Citrus rootstock responses to water stress

Tolerance to drought-stress (DS) of the citrus rootstock Forner–Alcaide no. 5 (FA-5) was tested and compared with that of its parents, Cleopatra mandarin (CM) and Poncirus trifoliata (PT). Nine-month-old seedlings of CM, PT and FA-5 and 15-month-old grafted trees of ‘Valencia’ orange scions on these three rootstocks were cultivated in sand under glasshouse conditions and irrigated with a nutrient solution. Plants were drought-stressed by withholding irrigation until leaves were fully wilted. Survival time of both seedlings and grafted trees under DS was linked to the water extraction rate from the soil, which depended mainly on leaf biomass and on transpiration rate. Seedling responses to DS affecting leaf water relationships and gas exchange parameters varied among genotypes. FA-5 seedlings survived longer than the other seedlings, maintaining the highest levels of water potential, stomatal conductance, transpiration rate and net CO₂ assimilation towards the end of the experiment, when water stress was most severe. Thus, FA-5 was more resistant to DS than its parents (CM and PT). Moreover, rootstock affected the performance of grafted trees under water stress conditions. The higher drought tolerance induced by FA-5 rootstock could be related to the greater osmotic adjustment (OA), which was reflected by smaller reductions in leaf relative water content (RWC) and in higher turgor potentials and leaf gas exchange than the other rootstocks.     

Water relations of pistachio (Pistacia vera L.) as affected by phenological stages and water regimes

Pistachio is a drought tolerant fruit tree that can be cultivated in rainfed and irrigated conditions. The water requirements of the tree, however, are considerable so in most of the commercial orchards deficit irrigation is a common practice. Regulated deficit irrigation in pistachio trees has been described in several works, which reported that the phenological stage of shell hardening, so called stage II, is the most drought tolerant. This paper proposes that such drought resistance is related to changes in water relations linked to the phenological stages, even in conditions of no water stress. In order to evaluate such changes, the daily pattern of stem water potential and gas exchange (net photosynthesis, P_n, and leaf conductance, g_s) was measured, determining also the pressure–volume curves, in three different phenological stages of mature pistachio trees (Pistacia vera cv Kerman on P. terebinthus L. rootstock.). The daily pattern of stem water potential and gas exchange were performed in three different irrigation treatments: control, regulated deficit irrigation and rainfed. The pressure–volume curves were made only in the control and rainfed treatments. Significant differences were found in the daily pattern of stem water potential in all the phenological stages considered, while only in the last one the net photosynthesis was affected by water stress. The daily pattern of gas exchange at the beginning of the season was not affected by the evaporative demand, with a constant value when radiation was not limiting. Moderate levels of water stress during the last measurement date reduced the maximum values of g_s and P_n resulting also in a clear change in the pattern of the daily curve, with maximum values only at the beginning of the day. The relationships between stem water potential and gas exchange parameters were different during stage II and almost the same in stages I and III. The parameters drawn from the pressure–volume curves also indicated a change in the elastic modulus of the leaf cells in stage II. In addition, differences in the osmotic adjustment (OA) index suggested different degree of osmotic adjustment of the phenological stages in the response to water stress. The results showed that different mechanisms of drought resistance are operating in the different phenological stages in pistachio trees.     

The effects of temperature on in vitro pollen germination and pollen tube growth of Pistacia spp.

The pollen germination and pollen tube growth among nine Pistacia genotypes was quantified in order to identify differences in the tolerance of pollen to temperature variations. The effect of temperature on in vitro pollen germination and pollen tube growth was investigated in Pistacia vera (Uygur, Atli, Kaska, Sengel, Kavak), P. atlantica, P. khinjuk, P. terebinthus and P. palaestina. When pollen was incubated in a germination medium for 24 h in darkness, distinct differences were observed in pollen germination and pollen tube growth at different temperatures.     

Evaluation of genetic relationships among Iranian pistachios using microsatellite markers developed from Pistacia khinjuk Stocks

To evaluate the genetic relationships among wild and cultivated Pistacia species grown in Iran and the analysis of genetic variation among Iranian pistachio genotypes, two DNA libraries enriched for dinucleotide (AG)_n and trinucleotide (ATG)_n microsatellite motifs were developed from Pistacia khinjuk genome. Following screening of clones by colony PCR technique, 44 clones were sequenced and 27 pairs of primers designed from flanking regions of the repeats. The examination of primer pairs, designed from P. khinjuk sequences, showed successful cross-species amplification within the genus Pistacia. A dendrogram constructed on the basis of the Minimum Evolution clustering algorithm revealed that Pistacia vera has closer relationships with P. khinjuk, than with Pistacia integerrima, Pistacia palaestina, Pistacia atlantica and Pistacia mutica. The dendrogram further distinguished the wild Sarakhs pistachio from the rest of P. vera genotypes suggesting that the domesticated genotypes of P. vera are evolved from P. vera var. Sarakhs and then this wild genotype likely develops to other local pistachios. Hence, it seems that the wild Sarakhs pistachio plays an important role in evolutionary trend of the edible pistachios in Iran. The results indicated that microsatellites developed in P. khinjuk are distributed in the genome of indigenous pistachio species including P. vera genotypes and therefore they will be useful in characterization of Iranian pistachio genotypes.     

Daily and seasonal variation of water relationship in sugar apple (Annona squamosa L.) under different irrigation regimes at semi-arid Brazil

In the northeast of Brazil the drought period determines the yield period of the sugar apple (Annona squamosa L.). As a result, the use of irrigation is essential to stagger production over the course of the year. The results shown here represent an analysis of water status levels in sugar apples in daylight and seasonal periods in semi-arid regions. Two plant groups were studied: one without irrigation and the other with irrigation during drought months. This study showed that younger leaves displayed greater stomatal conductance and transpiration. In drought months, even in irrigated plants, the high air moisture deficit had a strong influence on the stomatal closure, which did not translate into a reduction in transpiration. Over the same period, the leaf water potential was −1.8 and −2.9 MPa at mid-day in irrigated and non-irrigated plants, respectively, and only the irrigated plants could recover their leaf hydration level at night. With a water deficit, plants showed greater control of transpiration through stomatal closure, with a linear relationship between stomatal conductance and transpiration.     

Effect of alleviating products with different mode of action on physiology and yield of olive under drought

Two years old self-rooted Koroneiki olive trees (Olea europaea L.) were subjected to two irrigation regimes, i.e. the fully irrigated and the severely water stressed trees, while they were treated with three alleviating products of different mode of action. The products used were the osmolyte glycine betaine, the antioxidant Ambiol and the heat and irradiance reflecting kaolin clay particles. The effects of product application and water regime on leaf characteristics, shoot and root growth, photosynthesis, leaf compatible solids (carbohydrates) concentration and yield were evaluated. All products applied, exhibited significant alleviating action, based on the relative alleviation index. Irrigated trees exhibited greater growth than drought stressed ones, while the ameliorating products maintained the water content of the leaves under drought conditions and resulted in lower leaf tissue density. On the other hand carbon assimilation rate, stomatal conductance and intrinsic water use efficiency were significantly reduced under drought stress, while the opposite stood for intercellular CO₂. Drought stress resulted in elevated sucrose leaf concentration, while the application of Ambiol increased stachyose concentration and that of glycine betaine did the same with the mannitol concentration. Among the alleviating products tested in this experiment Ambiol and glycine betaine had a significant positive effect on leaf water content, photosynthesis and yield under both drought and well irrigated conditions.     

Eggplant relatives as sources of variation for developing new rootstocks: Effects of grafting on eggplant yield and fruit apparent quality and composition

We propose the utilization of eggplant (Solanum melongena L.) interspecific hybrids derived from crosses with closely related species as an approach for developing new improved rootstocks for eggplant. Here we investigate rootstock effects on fruit yield, apparent quality and proximate and mineral composition of S. melongena ‘Black Beauty’ (BB) scions grafted on interspecific hybrid rootstocks developed from crosses of S. melongena with Solanum incanum L. (SI × SM) and Solanum aethiopicum L. (SM × SA). The results are compared with non-grafted (BB control) and self-grafted (BB/BB) controls and with S. melongena ‘Black Beauty’ scions grafted onto Solanum torvum Sw. (STO) and Solanum macrocarpon L. (SMA) rootstocks. All treatments were grown in a soil naturally infested with root-knot nematodes (mostly Meloidogyne incognita (Kofoid and White) Chitwood). SI × SM and SM × SA interspecific hybrids had high germination (≥90%) and total graft success (100%). Contrary to what occurred with all other treatments, no plants from scions grafted onto these hybrid rootstocks died during the experiment. In particular, the SI × SM hybrid rootstock conferred the highest vigour to the scion, which resulted in the highest values for fruit earliness and early and total yield. Little difference was observed among treatments for apparent fruit quality traits, except for a greater fruit calyx length and prickliness of fruit grafted onto SMA rootstocks. A similar result was obtained for fruit composition where phenolics content was higher in fruit from plants grafted onto SMA rootstocks. Grafting eggplant onto interspecific eggplant hybrids, especially on the SI × SM hybrid, has proved advantageous for eggplant production, as the high vigour and good compatibility of the rootstock with scion results in improved early and total yield without negative effects on apparent fruit quality or composition. Interspecific hybrids represent an alternative to the commonly used STO rootstock, which is a wild species with irregular germination.     

Zinc influence and salt stress on photosynthesis,water relations,and carbonic anhydrase activity in pistachio

A greenhouse study was conducted to evaluate the ameliorative effects of zinc (0, 5, 10 and 20 mg Zn kg⁻¹ soil) under saline (800, 1600, 2400 and 3200 mg NaCl kg⁻¹ soil) conditions on pistachio (Pistacia vera L. cv. Badami) seedlings’ photosynthetic parameters, carbonic anhydrase activity, protein and chlorophyll contents, and water relations. Zn deficiency resulted in a reduction of net photosynthetic rate and stomatal conductance. The quantum yield of photosystem II was reduced at zinc deficiency and salt stress. Zinc improved plant growth under salt-affected soil conditions. Increasing salinity in soil under Zn-deficient conditions, generally decreased carbonic anhydrase activity, protein, chlorophyll a and b contents. However, these adverse effects of salinity alleviated by increasing Zn levels up to 10 mg kg⁻¹ soil. Under increasing salinity, chlorophyll a/b ratio significantly increased. Zinc treatment influenced the relationship between relative water content and stomatal conductance, and between leaf water potential and stomatal conductance. It concluded that Zn may act as a scavenger of ROS for mitigating the injury on biomembranes under salt stress. Adequate Zn also prevents uptake and accumulation of Na in shoot, by increasing membrane integrity of root cells.     

Development of sex-associated RAPD markers in wild Pistacia species

Summary

Marker assisted selection may greatly facilitate pistachio rootstock breeding as well as cultivar improvement, because of the long juvenile period of Pistacia species. Early diagnosis of seedling sex type would assist breeding and nurserymanagement in these dioecious species. We searched for RAPD markers linked to sex in P. atlantica, P. terebinthus and P. eurycarpa, the main wild species in Turkey that are used as rootstocks for P. vera. For this purpose, leaf samples were collected from male and female individual trees from each species and sex-pooled DNA samples were prepared by mixing the DNA of ten male and ten female individuals, to screen for sex associated RAPD bands. A total of 472 primers have been screened so far and two bands, amplified by primers BC156 and BC360, appeared to be sex assocaited in P. eurycarpa. The bands were tested in 30 male and 37 female individuals. Band BC156 (1300) was present in all, except one, female trees and was absent from all the male trees. Band BC360 (500) was amplified in 31 out of 37 females and was absent from all the males. In P. atlantica, one primer, OPAK09, amplified a femaleassociated band (850 bp), that was present in all 46 female individuals tested and absent in all the 38 male trees tested. It is likely that these markers are linked to sex-determining loci. The sex determination mechanism has not been characterized in Pistacia and segregating populations from controlled crosses are required to elucidate such mechanism and also to measure the genetic distance of our markers from the putative sex loci.     

Causes of defoliation and low survival rate of grafted sweet pepper plants

We investigated the cause of defoliation in sweet pepper (Capsicum annuum L.) plants after grafting. Grafted plants of old-stage sweet pepper showed a higher defoliation rate than young-stage grafted plants. Old-stage grafted plants had lower stomatal resistance and water potential than young-stage plants, and showed poorly developed xylem connections at the graft site. Foliar application of abscisic acid (ABA) to the grafted plants increased stomatal resistance and water potential, decreased the defoliation rate, and promoted graft take among old-stage plants. Our results indicated that low stomatal resistance under low humidity induces water stress, defoliation, and low survival rate in old-stage grafted sweet pepper plants. ABA treatment increased stomatal resistance, water potential, and survival rate, and decreased the defoliation rate among old-stage sweet pepper plants.     

Effects of simple and double grafting melon plants on mineral absorption,photosynthesis, biomass and yield

The Spanish type cultivar ‘Piel de Sapo’ (Cucumis melo L. var. saccharinus), has a limited compatibility with the Cucurbita maxima × Cucurbita moschata hybrids currently used as rootstocks. Double grafting can be used to improve compatibility between rootstock and scion by means of an intermediate rootstock compatible with both. Non-grafted, single, and double grafted melon plants of the cultivar Piel de Sapo were evaluated for water, nutrient absorption, photosynthesis activity, biomass production in early phases, as well as for yields and fruit quality in a long term trial. The hybrid ‘Shintoza’ (C. maxima × C. moschata) was used as rootstock, and the cantaloupe type melon cultivar ‘Sienne’ as an intermediate scion. Grafting did not affect net photosynthetic values, yet increased water use efficiency (35%). Double grafted plants increased aerial dry weights (66% and 31% with respect to non-grafted and simple graft plants, respectively), and also increased capacity for uptaking beneficial minerals (between 61% and 13% and particularly for NO₃⁻, P, K, Ca, Mn, and Zn) with respect to non-grafted and single grafted plants. The quantum efficiency PSII photochemistry values increased in double grafted plants (12%) with respect to the control plants. Consequently, double grafting on a vigorous rootstock such as ‘Shintoza’, with an intermediate scion, results in improved mineral and water absorption and achieves an increase in ion influx to the scion – so enabling an increase in light photosynthetic reaction and biomass. Double grafted plants increased fruit yield when compared to simple grafted and non-grafted plants (12% and 56%, respectively) and did not affect fruit quality in terms of °Brix and colour. In conclusion, double grafting presents several beneficial aspects that are counter-balanced by the extra cost of the technique. The difference in yields reflects compatibility problems.     

Transpiration,photosynthetic responses,tissue water relations and dry mass partitioning in Callistemon plants during drought conditions

Callistemon is an Australian species used as ornamental plant in Mediterranean regions. The objective of this research was to analyse the ability of Callistemon to overcome water deficit in terms of adjusting its physiology and morphology. Potted Callistemon laevis Anon plants were grown in controlled environment and subjected to drought stress by reducing irrigation water by 40% compared to the control (irrigated to container capacity). The drought stress produced the smallest plants throughout the experiment. After three months of drought, the leaf area, number of leaves and root volume decreased, while root/shoot ratio and root density increased. The higher root hydraulic resistance in stressed plants caused decreases in leaf and stem water potentials resulting in lower stomatal conductance and indicating that water flow through the roots is a factor that strongly influences shoot water relations. The water stress affected transpiration (63% reduction compared with the control). The consistent decrease in g_s suggested an adaptative efficient stomatal control of transpiration by this species, resulting in a higher intrinsic water use efficiency (P_n/g_s) in drought conditions, increasing as the experimental time progressed. This was accompanied by an improvement in water use efficiency of production to maintain the leaf water status. In addition, water stress induced an active osmotic adjustment and led to decreases in leaf tissue elasticity in order to maintain turgor. Therefore, the water deficit produced changes in plant water relations, gas exchange and growth in an adaptation process which could promote the faster establishment of this species in gardens or landscaping projects in Mediterranean conditions.     

Impacts of water stress on gas exchange,water relations,chlorophyll content and leaf structure in the two main Tunisian olive (Olea europaea L.) cultivars

Leaf structural adaptations for the reduction of water loss were examined in two olive (Olea europaea L.) cultivars (Chemlali and Chétoui) growing under water stress conditions. Leaf measurements included leaf tissue thickness, stomatal density, trichome density, specific leaf area, leaf density, water relations, and gas exchange. We found considerable genotypic differences between the two cultivars. Chemlali exhibited more tolerance to water stress, with a thicker palisade parenchyma, and a higher stomatal and trichome density. Chemlali leaves also revealed lower specific leaf area and had higher density of foliar tissue and lower reduction in net CO₂ assimilation rate. The mechanisms employed by these two cultivars to cope with water deficit are discussed at the morpho-structural level. The morphological and structural characteristics of the leaves are in accordance with physiological observations and contribute to the interpretation of why the olive cv. Chemlali is more drought-tolerant than cv. Chetoui. Furthermore, from the behaviour of Chemlali plants we consider this cultivar very promising for cultivation in semi-arid areas.     

Horticultural performance of ‘Folha Murcha’ sweet orange onto twelve rootstocks

Despite its outstanding position, the Brazilian citriculture is established on a very limited pool of varieties that limits its expansion and restricts the fruit availability throughout the year. This situation determines the urgent necessity of developing alternative scion and rootstock cultivars, with good performance under local conditions. ‘Folha Murcha’ sweet orange (Citrus sinensis (L.) Osbeck) is a late-harvest cultivar, suitable both for the juice processing industry and the fresh fruit market, being described as tolerant to citrus canker (Xanthomonas citri subsp. citri Schaad et al.), and less affected by citrus variegated chlorosis (Xylella fastidiosa Wells et al.). A study was conducted in Bebedouro, São Paulo State, Brazil, to evaluate the horticultural performance of ‘Folha Murcha’ sweet orange budded onto 12 rootstocks: the citrandarin ‘Changsha’ mandarin (Citrus reticulata Blanco) × Poncirus trifoliata ‘English Small’; the hybrid ‘Rangpur’ lime (Citrus limonia Osbeck) × ‘Swingle’ citrumelo (P. trifoliata (L.) Raf. × Citrus paradisi Macfad.); the trifoliates (P. trifoliata (L.) Raf.) ‘Rubidoux’, ‘FCAV’, and ‘Flying Dragon’ (P. trifoliata var. monstrosa); the ‘Sun Chu Sha Kat’ mandarin (C. reticulata Blanco); the ‘Sunki’ mandarin (Citrus sunki (Hayata) Hort. ex. Tanaka); the ‘Rangpur’ limes (C. limonia Osbeck) ‘Cravo Limeira’ and ‘Cravo FCAV’; ‘Carrizo’ citrange (C. sinensis × P. trifoliata), ‘Swingle’ citrumelo (P. trifoliata × C. paradisi), and ‘Orlando’ tangelo (C. paradisi × Citrus tangerina cv. ‘Dancy’). The experimental grove was planted in 2001, using a 7 m × 4 m spacing, in a randomized block design, with five replications and two plants per plot. No supplementary irrigation was applied. Fruit yield, canopy volume, tree tolerance to drought and to citrus variegated chlorosis, and fruit quality were assessed for each rootstock. Trees grafted onto the ‘Flying Dragon’ trifoliate were smaller in size, but had largest yield efficiency when compared to those grafted onto other rootstocks. Lower alternate bearing index was observed on trees budded onto ‘Cravo FCAV’ ‘Rangpur’ lime. Both ‘Rangpur’ lime rootstocks and the ‘Sunki’ mandarin induced higher tree tolerance to drought. The ‘Flying Dragon’ trifoliate induced better fruit quality and higher tolerance to citrus variegated chlorosis (CVC) to ‘Folha Murcha’ trees. A cluster multivariate analysis identified three groups of rootstocks with similar effects on ‘Folha Murcha’ tree performance. Among the 12 evaluated rootstocks, the ‘Flying Dragon’ trifoliate has a unique effect on plant growth, tolerance to drought and CVC, fruit yield and fruit quality of ‘Folha Murcha’ trees, and may be better suited for high-density plantings.     

Nutrient deficiency disorders in Pistacia vera seedling rootstock in relation to eco-physiological,biochemical characteristics and uptake pattern of nutrients

This study examines the effects of nitrogen (N), iron (Fe), magnesium (Mg), manganese (Mn) and molybdenum (Mo) deficiencies on the eco-physiological, biochemical and growth characteristics of pistachio seedlings (Pistacia vera) in sand culture situation. This experiment, which was carried out in Iran's Pistachio Research Institute (IPRI), seedlings of ‘Badami-e-Zarand’ were used as common rootstock. The following treatments were employed: (1) complete Hoagland's nutrient solution; nutrient solution lacking either: (2) N, (3) Fe, (4) Mg, (5) Mn, (6) Mo, (7) distilled water without Hoagland's solution (Control), (8) Fe–N, (9) Fe–Mn and (10) Fe–Mo. The main deficiency symptoms observed after 7 months of planting were; leaf discoloration, necrosis, scorching, defoliation and stunted growth. Seedlings that received complete nutrient solution were healthy with dark green foliage. Visual symptoms of N-deficient seedlings also coincided with the reduction in foliar levels of the concerned element. Shoot and root growth of the seedlings deficient in nutrients were also affected. Changes in shoot and root biomasses production due to treatments were statistically significant at 1% level. A reduction in height, leaf area and leaf number was noticed for various levels of nutrient element deficiencies. Analysis of some biochemical indices (chlorophyll content) and eco-physiological indices such as primary florescence chlorophyll (Fo), ratio of variable chlorophyll to maximum (Fv/Fm), leaf temperature, transpiration, stomata conduction and resistance of stomata, showed that fractions of chlorophyll, transpiration, stomata conduction and resistant of stomata in treated seedlings, particularly N-deficient seedlings, declined significantly. Chlorophyll (Fo) and ratio of variable chlorophyll to maximum (Fv/Fm) were significant at 5% level. The effects of Fe, Mn, Mg and Mo on dry matter production were statistically significant at 1% level. Synergic effects of certain elements were also evident in the present study. The typical symptoms of deficiencies of various nutrient elements can be used as a guideline for diagnosing nutrient deficiencies of pistachio in commercial nurseries and plantations. The present study also showed multi-deficiency of nutrients, produces new symptom in leaves, which differs from single deficiencies.     

The response of different almond genotypes to moderate and severe water stress in order to screen for drought tolerance

In order to screen almond genotypes for drought tolerance, three different irrigation levels including moderate and severe stress (Ψs = −1.2 and −1.8 MPa respectively) and a control treatment (Ψs = −0.33 MPa) were applied for five weeks to six different cultivated almond seedlings. A factorial experiment was conducted with a RCBD which included 3 irrigations factors, 6 genotype factors and 3 replications. Seeds were prepared from controlled pollination of the bagged trees (after emasculation and flower isolation using isolator packets in the previous year). Genotypes included: homozygote sweet (Butte), heterozygote sweet (SH12, SH18, SH21 and White) and homozygote Bitter (Bitter Genotype). Leaf and root morphological and physiological traits including; midday relative water content, midday leaf (xylem) water potential, shoot dry weight and growth, total leaf area, leaf size, total leaf dry weight, specific leaf area, leaf greenness (SPAD), stomatal size and density, root and leaf nitrogen content and chlorophyll fluorescence were measured throughout the study. Results showed the six genotypes had different reactions to water stress but all genotypes showed an ability to tolerate the moderate and severe stresses and they showed different degrees of response time to drought stress. Almond seedling leaves could tolerate Ψ_w between −3 and −4 MPa in short periods. Water availability did not significantly affect stomatal density and size of young almond plants. The analysis of leaf anatomical traits and water relations showed the different strategies for almond genotypes under water stress conditions. Although almond seedlings even in severe stress kept their leaves, they showed a reduction in size to compensate for the stress effects. All genotypes managed to recover from moderate stress so Ψ_w = −1.2 could be tolerated well by almond seedlings but Ψ_w = −1.8 limited young plant growth. Leaf greenness, leaf size, shoot growth, shoot DW, TLDW and stomatal density were not good markers for drought resistance in almond seedlings. Root DW/LA, lower stomatal size and lower SLA might be related to drought resistance in cultivated almonds. Butte had the least resistance and White showed better performance during water stress while other genotypes were intermediate. Bitter seedlings showed no superiority in comparison with other genotypes under water stress conditions except for better germination and greater root DW which might make them suitable as rootstocks under irrigation conditions.     

Early detection of graft incompatibility in apricot (Prunus armeniaca L.) using phenol analyses

The study investigated the role of phenols in apricot graft incompatibility. Assays of phloem with cambium from 1-year-old apricot trees of cultivars Marlen, Leskora and Betinka which were grafted on the rootstocks of different genetic origin: M-LE-1, Lesiberian, MY-KL-A, Tetra, Penta, Green Gage, Julior, MRS 2/5 and Isthara were analysed with HPLC (together 23 scion/stock combinations). The phloroglucinol, catechin, p-coumaric acid and further non-identified phenols with the retention time 23–25 and 30 min were determined. The content of individual phenol compounds was related to specific cultivar/rootstock combination. The minimum number of statistical significant differences in the phenol content between tissues above and below graft union was established in homospecific combinations (P. armeniaca/P. armeniaca). Cultivars Marlen, Leskora and Betinka differ in the degree of compatibility or incompatibility with rootstocks. The pattern of non-identified phenol 23 in different graft combinations is similar to catechin and p-coumaric acid.     

Morphological,anatomical and physiological responses of Campylotropis polyantha (Franch.) Schindl. seedlings to progressive water stress

In this study we implemented a potted water supply experiment for 100 days by a completely random sole-factored design with five treatments: 100% (W₁₀₀), 80% (W₈₀), 60% (W₆₀), 40% (W₄₀) and 20% (W₂₀) of water holding capacity (WHC), corresponding to the soil volumetric water content (SVWC) maintained at 38.8 ± 0.3%, 31.6 ± 1.7%, 25.6 ± 1.3%, 16.5 ± 0.7%, and 8.1 ± 1.1%, respectively. The objective was to evaluate the ability of the 2-month-old Campylotropis polyantha (Franch.) Schindl. seedlings to tolerate drought and to explore the mechanism resisting drought. We monitored the growth process of seedling height and leaf number monthly and further investigated those changes in plant growth, dry mass accumulation and allocation, water-use efficiency (WUE), leaf functional traits, chlorophyll a fluorescence and pigment contents across the water deficit gradient. We found that the seedlings presented optimal growth, dry mass production, and physiological activity only at the W₁₀₀ and W₈₀ treatments and afterwards significantly decreased with progressive water deficit; the WUE was improved under moderate water stress (W₆₀ and W₄₀) but reduced under severe stress (W₂₀). The serious leaf shedding, growth stopping and seedling death under the W₂₀ condition revealed that the current-year shrub seedlings could not withstand severe drought. Water stress-induced decrease in total plant leaf area due to a combination of limited expansion of younger leaves and shedding of old leaves caused the leaf area ratio reduction under drought. The reduced mesophyll cell was a major anatomical response of leaves along the water stress gradient. The progressive water stress significantly damaged light harvesting complex and reduced photochemical processes and PSII activity. Our results clearly showed that the current-year shrub seedlings took the avoidance and tolerance mechanisms to withstand progressive drought stress and around 25.6% SVWC and around 12.3% SVWC separately are thresholds to limit the optimal growth and dry mass production and to last growing and surviving for the current-year shrub seedlings.     

Sap flow in ‘Hass’ avocado trees on two clonal rootstocks in relation to xylem anatomy

The rates of sap flow and xylem vessel features were studied in two-year-old nongrafted and grafted avocado (Persea americana Mill.) trees. Daily sap flow rates were measured with heat and balance stem gauges in clonal Duke 7 (D7) and Toro Canyon (TC) trees and ‘Hass’ clonal scions grafted onto clonal D7 (H/D7) and TC (H/TC) rootstocks. Vessel features as size, number and total vessel area were determined histologically in the stem of the scion and rootstock and the roots of the grafted trees. Significant differences in the sap flow rate were found among the rootstocks, where D7 had a 29% higher sap flow rate than did TC (grafted and nongrafted trees). There were no differences among xylem vessel features in the stems of any of the varieties. However in the roots, D7 had wider and fewer vessels then TC do. Also, D7 had a 19% higher total vessel area than TC. These results suggest that the differences in water consumption of ‘Hass’ on different rootstocks may be associated with differences in the efficiency of the roots to absorb water across conductive tissue which may be linked to differences in the area of xylem vessels in the root.     

Rootstocks influence fruit oleocellosis in ‘Hamlin’ sweet orange (Citrus sinensis L. Osbeck)

Oil spotting or oleocellosis, is a major problem in citrus crops. As the rootstock and fertilization play important roles in citrus growth and fruit development, we investigated the influence of different rootstocks on the growth, mineral nutrition metabolism, water relations, and fruit oleocellosis of eight-year-old field ‘Hamlin’ sweet orange trees. Trees grafted onto Lichi16-6 trifoliata (Poncircus trifoliate) had the greatest rate of oleocellosis (RO), and trees grafted onto Goutou orange (Citrus aurantium) had the greatest degree of oleocellosis (DO). In contrast, trees grafted onto Rangpur lime (Citrus limonia Osbeck) had the lowest RO and DO. Trees were the most vigorous on Rangpur lime rootstocks, followed by Lichi16-6 trifoliata, and then Goutou orange. In addition, because the scion/stock girth ratio showed significant correlations with the RO and DO, oleocellosis parameters can be a good indicator of scion/stock affinity. The total N, total P, Ca²⁺, and Mg²⁺ in leaves from trees on Rangpur lime were significantly lower than in leaves from trees on Goutou orange or Lichi16-6 trifoliata. In addition, the RO showed a significant correlation with the leaf Ca²⁺ and S concentrations and with the peel Mg²⁺ concentration. The DO was significantly correlated with the total peel N and S concentrations. In addition, the RO showed a significant correlation with the net assimilation of CO₂ (ACO₂), stomatal conductance (GS), transpiration rate (ET), and water-use efficiency (WUE). However, the DO showed a significant correlation with the GS, ACO₂, and WUE. Taken together, these results indicate that rootstocks affect the development of oleocellosis in ‘Hamlin’ sweet orange due to their effects on the mineral nutrition balance and water relations.