Jasna Sehic

Genetic diversity in watermelon (Citrullus lanatus) landraces from Zimbabwe revealed by RAPD and SSR markers.

Low polymorphism in cultivated watermelon has been reported in previous studies, based mainly on US Plant Introductions and watermelon cultivars, most of which were linked to breeding programmes associated with disease resistance. Since germplasm sampled in a putative centre of origin in southern Africa may harbour considerably higher variability, DNA marker-based diversity was estimated among 81 seedlings from eight accessions of watermelon collected in Zimbabwe; five accessions of cow-melons (Citrullus lanatus var. citroides) and three of sweet watermelons (C. lanatus var. lanatus). Two molecular marker methods were used, random amplified polymorphic DNA (RAPD) and simple sequence repeats (SSR) also known as microsatellite DNA. Ten RAPD primers produced 138 markers of which 122 were polymorphic. Nine SSR primer pairs detected a total of 43 alleles with an average of 4.8 alleles per locus. The polymorphic information content (PIC) ranged from 0.47 to 0.77 for the RAPD primers and from 0.39 to 0.97 for the SSR loci. Similarity matrices obtained with SSR and RAPD, respectively, were highly correlated but only RAPD was able to provide each sample with an individual-specific DNA profile. Dendrograms and multidimensional scaling (MDS) produced two major clusters; one with the five cow-melon accessions and the other with the three sweet watermelon accessions. One of the most variable cow-melon accessions took an intermediate position in the MDS analysis, indicating the occurrence of gene flow between the two subspecies. Analysis of molecular variation (AMOVA) attributed most of the variability to within-accessions, and contrary to previous reports, sweet watermelon accessions apparently contain diversity of the same magnitude as the cow-melons.

Modern apple breeding is associated with a significant change in the allelic ratio of the ethylene production gene Md-ACS1

Summary Inreasing consumer demand for firm apple fruit has raised interest among scientists and breeders to identify heritable traits that affect fruit texture. One such candidate gene is the bi-allelic Md-ACS1 locus, that shows a strong association between genotype and internal ethylene content in ripening fruit. However, associations between genotype and fruit firmness, or between genotype and fruit softening during storage, have been somewhat unclear. In order to determine the potential importance of allelic variation at this locus, we used PCR methods to investigate Md-ACS1 alleles in 137 apple cultivars. In addition, we also compiled data from previously published studies, to achieve an eventual dataset with 270 cultivars. Allele 1, associated with higher ethylene concentrations in ripening apples, was much more common in older cultivars (relative frequency = 0.88 in cultivars introduced before 1800; 0.84 in cultivars introduced between 1800 – 1899; and 0.70 in cultivars introduced in 1900 – 1959). Conversely, allele 2 associated with lower ethylene concentrations, was more common in modern cultivars (relative frequency = 0.57 in cultivars introduced since 1960). The frequencies of the three Md-ACS1 genotypes (1/1, 1/2, 2/2), as well as the relative allele frequencies (1 vs. 2), varied significantly depending on the date of introduction of the investigated cultivars ( i.e., 1800 – 1899 vs. 1900 – 1959; and 1900 – 1959 vs. ≥ 1960). The significant shift in allelic ratios at the Md-ACS1 locus observed during the 20th century was probably associated with the substantial impact that a small number of heterozygous cultivars have had on modern apple breeding. Allelic variation at the Md-ACS1 locus may thus be one of the most influential factors in modern apple breeding.

Cut-off shoots method for estimation of partial resistance in apple cultivars to fruit tree canker caused by Neonectria ditissima

Fruit tree canker, caused by the fungus Neonectria ditissima, is an economically devastating disease in apple orchards, especially in north-western Europe. Complete resistance has not yet been reported in apple, but variation in levels of partial resistance has been described and could be valuable in plant breeding programmes. A screening method based on spore inoculation of manually inflicted leaf scars on cut shoots was evaluated for reliability and repeatability in discrimination of 11 apple cultivars during two years – 2012 and 2013 – in two different facilities – biotron and standard greenhouse – and different time periods (February–May). The resulting cankers were counted (infection percentage), first appearance noted (incubation period) and lesion size measured at regular intervals during a period of 25–29 days for comparison of resistance levels. Results of two-way analysis of variance and correlation analyses showed that the area under the disease progress curve yielded the most robust data. This parameter was then applied for screening 30 apple cultivars using the same cut-shoot method. ‘Elise’ showed very high susceptibility, while the ornamental ‘Prairifire’ showed the highest level of partial resistance. Results suggested that cut shoots can be used to assess levels of resistance among cultivars, but great care must be taken to provide stable experimental conditions.

Self-incompatibility alleles of 104 apple cultivars grown in northern Europe

Summary Gametic self-incompatibility in apple is determined by a set of S-locus alleles, which can be identified using PCR with allele-specific DNA primers. Allele composition has previously been determined for a large number of apple cultivars grown in North America, central and southern Europe, and Asia. In the present study, 103 not previously studied apple cultivars that are grown mainly in northern Europe were scored for their S-allele composition in order to provide apple growers and breeders with information on incompatibility among cultivars. In addition, S-allele frequencies were determined in some control cultivars and compared with data reported previously. A different genotype was found for ‘Discovery’, which was therefore added to our list. The most common S-allele in the resulting set of 104 cultivars investigated at Balsgård was S7 (18%) followed by S3 (17%), S5 (14%), and S1 and S2 (both at 11%). Comparisons of allele frequencies obtained from previous compilations showed that the frequency of S9, in particular, deviated considerably; 15–16% was noted in two other studies, but only 1% in the Balsgård study. This discrepancy is most likely due to the importance of ‘Red Delicious’ (S9S28) in almost all areas of the World except northern Europe. A preponderance (30%) of the S3 allele was seen in a collection of 23 scab-resistant cultivars, suggesting that cross-compatibility may become a problem, especially in organic orchards.

Alteration of Neutrophil Reactive Oxygen Species Production by Extracts of Devil’s Claw (Harpagophytum)

Harpagophytum, Devils Claw, is a genus of tuberiferous xerophytic plants native to southern Africa. Some of the taxa are appreciated for their medicinal effects and have been traditionally used to relieve symptoms of inflammation. The objectives of this pilot study were to investigate the antioxidant capacity and the content of total phenols, verbascoside, isoverbascoside, and selected iridoids, as well as to investigate the capacity of various Harpagophytum taxa in suppressing respiratory burst in terms of reactive oxygen species produced by human neutrophils challenged with phorbol myristate acetate (PMA), opsonised Staphylococcus aureus, and Fusobacterium nucleatum. Harpagophytum plants were classified into different taxa according to morphology, and DNA analysis was used to confirm the classification. A putative new variety of H. procumbens showed the highest degree of antioxidative capacity. Using PMA, three Harpagophytum taxa showed anti-inflammatory effects with regard to the PBS control. A putative hybrid between H. procumbens and H. zeyheri in contrast showed proinflammatory effect on the response of neutrophils to F. nucleatum in comparison with treatment with vehicle control. Harpagophytum taxa were biochemically very variable and the response in suppressing respiratory burst differed. Further studies with larger number of subjects are needed to corroborate anti-inflammatory effects of different taxa of Harpagophytum.