Nitrogen partitioning and remobilization in field-grown apple trees

Uptake and cycling of nitrogen (N) in mature trees are not well understood. Fertilizer-N uptake, partitioning, and use-efficiency were studied in standard strain 'Topred Delicious' and spur strain 'Redspur Delicious' mature apple trees {Malus domestica Borck) on 'Malling 7A' (M.7A) rootstocks. The treatments consisted of a ground application in spring, a preharvest ground application in August, a foliar spray in fall, or a combination of each of the last two treatments with the first. When soil-applied in spring, labeled N (¹⁵N) was allocated preferentially to above ground tissues and to a lesser extent to roots of both strains. The amount of newly absorbed soil-N allocated to above ground tissues decreased as the season progressed, little ¹⁵N from preharvest ground applications reached the leaves, fruit, buds, or branches, while roots were heavily labeled. Total fertilizer-N recovery in the trees was similar regardless of the time of fertilizer application. However, losses of ¹⁵N to fruit removal, leaf fall, and pruning were most severe when N was applied in spring and minimal for the pre-harvest timing compared to all others. About a third of the variability in recovery was due to variation in tree size. When recoveries were adjusted to account for size differences, spur-type trees tended to be more efficient at utilizing fertilizer-N. When ¹⁵N-urea was applied in April to young apple leaves, the label was not exported. Labeled N from fall urea sprays was exported from the leaves to the buds, but was restricted to the treated spurs and branches. Foliar urea sprays immediately after harvest contributed more N to the buds than later applications. Mobilization of ¹⁵N from storage in various tree parts was assessed. In moderately vigorous trees, N stored in aerial parts of the tree was mobilized first, followed by simultaneous mobilization of root and soil N. Utilization of root reserves depended on the N status of the tree. When the buds were low in N but the roots had adequate N reserves, root to shoot N transport started early in winter

Influence of canopy orientation on fruiting of 'Ànjou' pears and postharvest urea spray on ovule longevity and fruit set of 'C̀omice' pears

The effect of canopy orientation on fruiting performance of 'Beurre d'Anjou' pears (Pyrus communis L.) and postharvest urea spray on ovule longevity and fruit set of 'Doyenne du Comice' pears were studied. Hedgerows of 'Beurre d'Anjou' pear trees planted in 1969 in two orientations north-south (N-S) and east-west (E-W) were used to study the effect on pear fruiting. The trees were spaced 1.3 x 3.7 m, trained to a central leader, and mechanically pruned to a tree wall 3.7 m high and 1.8 m wide at the base with a wall angle of 170 from the vertical. Flower density (FD), flower buds per unit branch cross-sectional area (BCSA), was lowest on the N wall of the E-W rows in 1990 and on the S wall of the same rows in 1991. In both years, N-S rows had higher FD. Fruit set (FS), fruit per flower buds, was highest on the S wall and lowest on the N wall of the E-W rows, whereas, the E and W walls of the N-S rows were intermediate. Crop density (CD), fruit per unit BCSA, had a similar pattern as FS with more fruits on the S wall and less on the N wall of the E-W rows. However, CD was more evenly distributed between the walls of the N-S hedgerows. Differences in FS and CD between sides were correlated to different levels of sunlight interception. For instance, the mid height of the N wall of the E-W rows received less than 20% full sunlight throughout the growing season whereas the S wall received more than 35% of irradiance especially towards the equinoxes. Increased solar heating on the S and W walls late in the season led to more sunburned fruits. Fruits from E-W rows were larger and less firm. 'Doyenne du Comice' is generally considered as a commercial pear variety with highly palatable fruits. A shortcoming of this variety is, however, that its trees come into bearing late and then set a small crop. The possibility of altering ovule longevity and fruit set of this cultivar by nitrogen fertilization was investigated. Mature trees were given a single foliar application of 5% or 10% urea immediately after harvest. Ovule senescence was detected by fluorescence microscopy. Ovule longevity was extended in both treatments in comparison to control. FS was increased after a foliar application of urea when based on trunk cross sectional area. There was no effect on FD, CD, fruit fresh weight, and yield efficiency of 'Comice' trees treated with postharvest urea sprays

Physiological and biochemical responses at leaf and root levels in two Acacia species (A. cyclops and A. salicina) subjected to dehydration

To set-up afforestation and reforestation projects in arid regions southern Tunisia, several indigenous and exotic forest species were used among them are Acacia spp. However, the success of these projects remains highly sceptical because of the intensified aridity during the last decade. To overcome this issue, the selection of genotypes resistant to severe drought is crucial as first step. For this reason, the aim of the present study is to compare tolerance capacity to severe drought between two Acacia species (A. cyclops and A. salicina) and evaluate efficacy of their biochemical responses at leaf and root levels. Combined physiological and biochemical approaches were adopted. Two-years-old plants of two Acacia species (A. cyclops and A. salicina), frequently used in forestation projects in arid regions southern Tunisia, were subjected to severe water stress by withholding watering during 60 days. At regular intervals, water relations and net photosynthetic rate (Pn) were measured. In addition, the biochemical response was characterized by quantifying one sugar alcohol (arabitol) and three cyclitols (myo-inositol, pinitol and quercitol) in leaves and roots. Our results revealed that A. cyclops was more tolerant to severe drought than A. salicina. The turgor of its leaf tissues and its Pn were less affected. The superiority of A. cyclops to tolerate severe water stress might be attributed to greater efficiency of its biochemical defense mechanisms compared to A. salicina. Comparison of biochemical profiles between species exhibited some differences depending on the organs and the species. For development and survival under severe drought conditions, A. cyclops accomplished efficient osmoregualation and osmoprotection mechanisms by massive accumulation of specific polyols distinctly in leaves and roots. Indeed, compared to A. salicina, A. cyclops accumulated higher amount of arabitol, myo-inositol and quercitol in roots, but pinitol in leaves. So, contents of these polyols might be used as promising criteria for the selection of drought-tolerant Acacia species.&nbsp

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

Priming improves germination and seed reserve utilization, growth, antioxidant responses and membrane stability at early seedling stage of Saudi sorghum varieties under drought stress

Seeds of three sorghum (Sorghum bicolor (L.) Moench.) varieties from Southwest Saudi Arabia were used to investigate the potential of osmopriming with polyethylene glycol (PEG 8000) to improve germination performance, seed reserve utilization and early seedling growth and drought stress tolerance. The primed (PS) and unprimed (UPS) seeds of the three sorghum varieties were germinated for 8 days under increasing PEG-induced osmotic stress. The treatments were arranged in a completely randomized design, in a factorial arrangement, with three sorghum cultivars (‘Zaydia’, ‘Shahbi’ and ‘Ahmar’) and four osmotic potentials (0.0; -0.4; -0.8 and -1.2 MPa) with four replicates of 50 seeds each. The results showed that drought stress affected seed germination and seedling emergence and establishment, but increased the activity of the antioxidant enzyme catalase (CAT). The strongest inhibition of germination and growth occurred at the highest PEG concentration and a significant difference was noticeable between the studied varieties. We confirmed also that seed osmopriming improved seed germination performance, seedling growth and enhanced the CAT activities while reduced malonyldialdehyde (MDA) accumulation and electrolyte leakage (EL) in the drought-stressed seedlings. Seed priming have enhanced also the α-amylase and total proteases activities in all varieties. The largest increase of these hydrolysing enzymes was shown in ‘Ahmar’. Furthermore, the PEG priming lead to improvement of the weight of utilized (mobilized) seed reserve (WUSR), seed reserve depletion percentage (SRDP) and total seedling dry weight (SLDW) of sorghum seedlings under water stress conditions. Still, the highest values or all three parameters were found in the ‘Ahmar’ variety. Under increasing drought stress conditions, ‘Ahmar’ showed the highest yield stability index (YSI) and the least EL and MDA contents in comparison to the other two varieties during the seedling establishment stage. Therefore, the former variety can tolerate better a rigorous water stress condition. ‘Zaydia’ appears to be the most vulnerable to drought stress. Thus, the use of species or varieties with eminent seed metabolic quality is an advantageous trait in drought-prone regions

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

Diversity among Coffea arabica populations in southwestern Saudi Arabia as revealed by their morphometric features

Coffee (Coffea arabica L.) is one of the most important agricultural commodities traded worldwide. The livelihoods of millions of households in Asia, Africa and America depend on it. The sustainability of the supply chain of this crop is increasingly under threat due to the impact of climate change in the main producing countries in the tropics and sub-tropics. The resilience of these agro-ecosystems will depend on the ability of breeders to develop new coffee varieties that can better adapt to changing environmental conditions. Therefore, studying the diversity of coffee populations in the Arabian Peninsula could reveal agronomically interesting genotypes that can be exploited in breeding programs. The objective of the study was to evaluate the diversity among coffee populations in southwestern Saudi Arabia using quantitative morphological, pomological and agronomic traits. The analysis of variance of the data showed differences among the accessions for most of the measured quantitative traits. The accessions varied in growth habit, canopy shape and cherry, bean and leaf dimensions. Cherry fresh mass ranged from 96.5 to 234.8 g in 100 cherries while 100-bean dry mass varied from 9.3 to 22.5 g. The hierarchical cluster analysis divided the accessions into four main groups. The study revealed considerable variability among the 61 accessions. Based on this investigation, accessions KSA-7R, KSA-8 and KSA-9R from Tallan valley, KSA20, KSA21 and KSA52 from Fayfa, KSA38 from Eddayar district, KSA10 and KSA60 from Assir region and KSA61 from Jebel Shada are recommended for further investigation for their promising agronomic traits