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

Management of Nitrogen and Calcium in Pear Trees for Enhancement of Fruit Resistance to Postharvest Decay

Management of pear (Pyrus communis L.) trees for low N and high Ca content in the fruit reduced the severity of postharvest fungal decay. Application of N fertilizer 3 weeks before harvest supplied N for tree reserves and for flowers the following spring without increasing fruit N. Calcium chloride sprays during the growing season increased fruit Ca content. Nitrogen and Ca management appear to be additive factors in decay reduction. Fruit density and position in the tree canopy influenced their response to N fertilization. Nitrogen: Ca ratios were lower in fruit from the east quadrant and bottom third of trees and from the distal portion of branches. High fruit density was associated with low N: Ca ratios. Nutritional manipulations appear to be compatible with other methods of postharvest decay control.EEA Alto ValleFil: Sugar, David. Oregon State University. Southern Oregon Experiment Station; Estados UnidosFil: Righetti, Timothy L. Oregon State University. Department of Horticulture; Estados UnidosFil: Sanchez, Enrique Eduardo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Alto Valle; ArgentinaFil: Khemira, Habib. Oregon State University. Department of Horticulture; Estados Unido

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

Improvement to the air-injection technique to estimate xylem vulnerability to cavitation

Several techniques have been developed to quantify the degree of embolism of the xylem using hydraulic conductance. Although there have been several improvements to these techniques, their reliability is still questionable and many technical pitfalls persist. We are proposing here a manometric approach to improve the accuracy of xylem cavitation measurement by the original air-injection technique which uses twigs exposed to pressurized air to cause cavitation. The measured parameter is air bubble production (P (b)) caused by xylem cavitation in birch (Betula pendula Roth) twigs from which the percent increase in bubble production is calculated to quantify xylem cavitation. Data produced by three different methods (bench-drying, air-injection, and manometric approach) are compared. Xylem vulnerability curves (VCs) constructed by the reference and reliable bench-drying technique and the manometric approach show similar sigmoid "S" shape, but a small anomaly appeared in the VC constructed by the original air-injection technique. The xylem pressure inducing 50% of embolism (P (50)) was the same with the three techniques. Furthermore, there was a strong positive correlation between the estimators of xylem cavitation measured by the three different methods. For its reliability, precision and ease we recommend the manometric technique as an improved version of the original hydraulic air-injection method

Comparative impacts of water stress on the leaf anatomy of a drought-resistant and a drought-sensitive olive cultivar

The effects of drought on several major morphological and anatomical features of leaves were investigated in an attempt to explain the origin of the difference in drought resistance between two olive (Olea europaea L.) cultivars, ('Chemlali' and 'Meski') previously demonstrated to be drought-resistant and drought-sensitive, respectively. Under water deficit conditions, 'Chemlali' maintained higher rates of photosynthetic assimilation and lower rates of transpiration compared to 'Meski'. In the present study, we found cultivar-dependent differences in leaf morpho-anatomical adaptations to drought stress. When subjected to water stress, the leaves of 'Chemlali' increased the thickness of their upper palisade and spongy parenchyma by 17% and 22%, respectively, compared with only 9% and 13% in the case of 'Meski'. A thicker palisade parenchyma could contain larger numbers of CO(2)-fixation sites, while a thicker spongy parenchyma could result in easier diffusion of CO(2) to these sites. Furthermore, stomatal density (SD) in 'Chemlali' leaves increased by 25% (vs. 7% for 'Meski' leaves) during drought treatment, which could also enhance the external supply of CO(2). Other morpho-structural traits implicated in the control of water loss were enhanced more in 'Chemlali' than in 'Meski' leaves. Under conditions of lower water availability, leaf size decreased by 24% in 'Chemlali' (vs. 15% in 'Meski'), trichome density (TD) increased by 25% (while remaining unchanged in 'Meski'), and the thickness of the upper and lower epidermis increased by 32% and 25%, respectively (while remaining unchanged in 'Meski'). The above morpho-anatomical adaptations should improve the water-use efficiency of the tree. These differential changes in leaf morphology and anatomy can explain, at least in part, the difference in drought resistance between the two cultivars. In particular, the upper palisade parenchyma, the spongy parenchyma, SD, and TD could be considered key structural features of leaves that govern the ability of a tree to withstand water stress. They could therefore be used as criteria to select olive cultivars that are more resistant to drought

How reliable is the double-ended pressure sleeve technique for assessing xylem vulnerability to cavitation in woody angiosperms?

he reliability of a double-ended pressure sleeve technique was evaluated on three woody angiosperm species with contrasting maximum vessel lengths. Vulnerability curves (VCs) were constructed by varying sample length and the size of the pressure sleeves. VCs were compared against curves obtained with reference techniques. For the two diffuse-porous species, Betula pendula and Prunus persica, VCs built with shoot segments shorter than maximum vessel length strongly overestimated species vulnerability. Furthermore, increasing the size of the pressure sleeve also tended to lead to overestimated VCs. For the ring-porous species Quercus robur, the technique strongly overestimated vulnerability to embolism, whatever the sample length or chamber tested. In conclusion, the double-ended pressure sleeve technique only gives reliable VCs on diffuse-porous angiosperms with short pressure sleeves, only when segments are longer than maximum vessel length

Near-lethal heat treatment induced metabolic changes associated with endodormancy release of Superior Seedless grapevine cv. (Vitis vinifera L.) buds

Abstract To assess the efficacy of near lethal heat stress for endodormancy release of Superior Seedless grapevine buds, single-node cuttings were soaked for 1 h in hot water (50°C) and then forced for one month. The effects of hot water treatment (HWT) on budburst, metabolic changes of carbohydrates, proline, free polyamines PAs (putrescine (Put), spermidine (Spd) and spermine (Spm)) and antioxidant enzymes' activity were investigated in bud under forcing conditions. Near-lethal heat stress caused a transient increase in starch hydrolysis, leading to an abrupt accumulation of soluble sugars, especially sucrose concentration during the first 3 days after treatment. This accumulation of soluble sugars coincided with a brief stimulation of the antioxidant system represented by ascorbate peroxidase (APX; EC 1.11.1.11), peroxidase (POD; EC 1.11.1.7) as well as an increase in the concentration of proline and free polyamines, especially putrescine (Put) and spermidine (Spd). These changes, which occurred immediately upon treatment, appear to be related with a process leading to endodormancy release. These results support the argument that a temporary and acute oxidative stress is involved in the mechanism leading to dormancy release and budbreak. Furthermore, it is possible that the stimulation of both peroxidases' activity and proline biosynthesis activated the pentose phosphate pathway (PPP) which helped the bud to overcome endodormancy. After this initial period and towards budbreak initiation, there was a rapid decline in the concentration of soluble sugars, proline and Put, while, Spm and Spd became abundant. Such post stress changes appear to be associated with the reactivation of growth leading to an earlier and more vigorous budbreak. The metabolic response to HWT was compared to those observed after bud chilling or the application of restbreaking agents such as hydrogen cyanamide (HC). The similarity in the response to these various stimuli suggests the presence of common regulatory pathways involved in bud dormancy release and subsequent sprouting