Molecular Assessment of Genetic Diversity among Egyptian Landraces of Wheat (Triticum aestivum L.) Using Microsatellite Markers

To increase the genetic progress in wheat (Triticum aestivum L.) yield, breeders search for germplasm of high genetic diversity, one of them is the landraces. The present study aimed at evaluating genetic diversity of 20 Egyptian wheat landraces and two cultivars using microsatellite markers (SSRs). Ten SSR markers amplified a total of 27 alleles in the set of 22 wheat accessions, of which 23 alleles (85.2%) were polymorphic. The majority of the markers showed high polymorphism information content (PIC) values (0.67-0.94), indicating the diverse nature of the wheat accessions and/or highly informative SSR markers used in this study. The genotyping data of the SSR markers were used to assess genetic variation in the wheat accessions by dendrogram. The highest genetic distance was found between G21 (Sakha 64; an Egyptian cultivar) and the landrace accession No. 9120 (G11). These two genotypes could be used as parents in a hybridization program followed by selection in the segregating generations, to identify some transgressive segregates of higher grain yield than both parents. The clustering assigned the wheat genotypes into four groups based on SSR markers. The results showed that the studied SSR markers, provided sufficient polymorphism and reproducible fingerprinting profiles for evaluating genetic diversity of wheat landraces. The analyzed wheat landraces showed a good level of genetic diversity at the molecular level. Molecular variation evaluated in this study of wheat landraces can be useful in traditional and molecular breeding programs.

Genetic Variation in Pawpaw Cultivars Using Microsatellite Analysis

Pawpaw (Asimina triloba) is a tree fruit native to eastern North America, which is in the early stages of domestication. Most early 20th century pawpaw cultivars have been lost; however, recent cultivar releases and potential new releases may have enhanced genetic diversity. The objective of this study was to compare the genetic variation exhibited among older and new pawpaw cultivars and Kentucky State University (KSU) advanced selections using simple sequence repeat (SSR) markers. Polymorphic microsatellite marker analysis was conducted with nine older pawpaw cultivars, six recently released PawPaw Foundation (PPF) cultivars, and nine KSU advanced selections. Using 18 microsatellite loci, a total of 179 alleles were amplified in the set of 24 genotypes. The major allele frequency (0.13 to 0.96), number of genotypes (two to 23), and allele size (96 to 341 bp) varied greatly by locus. Eighteen loci were highly polymorphic, as indicated by high expected heterozygosity (He = 0.71) and observed heterozygosity (Ho = 0.65) values as well as high polymorphism information content (polymorphism information content = 0.69). The dinucleotide SSR (GA and CA motifs) loci were more polymorphic than trinucleotide (ATG and AAT motifs) SSRs. The PPF cultivars and KSU advanced selections were more closely grouped genetically than with older cultivars. Older cultivars displayed the greatest genetic diversity (Ho = 0.69). The pawpaw cultivar base of older and PPF cultivars does appear to be genetically diverse. However, KSU advanced selections contain unique pawpaw germplasm that should enhance the genetic base of cultivars if these selections are released to the public.

Microsatellite Markers for Raspberry and Blackberry

Twelve microsatellites were isolated from simple sequence repeat (SSR)-enriched genomic libraries of ‘Meeker’ red raspberry (Rubus idaeus) and ‘Marion’ blackberry (Rubus hybrid). These primer pairs plus one developed from a GenBank red raspberry sequence were evaluated in 48 raspberry and 48 blackberry genotypes. Only RhM031 did not generate a product in raspberry, whereas RiG001 failed to amplify in blackberry and hybrid accessions. The number of polymerase chain reaction products per primer pair in the 12 SSRs that successfully amplified was higher in blackberry genotypes and their hybrids than in raspberry, ranging from three to 29 in blackberry (average, 14.4) and from one to 15 in red raspberry (average, 7.5). Diversity estimates were determined for 10 of 12 SSRs that amplified up to two products in 44 red raspberry genotypes. The best SSR loci based on high observed and expected heterozygosities, high polymorphism information content, and low inbreeding coefficient were RiM019, RhM003, and RhM011. They mapped to three different linkage groups (5, 2, and 7, respectively) in red raspberry and differentiated the unique genotypes identified with the 12 SSRs in each crop type.