese wild species Aquilegia oxysepala and the cultivar Aquilegia flabellata ‘pumila’. Resulting CIM analysis identified 39 QTLs associated with these traits, which were mapped on seven linkage groups. These QTLs could explain 1.22–53.28% of the phenotypic variance. Thirty‐one QTLs, which explained more than 10% of the phenotypic variation, were classified as major QTLs. Graphical representations of the QTLs on seven linkage groups were made. Our research provides the potential for future molecular assisted selection breeding programmes and the cloning of target genes through fine mapping.
The production of African nightshade is below its potential due to a lack of superior varieties. The development of varieties through breeding programmes has been initiated in order to supply farmers ...with quality seeds. However, systematic studies on the agronomic performance of African nightshade germplasm have been started only recently, and publications in this area are very scarce. In this study, we analysed morphological traits relevant for the agronomic performance of 54 entries comprising two species:
Solanum villosum
and
S. scabrum
. In addition, AFLP markers and newly developed SSR markers were used to assess genetic diversity and differentiation in the African nightshade entries. An analysis of molecular variance showed higher variation within than among entries. A cluster analysis grouped the entries into two clusters representing the two species. The analysis of agronomic traits revealed significant differences among entries. The genetic diversity of the released cultivars and accessions was comparable to but lower than that of the local cultivars. Additionally, the local cultivars had higher allelic richness and a larger number of unique alleles than did the developed cultivars and could serve as a useful gene pool for future breeding of superior germplasm.
Pollen viability and male meiosis in intraspecific hybrids of Hydrangea aspera subsp. aspera Kawakami group (2n = 2x = 36) and subsp. sargentiana (2n = 2x = 34) were investigated. Although it had ...been assumed that they were sterile, pollen viability was observed; it varied from 2.5% to 12.1%. The production of gametes with different chromosome numbers was implied by the analysis of the dispersion of the diameter distribution of pollen grains. Analysis of male meiosis made it possible to identify the origins with two major categories of meiotic aberrations: abnormal chromosome distribution (early chromosome migration at metaphase, lagging chromosomes at anaphase, micronuclei at telophase), leading to the formation of unbalanced tetrads and/or ones with supernumerary microspores; and abnormal spindle orientation in metaphase II (tripolar, fused and parallel spindles), leading to the formation of dyads or triads. The mode of 2n pollen formation is of the First Division Restitution type. The high level of parental heterozygosity that is normally associated with them should facilitate the transfer of a polygenic trait in breeding programme.
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