Status and Need of Research on Rhizobia and Arbuscular Mycorrhizal Fungi Associated with Leguminous Plants in Saudi Arabia

Most regions of Saudi Arabia are frequently subjected to high temperature and drought spells which destroy natural vegetation and lead to soil erosion and the advance of sand dunes.  The use of legume plants may help to preserve these ecosystems and to slow down desertification processes. Legumes produce extensive, deep root systems with a capacity to develop mycorrhizal and rhizobial symbioses facilitating the plant’s nutrition via enhanced soil nutrients absorption and atmospheric nitrogen fixation, respectively. These associations play a vital role in preserving and even restoring the fertility of poor and eroded soils. Research on tripartite associations of Arbuscular mycorrhizal fungi (AMF), rhizobia and legumes is rare in Saudi Arabia. Little is known about the diversity of these beneficial symbioses in Saudi ecosystems and their beneficial role for the sustainable management of range land. We attempted to explore the present status of research on rhizobia and AMF associated with various legumes in Saudi Arabia. The use of legume plants associated with microbial symbionts may be a useful asset in preserving fragile ecosystems and combating desertification. The identification of adapted and efficient legume-rhizobia-fungi tripartite associations in local ecosystems is of paramount importance for successful ecosystem restoration, rangeland and forest management and agricultural sustainability especially under unfavorable environmental conditions due to soil salinity, drought and heat stress

Influence of light intensity and salinity on growth and antioxidant machinery of Thymus vulgaris L.

323-335Thymus vulgaris L. commonly known as Thyme or Garden Thyme, is important medicinal herb used for their wide-ranging therapeutic properties. Agriculture practices of thyme plants influence their growth and biochemical composition. Here, we have evaluated the effects of two production systems and irrigation with saline water on growth, physiological characteristics and antioxidant capacity of T. vulgaris. Two levels of salinity stress (50 and 150 mM) were applied for 2 and 4 weeks under shade enclosure or open field. The results showed that NaCl-treated plants grown in shade enclosure showed reduced total dry weight and relative water content, photosynthetic characteristics and leaf pigments when compared to full sunny conditions. However, the shade conditions enhanced glucose and fructose accumulation mainly after a short period of NaCl stress application. The reduction of Ca2+ and K+ was lower in NaCl-stressed plants grown under open-field conditions. Besides, under sunny conditions, plants showed significant increase in malondialdehyde (MDA) and H2O2 contents. Our results demonstrated that these plants in open field have higher contents of reduced ascorbate (ASC) and reduced glutathione (GSH) than plants grown in shade enclosure, which could be related to enhanced activity of APX and GR. An increase in superoxide dismutase (SOD) and catalase (CAT) activity was also recorded. Moreover, activities of dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR) were mainly dependent on the intensity of NaCl stress

influence of light intensity and salinity on growth and antioxidant machinery of Thymus vulgaris L

Thymus vulgarisL. commonly known as Thyme or Garden Thyme, is important medicinal herb used for their wide-ranging therapeutic properties. Agriculture practices of thyme plants influence their growth and biochemical composition. Here, we have evaluated the effects of two production systems and irrigation with saline water on growth, physiological characteristics and antioxidant capacity of T. vulgaris. Two levels of salinity stress (50 and 150 mM) were applied for 2 and 4 weeks under shade enclosure or open field. The results showed that NaCl-treated plants grown in shade enclosure showed reduced total dry weight and relative water content, photosynthetic characteristics and leaf pigments when compared to full sunny conditions. However, the shade conditions enhanced glucose and fructose accumulation mainly after a short period of NaCl stress application. The reduction of Ca2+ and K+ was lower in NaCl-stressed plants grown under open-field conditions. Besides, under sunny conditions, plants showed significant increase in malondialdehyde (MDA) and H2O2contents. Our results demonstrated that these plantsin open fieldhave higher contents of reduced ascorbate (ASC) and reduced glutathione (GSH) than plants grown in shade enclosure, which could be related to enhanced activity of APX and GR. An increase in superoxide dismutase (SOD) and catalase (CAT) activity was also recorded. Moreover, activities of dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR) were mainly dependent on the intensity of NaCl stress

Perspective Chapter: Rootstock-Scion Interaction Effect on Improving Salt Tolerance in Fruit Trees

Salt stress is a sever threat to global agriculture. Improving salt tolerance is a problematic task due to the large number of characteristics involved. Graft technique is a potential substitute to breeding and interesting practices to salt tolerance since it unites a scion and rootstock of two genotypes. Increased salinity tolerance in fruit trees will alter water relations, disrupt ionic balance, which can harm plant tissues and thus limit plant productivity. Therefore, the ability of fruit trees to resist salinity varies by species, although it is mostly determined by the type of their root systems. In this regard, the selection of salt-tolerant rootstocks can help maintain productivity under salinity. Several physiological and biochemical changes are attributed to the favorable response of grafting exerted by tolerant rootstocks or scion-rootstock interactions on yield and fruit attributes of plants in saline environments. Rootstocks provide grafted plants different salt tolerance mechanisms including the accumulation of compatible solutes and enhancing the antioxidant mechanisms in scion. The importance of grafting, strategies for selecting appropriate rootstocks, scion-rootstock interaction for growth and the tolerance mechanisms used by plants to avoid the effects of salt stress, are all discussed in this review. Grafting’s potential challenges are also discussed

Water relations and drought-induced embolism in olive (Olea europaea) varieties 'Meski' and 'Chemlali' during severe drought

We examined the effects of drought on the water relations, osmotic adjustment and xylem vulnerability to embolism of olive (Olea europaea L.) varieties, 'Meski' and 'Chemlali'. Two-year-old self-rooted cuttings growing in sand-filled pots in a greenhouse were subjected to water stress by withholding water for 60 days. Water relations and gas exchange measurements showed that 'Chemlali' was more drought resistant than 'Meski' and had a greater capacity for osmotic adjustment through solute accumulation. However, when water stress was acute, the effect of osmoregulation on leaf cell turgor was largely counteracted by xylem cavitation. Cavitation vulnerability curves showed that both varieties were highly resistant to embolism formation. The xylem water potential inducing 50% loss of stem conductivity approached -7 MPa in 'Meski' and only slightly less in 'Chemlali'. Although the difference between varieties in susceptibility to xylem embolism was small, it appears to account in large part for the difference between them in the ability to tolerate severe drought

Salt-induced oxidative stress in rosemary plants:Damage or protection?

Mechanisms of photoprotection and antioxidant protection, including changes in chlorophylls, xanthophyll cycle components and levels of low-molecular-weight chloroplastic antioxidants (lutein, beta-carotene and alpha-tocopherol) were studied together with levels of malondialdehyde, a product of lipid peroxidation, in the response of rosemary (Rosmarinus officinalis L) plants to salt stress. Plants were exposed to increasing NaCl concentrations (50, 100 and 150 mM) for 6 weeks, and two concentrations of the following chloride salts: KCl, CaCl(2), MgCl(2) and FeCl(3), were used together with 100 mM NaCl to explore the extent to which these salts can alter the mechanisms of photoprotection, antioxidant protection and malondialdehyde accumulation in leaves. Increasing concentrations of NaCl decreased leaf water contents and photosynthetic pigment levels, while the contents of alpha-tocopherol and malondialdehyde increased. but with completely different kinetics. alpha-Tocopherol levels increased in a dose-dependent manner as stress progressed, while malondialdehyde levels increased at the highest dose (150 mM NaCl) but only during early phases of stress. Furthermore, although the addition of chloride salts to NaCl-treated plants apparently improved leaf physiological status, in terms of water and chlorophyll contents, plants showed an increased photoprotective demand and increased oxidative stress, particularly in FeCl(3)-treated plants. It is concluded that (i) rosemary plants can withstand moderate doses of NaCl in the medium (at least 150 mM NaCl for 6 weeks), (ii) oxidative stress may be a mechanism for protecting plants from moderate doses of salt stress rather than causing damage to plants, and (iii) the addition of chloride salts to NaCl-treated plants may dramatically increase the photoprotective demand and oxidative stress of leaves, while plant growth is not negatively affected. (C) 2010 Elsevier B.V. All rights reserved

Assessment of genetic diversity and phylogenetic relationship of local coffee populations in southwestern Saudi Arabia using DNA barcoding

The genetic diversity of local coffee populations is crucial to breed new varieties better adapted to the increasingly stressful environment due to climate change and evolving consumer preferences. Unfortunately, local coffee germplasm conservation and genetic assessment have not received much attention. Molecular tools offer substantial benefits in identifying and selecting new cultivars or clones suitable for sustainable commercial utilization. New annotation methods, such as chloroplast barcoding, are necessary to produce accurate and high-quality phylogenetic analyses. This study used DNA barcoding techniques to examine the genetic relationships among fifty-six accessions collected from the southwestern part of Saudi Arabia. PCR amplification and sequence characterization were used to investigate the effectiveness of four barcoding loci: atpB-rbcl, trnL-trnF, trnT-trnL, and trnL. The maximum nucleotide sites, nucleotide diversity, and an average number of nucleotide differences were recorded for atpB-rbcl, while trnT-trnL had the highest variable polymorphic sites, segregating sites, and haploid diversity. Among the four barcode loci, trnT-trnL recorded the highest singleton variable sites, while trnL recorded the highest parsimony information sites. Furthermore, the phylogenetic analysis clustered the Coffea arabica genotypes into four different groups, with three genotypes (KSA31, KSA38, and KSA46) found to be the most divergent genotypes standing alone in the cluster and remained apart during the analysis. The study demonstrates the presence of considerable diversity among coffee populations in Saudi Arabia. Furthermore, it also shows that DNA barcoding is an effective technique for identifying local coffee genotypes, with potential applications in coffee conservation and breeding efforts