Leaf Burn Research Articles

Growth, Evapotranspiration and Mineral Content of Gerbera Under Combined Salinity and Excess Boron

Abstract Gerbera is a very important plant widely grown for cut flowers. To check the influence of salinity and boron excess in nutrient solution, nine treatments as factorial combination of three sodium chloride (NaCl) (1, 15 and 30 mM) and three boron (B) (0.1, 1 and 2 mM) concentrations in the nutrient solution were applied during the gerbera cultivation. The effects of experimental treatments on gerbera growth, flowering and the interaction in morphological and nutritional aspects were tested. The formation of leaves, stems and flowers, flower dry mass and evapotranspiration (ET) were more negatively affected when plants were irrigated with 2 mM B than with 0.1 mM B concentration. High levels of boron (1 and 2 Mm) in nutrient solution resulted in leaf chlorosis and necrosis. The severity of leaf burn was correlated with leaf B content. Salinity acted as a protector against boron content in leaves and flowers at 1 Mm B. However, at the 2 Mm B in nutrient solution, leaf B accumulation was not reduced by the presence of NaCl but also increased with the increased levels of salinity. The external levels of boron used in this study, which were found to be the highest in the literature, and the high sensitivity of gerbera to boron, suggested that boron acted as the dominant factor. Lower external boron concentrations would be needed to establish to what extent salinity would be able to mitigate the negative effects of boron.

Breeding program by interspecific cross utilizing Actinidia rufa native to Japan

To widen the range of characteristics of kiwifruit, a breeding program for selecting small-fruited cultivars with high eating quality and good climatic adaptability has been conducted by utilizing Actinidia rufa, indigenous to warm regions of Japan, since 2004. Here, we review the process of selection and the characteristics of cultivars registered in 2014. Inter- and intraspecific crosses were conducted among A. rufa (two female lines, [Fuchu] and [Awaji], one male line, [Kochi]) and diploid Actinidia chinensis (two female cultivars, ‘Kohi’ and ‘Yellow Queen’, and two male lines, [FCM1] and [FCM3]). The fruit size was much larger and total soluble solids (TSS) content was higher in the interspecific cross seedlings between A. rufa and A. chinensis than in intraspecific cross seedlings in A. rufa. In the interspecific cross with A. chinensis, the progenies of [Fuchu] had lower titratable acidity (TA) than those of [Awaji]. After evaluating performance in commercial fields, four selections from the progenies of A. rufa [Fuchu] × A. chinensis [FCM1] were registered in 2014. Fruits had oblong shape and hairless brown skin with green or yellow flesh. Fruit weight ranged from 40 to 60 g. Timing of commercial harvest was late October to early November. The fruit ripened on the vine when they were left until late November. By ethylene treatment, fruit ripened easily, and they contained 17-20% TSS, 0.6-0.8% TA, and 30-60 mg ascorbic acid 100 g-1 FW. Activity of protease was quite low. Under refrigerating conditions, fruit could be stored in good condition for 3-4 months. Average yield was as high as 40 t ha-1. Vines were tolerant to hot and dry conditions and leaf burn hardly occurred. In some area, buds may suffer frost damage, as they burst earlier. These cultivars are promising as a new category of kiwifruit.

Relative Salt Tolerance of 22 Pomegranate (Punica granatum) Cultivars

A greenhouse experiment was conducted to determine the relative salt tolerance of pomegranate (Punica granatum) cultivars. Twenty-two pomegranate cultivars were irrigated weekly with a saline solution at an electrical conductivity (EC) of 10.0 dS·m–1 for 4 weeks and subsequently with a saline solution at an EC of 15.0 dS·m–1 for another 3 weeks (salt treatment). Another group of uniform plants was watered with a nutrient solution without additional salts at an EC of 1.2 dS·m–1 (control). No visual foliar salt damage (leaf burn, necrosis, or discoloration) was observed during the entire experimental period; however, salt treatment impacted pomegranate growth negatively, with a large variation among cultivars. Salt treatment reduced shoot length by 25% and dry weight (DW) by 32% on average for all cultivars. Cluster analysis classified the 22 tested pomegranate cultivars in two groups. The group consisting of ‘Arturo Ivey’, ‘DeAnda’, ‘Kazake’, ‘Russian 8’, ‘Apseronski’, ‘Purple Heart’, ‘Carolina Vernum’, ‘Chiva’, ‘Kunduzski’, ‘Larry Ceballos 1’, ‘ML’, ‘Salavatski’, ‘Spanish Sweet’, and ‘Wonderful’ was more salt tolerant than the group including ‘Al-Sirin-Nar’, ‘Kandahar’, ‘Surh-Anor’, ‘Early Wonderful’, ‘Angel Red’, ‘Ben Ivey’, ‘Utah Sweet’, and ‘Mollar’. The sodium (Na) concentration in the leaf tissue of all 22 pomegranate cultivars was less than 1 mg·g–1 on a DW basis. All pomegranate cultivars in the salt treatment had an average leaf chloride (Cl) content of 10.03 mg·g–1 DW—an increase of 17% from the control. These results indicate that pomegranate plants have a strong capability to exclude Na and Cl accumulation in leaf tissue. In conclusion, the pomegranate plant is very tolerant to saline water irrigation up to an EC of 15 dS·m–1 with little foliar salt damage and a slight growth reduction. Investigation is needed to determine the effects of saline water on the fruit yield and nutritional quality of pomegranate.

Zinc bioavailability and nitrogen concentration in grains of wheat crop sprayed with zinc sulfate, ammonium sulfate, ammonium chloride, and urea

It is still unclear if different sources of nitrogen (N) can variably influence grain accumulation of zinc (Zn), N, and phytate. We tested foliar treatments of 0 or 0.25% Zn as zinc sulfate in combination with 0 or 1% N as ammonium chloride, ammonium sulfate or urea sprayed on field-grown-wheat (Triticum aestivum L.) foliage at anthesis and 10 days later. Leaf burning caused by ammonium chloride significantly decreased grain yield. Grain N concentration was the highest in the urea +0.25% Zn treatment. Foliar N application influenced grain Zn concentration only if Zn was included in the spray. Grain phytate concentration was significantly decreased by both N and Zn sprays. Estimated Zn bioavailability in grains was the highest at 0.25% Zn and was not influenced by the N sources. Based on grain yield, grain N concentration, and Zn bioavailability in grains, foliar application of Zn + urea is an optimal strategy.

Regulations of cloudiness on energy partitioning and water use strategy in a riparian poplar plantation

Cloudiness is an important environmental variable that affects the total and proportion of diffuse radiation reaching the ground and thereby the rate of plant carbon assimilation. However, its regulations on ecosystem energy partitioning and water use strategy are not well understood, particularly for riparian ecosystems. We used the eddy covariance technique and micrometeorological sensors to measure the energy fluxes and environmental conditions for a poplar plantation adjacent to the Chaobai River in North China during the growing seasons (April–October) in 2014 and 2015. We found that canopy conductance (Gs) was the primary biophysical factor regulating the ecosystem energy partitioning, while vapor pressure deficit (VPD) did not impose significant effects on evaporative fraction (EF). Cloudiness suppressed EF primarily due to the stomatal closure caused by the decrease in direct radiation (Rdir). Furthermore, the ratio of stomatal sensitivity (m) and reference conductance (Gsref) was 0.36 and 0.48 mol m−2 s−1 ln(kPa)−1 during clear sky and cloudy sky conditions, respectively. These results indicated that this poplar plantation with an anisohydric behavior weakened stomatal control on water loss under clear skies by avoiding leaf burn arising from higher direct sunlight and temperature. Finally, the mean Priestley–Taylor coefficient (α) and EF was 1.01 and 0.61 across two growth periods, respectively, and ecosystem evapotranspiration (ET) exceeded rainfall, even in rainy year, suggesting that a certain amount of groundwater might be consumed by this riparian poplar plantation, which would exacerbate regional drought.

Effects of plastic mulching film-induced leaf burning on seedling growth in tobacco cultivation: Different findings beyond conservation view

Solving high-temperature plastic mulching film-induced leaf burning in the first week during tobacco cultivation would take much time and effort. In the present study, the growth as well as the leaf sugar and nicotine contents of seedlings with or without leaf burning induced by high-temperature plastic mulching film were tested at two independent sites in 2015 and 2016 to identify the influence of leaf burning on seedling growth. The results showed that the growth of seedlings with leaf burning was improved with increased leaf area, leaf number and plant height compared to those without leaf burning, combined with an increased seedling survival rate at two sites in two years. In seedlings with leaf burning, the contents of fructose and glucose increased and peaked at 11:00 and 13:00 in the leaf and root, respectively, with an increased root nicotine content beginning at 13:00, highlighting the signalling role of sugars. Activities of antioxidant enzymes including peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) were all increased in seedlings with leaf burning. More plant biomass was allocated to roots in seedlings with leaf burning with increased root volume compared to control seedlings, which might facilitate the absorption of water and nutrients from the soil. Our findings demonstrate that high-temperature plastic mulching film-induced leaf burning not inhibited but benefited seedling survival and growth, suggesting that the time and labour-consuming manual plucking of burnt leaves can be avoided during tobacco cultivation.

The effect of humic acid on leaf morphophysiological and phytochemical properties of Echinacea purpurea L. under water deficit stress

Abstract Purple coneflower (Echinacea purpurea) is one of the most important medicinal plants used in most developed countries and drought stress is one of the most serious living stresses that reduces the quality and quantity of plant yield. Therefore, an experiment was performed in a factorial form based on a randomized complete block design during the crop year, 2014, that treatments included water deficit stress at four levels (control (non-consumption), 40, 60 and 80% of field capacity) and humic acid including four levels (zero (control), 250, 500 and 1000 mg/kg). The results showed that drought stress significantly reduced the chlorophyll, carotenoid and relative water content of the leaf and increased ion leakage, leaf burn percentage and proline content of the plant. However, acidic treatments improved plant growth and somewhat moderated the effects of drought. Three phenolic compounds, cichoric acid, caffeic acid and chlorogenic acid are the most important active ingredients in this plant. Also, cichoric acid and chlorogenic acid were increased (91.1 and 05.1, respectively) under water deficit stress. In addition, humic acid treatment increased the chlorogenic acid content. Drought stress showed a significant difference on trichome size at 1% level. However, no significant differences were observed regarding the effect of humic acid treatments on the trichome size and the diameter of the stomata. E. purpurea is recommended for growth conditions that receive average supplemental irrigation and humic acid treatments could reduce these effects of drought stress.

Responses of Marigold Cultivars to Saline Water Irrigation

Marigolds (Tagetes sp.) are ornamental plants with fine-textured, dark green foliage, and yellow, orange, or bicolored flowers. The relative salt tolerance of eight marigolds [‘Discovery Orange’, ‘Discovery Yellow’, ‘Taishan Gold’, ‘Taishan Orange’, and ‘Taishan Yellow’ african marigold (Tagetes erecta); ‘Hot Pak Gold’, ‘Hot Pak Orange’, and ‘Hot Pak Yellow’ french marigold (Tagetes patula)] was evaluated in a greenhouse experiment. Plants were irrigated weekly with nutrient solution at an electrical conductivity (EC) of 1.2 dS·m−1 (control) or saline solutions at an EC of 3.0 or 6.0 dS·m−1 (EC 3 or EC 6). Marigold plants began to show foliar salt damage (leaf burn and necrosis) at 6 weeks after the initiation of treatment. At harvest (9 weeks after the initiation of treatment), ‘Discovery Orange’, ‘Discovery Yellow’, ‘Taishan Gold’, and ‘Taishan Yellow’ plants exhibited severe foliar salt damage with visual scores less than 2 (on a scale of 0 to 5, with 0 = dead and 5 = excellent with no foliar salt damage) in EC 6. In the same treatment, ‘Hot Pak Gold’ and ‘Taishan Orange’ plants all died and only one of nine ‘Hot Pak Orange’ and ‘Hot Pak Yellow’ plants survived. In EC 3, all cultivars had slight or minimal foliar salt damage with visual scores ≈4 with the exception of Taishan Gold and Taishan Orange plants that showed moderate foliar damage with a visual score of 2.3 and 2.1, respectively. Treatment EC 3 reduced the flower number of ‘Discovery Orange’, ‘Discovery Yellow’, ‘Hot Pak Gold’, and ‘Hot Pak Yellow’ by 52%, 28%, 50%, and 30%, respectively, whereas EC 6 decreased the flower number of ‘Discovery Orange’ and ‘Discovery Yellow’ by 48% and 52%, respectively. In addition, both EC 3 and EC 6 did not reduce total dry weight (DW) of any cultivars, except Hot Pak Yellow and Taishan Yellow. In conclusion, all marigold cultivars are moderately sensitive to salt. ‘Discovery Orange’, ‘Taishan Yellow’, ‘Discovery Yellow’, and ‘Taishan Gold’ were more tolerant than ‘Hot Pak Gold’, ‘Hot Pak Orange’, ‘Hot Pak Yellow’, and ‘Taishan Orange’.

Intercropping of taro and sunn hemp with cutting periods during the cycle

ABSTRACT Intercropping using legumes is one of the ways to protect the main crop, and in long term improve the physical and chemical properties of the soil. The aim of this work was to evaluate the intercropping of Colocasia esculenta (L.) Schott (taro) and the tropical legume Crotalaria juncea L. (sunn hemp), cutting sunn hemp at ten periods during the cycle. The experiment was carried out under field conditions between 09/23/2010 and 06/04/2011. It consisted of 11 treatments related to the 10 cutting times of sunn hemp (55, 70, 85,100, 115, 130, 145, 160, 190, and 220 days after sowing - DAS) plus a control of taro with no sunn hemp. During the cycle, taro was evaluated for plant height and incidence of leaf burn. At the time of cutting the sunn hemp, the plant height, fresh and dry matter masses, and nutrient content of the biomass were calculated. During taro harvest, we evaluated the productivity of the mother rhizomes and classified the cormels. Taro plants shaded by sunn hemp showed a lower incidence of leaf burn. The sunn hemp cut from 145 DAS onwards affected the yield of comercial rhizomes and total and agroeconomic indexes. Sunn hemp cut up to 130 DAS provided better performance of taro, without compromising productivity and economic indicators, with the highest amounts of N and K observed in the biomass cut at 115 DAS.

In‐Season Canopy Reflectance Can Aid Fungicide and Late‐Season Nitrogen Decisions on Winter Wheat

Core Ideas Wheat grain yield response to foliar fungicide is highly dependent on environment. Late‐season N can offset protein dilution from fungicide‐driven yield increase. Foliar N rates necessary to impact grain protein have potential for leaf burn. Controlled‐release N and urea ammonium nitrate both impacted wheat responses similarly. In‐season canopy reflectance can aid in fungicide decision. Winter wheat (Triticum aestivum L) response to foliar fungicide and late‐season N is inconsistent. We evaluated various late‐season N fertilizer‐by‐foliar fungicide combinations to test whether wheat anthesis normalized difference vegetative index (NDVI) could aid fungicide decisions. Six site‐years were conducted with N fertility >120 kg N ha−1 during 2012–2013 and 2013–2014 in Oklahoma, using a three‐way factorial arrangement of a randomized complete block design with four replications. Fungicide treatment (with or without), foliar N source (urea ammonium nitrate [UAN] or controlled‐release N), and N rate (0, 2.8, 5.6, or 28 kg N ha−1) were applied during anthesis. Statistical analyses were performed by site‐year, by yielding environment (low [LY] <3.2 Mg ha−1 and high [HY] >3.2 Mg ha−1), and pooled across site‐years. Grain yield was 0.21 Mg ha−1 greater due to fungicide in the pooled analysis, mostly led by the 0.59 Mg ha−1 yield advantage in HY as opposed to non‐significance in LY. Fungicide increased test weight in 6 to 7 kg m−3 across all analyses, and 28 kg N ha−1 increased grain protein by ∼10 g kg−1 but caused leaf burn. Anthesis NDVI <0.6 occurred when preanthesis abiotic stresses restricted yield potential, not warranting fungicide application. Fungicide can benefit grain yield and test weight and could be considered when anthesis NDVI >0.6, but yield response will depend on grain‐filling conditions. Foliar N rates needed to increase grain protein in a well‐fertilized crop have potential for leaf burn.

Towards Development of Hybrid Tossa Jute (Corchorus olitorius L.) using Chemical Hybridizing Agent: Insight into Agro- Morphological and Reproductive Response

Three male gametocides (maleic hydrazide, benzotriazole, surf excel detergent) were tested on tossa jute cv. JRO-204 for induction of male sterility in randomized block design with three replications. Effect of different treatments was assessed on different plant parts including morphological traits (seed yield and attributing traits) and reproductive parts (anther and stigma). Phytotoxic effects associated with different male gametocides were observed on different vegetative and reproductive parts. Visual toxic effects included stunted growth, leaf burning, delayed flower initiation and deformity of flower buds. Amongst different treatment maleic hydrazide induce more sterility with less phytotoxic effects on jute plant..

Effects of Micronutrients on the Nutritional Status of Clonal Tea Replanted in Areas Where Old Tea Was Uprooted

Tea yields peak is 21-30 years after which yields decline. The declining productivity and moribuncy has been reported in many tea fields due to prolonged period of monoculture under tea, physicochemical and biological properties of soil deteriorate considerably causing diseases, pests, acidic soils among others which leads to uprooting of old tea bushes. Deficiency of micronutrients in some tea sections has been reported which has been corrected by foliar application. Though the deficiency could be corrected through foliar application, this mode of application has its shortcomings including leaf burn and the mobility of nutrients from the leaves to the roots is very slow. This study aimed at determining the effect of soil application and variation of micronutrients on the nutritional status of clonal tea replanted in old tea lands.Leaf and soil samples were collected in a random complete block design and the micromutrient levels determined using Inductively Coupled Plasma Emission (ICPE). Data analysis was done using MSTAT-C software.The changes in the levels of micronutrients with varied eight micronutrient combinations subjected on different clones were studied. Clone 12/28 significantly (P≤0.05) varied with the other clones indicating that different clones have varied abilities to absorb nutrients. Clone 303/577 gave a significantly higher uptake of B in the order TRFK303/577 >S15/10 >12/28 >31/8. Clone 12/28 recorded a higher uptake of N with mean levels of 3.075, clone 31/8 had significantly higher uptakes of Fe and Zn. None of the micronutrients subjected on the clones brought an impact in the uptake of N and Mg. This study therefore recommends the use of soil application of micronutrients as an alternative to foliar application in areas where old tea bushes were uprooted.

Bacterial Wilt of Southern Highbush Blueberry Caused by Ralstonia solanacearum

Bacterial wilt is a newly discovered disease of blueberry in Florida. Plants with bacterial wilt will show signs of water stress such as wilting and marginal leaf burn. The disease was initially confirmed on three farms in Florida. This 3-page fact sheet describes the symptoms, occurrence, and management of bacterial wilt in blueberry. Written by Philip F. Harmon, Carrie Harmon, and Dave Norman, and published by the Plant Pathology Department, November 2016. PP332/PP332: Bacterial Wilt of Southern Highbush Blueberry Caused by Ralstonia solanacearum (ufl.edu)

Palmer Amaranth (Amaranthus palmeri) Control and Grain Sorghum (Sorghum bicolor) Injury with Pyrasulfotole plus Bromoxynil and Tank Mixtures

Field studies were conducted in 2009 and 2010 to determine control of Palmer amaranth and crop injury resulting from a postemergence (POST) premix application of pyrasulfotole + bromoxynil and various tank‐mix partners. The objectives were to (i) determine the effects of different pyrasulfotole + bromoxynil rates and tank‐mix partners applied at early and mid‐POST (EPOST and MPOST) on Palmer amaranth control; (ii) evaluate weed control following application at different Palmer amaranth sizes; and (iii) assess sorghum injury and yield as affected by herbicides applied at the 4‐leaf, 10‐leaf, and boot stages. At both EPOST and MPOST, pyrasulfotole + bromoxynil + atrazine alone or mixed with 2,4‐D or dicamba consistently provided better Palmer amaranth control (>98% at EPOST and >90% at MPOST) than bromoxynil + atrazine (94% at EPOST and 58% at MPOST). At EPOST, control of Palmer amaranth by pyrasulfotole + bromoxynil alone varied with year, but the control was 100% at 42 days after treatment (DAT) when pyrasulfotole + bromoxynil was tank‐mixed with atrazine at 0.50 lb a.i./acre or dicamba at 0.20 lb a.i./acre. Pyrasulfotole + bromoxynil at more than 0.02 + 0.14 lb a.i./acre plus atrazine at 0.50 lb a.i./acre provided 100% control at 42 DAT when Palmer amaranth was less than 9 inches tall. In controlling 15‐ to 18‐inch‐tall Palmer amaranth, the efficacy of pyrasulfotole + bromoxynil + atrazine ranged from 83% to 99%. Pyrasulfotole + bromoxynil + atrazine resulted in up to 28% leaf burn at 3 DAT when applied to 4‐leaf sorghum, but plants completely recovered from the injury within 28 DAT. Addition of dicamba to pyrasulfotole + bromoxynil + atrazine tended to reduce sorghum injury. However, application of pyrasulfotole + bromoxynil + atrazine + dicamba at the boot stage reduced sorghum grain yields up to 37%.

Irrigated and rain-fed maize response to different nitrogen fertilizer application methods

ABSTRACTWith the demand for maize increasing, production has spread into more water limited regions. Couple this with increasing resource costs and environmental concerns and the need for efficient nutrient and water management practices has increased. The objective of this trial was to evaluate the effects of different nitrogen (N) fertilizer application methods and timings on maize grain yield, N use efficiency (NUE), and water use efficiency (WUE) under irrigated and rain-fed conditions. Four site-years of data were collected. Fertilizer treatments consisted of all N applied preplant, split surface applied, and split foliarly applied. Irrigation applied prior to and during reproductive growth increased grain yield, NUE, and WUE compared to rain-fed treatments for all site-years. Split surface applied N fertilizer applications typically increased NUE, but not always grain yield compared to preplant applications. The use of split foliar N fertilizer applications was only beneficial in the site-years when leaf burn was not as severe.

EFFECTS OF SALINITY ON SOME CITRUS ROOTSTOCKS

Citrus is a major horticultural crop worldwide and known as relatively susceptible to salinity. Salt damages are usually displayed as leaf burn and defoliation and are associated with accumulation of toxic levels of Na+ and/or Cl- in leaf cells. Reactions against these toxicities depends on the rootstock used. In this study we have evaluated Tuzcu 891 sour orange, Swingle citrumelo, Volkameriana, Rubidoux trifoliate and Citremon in terms of salinity. The experiment was carried out in a greenhouse. The treatments were control [nutrient solution with electrical conductivity [EC(w) of 0.41 dS m] and salinity [nutrient solution with EC(w) 6.0 dS m(-1)] in a randomized block design with thirty replicants during 90 days period. Shoot and root dry weights, leaf and root potassium (K) concentrations, leaf and root calsium (Ca) concentrations, leaf and root chloride (Cl) concentrations, leaf and root sodium (Na) concentrations and symptoms in leaves were observed. Although root dry weight did not differ among those rootstocks, significant differences were determined in K, Ca, Cl, Na concentrations and shoot dry weights.

Investigating the impacts of recycled water on long-lived conifers.

Recycled wastewater is a popular alternative water resource. Recycled water typically has higher salinity than potable water and therefore may not be an appropriate water source for landscapes planted with salt-intolerant plant species. Coast redwoods (Sequoia sempervirens) are an important agricultural, horticultural and ecological species assumed to be salt intolerant. However, no studies have analysed how salinity impacts coast redwood growth. To determine salt-related growth limitations, as well as susceptibility to particular salt ions, we divided 102 S. sempervirens 'Aptos Blue' saplings evenly into 17 salinity treatments: a control and four different salts (sodium chloride, calcium chloride, sodium chloride combined with calcium chloride, and sodium sulfate). Each salt type was applied at four different concentrations: 1.0, 3.0, 4.5 and 6.0 dS m(-1). Trees were measured for relative growth, and leaves were analysed for ion accumulation. Results showed that the relative stem diameter growth was inversely proportional to the increase in salinity (electrical conductivity), with R(2) values ranging from 0.72 to 0.82 for different salts. Analysis of variance tests indicated that no particular salt ion significantly affected growth differently than the others (P > 0.1). Pairwise comparisons of the means revealed that moderately saline soils (4-8 dS m(-1)) would decrease the relative height growth by 30-40 %. Leaf tissue analysis showed that all treatment groups accumulated salt ions. This finding suggests reduced growth and leaf burn even at the lowest ion concentrations if salts are not periodically leached from the soil. Regardless of the specific ions in the irrigation water, the results suggest that growth and appearance of coast redwoods will be negatively impacted when recycled water electrical conductivity exceeds >1.0 dS m(-1). This information will prove valuable to many metropolitan areas faced with conserving water while at the same time maintaining healthy verdant landscapes that include coast redwoods and other long-lived conifers.

BEHAVIOR OF DIPLOID AND TETRAPLOID GENOTYPES OF 'CARRIZO' CITRANGE UNDER ABIOTIC STRESS

Tetraploidy is a spontaneous phenomenon in citrus and some anatomical differences have been described between tetraploid (4x) citrus plants and their corresponding diploids (2x). The choice of a suitable rootstock is often very restricted by a combination of biotic and abiotic stresses. Recent data points out that tetraploidy in citrus induces interesting phenotypes like dwarfing and tolerance to abiotic constraints. In this work we investigated the behavior of 4x and 2x 'Carrizo' citrange (Citrus sinensis X Poncirus trifoliata) subjected to the main abiotic stresses that threat Spanish citrus industry. Seedlings were exposed to salinity, drought and iron deficiency and physiological parameters were measured. Results suggest that 4x plants stressed by drought were able to maintain high leaf water potential more efficiently than 2x, thus gas exchange parameters (transpiration, stomatal conductance, and photosynthesis) were less affected. Under salt stress no difference was found in leaf chloride content neither in gas exchange parameters, but leaf burn was less severe in 4x than in 2x. Concerning iron deficiency, a better tolerance of 4x compared to 2x was supported by higher ferricchelate reductase activity, SPAD index and chlorophyll fluorescence. These preliminary results suggest that 4x 'Carrizo' citrange could be a promising rootstock, having the same general performance than the original 2x, but producing smaller trees more tolerant to abiotic stresses. (Resume d'auteur)

Organic Compound Concentrations of Size-Segregated PM10 during Sugarcane Burning and Growing Seasons at a Rural and an Urban Site in Florida, USA

ABSTRACTFlorida has the most land used to grow sugarcane crops in the United States. The preharvest sugarcane leaf burning elevates ambient particle matter (PM) concentrations in rural areas with dominant sugarcane agriculture (Belle Glade) and affects the air quality of coastal urban sites (Delray Beach). In this study, ambient particles segregated by size were analyzed to identify trace organic compounds from PM sources that may cause adverse health effects. The sampling campaign was conducted simultaneously at urban and rural sites, and revealed that the organic compound concentration of each particle size varies significantly between the sugarcane burning season (SBS) in January and sugarcane growing season (SGS) in May. The results indicated that PM3 contains at least 76% of the organic compound concentrations detected in the samples collected from both sites and during both seasons. The concentrations of trace organic compounds were higher in the SBS than in the SGS. Combustion-oriented hopanes, polycyclic aromatic hydrocarbons (PAHs), and oxygenated PAHs were mainly detected in PM0.49. The detection of elevated levoglucosan concentrations at the urban site indicates that fine particles generated from biomass burning traveled from the rural site to the urban site. Secondary organic compounds such as dicarboxylic acids, phytol, and 6,10,14-trimethyl-2-pentadecanone exhibited similar concentration patterns in the rural and urban sites during both seasons. In the SGS, PM10 concentrations at both sites were extremely similar; however, the organic compound levels were lower at the rural site than at the urban site in the SBS. This result should be investigated further by researchers investigating the health aspects of organic compound concentrations.

ASSESSMENT OF MORPHOLOGICAL AND PHYSIOLOGICAL RESPONSES OF PEACH ROOTSTOCKS UNDER DROUGHT AND ALUMINUM STRESS

The challenging constrain of peach production in highlands of northern Thailand is limited irrigation water and acidic soil. These problems could be alleviated by using a suitable rootstock. Field screening for drought and acidic soil tolerant rootstocks is time consuming and costly. Therefore, any parameter related to these traits detected in a greenhouse screening would be very useful as a selection index for a breeding program. In acidic soil, aluminum toxicity is one of the major confinements on plant growth. The aim of this study was to evaluate potential morphological (shoot fresh and dry weight, leaf size and leaf burn) and physiological (photosynthesis, chlorophyll a content, leaf conductance, leaf water potential and proline content) parameters related to drought and aluminum stress. A factorial experiment with two levels of the irrigation: 1) well watered (100% of evapotranspiration, ET) and 2) drought treatment (25-50% of ET), combined with three levels of aluminum: 1) no aluminum, 2) 50 mg kg-1 of aluminum and 3) 100 mg kg-1 of aluminum was done with four-week-old ‘Flordaguard’ rootstocks. The results showed that drought and aluminum stress caused leaf burn. Drought treatment significantly reduced shoot fresh weight (50%), shoot dry weight (35%), photosynthesis rate (80%), leaf conductance (90%) and leaf water potential (75%). Conversely, drought effect increased proline content by 10%. Aluminum stress caused linear decrease in shoot fresh weight and quadratic decrease in shoot dry weight and leaf size, but leaf burn was quadratic increased. For drought stress all parameters, except leaf size, leaf burn and chlorophyll content, were potentially selection index. Meanwhile, for aluminum stress, potential selection parameters were shoot fresh and dry weight, leaf size and leaf burn.