Growth Cabinet Conditions Research Articles

Cytological observation of anther structure and genetic investigation of a thermo-sensitive genic male sterile line 373S in Brassica napus L

BackgroundPhotoperiod and/or thermo-sensitive male sterility is an effective pollination control system in crop two-line hybrid breeding. We previously discovered the spontaneous mutation of a partially male sterile plant and developed a thermo-sensitive genic male sterile (TGMS) line 373S in Brassica napus L. The present study characterized this TGMS line through cytological observation, photoperiod/ temperature treatments, and genetic investigation.ResultsMicroscopic observation revealed that the condensed cytoplasm and irregular exine of microspores and the abnormal degradation of tapetum are related to pollen abortion. Different temperature and photoperiod treatments in field and growth cabinet conditions indicated that the fertility alteration of 373S was mainly caused by temperature changes. The effects of photoperiod and interaction between temperature and photoperiod were insignificant. The critical temperature leading to fertility alteration ranged from 10 °C (15 °C/5 °C) to 12 °C (17 °C/7 °C), and the temperature-responding stage was coincident with anther development from pollen mother cell formation to meiosis stages. Genetic analysis indicated that the TGMS trait in 373S was controlled by one pair of genes, with male sterility as the recessive. Multiplex PCR analysis revealed that the cytoplasm of 373S is pol type.ConclusionsOur study suggested that the 373S line in B. napus has a novel thermo-sensitive gene Bnmst1 in Pol CMS cytoplasm background, and its fertility alteration is mainly caused by temperature changes. Our results will broaden the TGMS resources and lay the foundation for two-line hybrid breeding in B. napus.

RNA-Seq effectively monitors gene expression in Eutrema salsugineum plants growing in an extreme natural habitat and in controlled growth cabinet conditions

BackgroundThe investigation of extremophile plant species growing in their natural environment offers certain advantages, chiefly that plants adapted to severe habitats have a repertoire of stress tolerance genes that are regulated to maximize plant performance under physiologically challenging conditions. Accordingly, transcriptome sequencing offers a powerful approach to address questions concerning the influence of natural habitat on the physiology of an organism. We used RNA sequencing of Eutrema salsugineum, an extremophile relative of Arabidopsis thaliana, to investigate the extent to which genetic variation and controlled versus natural environments contribute to differences between transcript profiles.ResultsUsing 10 million cDNA reads, we compared transcriptomes from two natural Eutrema accessions (originating from Yukon Territory, Canada and Shandong Province, China) grown under controlled conditions in cabinets and those from Yukon plants collected at a Yukon field site. We assessed the genetic heterogeneity between individuals using single-nucleotide polymorphisms (SNPs) and the expression patterns of 27,016 genes. Over 39,000 SNPs distinguish the Yukon from the Shandong accessions but only 4,475 SNPs differentiated transcriptomes of Yukon field plants from an inbred Yukon line. We found 2,989 genes that were differentially expressed between the three sample groups and multivariate statistical analyses showed that transcriptomes of individual plants from a Yukon field site were as reproducible as those from inbred plants grown under controlled conditions. Predicted functions based upon gene ontology classifications show that the transcriptomes of field plants were enriched by the differential expression of light- and stress-related genes, an observation consistent with the habitat where the plants were found.ConclusionOur expectation that comparative RNA-Seq analysis of transcriptomes from plants originating in natural habitats would be confounded by uncontrolled genetic and environmental factors was not borne out. Moreover, the transcriptome data shows little genetic variation between laboratory Yukon Eutrema plants and those found at a field site. Transcriptomes were reproducible and biological associations meaningful whether plants were grown in cabinets or found in the field. Thus RNA-Seq is a valuable approach to study native plants in natural environments and this technology can be exploited to discover new gene targets for improved crop performance under adverse conditions.

Potential biological control of clubroot on canola and crucifer vegetable crops

Clubroot caused by Plasmodiophora brassicae is an emerging threat to canola (Brassica napus) production in western Canada, and a serious disease on crucifer vegetable crops in eastern Canada. In this study, seven biological control agents and two fungicides were evaluated as soil drenches or seed treatments for control of clubroot. Under growth cabinet conditions, a soil‐drench application of formulated biocontrol agents Bacillus subtilis and Gliocladium catenulatum reduced clubroot severity by more than 80% relative to pathogen‐inoculated controls on a highly susceptible canola cultivar. This efficacy was similar to that of the fungicides fluazinam and cyazofamid. Under high disease pressure in greenhouse conditions, the biocontrol agents were less effective than the fungicides. Additionally, all of the treatments delivered as a seed coating were less effective than the soil drench. In field trials conducted in 2009, different treatments consisting of a commercial formulation of B. subtilis, G. catenulatum, fluazinam or cyazofamid were applied as an in‐furrow drench at 500 L ha−1 water volume to one susceptible and one resistant cultivar at two sites seeded to canola in Alberta and one site of Chinese cabbage in Ontario. There was no substantial impact on the susceptible canola cultivar, but all of the treatments reduced clubroot on the susceptible cultivar of Chinese cabbage, lowering disease severity by 54–84%. There was a period of 4 weeks without rain after the canola was seeded, which likely contributed to the low treatment efficacy on canola. Under growth cabinet conditions, fluazinam and B. subtilis products became substantially less effective after 2 weeks in a dry soil, but cyazofamid retained its efficacy for at least 4 weeks.

Development and use of a model system to monitor clubroot disease progression with an Australian field population ofPlasmodiophora brassicae

A modified sand–liquid culture method facilitated easy visualisation of the primary life cycle stages of Plasmodiophora brassicae within clean root hairs of the Arabidopsis host. Pathogen penetration occurred from day 4 onwards and then primary plasmodia developed within the host root. Several Arabidopsis ecotypes tested in varying growth conditions showed differences in disease expression. Defined growth cabinet conditions were found most suitable for studying disease progression in the ecotypes and for achieving uniform infection and disease development. Arabidopsis ecotypes Ta-0 and Tsu-0 known to be partially resistant to a German single-spore isolate of P. brassicae were susceptible to an Australian (Victorian) field population of P. brassicae. The European clubroot differential test was used to confirm virulence and describe the pathotype of the Victorian field population. Knowledge of the interaction of an Australian population of P. brassicae with its host will provide valuable information on a disease which is very difficult to control.

Factors Affecting Seed Germination of Perennial Wall Rocket (Diplotaxis tenuifolia) in Southern Australia

Germination response of perennial wall rocket to temperature, light, osmotic potential, and depth of burial emergence was evaluated under controlled environmental conditions. The effect of seed burial depth on seedling recruitment in the field was also investigated at Roseworthy, South Australia. Under optimal conditions (30 C, light/dark) germination of perennial wall rocket was rapid, with 90% of seeds germinating within 48 h of imbibition. Germination was reduced (20%) at lower, suboptimal temperatures (10 to 20 C) when seeds of perennial wall rocket were exposed to light. Germination declined with increasing osmotic potential and was completely inhibited at osmotic potentials of −1.5 MPa. Perennial wall rocket emergence was greatest from seeds placed on the soil surface, but some seedlings (< 10%) emerged from a depth of 0.5 to 2 cm. Under both field and growth-cabinet conditions, the greatest seedling emergence of perennial wall rocket occurred from seed present on the soil surface; however, the level of absolute recruitment from the seed bank was much lower (< 5%). Information gained from this study will further improve our understanding of the germination behavior of perennial wall rocket and contribute to developing sustainable strategies for its control.

Effect of genotype on callus induction and plant regeneration from leaf explants of sugarcane ( Saccharum sp.)

Nine sugarcane genotypes (CP59-73, CP63-588, CP80-314, SP71-1081, F160, L62-96, CP70-321, CP57- 614 and Clone III) were evaluated for their callus induction capacity, embryogenic callus production and plant regeneration ability. Leaf cylinders were used as explants using Murashige and Skoog (MS) based medium supplemented with 3 mg l-1 2,-4 dichlorophenoxyacetic acid. Plant regeneration was accomplished on hormone free modified MS medium supplemented with casein hydrolyzate. The genotypes tested showed high callus induction percentage (69 to 95%) and high embryogenic callus percentage (60 to 100%). These genotypes also showed excellent regeneration capacities, with regeneration percentages ranged between 88 and 100%. Significant differences were observed between genotypes for callus induction capacity, embryogenic response and plant regeneration ability indicating that these criteria are genotype dependent. Plant regeneration ability is highly correlated with embryogenic callus production. The in vitro regenerated plants were successfully rooted and well acclimatised in growth cabinet conditions.

The effect of heat stress on the symbiotic interaction between Sinorhizobium sp. and Acacia senegal

Sinorhizobium sp. strain HAMBI 2180, marked with the β-glucuronidase (GUS) encoding gusA gene, was used for studying the effect of heat stress on the symbiotic interaction between Acacia senegal seedlings and Sinorhizobium sp. in growth cabinet conditions. The infection process, observed during 18 days after inoculation, was delayed at a root temperature of 40°C compared to a root temperature of ≤38°C, but nodulation was retarded already at 38°C. At 42°C no nodules were formed. At this root temperature the development of lateral roots and root hairs was one week delayed. Although the roots had normally deformed root hairs in addition to abnormally deformed ones, only disintegrated infection threads were present. However, the ability to form symbiosis was reversible. Nitrogen-fixing nodules developed on those parts of the roots which were formed after completion of the thermal stress at 42°C. A root temperature of 42°C did not affect the numbers of culturable rhizobia in the A. senegal rhizosphere.

The effect of heat stress on the symbiotic interaction between Sinorhizobium sp. and Acacia senegal

Sinorhizobium sp. strain HAMBI 2180, marked with the β-glucuronidase (GUS) encoding gusA gene, was used for studying the effect of heat stress on the symbiotic interaction between Acacia senegal seedlings and Sinorhizobium sp. in growth cabinet conditions. The infection process, observed during 18 days after inoculation, was delayed at a root temperature of 40°C compared to a root temperature of ≤38°C, but nodulation was retarded already at 38°C. At 42°C no nodules were formed. At this root temperature the development of lateral roots and root hairs was one week delayed. Although the roots had normally deformed root hairs in addition to abnormally deformed ones, only disintegrated infection threads were present. However, the ability to form symbiosis was reversible. Nitrogen-fixing nodules developed on those parts of the roots which were formed after completion of the thermal stress at 42°C. A root temperature of 42°C did not affect the numbers of culturable rhizobia in the A. senegal rhizosphere.

Analysis of genetic variability of aluminium tolerance response in triticale.

Comparative analyses of genetic variability of aluminium tolerance response were made in a range of triticale genotypes of two sets, one consisting of six Australian cultivars (or lines), the other consisting of eight South African lines and an Australian check, by following solution culture and screening under controlled growth cabinet conditions. Results showed that Tahara, Tahara ‘S’ and Abacus were the most Al-tolerant triticales among the Australian genotypes in terms of root regrowth characteristics at 10 μg.g-1 Al. The 19th ITSN 70-4, along with the standard cultivar Tahara was superior to all other South African genotypes; the eight South African genotypes spanned the range from Al-tolerant, moderately Al-tolerant to Al-sensitive. Regrown root length and percentage of seedlings with root regrowth were the two key indicators for screening and evaluating Al tolerance response. Considerable genetic variability of tolerance to Al stress among the two sets of tested genotypes was revealed by the estimates of genetic parameters. High heritability values were recorded for those two indicators, with associated high levels of relative genetic advance (RGA). Further improvement of varietal tolerance to Al stress in triticale could be anticipated through selection and breeding.

Effects of snowdrop lectin (GNA) delivered via artificial diet and transgenic plants on the development of tomato moth ( Lacanobia oleracea) larvae in laboratory and glasshouse trials

The effects of snowdrop lectin ( Galanthus nivalis agglutinin, GNA) on Lacanobia oleracea larval growth, development, consumption, and survival, were examined by 3 distinct bioassay methods. Larvae were reared on artificial diet containing GNA at 2% (w/w) dietary protein; on excised leaves of transgenic potato expressing GNA at approx. 0.07% of total soluble proteins; and on transgenic potato plants expressing GNA at approx. 0.6% of total soluble proteins in glasshouse trials. Significant effects on larval growth were observed with all three treatments. At 21 days after hatch mean larval biomass was reduced by 32 and 23%, in the artificial diet and excised leaf bioassays respectively. In glasshouse trials a 48% reduction in insect biomass per plant was observed after 35 days. The artificial diet and excised leaf assays also showed that GNA significantly slowed larval development as assessed by instar duration. GNA caused a 59% overall reduction in mean daily consumption in the artificial diet assay, and a significant reduction in leaf damage in glasshouse trials. However, prolonged compensatory feeding by larvae in the excised leaf assay resulted in their consuming 15% more total leaf material than the control group. Adaptation to low levels of GNA, in terms of biomass recovery and compensatory feeding, was observed within one larval generation in the detached leaf assay. No significant effects of GNA on larval survival were observed in the artificial diet and detached leaf bioassays, whereas survival was decreased by approx. 40% in the glasshouse bioassay. The assays show that the insecticidal effects of GNA can be observed both in vitro when fed in artificial diet and in planta, and can be demonstrated in the glasshouse as well as under growth cabinet conditions.

Inheritance of powdery mildew resistance in pea

Pea, an important grain legume crop, suffers significant yield and quality losses because of infections by the parasitic fungus Erysiphe pisi Syd., the causal agent of powdery mildew. Most pea cultivars in western Canada are susceptible to this fungus. The genetic basis of resistance found in certain Canadian cultivars is unclear. Resistant cultivars and lines were intercrossed with each other and crossed with susceptible lines to determine the genetic basis of resistance. Resistance in the cultivars Highlight, AC Tamor, Tara, Mexique 4, Stratagem and lines JI 210, JI 1951, JI 1210 was found to be conferred by a single recessive gene, er-1. The resistance in line JI 2480 is conferred by a different recessive gene, er-2. Resistance provided by er-1 was durable under both field and growth cabinet conditions, however, resistance of er-2 was broken under controlled growth conditions. Combining er-1 and er-2 in a cultivar could increase the durability of resistance. Key words: pea, Pisum sativum, powdery mildew, Erysiphe pisi, inheritance, resistance

Chloroplast ultrastructure changes in Pisum sativum associated with supplementary ultraviolet (UV‐B) radiation

ABSTRACTPea plants (Pisum sativum L. cv. Greenfeast) were grown and exposed to supplementary UV‐B radiation from day 17 after planting under growth cabinet conditions. The effects of this exposure on the ultrastructure of chloroplasts and the total soluble sugar and starch concentrations were estimated. Supplementary UV‐B radiation was shown to damage the structure of chloroplasts, as manifested by dilation of thylakoid membranes, a progressive disruption of the thylakoid structure and disintegration of the double membrane envelope surrounding the chloroplast, accompanied by the accumulation of large starch grains. Diurnal changes observed in starch concentration suggest that the higher concentration of starch in supplementary UV‐B‐treated leaves is due to its immobilization, rather than to any increase in starch synthesis: soluble sugars accumulated and remained at a higher level and then later declined.

Spectral balance and UV‐B sensitivity of soybean: a field experiment

ABSTRACTSoybean [Glycine max (L.) Merr.] cultivar Essex was grown and tested for sensitivity to UV‐B radiation (280–320 nm) under different combinations of UV‐A (320–400 nm) and PFD (400–700 nm) radiation in four simultaneous field experiments. The radiation conditions were effected with combinations of filtered solar radiation and UV‐B and UV‐A lamps electronically modulated to track ambient radiation. Significant UV‐B‐caused decreases in total aboveground production and growth were seen only when PFD and UV‐A were reduced to less than half their flux in sunlight. When PFD was low, UV‐A appeared to be particularly effective in mitigating UV‐B damage. However, when PFD was high, substantial UV‐A did not appear to be required for UV‐B damage mitigation. Leaf chlorophyll fluorescence did not indicate photosynthetic damage under any radiation combination. With UV‐B, leaves in all experiments exhibited increased UV‐absorbing pigments and decreased whole‐leaf UV transmittance. Results of these field experiments indicate difficulties in extrapolating from UV‐B experiments conducted in glasshouse or growth cabinet conditions to plant UV‐B sensitivity in the field. Implications for UV radiation weighting functions in evaluating atmospheric ozone reduction are also raised.

Biological control of bacterial wilt of potatoes caused byPseudomonas solanacearum

Microbial antagonism was investigated as a possible method for control of bacterial wilt of potatoes (Solanum tuberosum L.), caused byPseudomonas solanacearum. Seed potato tubers were treated with a selected antagonistic bacterial isolate and coated with CaCO3. An amendment was also prepared, containing the same bacterial isolate. The bacterium used as a biological control and designated as isolate BC8 caused strong inhibition ofP solanacearum in both “in vitro” assays and growth cabinet conditions. In order to test the antagonistic capacity of isolate BC8 under field conditions, a completely randomized design was established in a soil naturally infested withP. solanacearum that included 12 treatments repeated 10 times, each one with 5 replications. The field experiment was planted on November 26, 1986 and the rate of wilt symptoms for each treatment was recorded periodically. Three tubers from each plant in each treatment were assayed for either presence ofP. solanacearum or the antagonistic isolate BC8. Treatments that included isolate BC8 gave the lowest amount of wilted plants and fewest tubers latently infected as well. Using this system, about 80% of the tubers assayed from plants growing in the naturally infested soil were colonized by the antagonistic isolate BC8 and free ofP. solanacearum. It was established that the pathogen was still present in the soil after 2 years of non-potato cropping and that latent infections play an important role in the dispersal ofP. solanacearum. The system of delivering bacteria in an amendment, as used in this work, proved to be much more efficient in the biological control ofP. solanacearum than just coating the seed potato tubers with the antagonistic isolate BC8.

The genetics of maize (Zea mays L.) growing at low temperatures. I. germination of inbred lines and their F1s

Two collections of inbred lines were divided into early (E), medium (M) and late (L) germinating lines, on the basis of days to germination under growth-cabinet conditions at 8°C and 6°C constant temperatures. Tolerance of low temperatures was found to be an heritable trait and characteristic of each inbred line. When the inbreds and F1s were tested at 6°C the single crosses of early germinating lines showed earlier germination than crosses between slow germinating lines. Thus the performance of F1s greatly depends on the parental lines used in the crosses. Differences observed in some of the reciprocal crosses were attributed to maternal effects.

The effect of source, concentration and time of application of nitrogen on the growth, nodulation and nitrogen fixation ofLotus pedunculatus andTrifolium repens

Studies under growth cabinet conditions investigated the effect of source and concentration of nitrogen and timing of nitrogen application on the growth and nitrogen fixation byLotus pedunculatus cv. Maku andTrifolium repens cv. S184. KNO3, NaNO3 and NH4NO3 were added at transplanting at the following rates: 3.33, 7.78 and 13.33 mg N/plant. KNO3 was added at 3.33 and 7.78 mg N/plant at 0, 6, 12, 18, 24 or 30 days after transplanting.

Effect of low temperatures during flowering on floral cycle and pollen tube growth in nine avocado cultivars

The floral response of the type A avocado cultivars ‘Reed’, ‘Wurtz’, ‘Rincon’ and ‘Jalna’, and the type B cultivars ‘Bacon’, ‘Ryan’, ‘Edranol’, ‘Sharwil’ and ‘Hazzard’ was tested under growth-cabinet conditions of 17° C day, 12° C night, with a 12-h photoperiod and photon flux density of 400 μE m −2 s −1 (400–700 nm). Most of the flowers of all type A cultivars and the type B cultivar ‘Bacon’ had both a female and a male stage. None of the flowers of the other type B cultivars had a female stage but opened in the male stage only. Hand pollination resulted in some ovule penetration in the cultivars with female stage flowers. In those with only male-stage flowers, the pollen tubes grew no further than the style. Maintenance of fertility under low-temperature conditions during flowering appeared to be partly, but not entirely, linked to the type A flowering cycle.

Re-utilization by perennial ryegrass (Lolium perenne L.) of labelled fertilizer sulphur incorporated in field-grown tops and roots of pasture plants added to soils

35S-labelled gypsum fertilizer was incorporated under field conditions into pastures which were separated into white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.) tops and roots. These were added to four soils from improved and unimproved pastures. The re-utilization of labelled fertilizer sulphur (S) was assessed under growth cabinet conditions (20°C day, 13°C night, daylength 16 h, light intensity 120–170 lx) by growing perennial ryegrass plants for 23 weeks.

Electron microscopy of African cereal streak diseased plants

The African cereal streak disease (ACS) was further characterized as to transmissibility and cytological changes produced in cells of affected plants. Virus-like particles were regularly associated with diseased plants grown under field conditions, but no similar particles could be found in diseased plants of wheat, triticale, rice, Harpachne schimperi, Chloris pycnothrix, or Eragrostis tenuifolia grown in a growth cabinet set on an 18-h–6-h light–dark cycle and a corresponding 24 °C–17.5 °C temperature cycle. The efficiency of continuous transmission by Toya catilina Fenn. under growth-cabinet conditions was low, at 5%, 3%, and 5% for females, males, and nymphs, respectively.Except for the absence of recognizable virus-like particles in infected plants grown in the growth cabinet, the symptoms and cytological features of diseased plants grown under growth-cabinet and field conditions were similar. The main cytological features of diseased plants were as follows. (1) A dense, fine ground substance which filled many of the phloem cells was developed. (2) Large numbers of inclusion bodies, which were of globular and hexagonal-elongated forms, were formed. These forms are probably related. Virus-like particles were occasionally associated with the inclusions in diseased field-grown plants (3) Non-specific changes, such as may be induced by various types of pathogens, or are associated with senescence, e.g. phloem cell necrosis, abnormal callose-like cell wall deposits, and degenerative changes in the chloroplasts, were observed.