Volume 4 Special Issue 2 2010
Plant science and biotechnology in North America: Focus on Canada I

ISBN 978-4-903313-70-2

How to reference: Liu J-J, Ekramoddoullah AKM (2010) Stable Reporter Gene Expression in Western White Pine (Pinus monticola Dougl. ex D. Don) by Agrobacterium-mediated Genetic Transformation. In: Al-Mughrabi K (Ed) Plant science and biotechnology in North America: Focus on Canada I. The Americas Journal of Plant Science and Biotechnology 4 (Special Issue 2), 1-5

Guest Editor

Khalil Al-Mughrabi

Potato Development Centre, New Brunswick Department of Agriculture and Aquaculture, Canada

www.gnb.ca/0029/10/0029100001-e.asp

CONTENTS AND ABSTRACTS

Jun-Jun Liu, Abul K. M. Ekramoddoullah (Canada) Stable Reporter Gene Expression in Western White Pine (Pinus monticola Dougl. ex D. Don) by Agrobacterium-mediated Genetic Transformation (pp 1-5)

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Original Research Paper: An Agrobacterium-mediated transformation procedure was developed to transform the mature embryo from Pinus monticola (Dougl. ex D. Don) seeds with two binary vectors containing the reporter gene encoding the green fluorescent protein (GFP) or the β-glucuronidase protein (GUS), respectively. More than 1000 embryos from independent transformation events were tested for different western white pine seed families. Selection of kanamycin-resistant callus tissues showed that survival rates varied from 33 to 48% in different independent experiments. Transgenic callus tissues survived and continued to grow on the medium with kanamycin (25 μg/mL), whereas non-transgenic callus, regenerated from the embryos of the same seed family, died within 12 weeks. Integration and expression of the introduced reporter gene was confirmed in transgenic western white pine calli by GUS-staining analysis or microscopic observation of GFP fluorescence. Rates for stable reporter gene expression ranged from 2.9 to 6.5% for all embryos co-cultured with Agrobacterium. Our protocol has enabled the routine transformation of western white pine, a species that was previously difficult for gene manipulation. To our knowledge, this is the first report on genetic engineering of this conifer. Our results demonstrate that transgenic gene expression in western white pine is a feasible option for genetic improvement of this valuable conifer as well as for investigating its molecular interactions with the fungal pathogen Cronartium ribicola (J.C. Fisch.).

Christina E.N. Lord, Arunika H.L.A.N. Gunawardena (Canada) Isolation of Leaf Protoplasts from the Submerged Aquatic Monocot Aponogeton madagascariensis (pp 6-11)

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Original Research Paper: Aponogeton madagascariensis is the only aquatic plant which forms perforations in its leaves through a process known as programmed cell death (PCD). Although PCD can be studied in vivo, isolated protoplasts maintain many of the same physiological properties of the intact plant and, due to their accessibility and reduced complexity, make ideal research tools to investigate plant processes including PCD. The conditions for the isolation of protoplasts from the lace plant were examined. Several factors including leaf age, carbohydrate source, and enzyme incubation time all significantly influenced protoplast yield and viability from lace plant tissue. Viable protoplasts were successfully isolated from leaf tissue approximately 1 month in age, using an enzyme mixture comprised of 2% w/v cellulase onozuka R10 and 0.5% pectolyase Y-23 dissolved in 0.005 M MES and 0.6 M sorbitol, pH 5.5. Approximately 60.35 ± 1.08 x 10⁵ protoplasts/g fresh weight, with a viability of 92.75 ± 2.25%, were obtained from 4 hour isolations in the dark. Following successful isolation, these lace plant protoplasts can be used as an excellent model system for the study of environmentally induced PCD and can provide the first ever opportunity to compare this form of PCD with its developmentally regulated counterpart within one species of plant.

Appanna Vikram (Canada), Habiballah Hamzehzarghani (Iran), Khalil I. Al-Mughrabi, Ajjamada C. Kushalappa (Canada) Volatile Mass Ion and Metabolite Profiling to Detect and Discriminate Fungal Diseases in Different Mango Cultivars (pp 12-19)

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Original Research Paper: Gas chromatography and mass spectrometry was used to analyze the volatiles in the headspace of mango cultivars ‘Tommy Atkins’, ‘Keitt’ and ‘Kent’ inoculated with Alternaria alternata, Colletotrichum gloeosporioides and Lasiodiplodia theobromae. A total of 251, 255 and 224 volatile peaks were detected in the three cultivars ‘Tommy Atkins’, ‘Keitt’ and ‘Kent’, respectively. The volatile compounds were identified based on mass spectral match using NIST library. Thirty compounds were detected relatively consistently among replicates in ‘Tommy Atkins’ while the relatively consistent compounds in ‘Keitt’ and ‘Kent’ were 34 and 20, respectively. Several of these compounds were specific to a disease/inoculation or they varied in their abundances when being present in all treatments. In ‘Kent’, 2-butenoic acid, methyl ester was specific to Colletotrichum while propanoic acid, ethyl ester and 2-propenoic acid, 2-methyl-, ethyl ester was specific to Lasiodiplodia. 1-butanol and propanoic acid, ethyl ester was specific to both Colletotrichum and Lasiodiplodia in ‘Tommy Atkins’ cultivar while octanoic acid, methyl ester was specific to Colletotrichum in ‘Keitt’. Overall rate of disease classification based on metabolite profiles was poorer than discriminability of mass ion fingerprints. The average error rates for resubstitution and cross validation for separate metabolite profiles of each cultivar or pooled data of cultivars was higher than 40%. The utmost shortcoming of metabolite profile based discriminant models was their high rate of false negatives. The discriminant models developed on mass ion fingerprints correctly classified almost hundred percent of the entries both in resubstitution and cross validation procedures. The disease specific metabolite profiles and mass ion fingerprints produced could be used to differentiate cultivars and has the potential to be used in early detection of postharvest diseases of mango fruits after validation under commercial conditions.

Tissa Kannangara, Mona Cheng (Canada) Compost Teas for the Suppression ofGummy Stem Blight (Didymella byroniae) in Greenhouse Cucumbers (pp 20-24)

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Original Research Paper: Five vermicompost teas (four aerobic and one anaerobic) were tested for their ability to suppress gummy stem blight in conventionally and organically grown greenhouse cucumbers. Three aerobic teas were amended with clove, thyme or Japanese knott weed (JKW) while two were left un-amended. The fluorescent (Pseudomonas) and total microbial densities and physiological activities of all compost teas were determined. Teas containing clove, thyme and JKW had significantly higher fluorescent bacterial counts than un-amended teas. Aeration also enhanced fluorescent bacterial density. Total bacterial population density was greatest in clover -containing aerobic tea. However, physiological activity was lower in clove containing tea than in un-amended aerobic tea or aerobic tea amended with thyme. An in vitro plate test showed a significant reduction in the mycelia growth of D. byroniae on media containing clove, thyme or JKW. D. byroniae was completely inhibited when media contained 0.03 g/l clove. In conventionally grown cucumbers, lengths of stem lesions caused by D. byroniae were significantly reduced by all aerobic teas. Shortest stem lesion length was observed in plants treated with clove containing tea. The average lesion length in the control treatment for conventionally grown cucumber was 123 mm whereas that for organically grown cucumber was 77 mm. Stem lesion length did not differ significantly from the control in organically grown cucumber with respect to different compost tea treatments. In both conventionally and organically grown cucumbers, clove-amended teas resulted in the shortest stem lesions. Clove, because of its ability to suppress mycelial growth and enhance populations of fluorescent Pseudomonas, should be considered as a standard additive to compost teas, particularly those aimed at suppressing fungal pathogens.

Gefu Wang-Pruski, Robert H. Coffin, Rick D. Peters, Khalil I. Al-Mughrabi, Harold W. Platt, Devanand Pinto, Stephanie Veenhuis-MacNeill, William Hardy, Sangyhun Lim, Tess Astatkie (Canada) Phosphorous Acid for Late Blight Suppression in Potato Leaves (pp 25-29)

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Original Research Paper: Late blight is the most devastating disease of potatoes, resulting in global constraints in potato production. In this study, field trials were conducted in Prince Edward Island, Canada for three years to evaluate the efficacy of a phosphorous acid-based fungicide for the suppression of foliar late blight. Leaves from each treatment were detached from plants in early August of each year and were manually inoculated with a sporangial suspension of a local US-8 (A2) strain of P. infestans. Analysis of disease severity showed that the treatments had a significant effect on disease development and the treatment effect interacted with incubation time and cultivar type. In all three years, the combined treatment of phosphorous acid with chlorothalonil provided the best disease suppression, followed by treatment with chlorothalonil alone. Phosphorous acid alone provided increased protection to the leaves, but the effect was not as marked as the chlorothalonil alone or combination treatments. When late blight was detected in the field in 2008 and 2009, disease severity in the field was also evaluated. The results of field ratings matched the findings of the detached leaf experiments. The outcome demonstrated the value of detached leaf study as a reasonable replacement for field trials with late blight. Phosphorous acid-based fungicides appear to provide benefit in a foliar program for late blight control, particularly when combined with the regular application of a protectant fungicide. Phosphorous acid also has an excellent environmental profile, so that its usage will reduce the environmental impact of pesticides applied to the potato crop.

Godfrey P. Miles (USA), Rishi I. S. Gill (India), Marcus A. Samuel (Canada) Ectopic Overexpression of SIPK in Poplar Renders Plants Hypersensitive to Ozone (pp 30-34)

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Original Research Paper: Trees respond to a myriad of environmental stresses by activating an array of signalling molecules and genes whose functions enable the plant tissues to retain integrity and to counter the stressor. While a number of stress-induced genes have been identified, there is much less known about the process by which detection of a stress is linked to changes in transcriptional regulation and the ensuing phenotypic outcome. Here, we show that heterologous over-expression of salicylate-induced protein kinase (SIPK), a tobacco mitogen-activated protein kinase (MAPK) involved in transcriptional regulation and oxidant signalling, leads to increased sensitivity of transgenic poplar seedlings to ozone treatment. Ozone treatment of the transgenic poplar also resulted in rapid activation of the ectopically expressed SIPK, as well as the endogenous MAPK⁴⁶, with concomitant elevation of leaf-localized hydrogen peroxide (H₂O₂) levels. The results indicate a conserved function of MAPKs in regulating oxidant signalling in various plant species.

Karen L. Bailey (Canada), Wayne M. Pitt (Australia), Jo-Anne Derby, Stephen Walter, Wesley Taylor (Canada), Stuart Falk (USA) Efficacy of Phoma macrostoma, a Bioherbicide, for Control of Dandelion (Taraxacum officinale) Following Simulated Rainfall Conditions (pp 35-42)

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Original Research Paper: This study evaluated the efficacy of the bioherbicide P. macrostoma under simulated rainfall conditions to determine whether bioactivity was retained in the soil and whether bioherbicidal metabolites would be soluble in water possibly posing a risk to off-site hosts. Various application rates of the bioherbicide were leached with water equivalent to 25-250 mm of precipitation and tested for efficacy before and after leaching using a dandelion bioassay. The percolated water was collected in six fractions (F1-F6) and similarly tested for bioactivity using a dandelion bioassay. Relative concentrations of macrocidin A, the main bioherbicidal metabolite, were estimated by HPLC. DNA-specific primers were used to detect the presence of the fungus in soil. Of three soil types treated with the bioherbicide, all lost the ability to control dandelion after being leached. Clay, as compared to sandy loam and greenhouse soil mix, retained the most bioherbicidal activity. The bioherbicidal metabolite was soluble in water with up to 80% macrocidin A being released in 75 mm of water and bioactivity occurring in fractions F1-F3, with much less or no activity in fractions F4-F6. The impact of water on the distribution of the living component of the bioherbicide was not clearly determined. The study shows that water releases macrocidins from the bioherbicide allowing the compound to be taken up by the roots of the plant, subsequently resulting in plant death. When soils are at field capacity or drier, this amount of rainfall is of little concern as the bioactivity is localized. However under saturated soils, macrocidins may be released in the soil water and if not taken up by the plants, run-off water may pose a risk to off-site hosts. Factors that mitigate the risks associated with off-site movement are discussed.

Michael W. Harding, Lyriam L. R. Marques, Ronald J. Howard, Merle E. Olson (Canada) Biofilm Morphologies of Plant Pathogenic Fungi (pp 43-47)

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Original Research Paper: Microbial biofilms often complicate management of bacterial and fungal diseases. While much is known about biofilms formed by bacteria and yeasts, few descriptions of biofilms formed by filamentous fungi are available. A novel biofilm culture technology, the BEST Assay™, was used to culture biofilms of plant pathogenic fungi in vitro. Biofilm growth was characterized at 6-, 12-, 24-, and 48 h via scanning electron microscopy and compared with fungal growth seen in planta. Descriptions of the in vitro and in planta biofilm morphologies of Fusarium sp. Verticillium dahliae, and Botrytis cinerea are presented. The surface-associated growth of these plant pathogenic fungi is consistent with criteria for biofilm morphology indicating that filamentous fungi likely do form biofilms on host plant surfaces.

Allen G. Xue, Sylvie Rioux, Malcolm J. Morrison, Yuanhong Chen, Jinxiu Zhang, Weikai Yan (Canada) Resistance and Tolerance to Sclerotinia Stem Rot in Selected Short-Season Soybean Cultivars in Canada (pp 48-54)

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Original Research Paper: Fifteen short-season soybean cultivars released in Canada from 1934 to 2000 were evaluated under inoculated field conditions for resistance and tolerance to Sclerotinia stem rot (SSR), caused by Sclerotinia sclerotiorum, in Saint-Bruno, Quebec in 2001, 2002 and 2003. Resistance to SSR was measured by the disease incidence, the severity, a disease severity index, the area under the disease progress curve, and tolerance by the reduction of yield and thousand seed weight (TSW) compared to a non-inoculated control. Significant differences in cultivar responses were found for all parameters. Averaged across the test years, ‘AC Harmony’, ‘Maple Arrow’, ‘Maple Glen’, ‘Maple Ridge’, and ‘AC Orford’, released after 1976, were among the most resistant cultivars based on their disease responses and were significantly better than ‘Capital’, ‘Comet’, ‘Flambeau’ and ‘Mandarin’, released before 1953, suggesting that newer cultivars are more resistant to the disease than older ones. The disease reduced yield by approximately 7-45% and TSW by < 4%. ‘Altona’, ‘Crest’, ‘Mandarin’, ‘Maple Glen’, ‘Maple Ridge’, ‘Pagoda’, and ‘Portage’ were among the most tolerant cultivars, with yield reduced by <18%, and were significantly better than ‘AC Harmony’, ‘Capital’, ‘Comet’, and ‘Flambeau’, with yields reduced by >33%. ‘Maple Glen’ and ‘Maple Ridge’ were the only cultivars with high levels of both resistance and tolerance. The four disease parameters were highly correlated (r ≥ 0.98, P < 0.01), suggesting that a single measurement should be sufficient. All disease parameters were negatively correlated with yield and TSW under inoculation (r ≥ 0.36, P < 0.05) but not correlated with yield and TSW reduction, suggesting that resistance and tolerance to SSR are two separately inherited traits in soybean.

Yousef Abu-Nada, Ajjamada C. Kushalappa, Shiv O. Prasher, Khalil I. Al-Mughrabi, Agnes Murphy (Canada) Metabolic Profiling to Phenotype Potato Genotypes Varying in Horizontal Resistance to Leaf Infection by Phytophthora infestans (pp 55-64)

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Original Research Paper: Screening potato breeding lines, based on disease severity, for horizontal resistance to Phytophthora infestans is slow, time consuming and the results under field conditions are often inconsistent over years. This study reports a potential application of metabolic phenotyping as an additional tool for screening potato genotypes for disease resistance. Three potato cultivars ‘Libertas’, ‘Caesar’ and ‘Russet Burbank’ with high, moderate and low resistance to P. infestans, respectively, were inoculated with the pathogen or water, and metabolites were analyzed using GC/MS. Ninety-four metabolites were tentatively identified, of which 89 had significant treatment effects. Based on univariate analysis, 24 metabolites were identified as Resistance Related Constitutive (RRC) and 32 as Resistance Related Induced (RRI) metabolites. A canonical discriminant analysis of the 89 metabolites identified metabolic phenotypes comparable to disease severity phenotypes. The first three CAN-vectors explained 97% of the total variance. A total of 23 were RR metabolites associated with resistance in ‘Caesar’ and ‘Libertas’ (CAN1 = 65%), while 33 were RRI metabolites in ‘Libertas’ (CAN2 = 23%). In the latter, 25 metabolites were RRI-metabolites and mainly belonged to amino and organic acids group. Among these RRI-metabolites, the abundances of phenylalanine, tyrosine, shikimic acid, malonic acid and benzoic acid significantly increased following pathogen inoculation. These metabolites were previously reported to activate plant secondary defense metabolism particularly the phenylpropanoid and malonic acid pathways that produces several antimicrobial compounds. The potential application of the metabolic profiling technology for high throughput screening of potato breeding lines against late blight is discussed.

Khalil I. Al-Mughrabi, Appanna Vikram, René Poirier (Canada) Effect of Saponins of Chenopodium quinoa Applied as Seed or Foliar Treatments on Dry Rot, Common Scab and Black Scurf Diseases of Potato (pp 65-70)

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Original Research Paper: Dry rot, black scurf and common scab are three potato diseases of economic importance throughout the world. Field trials were conducted in 2005 and 2006 in New Brunswick, Canada to assess the efficacy of saponins extracted from Chenopodium quinoa (SCQ; HeadsUp^®) applied as a seed treatment and foliarly in suppressing dry rot, black scurf and common scab diseases of potato. The trials consisted of four treatments for each disease, namely 1) untreated inoculated or infected control; 2) seed inoculated or infected and treated with SCQ; 3) seed inoculated or infected and the foliage treated with SCQ; and 4) seed inoculated or infected and treated with Maxim^® PSP. After harvest, the tubers were assessed for the severity of dry rot, black scurf and common scab. The tubers were graded and assessed for total yield, tuber size, tuber number, and tuber weight. All of the treatments significantly reduced the severity of dry rot (32.4 to 46.7% reduction), common scab (~30% reduction) and black scurf (61.2 to 76.5% reduction) relative to the untreated, inoculated/infected controls. Seed and foliar treatments with SCQ increased both total yield and marketable yield compared to the untreated, inoculated/infected controls. Seed treatment with SCQ increased marketable yield by 23.8-26.2% while foliar treatment increased marketable yield by 16.8-23.8%. The results of this investigation indicate that saponins extracted from Chenopodium quinoa can be used as a potentially viable option for controlling dry rot, black scurf and common scab diseases of potato.

Susan Slater, Jessica Prystenski, Muhammad Tahir (Canada) A Link between Early Embryogenesis Transcription Factors and Brassica napus Oil Production (pp 71-73)

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Short Communication: Oil synthesis in Brassica napus is composed of a plastidal fatty acid synthesis component, a cytosol pool, and an ER-based triacylglycerol component. A number of the main embryogenic transcription factors such as LEC1, LEC2, WRI1 and FUS3 appear to affect the plastidal fatty acid synthesis component during the seed development. A comparison of the relative transcript concentrations of embryogenic transcription factors between high and low oil double haploid lines shows an increase in the WRI1 and FUS3 transcripts at 21 days after pollination in high oil lines and an increase in the LEC2 transcript at 28 days after pollination in the low oil lines. This indicates that variation in the transcript levels of embryogenic transcription factors which are linked to the plastidal component of B. napus oil synthesis, may affect the production of total seed oil.

Khalil I. Al-Mughrabi (Canada) Post Harvest Treatment with Hydrogen Peroxide Suppresses Silver Scurf (Helminthosporium solani), Dry Rot (Fusarium sambucinum), and Soft Rot (Erwinia carotovora subsp. carotovora) of Stored Potatoes (pp 74-81)

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Original Research Paper: Potato growers encounter high economic losses on a yearly basis due to potato diseases in storage. Current fungicides are becoming ineffective due to the development of resistance by potato tuber pathogens, and new and more effective chemicals are needed to replace them. Potato storage trials were conducted to determine the effect of hydrogen peroxide (H₂O₂) on the potato tuber diseases Fusarium dry rot, silver scurf, and soft rot. The effect of H₂O₂ on traits that affect processing quality, such as potato glucose content, sucrose content and French fry colour, were determined before and after treatment. Potato samples (cvs. ‘Shepody’ and ‘Norland’) were inoculated with Fusarium sambucinum, Helminthosporium solani, and Erwinia carotovora subsp. carotovora before treatment. Three treatments were included in this experiment: a control (tap water); 1:100 v/v H₂O₂ to water; and 1:50 v/v H₂O₂ to water. Potato storages were set at 10°C, with 90+% relative humidity and airflow of 0.035 m³/min/4536 kg of potatoes. Each treatment was applied as a mist using a separate humidifier at a rate of 1L/8 h. Airflow was turned on at the same time as the humidifier to allow the mist to spread through the samples. Treatments were applied daily for 2 weeks (8 h/day), and then once per week (8 h) for the duration of the experiment. H₂O₂ was effective in slowing the development of fusarium dry rot, silver scurf and soft rot and treated potatoes were significantly less diseased compared to the untreated controls. Relative to untreated tubers, silver scurf severity was 21.0 and 15.2% less in Shepody, and 23.0 and 14.0% less in Norland tubers treated with 1:50 and 1:100 H₂O₂, respectively. Dry rot severity was 8.1 and 5.6% less in Shepody, and 12.3 and 6.1% less in Norland tubers treated with 1:50 and 1:100 H₂O₂, respectively. The severity of soft rot was 1.4 and 2.3% less in Shepody, and 3.4 and 3.9% less in Norland tubers treated with 1:50 and 1:100 H₂O₂, respectively. Sucrose and glucose concentrations in tubers, and fry colour were unaffected by H₂O₂ treatment. Our findings indicate that hydrogen peroxide applied to potatoes after harvest is a viable option for suppressing potato diseases in storage while maintaining French fry color.

Pedro Jose González, Andrea Arias (USA), Venancio Arahana, Maria de Lourdes Torres (Ecuador) Cryopreservation of Naranjilla (Solanum quitoense var. quitoense) Shoot-tips by Vitrification (pp 82-86)

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Techniques Paper: Shoot tips of in vitro germinated naranjilla (Solanum quitoense var. quitoense) plants were cryopreserved by vitrification. Shoot tips (1-3 mm) of five week-old plants were pre-cultured on Murashige and Skoog (MS) culture medium with increasing sucrose concentrations (0.4, 0.5, 0.6 and 0.7 M) for 7 days under a 16-h photoperiod and maintained at 23 ± 2°C. Then, shoot tips were treated with a loading solution 2 M glycerol + 0.4 M sucrose, at 26°C for 25 min in a 2 mL cryo-tube; and cryoprotected with 1 mL of pre-cooled PVS 2 solution at 4°C for 60 min. Finally, shoot tips were immersed into liquid nitrogen and kept there for 10 days. Post-warming culture of these shoot tips was carried out on a basal MS medium supplemented with 0.1 mgL^-1 6-benzylaminopurine (BAP), 0.05 mgL^-1 indole-3-butyric acid (IBA) and 0.1 mgL^-1 gibberellic acid (GA₃). The optimized protocol for S. quitoense shoot tips preservation consisted of pretreatment with MS + 0.5 M sucrose, followed by a treatment with loading solution for 25 min at room temperature, PVS 2 at 4°C for 60 min and immersion in liquid nitrogen. Cryopreserved shoot tips started growing 15 days after re-warming. Shoot tips recovery was 70 to 95% with the above described protocol. Plantlets with a normal phenotype after 21 days of culture were acclimatized for 4 weeks in controlled conditions before they were finally transferred to the greenhouse. This is the first report of an effective protocol for the cryopreservation of S. quitoense shoot tips by vitrification.

Androniki C. Bibi, Derrick M. Oosterhuis, Evangelos D. Gonias, James McD. Stewart (USA) Comparison of Responses of a Ruderal Gossypium hirsutum L. with Commercial Cotton Genotypes to High Temperature Stress (pp 87-92)

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Original Research Paper: Global warming has focused attention on the need for improved understanding of crop response to heat stress and the need for enhanced tolerance. Cotton originates in hot climates and native cottons may have the ability to tolerate high temperature stress, however, research is lacking. In this study it was hypothesized that a ruderal cotton from coastal Oaxaca, Mexico will be more tolerant to high temperature stress than USA commercial cotton genotypes. The objective was to compare the responses to high temperature of quantum yield of PSII, leaf extension growth, and antioxidant enzymes of a ruderal G. hirsutum L. race Palmeri (PI681044) and four commercial cotton genotypes popular in the USA (Tamcot Sphinx, Fibermax 960BR, Stoneville 474, and Deltapine 444BR) to high temperature. The ruderal G. hirsutum race Palmeri was significantly more tolerant to high temperature stress than the commercial cultivars, and this observation was supported by all three methods of assessment. Palmeri had less decrease in quantum yield of PSII, increased catalase and glutathione reductase activity, and less decrease in leaf extension growth compared to the commercial cultivars. Among the commercial cultivars, Tamcot Sphinx showed some tolerance to high temperature however this was not supported by all techniques. This study showed that the rudural cotton has better ability than the commercial cultivars to withstand high temperature stress. This knowledge is of particular importance for germplasm improvement in Upland cotton for high temperature tolerance.

Robert S. Brown, Derrick M. Oosterhuis (USA) High Daytime Temperature Stress Effects on the Physiology of Modern Versus Obsolete Cotton Cultivars (pp 93-96)

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Original Research Paper: Year-to-year variability in yield of modern cotton cultivars is a major concern in the cotton industry, and it is speculated that this variability is due to modern cultivars being more sensitive to environmental stress conditions compared to obsolete cultivars. However, research is lacking to explain physiological responses of contrasting cultivars in response to environmental stress conditions. Therefore, a study was designed in Fayetteville, AR to determine the physiological response of modern (‘Stoneville 474’ and ‘Suregrow 747’) versus obsolete (‘Stoneville 213’ and ‘Deltapine 16’) cultivars to daytime high temperature stress in a controlled growth chamber environment. Modern cultivars had improved physiological function at lower daytime temperatures, but obsolete cultivars had improved physiological function at elevated temperatures of 38°C. Furthermore, plant physiological functioning decreased with increasing temperatures. No significant differences existed between modern and obsolete cultivars at 30 or 34°C, however at 38°C, obsolete cultivars showed significant improvements (P < 0.05) in measured leaf photosynthesis, chlorophyll fluorescence, and membrane integrity of leaves. There were no differences between modern and obsolete cultivars with regards to total soluble leaf protein levels or leaf chlorophyll; however, the obsolete cultivars had a numerically greater protein concentration at 38°C, whereas the modern had more leaf protein at the lower temperatures. Overall, it appeared that modern cultivars had improved physiological responses under ideal temperature environments; however, obsolete cultivars were less sensitive to extreme temperatures.

Evangelos D. Gonias, Derrick M. Oosterhuis, Androniki C. Bibi (USA) Measurement of Internal Temperature of Cotton Bolls (pp 97-100)

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Original Research Paper: Questions have arisen about the accuracy of the COTMAN accumulated heat units rule (i.e., 850 heat units after NAWF=5) to determine when to defoliate. It has been suggested that the actual temperatures of the developing bolls in the canopy may not be closely represented by ambient temperatures measured in a meteorological site. The objective of this field study was to measure the internal temperature of developing bolls and correlate it to ambient temperature. Internal boll temperatures were as much as 5°C warmer than ambient temperatures at midday and similar at night. There were no significant differences in boll temperature measurements recorded at different depths, 0.5 and 1.0 cm, in the boll, and there were no significant cultivar differences. A predictive equation was formulated to determine internal boll temperatures using ambient temperature data. Defoliation studies are required to determine the effect on yield and fiber quality when heat units are calculated based on ambient and internal boll temperatures.