Promising Application of Automated Liquid Culture System and Arbuscular Mycorrhizal Fungi for Large-Scale Micropropagation of Red Dragon Fruit.

Red dragon fruit (Hylocereus polyrhizus) is an economic and promising fruit crop in arid and semi-arid regions with water shortage. An automated liquid culture system using bioreactors is a potential tool for micropropagation and large-scale production. In this study, axillary cladode multiplication of H. polyrhizus was assessed using cladode tips and cladode segments in gelled culture versus continuous immersion air-lift bioreactors (with or without a net). Axillary multiplication using cladode segments (6.4 cladodes per explant) was more effective than cladode tip explants (4.5 cladodes per explant) in gelled culture. Compared with gelled culture, continuous immersion bioreactors provided high axillary cladode multiplication (45.9 cladodes per explant) with a higher biomass and length of axillary cladodes. Inoculation of H. polyrhizus micropropagated plantlets with arbuscular mycorrhizal fungi (Gigaspora margarita and Gigaspora albida) significantly increased the vegetative growth during acclimatization. These findings will improve the large-scale propagation of dragon fruit.

Evaluation of genetic diversity of Panicum turgidum Forssk from Saudi Arabia.

The genetic diversity of 177 accessions of Panicum turgidum Forssk, representing ten populations collected from four geographical regions in Saudi Arabia, was analyzed using amplified fragment length polymorphism (AFLP) markers. A set of four primer-pairs with two/three selective nucleotides scored 836 AFLP amplified fragments (putative loci/genome landmarks), all of which were polymorphic. Populations collected from the southern region of the country showed the highest genetic diversity parameters, whereas those collected from the central regions showed the lowest values. Analysis of molecular variance (AMOVA) revealed that 78% of the genetic variability was attributable to differences within populations. Pairwise values for population differentiation and genetic structure were statistically significant for all variances. The UPGMA dendrogram, validated by principal coordinate analysis-grouped accessions, corresponded to the geographical origin of the accessions. Mantel's test showed that there was a significant correlation between the genetic and geographical distances (r = 0.35, P < 0.04). In summary, the AFLP assay demonstrated the existence of substantial genetic variation in P. turgidum. The relationship between the genetic diversity and geographical source of P. turgidum populations of Saudi Arabia, as revealed through this comprehensive study, will enable effective resource management and restoration of new areas without compromising adaptation and genetic diversity.

Seed mycoflora of Ephedra aphylla and amino acid profile of seed-borne Aspergillus flavus.

Twenty-seven seed samples of Ephedra aphylla were collected from different rangelands in Riyadh region, Saudi Arabia during seed production season of 2010. They were assessed to determine the incidence of seedborne fungal flora using both agar plate and blotter paper methods. The investigation of the seeds yielded thirty four fungal species belonging to twelve genera, which are new record to seed-brone mycoflora of E. aphylla in Saudi Arabia. The agar plate method was found superior over blotter methods. The genus Aspergillus was the most prevalent one followed by Fusarium, Penicillium, Alternaria, and Chaetomium. Only eighteen isolates of A. flavus (∼ 28.6% of total isolates) were able to produce aflatoxins. Mycelial amino acids profile of selected aflatoxigenic isolates of A. flavus was investigated and five amino acids, namely cystein, lysine, praline, tryptophan and valine were common in mycelia and all of them were aflatoxins producers. Based on the dissimilarity coefficient between the isolates and their amino acids patterns, high diversity among the population of A. flavus has been recorded.

Effect of water stress by Polyethylene Glycol 8000 and Sodium Chloride on germination of Ephedra alata Decne seeds.

Ephedra alata Decne is a perennial shrub and it is a very effective sand-binder. In Saudi Arabia, the species is associated with sand dunes formation, especially the mobile, non-saline and low moisture content ones. Its geographical distribution in Saudi Arabia includes the Northern, Eastern and Central regions. The aims of this study were to determine the effects of temperature, water potential and Sodium Chloride on germination of E. alata. Seeds were collected from King Khalid Centre of Wildlife Research and Development at Thumama (80 km north east of Riyadh), Saudi Arabia. Seeds were germinated at four alternating temperature regimes (8/22; 9/23; 13/27 and 18/35 °C). Seeds were also germinated under stress of aqueous Polyethylene Glycol (PEG) solutions mixed to create water potentials of 0; -0.3; -0.6; -1.2 and -1.5 MPa. Seed were also germinated in Sodium Chloride solutions of 0, 0.05, 0.1, 0.2 and 0.3 mol l(-1). Optimum germination was attained at 13/28 °C that corresponds to temperatures prevailing during spring time. Seeds germinated in Polyethylene Glycol solutions exhibited significantly lower germination than control especially when water potential fell below -0.3 MPa. Germination was also negatively affected by 0.1 mol l(-1) Sodium Chloride solution or above. Results indicated that the germination temperature responses of the nondormant seeds synchronize the event of germination with the season when environmental conditions are more favorable for subsequent growth and seedling establishment. Germination was also sensitive to both water potential and salinity.