2017

Permanent URI for this collectionhttps://hdl.handle.net/1807/75479

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Opportunistic survival strategy of Welwitschia mirabilis: Recent anatomical and ecophysiological studies elucidating stomatal behaviour and photosynthetic potential
(Canadian Science Publishing, 2017-10-02) Krüger, Gert; Jordaan, Anine; Tiedt, Louwrens; Strasser, Reto; Kilbourn Louw, Michele; Berner, Jacques
We present new findings on leaf- and stomatal apparatus anatomy and ecophysiology of Welwitschia mirabilis relevant to desert survival. We show that the structure of the stomatal apparatus with thin areas in the guard cell walls is a key feature enabling an opportunistic survival strategy through reversible quick switch-over from water conservation to CO2 assimilation. Desert environment and greenhouse data demonstrated that stomatal conductance increased almost immediately after dawn to reach a maximum within approximately an hour, whereupon a steep decrease occurred. After discontinuation of induced drought in potted plants, fast recovery of stomatal conductance occurred while copious new root hairs developed within 50 hours. Stomatal limitation proved to be the main photosynthetic constraint under induced drought. Under severe drought stress biochemical limitation came into play. Chlorophyll fluorescence data of in situ plants showed that the photosynthetic potential of leaf tissue is highest near the basal meristem, but although decreasing with age, retains activity up to the leaf apex at the end of the green part. Photosynthetic potential of potted plants was optimal at 20 ยบC, analogous to mesophytic plants. Our data confirms our hypothesis that leaf surface and stomatal structure play a crucial role in moisture conservation and moderating leaf temperature for desert survival.
Leaf herbivory induces resistance against florivores in Raphanus sativus
(Canadian Science Publishing, 2017-11-21) McCall, Andrew; Case, Samantha; Espy, Kelsy; Adams, Grant; Murphy, Stephen J.
Florivory can have significant negative effects on plant fitness, driving selection for resistance traits in flowers. In particular, herbivory to leaves may induce resistance in flowers because herbivores on leaves often become florivores on flowers as plant ontogeny proceeds. The literature on inducible resistance in floral tissues is limited, so we used a series of experiments to determine if prior leaf damage by Spodoptera exigua caterpillars affected florivore preference and performance on wild radish (Raphanus sativus L.). We found that S. exigua larvae preferred petals from control plants versus petals from plants exposed to prior leaf damage, and that larvae gained more weight on petals from control plants, although this depended on the presence of anthocyanins in the petals. Our results suggest that leaf damage can induce changes in petals that reduce S. exigua larval fitness.
Regenerative potential of the soil seed bank along an elevation gradient of rupestrian grassland in Southeastern Brazil
(Canadian Science Publishing, 2017-12-22) Luz, Giovana Rodrigues; Mota, Graciene Silva; Spadeto, Cristiani; Tolentino, Gláucia Soares; Fernandes, Geraldo; Nunes, Yule Roberta Ferreira
The objective of this study was to determine the species richness and abundance of seed bank and the influence of soil attributes along an elevation gradient (800-1400 m). We examined floristic similarity among areas and determined the regional diversity along this gradient in Serra do CipĂł (Brazil). A total of 1975 individuals of 149 species were germinated. Richness and abundance were not linearly related to elevation and exhibited a threshold at 1200 m. The low degree of similarity among the areas reflects environmental heterogeneity, resulting from a rich mosaic of habitats, distinguished by the substrate configuration, continuity of vegetation, floristic composition, and proportion of exposed rock. Diversity between plots of different areas (Î˛2) contributed to regional diversity, and species turnover was the most important factor. The physical variables and base saturation which had high spatial heterogeneity may be the most important factors to determine species turnover and Î˛ diversity. The studied seed bank is strongly influenced by edaphic variables, with a gradient of increasing acidity and proportion of fine sand, and decreasing proportion of clay and organic matter, with elevation. In addition, species richness was influenced by cation exchange capacity, organic matter and clay and abundance by cation exchange capacity, H + Al, organic matter and base saturation.
Mechanisms by which basal branches suppress axillary bud outgrowth in pea (Pisum sativum)
(Canadian Science Publishing, 2017-12-17) Thomas, Roderick; Hay, Michael
This study examined whether the strong inhibitory influences of basal branches on axillary bud outgrowth seen in Trifolium repens similarly occur in Pisum sativum. Mechanisms by which basal branches in P. sativum suppress bud outgrowth were assessed using treatment combinations of main stem decapitation and excision, girdling and/or disbudding of basal branches. The combination of decapitation with basal branch excision provided a new avenue for investigation of correlative suppression of bud outgrowth. Results revealed a dual suppressive action of basal branch buds: girdling of basal branches confirmed they act via export of an inhibitory influence but also demonstrated, for the first time in P. sativum, their role as competitive sinks for a bud outgrowth stimulus. Although all axillary buds on the main stem had similar intrinsic potential for outgrowth, sensitivity to these suppressive influences varied with position on the stem. This suppressive influence of basal branches was, like apical dominance, a major influence on the regulation of bud outgrowth. The finding in P. sativum that basal branches suppress bud outgrowth via their action as competitive sinks for an outgrowth stimulus as they do in nodally-rooting clonal herbs suggests further investigation of this process is warranted.
Vacuolar processing enzymes, AmVPE1 and AmVPE2, as potential executors of ethylene regulated programmed cell death in the lace plant (Aponogeton madagascariensis)
(Canadian Science Publishing, 2017-12-05) Rantong, Gaolathe; Gunawardena, Arunika H.L.A.N
Perforation formation in Aponogeton madagascariensis (lace plant) is an excellent model for studying developmentally regulated programmed cell death (PCD). In this study, we isolated and identified two lace plant vacuolar processing enzymes (VPEs) and investigated their involvement during PCD and throughout leaf development. Lace plant VPE transcript levels were determined during seven different stages of leaf development. PCD and non-PCD cells from â windowâ stage leaves (in which perforations are forming) were separated through laser-capture microscopy and their transcript levels were also determined. VPE activity was also studied between the cell types, through a VPE activity-based probe JOPD1. Additionally, VPE transcript levels were studied in plants treated with an ethylene biosynthesis inhibitor, aminoethoxyvinylglycine (AVG). The two isolated VPEs, AmVPE1 and AmVPE2, are vegetative type VPEs. AmVPE1 had higher transcript levels during a preperforation developmental stage, immediately prior to visible signs of PCD. AmVPE2 transcripts were higher later during window and late window stages. Both VPEs had higher transcript and activity levels in PCD compared to non-PCD cells. AVG treatment inhibited PCD and associated increases in VPE transcript levels. Our results suggested that VPEs are involved in the execution of the ethylene related PCD in the lace plant.
Evidence of non-pathogenic relationship of Alternaria section Undifilum endophytes within three host locoweed plants species
(Canadian Science Publishing, 2017-12-21) Noor, Aziza; Nava, Amy; Cooke, Peter; Cook, Daniel; Creamer, Rebecca
Locoweeds are legumes of the Astragalus and Oxytropis genera that live symbiotically with the fungal endosymbionts belonging to Alternaria section Undifilum. These endophytes produce the toxin swainsonine that causes a neurological syndrome (locosim) when the plant is ingested by grazing animals. Here we characterize the growth of the endophytes within plant tissues using confocal and scanning electron microscopy (SEM) to define the physical relationship. Microscopy results reveal the endophyte distribution to be densely networked, with the mycelia aligned parallel to the long axis of the plant stem and with no pathology to plant cell walls, xylem or phloem. The autofluorescent mycelia were located intercellulary in the pith of stems. Stereofluoroscope observations of Alternaria oxytropis, A. cinerea, and A. fulva in phytoagar showed that mycelial growth occurred at the tip of hyphae. The growth rate of A. cinerea was significantly faster than for A. oxytropis or A. fulva. All three species of endophytes grew significantly faster at 3 days age of culture and grew slowly or not at all at 20 or 30 days. Analysis of the growth of these fungi support the hypothesis that there is a non-pathogenic symbiosis between the fungal endophytes and their host plants.
Breeding system and inbreeding depression in the rare orchid Platanthera praeclara in a fragmented grassland landscape
(Canadian Science Publishing, 2017-12-07) Travers, Steven E; Anderson, Kirk; Vitt, Pati; Harris, Marion O
An important consequence of self-compatibility in plants is that self-pollination can have deleterious effects on plant fitness due to inbreeding. We conducted a hand pollination experiment under field conditions to measure the magnitude of inbreeding depression associated with self-pollination in the rare western prairie fringed-orchid Platanthera praeclara Sheviak and Bowles. By comparing capsules and seeds resulting from cross versus self-pollination treatments, we determined that self-pollination reduces seed quality while having no detectable effect on capsule production or seed numbers. A smaller percentage of seeds resulting from self-pollination contained an embryo (18%) relative to seeds from cross-pollination (46%). Seeds that had an embryo were scored for the size of the embryo, small or large. A smaller proportion of seeds from self-pollination contained a large embryo (75%) relative to seeds from cross-pollination (92%). These results suggest that sexual reproduction and recruitment in this rare plant are dependent on the frequency of pollinator visitations that result in outcrossing.
Relationship between lichen species composition, secondary metabolites and soil pH, organic matter, and grain characteristics in Manitoba.
(Canadian Science Publishing, 2017-12-07) Zraik, Mohanad; Booth, Thomas; Piercey-Normore, Michele D
Many lichen secondary metabolites have functions related to the environmental conditions of lichen habitats but few studies have compared soil characteristics with lichen species composition or their secondary products. The goal of this study was to investigate the relationship between soil characteristics with lichen species composition and secondary metabolites. Five locations were chosen in Manitoba, each with five sites (transect), and each transect with five quadrats (1 m x 1 m). All species were collected from each of the quadrats, presence of secondary metabolites was determined by thin layer chromatography, and soil characteristics were examined. The results revealed that round sand grains were significantly higher in southeast Manitoba than other locations corresponding with a distinct species composition. Angular grains were significantly higher in northern locations, corresponding to a different group of species. Some of the significant relationships between soil characteristics and secondary metabolites include correlations of atranorin with pH, organic matter and sand content; fumarprotocetraric acid with organic matter and sand content; and usnic acid with pH and organic matter. A better understanding of the role of lichens with respect to soil characteristics will be important for improving soil stabilization in land reclamation.
Circinotrichum sinense, a new asexual fungus from Hubei, China
(Canadian Science Publishing, 2017-10-03) Li, De-Wei; Schultes, Neil P.; Chen, Jing-Yuan; Wang, Yi-Xun; Castañeda-Ruiz, Rafael Felipe
A setose hyphomycete was collected as part of a recent expedition for microfungi in the Duheyuan National Nature Reserve in Hubei, China. The conidia are typical of Circinotrichum, being curved or falcate, single-celled, colorless, smooth with a setula at the apical end, and similar to Circinotrichum rigidum. Circinotrichum sinense has a longer setula only at the apical end and verrucose setae, while C. rigidum has a setula on both ends and smooth setae. Phylogenetic analysis using ITS and LSU DNA sequence data and examination of morphological characters showed that this fungus cannot be identified as any previously described species of Circinotrichum. Thus, a new fungal taxon is described. A key to recognized species of Circinotrichum is also provided.
Remodeling of root morphology by CuO and ZnO nanoparticles: effects on drought tolerance for plants colonized by a beneficial pseudomonad.
(Canadian Science Publishing, 2017-12-15) Yang, Kwang Yeol; Doxey, Stephanie; McLean, Joan E; Britt, David; Watson, Andre; Al Qassy, Dema; Jacobson, Astrid; Anderson, Anne
Formulations that include nanosized-CuO and -ZnO are being considered for agricultural applications as fertilizers because they act as sources of Cu or Zn. Currently, few studies of the effects of these nanoparticles (NPs) consider the three way interactions of NPs with the plant plus its microbiome. At doses that produced root shortening by both nanoparticles (NPs), CuO NPs induced proliferation of elongated root hairs close to the root tip and ZnO NPs increased lateral root formation in wheat seedlings (Triticum aestivum). These responses occurred with roots colonized by a beneficial bacterium, Pseudomonas chlororaphis O6 (PcO6), originally isolated from roots of wheat grown under dryland farming in calcareous soils. The PcO6- induced tolerance to drought stress in wheat seedlings was not impaired by the NPs. Rather growth of the PcO6-colonized plants with NPs resulted in systemic increases in expression of genes associated with tolerance to water stress. Increased expression in shoots of other genes related to metal stress was consistent with higher Cu and Zn levels in PcO6-colonized shoots grown with the NPs. The work illustrates that the plants grown with CuO or ZnO NPs showed cross protection for different challenges of metal stress and drought.
Thermal acclimation of leaf respiration as a way to reduce source-sink imbalance at low temperature in Erythronium americanum, a spring ephemeral
(Canadian Science Publishing, 2017-11-07) Dong, Yanwen; Gérant, Dominique; Lapointe, Line
Many spring geophytes exhibit greater growth at colder than at warmer temperatures. Previous studies have suggested that there is less disequilibrium between source and sink activity at low temperature, which delays leaf senescence and leads to higher accumulation of biomass in the perennial organ. We hypothesize that dark respiration acclimates to temperature at both leaf and bulb level, mainly via the alternative pathway, as a way to reduce source-sink imbalance. Erythronium americanum was grown under three temperature regimes, 8/6 째C, 12/8 째C and 18/14 째C (day/night). Plant respiratory rates were measured at both growth and common temperature to determine whether differences were due to direct effects of temperature on respiratory rates or to acclimation. Leaf dark respiration exhibited homeostasis, which together with lower assimilation at low growth temperature, most likely reduced the quantity of C available for translocation to the bulb. No temperature acclimation was visible at the sink level. However, bulb total respiration varied through time, suggesting potential stimulation of bulb respiration as sink limitation builds up. In conclusion, acclimation of respiration at the leaf level could partly explain the better equilibrium between source and sink activity in low-temperature grown plants, whereas bulb respiration responds to source-sink imbalance.
Identification of native and invasive subspecies of common reed (Phragmites australis) in Alberta, Canada by RNase H-dependent PCR
(Canadian Science Publishing, 2017-11-07) Zuzak, Krista; Yang, Yalong; Kimmel, Nicole; Harding, Michael; Feindel, David; Feng, Jie
Colonies of the invasive subspecies of common reed (Phragmites australis) were found in Alberta in 2016. To facilitate rapid subspecies identification necessary to support management of the invasive subspecies, a simple and time saving protocol was developed to differentiate the invasive from the native subspecies. This protocol was based on the RNase H-dependent PCR (rhPCR) technique, which utilizes the DNA polymorphism found in two chloroplast DNA regions. Compared to the widely used restriction fragment length polymorphism (RFLP) protocol, the rhPCR had the same level of accuracy on subspecies identification but is simpler and less time consuming. Using both the rhPCR and RFLP techniques, twenty-seven P. australis samples derived from 21 colonies in nine Alberta counties were tested to determine their subspecies identity. Fourteen colonies were identified as invasive subspecies and seven were native subspecies. Based on these preliminary data, we concluded that the invasive subspecies has established across Alberta and now may be more common than the native subspecies. In addition, RFLP results confirmed that the rhPCR was accurate and could be used independently to identify P. australis subspecies in future studies.
Phytohormone Profiling reveals fungal Signatures and strong Manipulation of Infection Cycle in the Gymnosporangium juniper-virginianae Dual-Host Plant System
(Canadian Science Publishing, 2017-10-27) Moffatt, Kyle; Monroy Flores, Carolina; Andreas, Peter; Kisiala, Anna; Emery, Neil
The aim of this work was to examine the function of phytohormones in the pathogenesis of cedar-apple rust, a fungal disease caused by Gymnosporangium juniper-virginianae Schwein. on Eastern red cedar (Juniperus virginiana L.) and crabapple trees (Malus spp. Mill.). Control cedar branchlets, gall tissues, fungal telial horns, as well as healthy and infected apple leaves were collected throughout fungal and plant development and used for profiling endogenous cytokinins (CK) and abscisic acid (ABA) by high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS). Phytohormone composition implicates cytokinin involvement in the development of rust infection. Moreover, increased levels of total CKs, as well as the unique profiles of sporulating galls on cedar trees, telial horns, and infected apple leaves, dominated by cis-Zeatin (cZ) type CK, suggest that the fungus can synthesize hormones to facilitate the infection process. Distribution of ABA in the fungal and plant tissues indicates an important function of this stress hormone in regulating rapid changes in osmotic pressure during teliospore production by the galls. This study of the cedar-apple rust disease cycle is the first elucidation of phytohormones profiling between a pathogenic fungus and the attacked plant in a dual-host infection system.
Distinct domains within the NITROGEN LIMITATION ADAPTATION protein mediate its subcellular localization and function in the nitrate-dependent phosphate homeostasis pathway
(Canadian Science Publishing, 2017-11-07) Hannam, Carol; Gidda, Satinder; Humbert, Sabrina; Peng, Mingsheng; Cui, Yuhai; Dyer, John; Rothstein, Steven; Mullen, Robert
The NITROGEN LIMITATION ADAPTATION (NLA) protein is a RING-type E3 ubiquitin ligase that plays an essential role in the regulation of nitrogen and phosphate homeostasis. NLA is localized to two different subcellular sites, the plasma membrane and nucleus, and contains four distinct domains: i) a RING domain that mediates degradation of phosphate transporters at the plasma membrane; ii) an SPX domain that facilitates NLAâ s interaction with the phosphate transporters, and also exists in other proteins that regulate the nuclear transcription factors that control the phosphate starvation response pathway; iii) a linker domain that lies between the RING and SPX domains; and iv) a C-terminal domain, which, like the linker region, is of unknown function. Here we carried out a mutational analysis of NLA, which indicated that all the domains are not only essential for proper functioning of the protein, but also mediate its localization to the plasma membrane and/or nucleus, as well as to different subdomains within the nucleus. Overall, the results provide new insights to the distinct protein motifs within NLA and the role(s) that this protein serves at different subcellular sites with respect to the regulation of nitrogen-dependent phosphate homeostasis as well as other possible physiological functions.
HERB-CHRONOLOGY AS A TOOL FOR DETERMINING THE AGE OF PERENNIAL FORBS IN TROPICAL CLIMATES
(Canadian Science Publishing, 2017-10-28) Hiebert-Giesbrecht, Mickel Randolph; Novelo-Rodríguez, Candelaria; Dzib, Gabriel; Calvo-Irabien, Luz María; von Arx, Georg; Peña-Rodríguez, Luis Manuel
Age in wild plant populations is one of the most elusive developmental parameters in plant biology. Several approaches take advantage of plant morphological traits to determine developmental stages or plant age. Annual growth rings forming in woody tissues of perennial plants are one of the traits that have been widely used to determine the age of trees (dendrochronology) and, more recently, herbaceous perennials (herb-chronology). In temperate, alpine, and arctic climates, it has been reported that seasonal climatic variations lead to the formation of annual growth rings in herbaceous perennial forbs; however, to date, no similar studies have been carried out on plants from tropical regions. We have investigated the applicability of herb-chronology on the tropical plant Pentalinon andrieuxii, a native vine of the Yucatan peninsula. Our results show that herb-chronology is a potentially useful tool in determining the age of plants growing in tropical climates.
Immunocytochemical demonstration of cell wall components related to tissue compartments in the globoid galls induced by Clinodiplosis sp. (Cecidomyiidae) on Croton floribundus Spreng. (Euphorbiaceae)
(Canadian Science Publishing, 2017-10-19) Teixeira, Cristiane; Oliveira, Denis; Coelho Kuster, Vinícius; Isaias, Rosy Mary Santos
The dynamics of cell wall components during gall development are related to structural specialization to meet the defensive or nutritional requirements of gall tissues. Cell wall features have been studied mostly in galls induced by hemipterans (Psylloidea), while galls induced by Cecidomyiidae have been little explored. We applied monoclonal antibodies to epitopes of proteins and pectins in cell walls of non-galled leaves and galls induced by Clinodiplosis sp. (Diptera; Cecidomyiidae) on Croton floribundus (Euphorbiaceae). The complexity of tissue zonation in Clinodiplosis galls reflected the impairment of the activity of the pectin-methylesterases during development. The labeling of the epitopes of extensins in young galls denoted cell enlargement with resistant cell walls, while the labeling of the epitopes of AGPs, in senescent galls, indicated the involvement of these proteins with programmed cell death, at the end of cell cycles at the gall development site. We conclude that the cell wall profile in Clinodiplosis galls implies an imbalance between tissue porosity, cell-to-cell signaling, and resistance linked to tissue structural and functional compartments. Current data confirm the presence of the epitopes of extensins in young galls, and the compartmentalization of HGAs and RG-I in galls as an independent taxon feature.
A differential capacity of arbuscular mycorrhizal fungal colonization under well-watered conditions and its relationship with drought stress mitigation in unimproved vs improved soybean genotypes
(Canadian Science Publishing, 2017-11-14) Salloum, Maria Soraya; Menduni, Maria Florencia; Luna, Celina Mercedes
Modern breeding programs may cause a reductionin plant responsiveness to arbuscular mycorrhizal (AM) fungi. In this study, we tested the hypothesis that a higher arbuscule formation and mycorrhizal dependency (MD) response in unimproved soybean genotypes than improved is related to drought stress tolerance caused by enhanced growth parameters andoxidative stress regulation. Firstly, 4 unimproved and 4 improved soybean genotypes were compared under well-watered conditions. After 20 days, all unimproved soybean genotypes showed a higher increase in arbuscule formation, as well as a positive and higher MD index in foliar mineral nutrient and growth parameters than 4 improved. Secondly, tolerance to drought stress was evaluated in two improved soybean genotypes and two unimproved, selected for the most contrasting response to arbuscule formation, under well-watered conditions. After 20 days of 30% of field capacity, arbuscule formation was higher in unimproved than improved genotypes. Mycorrhizal dependency evaluated as leaf area, shoot and root dry mass were highest in AM unimproved genotypes. Moreover, malondiadehide was lower and proline was higher in unimproved than improved genotypes. The potential capacity of arbuscule formation is discussed as a selection criterion to identify improved soybean genotypes with increased efficiency under well-watered conditions and an enhanced capacity to relieve drought stress.
Jack pine becomes more vulnerable to cavitation with increasing latitudes under doubled [CO2]
(Canadian Science Publishing, 2017-11-24) Newaz, Shah; Dang, Qing-Lai; Man, Rongzhou
Trees may migrate northward in response to climate change and become exposed to new photoperiod and soil moisture regimes. This study assessed the impacts of photoperiod and its interaction with soil moisture and carbon dioxide concentration ([CO2]) on the hydraulic conductivity in jack pine and its vulnerability to xylem embolism. Seedlings were exposed to 400 vs. 950 µmol mol-1 [CO2], 60–70% vs. 30–40% (of field capacity) soil moisture and photoperiods of seed origin, and 5º and 10º north of seed origin in greenhouses. Cavitation vulnerability curves were measured for determining the xylem pressure at which 50% hydraulic conductivity was lost (ΨPLC50). It was found that elevated [CO2] significantly increased hydraulic conductivity while low soil moisture decreased it. Under elevated [CO2], the xylem became progressively more vulnerable to embolism with changes in photoperiod regime from the seed origin to 10º north of the seed origin, as indicated by the progressively less negative ΨPLC50. However, no such a trend was detected under the ambient [CO2]. The results suggest that the species may become less resistant to drought as the atmospheric [CO2] increases, hindering the northward migration or seed transfers. Even within its current natural distribution range, trees near its northern boundary of the range may be more vulnerable to embolism as the atmospheric [CO2] increases even without any change in moisture conditions.
Cross-incompatibility and self-incompatibility: unrelated phenomena in wild and cultivated potatoes?
(Canadian Science Publishing, 2017-10-13) Maune, Juan Federico; Camadro, Elsa Lucila; Erazzú, Luis Ernesto
Knowledge of internal hybridization barriers is relevant for germplasm conservation and utilization. The two pre-zygotic barriers are pollen-pistil self-incompatibility (SI) and cross-incompatibility (CI). To ascertain if SI and CI were phenotypically related phenomena in potatoes, extensive intra- and interspecific, both intra- and interploidy breeding relationships were established, without previous assumptions on the compatibility behavior of the studied germplasm. Pollen-pistil relationships were analyzed at the individual genotype/accession/family level. In two seasons, 828 intra- and interspecific genotypic combinations were performed, using accessions of the wild potatoes Solanum chacoense (2n=2x=24), S. gourlayi (2n=2x=24; 2n=4x=48) and S. spegazzinii (2n=2x=24), full-sib families (2n=2x=24) within/between the latter two diploids, and S. tuberosum (2n=4x=48) cultivars. Pollen-pistil incompatibility occurred in the upper first third of the style (I1/3) in all selfed diploids. In both intra- and interspecific combinations, the most frequent relationship was compatibility, followed by I1/3, but incompatibility also occurred in the stigma and the style (middle third and bottom third). We observed segregation for these relationships in full-sib families, and unilateral and bilateral incompatibility in reciprocal crosses between functional SI genotypes. Cross-incompatibility in potatoes is, apparently, controlled by genes independent of the S-locus or its S-haplotype recognition region (although molecular evidences are needed to confirm it), with segregation even within accessions.
Differences in early hyphal development of Podosphaera xanthii on Cucumis sativus leaves acclimatized to high or low relative humidity
(Canadian Science Publishing, 2017-10-13) Itagaki, Kaori; Shibuya, Toshio
This research investigated early hyphal development of cucurbit powdery mildew (Podosphaera xanthii) on cucumber (Cucumis sativus L.) leaves acclimatized to different relative humidities to clarify the factors that limit it. Cucumber seedlings were acclimatized to a low (10%) or high (90%) relative humidity (RH) at 30째C from germination. When the cotyledons had expanded and the first true leaf had begun to emerge, plants were inoculated, and initial conidial invasion, hyphal development, and secondary haustorial formation were evaluated. The initial invasion of P. xanthii into the epidermis was slower on the low-RH leaves than on the high-RH leaves, suggesting that structural properties, such as greater leaf mass per area, physically limited the development of P. xanthii. The hyphal development and secondary haustoria of conidia that had successfully infected the epidermis were also slower on the low-RH leaves. These post-invasion behaviors indicate that conidial development was also suppressed by non-structural properties of low-RH leaves such as nutrients which correlate with non-structural defense. Reduced leaf N content of the low-RH leaves may in part have inhibited the post-invasion behaviors of P. xanthii.

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