Effect of Alternaria alternata (Fr.) Keissl. on the physiology of Pea (Pisum sativum L.)

Alternaria alternata (Fr.) Keissl. is responsible for causing leaf spots and blight diseases on a large number of horticultural and agricultural crops including pea. The response and resistance of different pea varieties to this fungus might vary. Therefore, this study was aimed to investigate the varietal differences in the physiological response of Pisum sativum L. to A. alternata. Various physiological and biochemical parameters of two commercial pea varieties (Leina and Meature) were assessed at vegetative stage in pot experiment. Sterilized seeds were soaked in 1×105 mL conidial suspension of A. alternata for 15 min and control seeds were soaked in sterilized water. These sterilized seeds were sown in pots containing sterilized soil. In both varieties, germination percentage, germination rate, seedling vigor index, root and shoot length, dry and fresh biomass, leaf sugar, chlorophyll a, b, total chlorophyll and carotenoid contents, leaf osmotic potential, leaf relative water content, significantly decreased under A. alternata stress as compared to control. But proline and protein content significantly increased. It is concluded from the results that A. alternata caused adverse effects on the physiology of pea plant. The tested pea variety Leina was found to be more sensitive under fungal stress of A. alternata as compared to Meature and the extent of stress caused by both test varieties can be exploited in future studies.

Functional differentiation among 12 dipterocarp species under contrasting water availabilities in Northeast Thailand

Species composition varies greatly along with water availability gradients. In Northeast Thailand, dry deciduous forest (DDF) and dry evergreen forest (DEF) show contrasting species composition due to differences in soil structure and moisture. Although plant traits (physiological and morphological characteristics) are known to be involved in species distributions, which traits underpin these distinct distributions (either dry DDF or less-dry DEF) remain unclear. Here, we examined the differentiation of 21 leaf and stem traits between DDF and DEF, using 12 dipterocarp species. We found that DDF species showed higher water use efficiency and higher water storage capacity in the lamina and petiole, higher leaf nitrogen content, higher stomatal density, larger leaves, thicker mesophyll layers, and a higher rate of water loss under severe dehydration than DEF species. Leaf osmotic potential at full turgor, wood density, and wood water content were not significantly different between DDF and DEF. We also observed a negative relationship between the potential photosynthetic capacity and the water loss rate during severe dehydration across species. Our results suggest that the differences in leaf traits related to photosynthesis and dehydration avoidance cause a niche differentiation of the tree species along the soil water availability in tropical dry forests.

Specific leaf metabolic changes that underlie adjustment of osmotic potential in response to drought by four Quercus species

Osmotic adjustment is almost ubiquitous as a mechanism of response to drought in many forest species. Recognized as an important mechanism of increasing turgor under water stress, the metabolic basis for osmotic adjustment has been described in only a few species. We established an experiment with four species of the genus Quercus ranked according to drought tolerance and leaf habit from evergreen to broad-leaved deciduous. A cycle of watering deprivation was imposed on seedlings, resulting in well-watered (WW) and water-stressed (WS) treatments, and their water relations were assessed from pressure-volume (P-V) curves. Leaf predawn water potential (Ψpd) significantly decreased in WS seedlings which was followed by a drop in leaf osmotic potential at full turgor (Ψπ100). The lowest values of Ψπ100 followed the ranking of decreasing drought tolerance: Q. ilex < Q. faginea < Q. pyrenaica < Q. petraea. The leaf osmotic potential at the turgor loss point (ΨTLP) followed the same pattern as Ψπ100 across species and treatments. The pool of carbohydrates, some organic acids, and cyclitols were the main osmolytes explaining osmotic potential across species, likewise to the osmotic adjustment assessed from the decrease in leaf Ψπ100 between WW and WS seedlings. Amino-acids were very responsive to WS, particularly γ-aminobutyric acid (GABA) in Q. pyrenaica, but made a relatively minor contribution to osmotic potential compared with other groups of compounds. In contrast, the cyclitol proto-quercitol made a prominent contribution to the changes in osmotic potential regardless of watering treatment or species. However, different metabolites such as quinic acid, played a more important role in osmotic adjustment in Q. ilex, distinguishing it from the other species studied. In conclusion, while osmotic adjustment was present in all four Quercus species, the molecular processes underpinning this response differed according to their phylogenetic history and specific ecology.

Leaf turgor loss point at full hydration for 41 native and introduced tree and shrub species from Central Europe

The last years, Central European forests have suffered from drought as a direct consequence of climate change. All these forests have a long management history and it lies in the landowner’s responsibility to replant damaged forests. Hence, landowners and the government are searching currently for species suitable to replant in areas affected by tree die-offs. It is a matter of fact that good knowledge of drought resistance of species is a critical measure for the current replanting efforts. We determined a widely recognized trait for leaf drought tolerance (leaf water potential at turgor loss point at full hydration, πtlp) in 41 woody species native or introduced in Central Europe. The osmometric rapid assessment method was used to measure the leaf osmotic potential at full hydration (πosm) of sun-exposed leaves and converted to πtlp. Mean πtlp of the native species was −2.33 ± 0.33 MPa. The less negative πtlp was found in the introduced species Aesculus hypocastania and was at −1.70 ± 0.11 MPa. The most negative πtlp, and thus the potentially highest drought tolerance, were found in the introduced species Pseudotsuga menzesii and was at −3.02 ± 0.14 MPa. High or less negative πtlp is associated with lower drought tolerance, whereas low or more negative πtlp stands for higher resistance to drought stress. For example, the two native species Illex aquifolium and Alnus glustinosa are species naturally associated with moist habitats and are characterized by the least negative πtlp of −1.75 ± 0.02 and −1.76 ± 0.03 MPa, respectively.

Growth Response of Cassava to Deficit Irrigation and Potassium Fertigation during the Early Growth Phase

Cassava (Manihot esculenta Crantz) experiences intermittent water deficit and suffers from potassium (K) deficiency that seriously constrains its yield in the tropics. Currently, the interaction effect between deficit irrigation and K fertigation on growth and yield of cassava is unknown, especially during the early growth phase. Therefore, pot experiments were conducted under controlled greenhouse conditions using cassava cuttings. Treatments initiated at 30 days after planting included three irrigation doses (30%, 60%, 100% pot capacity) and five K (0.01, 1, 4, 16, and 32 mM) concentrations. The plants were harvested 90 days after planting. Decreasing irrigation dose to 30% together with 16 mM K lowered the leaf water potential by 69%, leaf osmotic potential by 41%, photosynthesis by 35%, stomatal conductance by 41%, water usage by 50%, leaf area by 17%, and whole-plant dry mass by 41%, compared with full-irrigated plants. Lowering the K concentration below 16 mM reduced the values further. Notably, growth and yield were decreased the least compared with optimal, when irrigation dose was decreased to 60% together with 16 mM K. The results demonstrate that deficit irrigation strategies could be utilized to develop management practices to improve cassava productivity by means of K fertigation under low moisture conditions.

Hydrogen sulfide, potassium phosphite and zinc sulfate as alleviators of drought stress in sunflower plants

ABSTRACT Drought is the most harmful environmental factor crop productivity. Some chemicals are used in agriculture to mitigate the damage from this stress on plants. Therefore, we examined whether the spraying of zinc sulfate (ZS), potassium phosphite (KPhi) and the hydrogen sulfide (H2S) donor sodium hydrosulfide (NaHS) would mitigate the deleterious effects of water deficit on sunflower plants by analyzing physiological and biometric characteristics. The experiment was carried out in a greenhouse using a randomized block design with five replications. The treatments were arranged in a 4 x 2 factorial scheme: [Factor A (Alleviators)] - spraying of KPhi (0.5 L ha-1), ZS (3.2 kg ha-1), NaHS (1.2 g ha-1), and water; [Factor B (substrate humidity, SH)] - 100% (well irrigated) and 30% (water deficit, WD) of field capacity. Under WD conditions, alleviators led to the maintenance of higher values of water potential (ΨW), a lower content of leaf malonaldehyde (MDA), and increased activity of the antioxidant enzyme peroxidase (POX), except for ZS. However, leaf osmotic potential, proline concentration, variables related to gas exchange and chlorophyll a fluorescence, and biometric characteristics differed only according to the SH factor. The results of ΨW and MDA for sunflower plants under WD are indicative of the mitigating capacity of ZS, KPhi, and H2S. Thus, the spraying of these compounds on sunflower plants mitigates the effects of WD, acting specifically in physiological processes related to antioxidant responses and in the maintenance of water in leaf tissues.

Diffusional conductance to CO2 is the key limitation to photosynthesis in salt-stressed leaves of rice (Oryza sativa)

Salinity significantly limits leaf photosynthesis but the photosynthetic limiting factors in salt- stressed leaves remain unclear. In the present work, photosynthetic and biochemical traits were investigated in four rice genotypes under two NaCl (0 and 150 mM) concentration to assess the stomatal, mesophyll and biochemical contributions to reduced photosynthetic rate (A) in salt stressed leaves. Our results indicated that salinity led to a decrease in A, leaf osmotic potential, electron transport rate and CO2 concentrations in the chloroplasts (Cc) of rice leaves. Decreased A in salt-stressed leaves was mainly attributable to low Cc, which was determined by stomatal and mesophyll conductance. The increased stomatal limitation was mainly related to the low leaf osmotic potential caused by soil salinity. However, the increased mesophyll limitation in salt stressed leaves was related to both osmotic stress and ion stress. These findings highlight the importance of considering mesophyll conductance when developing salinity-tolerant rice cultivars.AbbreviationsAphotosynthetic rateCc, CO2concentration at carboxylation sitesCEapparent Rubisco activityChltotal chlorophyll contentCiintercellular CO2 concentrationETRelectron transport rateF0initial fluorescence of photosystem II in darknessFmmaximum fluorescence of photosystem IIFvmaximum variable fluorescence of photosystem IIFv/Fmmaximum quantum efficiency of photosystem IIgmmesophyll conductiongsstomatal conductionJmaxmaximum electron transport rateKleaf K contentLMAleaf mass per areaNleaf N contentPleaf P contentOPosmotic potentialProteinleaf total soluble protein contentqNnon-chemical quenching efficiencyRdday respirationRdarkdark respirationRubiscoRubisco contentVcmaxmaximum carboxylation rateαleaf light absorptance efficiencyβthe distribution of electrons between PSI and PSIIΓ*CO2 compensation point in the absence of respirationΦPSIIquantum efficiency of photosystem II.

Physiological, Morphological Changes and Storage Root Yield of Sweetpotato [Ipomoea batatas (L.) Lam.] under PEG-Induced Water Stress

Sweetpotato is an important tuberous root crop rich in nutrients such as vitamins and carbohydrates, and can grow well in arid regions with less water consuming crop. The aim of this research was to evaluate the storage root yields, physiological, biochemical and morphological traits in sweetpotato cv. ‘Japanese Yellow’ subjected to polyethylene glycol (PEG)-induced water deficit. At harvest (4 months after planting) the number of storage roots per plant and storage root fresh weight in sweetpotato treated with 5% PEG (-0.54 MPa) in nutrient solution of hydroponic culture declined by 20.0% and 47.4% compared to the control without PEG, respectively. Leaf area and leaf dry weight significantly decreased by 85.6% and 95.3%, respectively when exposed to water deficit stress. Sucrose content (114.7 mg g-1 dry weight; DW) in storage roots of sweetpotato grown under PEG-induced water deficit conditions was enriched by 2.2 fold of control (52.5 mg g-1 DW) and was greater than in storage roots derived from soil culture (70.3 mg g-1 DW). Total soluble sugar in the root and storage root tissues was enriched and may play a key role as osmotic adjustment (OA) in PEG-induced water stressed plants. Free proline and sucrose contents were also dominated in the leaf tissues to maintain the leaf osmotic potential in water stressed plants. In addition, chlorophyll degradation, chlorophyll fluorescence diminution and stomatal closure were found in plants grown under PEG-induced water deficit conditions, leading to reduction in net photosynthetic rate (Pn) and subsequently lesser amounts of glucose and fructose contents in the leaf tissues. Sucrose and free proline in the roots of sweetpotato play a key role as major osmotic adjustment when subjected to PEG-induced water deficit condition. Basic knowledge gained from this research will further be investigated the drought defense mechanism in sweetpotato via osmoregulation system.