Here we describe an innovative, reproducible, and inexpensive method for in vitro cloning of guava using nodal stems segments. A novel process was established for completely inhibiting phenol-based browning by coating the explants at their cut ends with commercial silicon. A high regeneration frequency (98.33%) was achieved on MS medium supplemented with 4 mg/L BA and 0.4 mg/L IAA, with a maximum average number of 76.17 shoots per explant produced on the third subculture. The highest rooting percentage (95.83%) was obtained on shoots growing on half strength MS medium and supplemented with 4 mg/L IAA. The plantlets were acclimatized and successfully established in soil. RAPD analysis was used to compare the regenerated plants with their donor parents: the analysis showed a high similarity (94.50% on average) among the regenerated plants and their donor parents. Taking advantage of such highly regenerative technique in a woody plant like guava, an exponential increase in the number of in vitro produced plantlets can be achieved by utilizing the resulting shoots as nodal explant starting material to commercially propagate guava in vitro.

DNA based molecular markers allow precise, objective and rapid cultivar identification and discrimination. In the present study, the genetic variability and relationships among 65 hexaploid (Triticum aestivum L.) and 8 tetraploid (Triticum durum L.) wheat varieties were evaluated using five inter simple sequence repeats (ISSR) primers. The used primers generated 63 DNA fragments with an average of 12.6 bands per primer. Polymorphism percentage ranged from 53.33 % (ISSR-844) to 78.57 % (HB12) with an average of 64.95 %. The 308bp (HB12) DNA fragment was unique marker for durum wheat varieties while the 855bp (ISSR-814) fragment was unique maker for bread wheat genotypes. Low PIC values were found indicating the wide differences between the p and q alleles tested by the ISSR markers. The ISSR primers (HB12 and ISSR-844) possessed high RP values and therefore seem to be the most informative primers for distinguishing wheat varieties. The dendrogram indicated that the ISSR markers succeeded in distinguishing the tested varieties in relation to their ploidy level and location, which the tetraploid varieties were put together in one group as well as the hexaploid varieties.

Genetic diversity among in vitro plant regeneration in cumin has been examined by molecular markers analysis (ISSR and SRAP markers). Two landraces of cumin named Egyptian landraces (EGY genotype) and Indian landraces (IND genotype) were used as donor parents, three types of explants (hypocotyl, cotyledon and root) and four MS tissue culture media with different concentrations of growth regulators (auxin and cytokinin) were used to study the impact of genotype, type of explants and growth regulators on callus formation and plant regeneration in cumin. Significant differences among two cumin landraces were observed for regeneration rate and number of shoots per explant. These differences were depending on genotype, explant type and concentration of growth regulators. The best regeneration medium (MS with 0.5 mg/L 2,4-D) used for establishment of regenerated plants. Donor parent, Egyptian landraces (EGY) and Indian landraces (IND) and its regenerated plants on regeneration medium were selected and subjected to somaclonal variation analysis using molecular markers. ISSR (inter-simple-sequence-repeat) and SRAP (sequence-relatedamplified-polymorphism) markers were used to detect the genetic variations between two cumin landraces. Subsequently, primers which exhibited high polymorphism between donor parents were used to analysis of somaclonal variation between each donor parent and its regenerated plants (somaclones), as well as among somaclones. These markers revealed polymorphism showing clear different DNA fragment patterns in all somaclones, which were eminent in their differences from parents.

A total of 73 genotypes including 65 hexaploid (Triticum aestivum L.) and 8 tetraploid (Triticum durum L) wheat varieties were used in this study. Eleven microsatellite markers were used to test the genetic diversity of wheat genotypes, yielding a polymorphism. The total number of detected alleles was 89 with an average allele number of 8.1 per locus. The maximum number of polymorphic alleles (9 bands) was obtained by the primer SSR-9 while the minimum number (1 allele) was recorded for primer SSR-11 with an average 5 alleles per primer. Polymorphism percentage ranged from as low as 50 % (SSR-1, SSR-2 and SSR-5) to as high as 100% (SSR-10 and SSR-11) with an average of 68.24 %. Eleven alleles at molecular size [219 bp and 188 bp (SSR-1), 239 bp (SSR-3), 635 bp and 503 bp (SSR-4), 358 bp and 331 bp (SSR-8), 250 bp, 226 bp and 210 bp (SSR-9) and 532 bp (SSR-11)], were present only in bread wheat genotypes, while one allele at molecular size 312 bp generated with primer (SSR-6) was unique to durum wheat genotypes. These alleles could be used as marker to distinguish the durum wheat from the bread wheat genotypes. Polymorphism information content (PIC) value ranged from 0.06 (primer SSR-6) to 0.2 (primer SSR-11) with an average value of 0.13. These results reflect the wide range between the frequencies of alleles at loci of SSR studied in the tested wheat varieties. The dendrogram grouped the 73 wheat genotypes according to their ploidy levels into two main clusters. Cluster 1 included the durum wheat genotypes, while cluster 2 contained all bread wheat genotypes.

Generation mean analysis for drought tolerance was studied in wheat cross-1 (Pavon-76 X Gemmeiza-7) and cross-2 (ICR-DH18 X Pavon-76). The genotypes were evaluated under control and drought stress (15% polyethylene glycol 6000) at germination and seedling stage for seven traits. The additive-dominance model is adequate for explaining the inheritance of root and shoot lengths under both treatments and root fresh weight under drought stress in cross-1, and shoot length in both treatments and root length under drought stress in cross-2, while being inadequate in the other traits in the two crosses treatments. The additive-dominance and epistatic interaction effects recorded for germination percentage, root and shoot fresh and dry weights in both crosses suggested postponement of plant selections till the later generations for plant traits with such type of gene action. Epistasis absence and the contribution of considerable additive genetic variance in root and shoot lengths and root fresh weight indicating that recurrent selection in early segregating generations could be effective to select wheat lines with enhanced early tolerance to drought stress. Only two SSR primers and two TRAP primer pairs generated polymorphic bands from the tested genotypes. Four positive molecular markers were detected for drought tolerance. The UPGMA clustering analysis revealed correlation between drought tolerance genotypes and the studied molecular markers. The markers identified herein would allow implementing marker-assisted selection to screen wheat segregating populations for drought tolerance.