Unheated Plastic Research Articles

Crop rotations with Mi gene resistant and susceptible tomato cultivars for management of root-knot nematodes in plastic houses

Four crop rotations including the Mi resistant tomato cv. Monika (R) and the susceptible cv. Durinta (S), were assessed for three consecutive cropping seasons in three unheated plastic houses located in north-eastern (Barcelona), east (Eivissa) and south-western (Cádiz) Spain. Tomatoes were cultivated from March to July 2005 (1), 2006 (2) and 2007 (3) at Barcelona and Eivissa, and from March to July 2006 (1), September 2006 to February 2007 (2) and March to July 2007 (3) at Cádiz. The crop sequences in the rotation were R 1R 2S 3, R 1S 2S 3 S 1R 2S 3 and S 1S 2S 3. Nematode population densities in soil and roots, reproduction indices, and tomato yield were compared for each cropping cycle and rotation. Average pre-plant nematode densities (Pi) at the beginning of the study were 247, 7, and 172 juveniles per 250 cm 3 of soil at Barcelona, Eivissa and Cádiz, respectively. The Mi resistant tomato cv. Monika suppressed M. javanica at Barcelona and Eivissa, and M. arenaria and M. incognita at Cádiz, and prevented nematode population increases by more than 90% compared with the susceptible cv. Durinta. At Barcelona, the 3-year average tomato yield increased by 2.6 kg m −2 in the rotations including at least one resistant tomato crop, and by 6.1 kg m −2 when the resistant cultivar was cropped for two consecutive years. However, no differences in yield were found at Eivissa due to low Pi, nor at Cádiz where the resistant cultivar was poorly adapted to the agroclimatic conditions of the area.

EFFECT OF PLASTIC TUNNEL SIZE ON PRODUCTION OF CUCUMBER IN DELTA OF EGYPT

The experiments were carried out in the years of 2000, 2001 and 2003 at Kafr El-Sheikh. The main objective of this research was to study the influence of growing seasons and types of unheated plastic house on yields of two cucumber F 1 hybrids. Downy mildew and powdery mildew were lower in the winter season than during the early summer season. Likewise, they were lower inside the double span house than inside the single span house (at 60 days after transplanting).The highest total yield as number and weight was produced from Petostar hybrid grown inside the double span house during the early summer season.

Use of stem diameter variations to detect plant water stress in tomato

The sensitivity of stem diameter variations (SDV) measured with linear variable transducer (LVDT) sensors as indicators of plant water status in tomato was evaluated. Two tomato crops were grown sequentially in a sandy loam soil in an unheated plastic greenhouse. These were an autumn–winter tomato crop (autumn crop) and a spring–summer tomato crop (spring crop). One drying cycle of 61 days was imposed to the autumn crop in winter at 92 days after transplanting (DAT). Two drying cycles, each of 29 days, were applied to the spring crop, to young (58 DAT) and mature plants (121 DAT). For each drying cycle, four replicate plots did not receive irrigation, and four were well watered. During each drying cycle, LVDT sensors continuously measured SDV, and daily measurements were made of leaf (Ψ leaf) and stem water potential (Ψ stem). SDV data was interpreted using the SDV-derived indices, maximum daily shrinkage (MDS) and stem growth rate (SGR). The response of SDV-derived indices to water deficit differed with (1) climatic conditions during stress imposition and (2) crop age. In the winter drying cycle of the autumn crop, the responses of the SDV-derived indices to soil drying were relatively small and slower than Ψ leaf and Ψ stem. Under warmer conditions, the SDV-derived indices were much more responsive to soil drying. In rapidly growing young plants, where SDV was characterized by high SGR and small MDS, SGR was the most sensitive SDV-derived index. In more mature plants with little stem growth, MDS was the most sensitive SDV-derived index. In mature plants grown in warm to hot conditions, MDS (1) responded at a similar time or earlier than Ψ leaf and Ψ stem and (2) had larger “signal” values (ratio of values from unwatered to control plants) than Ψ leaf and Ψ stem. However, there was appreciably more “noise” (coefficient of variation, CV) associated with the SDV-derived indices, giving lower “sensitivity” values, determined from “signal” to “noise” ratios, than for Ψ leaf and Ψ stem. Regression analysis between MDS of well-watered plants and climatic variables gave best results for a linear relationship between MDS and daily maximum vapor pressure deficit. There were strong linear relationships between MDS and Ψ leaf for each drying cycle. The slopes of these relationships differed with crop age indicating that there was no constant relationship between MDS and Ψ leaf for a whole season. Overall these results demonstrated that MDS and SGR can be sensitive indicators of the water status of tomato crops under conditions of moderate to high evaporative demand. However, the variability associated with the SDV-derived indices and the changing MDS–Ψ leaf relationship with crop age represent major issues regarding the development of irrigation scheduling protocols for tomato.

Response of stem diameter variations to water stress in greenhouse-grown vegetable crops

SummaryThe ability of indices derived from stem diameter variations (SDV) to detect water stress in vegetable crops grown under greenhouse conditions was evaluated. Two crops, an Autumn-Winter pepper crop and a Spring-Summer melon crop, were grown in soil, in an unheated plastic greenhouse with drip irrigation, in conditions similar to commercial production. A pot study with pepper was also conducted during Autumn-Winter. In each study, two drying cycles were imposed for 7–21 d during the fruit production stage, and un-watered plants were compared with well-watered plants. During each drying cycle, linear variable displacement transducer (LVDT) sensors were used to measure SDV continuously, and daily measurements were made of leaf ( leaf) and stem water potential ( stem). Several indices derived from SDV measurements, including maximum daily shrinkage (MDS) and daily stem diameter growth rate (SGR) were evaluated. In the drying cycles of soil-grown pepper, conducted during Winter, under climatic conditions of low evaporative demand, SDV-derived indices were unaffected by 20-21 d of soil drying, despite both stem and leaf being moderately affected. Pepper plants grown in pots under very similar climatic conditions had appreciable and rapid responses in SDV-derived indices, with MDS increasing and SGR decreasing. In the drying cycles of soil-grown melon, imposed during the relatively higher evaporative demand conditions of Spring and Summer, MDS responded earlier and had larger “signal” values (ratio of values from un-watered to control plants) than leaf or stem. However, there was more variation associated with MDS. In melon, there were strong linear relationships between MDS and both leaf and stem. The present study suggested that SDV-derived indices can be sensitive indicators of plant water status in melon and pepper when grown (a) in pots with a restricted root volume under any climatic conditions, and (b) in soil during periods that do not include climatic conditions of low evaporative demand.

Responses of cucumbers to mulching in an unheated plastic greenhouse

SummaryPlastic greenhouses have become widespread in recent decades, predominantly as low–cost structures. Those using plastic houses often adopt techniques developed for more sophisticated glasshouses without prior studies to see if it is necessary to adapt them. White plastic mulching is used widely in heated glasshouses to increase available light during periods of low radiation, and thus benefit plant growth. A 2-year study was conducted to determine the response of a soilless cucumber crop to white plastic mulching, compared with an unmulched treatment, in unheated plastic greenhouses in southern Spain. The reflection of solar radiation by the plastic mulch reduced the mean substrate and air temperatures by up to 3.0ºC and 1.5ºC, respectively, during the early stages of canopy development. When substrate and air temperatures are sub-optimal, small temperature differences can be detrimental to crop growth and yield.The increase in available photosynthetically-active radiation (PAR) in mulched cucumbers could not compensate for the delay in growth in unheated greenhouses, and so yields were less than for unmulched cucumbers.

Evapotranspiration of horticultural crops in an unheated plastic greenhouse

Abstract Large unheated greenhouse areas are located in the coastal lands of the Mediterranean Basin, based on low-cost structures covered with plastic. Water is a scarce resource in these areas and therefore it is necessary to optimise irrigation practice by applying the crop water needs, thus avoiding waste. This work was undertaken to determine the water requirements of four major horticultural crops grown in an unheated plastic greenhouse located in Almeria, Spain. Drainage lysimeters were used to determine the seasonal evapotranspiration (ET) of four crops (melon, green beans, watermelon and pepper), which ranged from 170 to 371 mm and it was associated with the reference ET (ET 0 ). Compared to irrigated crops outdoors, the seasonal ET of the greenhouse horticultural crops is relatively low due to the lower evaporative demand inside the greenhouse and to a further reduction in solar radiation transmission by whitening in late spring and summer. Additionally, off-season greenhouse crops are grown during low evaporative demand periods, thus the low water requirements. Crop coefficient ( K c ) curves were obtained for the four crops under different conditions. The K c values varied with the crop, stage of development, and with management practices. Measured peak K c values for crops, which were not vertically supported (melon and watermelon) were between 1 and 1.1, similar to the measured values for the same crops under field conditions. By contrast, peak K c values for vertically supported (VS) crops (melon, green bean and sweet pepper) varied between 1.3 and 1.4, which are higher than those reported for outdoors. The tall and open canopy structures of the VS greenhouse crops, their high leaf area indices, along with the high proportion of diffuse radiation inside the greenhouse, allowed for more uniform light penetration within the canopies and ET rates in those crops higher than those of the short, non-supported crops. Management and climatic conditions combined to define an unusual K c curve for sweet pepper. The crop is transplanted in late summer and reaches the peak K c in early winter. Because of the low temperatures, K c decreased thereafter down to about 1.0, until climatic conditions inside the greenhouse improved. From late winter to the end of the season, K c was either stable or increased steadily. A simple K c model based on thermal time for greenhouse crops with and without pruning, was proposed and validated. The model gave accurate estimates of measured K c values for melon and pepper.

Responses of native Lupinus varius (L.) to culture conditions: effects of photoperiod and sowing time on growth and flowering characteristics

The effects of photoperiod and sowing time on growth and flowering characteristics of Lupinus varius were investigated during two growing periods to determine its responses to culture conditions as a potential native cut-flower crop. The seeds were sown in an unheated plastic greenhouse on 28 September, 28 October and 28 November under natural, 14- and 16-h day-length treatments. 14- and 16-h day-lengths were established by lengthening the natural day-lengths to 14 and 16 h with the use of night break photoperiodic lighting at 1.8–1.9 μmol m −2 s −1 in 400–700 nm. Photoperiodic lighting, in particular the 16-h day-length treatments, slightly (maximally 15 days) shortened days to flowering and increased plant height in all sowing times relative to natural photoperiods. There were no significant differences in stem and branch inflorescence diameters, in lengths of branch, in main and branch inflorescences in plants grown under natural photoperiod, and 16-h day-length treatments. The highest main inflorescence diameter, the number of branches per plant, and flower numbers on main and branch inflorescences were recorded in plants grown under natural photoperiods, whereas 14-h day-length treatments did not provide sufficient specimens to allow for the measurement of most of the characteristics studied. These findings were interpreted to indicate that L. varius behaves as a facultative long day plant. Additionally, there was a particular shortening of days to flower and growth, and flowering quality decreased linearly with delayed sowing dates under all photoperiodic treatments. The earliest and latest flowering dates were recorded for plants sown in September under 16-h day-length, and plants sown in November under natural photoperiods, respectively. Therefore, sowing in September under natural photoperiods or 16-h artificial day-length resulted in earlier flowering dates and a longer time from sowing to flowering and was consequently the best sowing time with respect to all of the characteristics considered in this study.

Differences in the effects of simulated sea aerosol on water relations, salt content, and leaf ultrastructure of rock-rose plants.

White-leaf rock-rose (Cistus albidus L.) and Montpellier rock-rose (C. monspeliensis L.) plants were sprayed 2 to 3 min per day over a 7-d period, in an unheated plastic greenhouse, with different aqueous solutions containing deionized water alone (control); an anionic surfactant (sodium dodecylbenzenesulfonate 82.5%, 50 mg L(-1)) (S1); a solution simulating the composition of sea aerosol (S2); and a solution simulating sea aerosol with anionic surfactant (S3). White-leaf rock-rose was more sensitive to sea aerosol, showing greater leaf damage and markedly decreased growth, and the presence of surfactant enhanced the phytotoxic effect leading to greater increases in mortality. Montpellier rock-rose did not appear to be more adversely affected when surfactant was used in combination with sea aerosol, and manifested slight or less severe symptoms than white-leaf rock-rose. There was a significant increase in leaf turgor potential in the plants treated with both sea aerosol treatments by osmotic adjustment effect. The decrease in photosynthesis level seems to be due to both stomatal and nonstomatal factors. The results of microscopical analysis of Montpellier rock-rose plants show that sea aerosol treatment caused alterations in the chloroplast structure, reducing the starch grain and swelling the thylakoid membranes. The results of this study indicated that Montpellier rock-rose was more tolerant to sea aerosol than white-leaf rock-rose, showing a lower reduction in plant growth and less leaf damage, probably because of its ability to compartmentalize the toxic ions at the intracellular level.

First Report of Cucumber Black Root Rot Caused by Phomopsis sclerotioides in Italy.

During April 2002 to September 2003 in unheated plastic greenhouses located in Fondi and Sperlonga (Latium Region of central Italy), in which more than 100 ha of cucumber (Cucumis sativus L.) were cultivated, an unusual disease causing decay of roots and plant wilting was observed. Many of the most common cultivars showed susceptibility, and in some farms, severe economic losses occurred. Disease symptoms observed on young plants included stunting, wilting, black root rot, and marked reduction of root development where pseudosclerotial structures were produced. The degree of root symptoms was proportional to the wilting. During periods of high evapotranspiration, wilting was severe in plants at the early stages of disease development, and even lightly infected plants wilted rapidly. Symptoms resembled those caused by vascular wilt fungi and were generally more severe in greenhouses with poorly drained soils. Samples from each of four greenhouses were collected during different periods of the growing season. Each sampling unit consisted of five to eight root pieces that were surface disinfected in 0.1% HgCl2 for 30 s, rinsed in sterile water, placed on petri dishes containing potato dextrose agar (pH 5.5), and incubated for 7 days at 25°C. Phomopsis sclerotioides van Kesteren (1,2) (identification confirmed by R. A. Samson, Centraalbureau voor Schimmelcultures of Utrecht, the Netherlands) was consistently recovered from affected tissues. Subcultures of three isolates were prepared and evaluated for pathogenicity. The experiments were conducted in a greenhouse with a 12-h photoperiod at 25 to 32°C. Seven-week-old seedlings (20 representatives per isolate) of a susceptible hybrid were dipped for 2 min in an agar slurry suspension of the pathogen and then returned to pots. Within 4 to 5 weeks after inoculation, all plants inoculated with each P. sclerotioides isolate showed the same symptoms observed in the field and caused wilting and death of approximately 80% of the inoculated plants. P. sclerotioides was consistently reisolated from the symptomatic test plant, whereas the fungus was never isolated from control plants. Another experiment using naturally infested soil in comparison with sterilized soil confirmed the soilborne nature of the fungus and its pathogenicity. To our knowledge, this is the first report of P. sclerotioides on cucumber in Italy. According to the experience of farmers and agricultural consultants, the disease was first observed in the last 3 to 4 years in unheated plastic greenhouses. However, we cannot exclude the possibility that the disease may have been present in central Italy prior to our observations, since it can be misdiagnosed and the symptoms can be masked by symptoms of other diseases. For these reasons, an accurate monitoring of the pathogen is necessary to determine the magnitude of the problem and its impact on the industry. Management practices that include long-term crop rotation with nonsusceptible hosts, removal and destruction of infected crop debris, and steam soil sterilization are suggested to reduce the economic losses.

Contrasting physiological responses of dwarf sea-lavender and marguerite to simulated sea aerosol deposition.

Plants of two wild native species from littoral areas, marguerite [Argyranthemum coronopifolium (Willd.) C.J. Humphries] and dwarf sea-lavender [Limonium pectinatum (Aiton) O. Kuntze], grown in an unheated plastic greenhouse, were sprayed 2 to 3 min per day over a 7-d period with different aqueous solutions containing (i) an anionic surfactant (S1); (ii) a solution simulating the composition of sea aerosol (S2); (iii) a solution simulating sea aerosol with anionic surfactant (S3), and (iv) deionized water alone (control). The plant resistance to sea aerosol and the ability to recover from treatments were studied. By the end of the spraying period, marguerite showed a significant reduction in growth compared with control. However, most of the growth parameters were significantly unaffected in dwarf sea-lavender when plants were treated with sea aerosol containing surfactant. Measurements of water relations variables in marguerite showed a slight decrease in leaf turgor potential after spraying with sea aerosol containing surfactant. The surfactant enhanced the foliar absorption of salt in marguerite plants, inducing reductions in leaf stomatal conductance and causing such damage in the photosynthetic apparatus that the level of net photosynthesis decreased and had not recovered by the end of the experiment. The treatments had no effect on leaf stomatal conductance and photosynthesis rate in dwarf sea-lavender plants. The response of the species studied to sea aerosol was related to the degree of salinity tolerance. Although both species are wild native plants from littoral areas, marguerite is not salt tolerant and was the most sensitive to the sea aerosol treatments, while dwarf sea-lavender, a halophyte species, was more efficient at decreasing the toxic salt content of the tissues as its growth and ornamental characteristics were not affected.

YIELD AND FRUIT QUALITY OF TOMATO GROWN IN GREENHOUSE WITH SALINE IRRIGATION WATER

The aim of this article was to analyse the influence of irrigation water regime and water salinity on yield and fruit quality of a tomato crop (Marmande Raf) growing in an unheated plastic greenhouse in Sicily (south Italy). Two salinity levels of irrigation water (electro conductivity EC=1.6 dS m-1 and 6.0 dS m-1, respectively) and two irrigation regimes (100% of maximum evapotranspiration, ETM, and 100% ETM plus leaching requirements, Lr) were studied. Total yield cumulated over the harvest periods was significantly higher for EC=1.6 dS m-1 than EC=6.0 dS m-1 and for 100% ETM + Lr than 100% ETM. Nevertheless, when plants were irrigated with both high saline concentration of water and high water supply (100% ETM + Lr) crop yield was similar to that observed on plants grown under low salinity (EC=1.6 dS m-1 ) and 100 % ETM but without considering Lr requirements. Fruit quality (dry matter content, reducing sugars concentration, tirable acidity and firmness) was improved with greater salinity, but was unaffected by water irrigation regime with the exeption of dry matter. These results suggested that using an irrigation regime equivalent to 100% ETM + Lr reduced the negative influence induced by high salinity of the irrigation water on yield, still keeping the beneficial effect on fruit quality.

Evaluating Pochonia chlamydosporia in a double‐cropping system of lettuce and tomato in plastic houses infested with Meloidogyne javanica

The effect of Pochonia chlamydosporia, a facultative fungal parasite of nematode eggs, alone or in combination with oxamyl was evaluated in a double‐cropping system of lettuce and tomato in unheated plastic houses infested with Meloidogyne javanica at two sites for two consecutive growing seasons. An additional treatment of methyl bromide fumigation was included to compare crop yield in nematode‐free vs. nematode‐infested soil. Final population densities, reproductive rate, root gall rating, and egg production were determined after each crop. Pochonia chlamydosporia was isolated from nematode eggs up to nine months after application to soil. The fungus survived in the rhizosphere for the entire growing season at one site, but only at low densities. Final population densities of M. javanica decreased after cultivation of lettuce and increased after tomato, and this pattern of population fluctuation was unaffected by treatment, experiment or site. The reproductive rate on lettuce was equal to or below 1, and it was similar among treatments in both experiments at both sites. Eggs were not found on lettuce roots. On tomato, the reproductive rate in the fungus + oxamyl treatment was significantly lower (P < 0·05) than other treatments in experiment 1 at both sites. Fungus + oxamyl consistently reduced root gall ratings on tomato in all cases, but numbers of eggs per g root varied depending on treatment. Methyl bromide‐treated plots remained free of M. javanica at the end of the 2‐year study.

PRODUCING SUITABLE HYBRIDS OF SWEET PEPPER TO SALINITY, LOW TEMPERATURE AND SANDY SOIL CONDITIONS

Six genetically diverse cultivars of sweet pepper were used in the present study. The 6 parents, 15 F1’s and one commercial hybrid (Majester F1) as a control hybrid were evaluated for fruit yield and fruit quality under unheated plastic houses in winter season of 2001/02. Results are summarized as follow: In all the studied traits, the best hybrid outyielded each of better parent and the control hybrid. Both general and specific combining ability were highly significant for most studied traits. The local cultivar “Balady” was good combiner for number of fruits/plant. While, AK-534 and AK 208 cvs were good combiners for early and total fruit weight. Taltos cv. was good combiner for V.C. content and T.S.S.%. Heritability estimates in broad sense were high for all studied traits. However, heritability estimates in narrow sense were moderate for number of fruits in early and total yield, pericarp thickness, and V.C. content, while it was low for the other traits.

STABILITY OF MICROPROPAGATED PLANTS AND MINI-TUBERS OF POTATO

Potato cv. `Red Pontiac was cultured and multiplied through several passages in vitro. The microplants and mini-tubers produced from two-year old in vitro cultures were investigated for phenotypic stability under glasshouse and plastic tunnel. Only one branch of a single plant among the many thousand derived from tissue culture showed variegated leaves. However, a few off-type mini-tubers were observed for changed tuber skin colour, which propagated true to type in the subsequent propagation. Tuber skin colour was markedly affected with the planting season. Red skin tubers planted in late autumn produced light pink tubers under unheated plastic tunnel during off-season from September to December. However, tuber shape, skin colour and skin texture were stable traits, and could be used for detecting off-types among mini-tubers derived from tissue cultured plants.

りん茎の高温遭遇がアリウム・コワニーの開花に及ぼす影響

ハウス養成球と露地養成球を用い, 7月1日から25℃で3カ月間貯蔵した後, 最低夜温を10℃に維持して栽培すると, ハウス養成球の方が開花が早く, 開花花序数も多かった.また, ハウス養成球であっても, 掘り上げ後25℃貯蔵開始までの期間をハウス内で貯蔵したりん茎では室内で貯蔵したものより開花が11日早く1月上旬となったうえ, 開花花序数も3本に増加した.ハウス養成球を5月上旬から25または30℃で0, 4, 8, 12週間貯蔵した後, 9℃で3カ月間貯蔵すると, 25℃で12週間もしくは30℃で4週間以上貯蔵したりん茎ですべての個体が花芽分化し, その発達段階は高温遭遇の程度が多いほど進んだ.ハウス養成球を用い, 5月上旬から25, 30, 35または35/25℃(昼/夜)で8週間高温処理した後, 25℃で3カ月間貯蔵した場合, 30℃および35℃貯蔵球は, 植え付け時の花芽の発育が最も促されたうえ, 12月下旬から3花序を開花させた.また, 30℃の期間を0, 4, 8, 12週間と変えた場合, 4または8週間処理区で植え付け時の花芽の発育と植え付け後の開花が最も促された.ハウス養成球を30℃で8週間処理後, 20℃で3カ月間貯蔵して10月上旬に植え付けると, 開花は11月下旬まで早められるが, 開花花序数は2本となり, 25℃で2カ月間, その後20℃で1カ月間貯蔵すると, 12月中旬から株当たり3花序を開花させることができた.

FEASIBILITY OF AN ELECTRICAL RADIATIVE HEATING SYSTEM IN GREENHOUSES

Electrical heating elements were tested for their possible use as a radiative heating system in greenhouses and to find out whether these elements - despite the high cost of electrical energy - could economically be used for the prevention of frost damage in those greenhouses where conventional heating systems cannot be considered because of their high capital cost. The performance of the heating elements was studied in, an unheated plastic tunnel and in a single glazed glasshouse heated to 5 degrees C by means of a conventional pipe heating system. Heating elements were spaced 1, 1.5, and 2 m apart and the effect on vegetation temperature was followed. To simulate the maximal performance of the radiative heating elements, a simple steady state model describing vegetation and element temperatures as a function of inside climate, temperature of the surroundings and power input into the elements was built. From the experiments it was found that the radiative heating system could not be used successfully in the tunnel: the vegetation temperature almost equalled the outside air temperature. In the glasshouse the use of the radiative elements resulted only in a slight increase of the vegetation temperature. Comparison between experimental and simulated results showed that only 40% of the maximally achievable vegetation temperature increase was really obtained. Since even the maximum vegetation temperature increase at rather high electrical energy inputs (100 W.m(-2) greenhouse floor area) was too low, it was concluded that the system was not beneficial from both a technical and economic point of view.

Ａｌｌｉｕｍ ｕｎｉｆｏｌｉｕｍの生育・開花に及ぼす温度の影響

The growth periodicity of Allium unifolium plants grown in an unheated plastichouse was assessed while simultaneously investigating the effect of temperatureon the initia-tion and development of flower buds.In bulbs grown in an unheated plastic house, the first inflorescences were initiated in mid-November. They formed tepals and stamens in mid-January of the following year and bloomed from early to mid-April. Two weeks later, the 2nd and 3rd inflorescences were initiated in axillary buds and bloomed in mid- to late April.When bulbs, which were planted in early October were grown in an unheated plastic house or a greenhouse kept above 10°C, they flowered satisfactorily. However, those grown in a greenhouse kept above 20°C had fewer flowered and shorter scapes.When bulbs were stored at 9°, 15°, 20°, 25° or 30°C from 1 August to 1 October, flower bud initiation occurred at 9° to 20°C, but the optimum range was 9°-15°C. Bulbs stored at 9°C bloomed earlier, but had fewer inflorescences when they were grown in a greenhouse kept above 10°C.Flower buds of bulbs stored at 10°C for 3 months were the earliest to differentiate; they flowered in mid-January if the greenhouse was kept above 10°C.Bulbs harvested from plants grown in an unheated plastic house in the previous season flowered 1 month earlier than did those harvested from plants grown outdoors, when they were stored at 10°C for 3 months (early July to October) and grown at or above 10°C.

アリウム・コワニーの生育と開花に及ぼす温度の影響

In this study, the growth periodicity of plants of Allium cowanii (syn. A. neapolitanum with large flowers), grown in an unheated plastic house, was clarified. Simultaneously, the effect of temperature on the initiation and development of flower buds was investigated.A bulb shows a sympodial branching system from mid-September to early December; 2 to 3 inflorescences are initiated as a result of repeated sympodial branching. The first inflorescence initiated in mid-September, the primordium of florets becoming visible in early and mid-October; the tepals and stamen are differentiated from late October to mid: November, leading to anthesis in mid-February of the following year. A second inflorescence is initiated in mid-October and bears flowers in early March. To assess a) the starting time of bulb storage, b) duration of storage, and c) storage temperature, bulbs were stored at 15°, 20°, 25°C, or 30°C from 1 July to 1 October or at 9°, 15°, 20°, 25°C, or 30°C from 1 August to 1 October. At the end of the storage periods, the initiation of the first inflorescence was observed at all temperetures below 25°C, but the optimum temperature was 15°20°C. Most bulbs stored at 30°C were in the vegetative state.When bulbs were grown in a greenhouse kept above 10°C after different periods of temperature treatment, those stored at lower temperatures bloomed earlier, except for those stored at 15°C from 1 July; they had low percentages of flowering plants. However, the number of flowering inflorescences per bulb was small.Plants grown above 20°C after planting in early October flowered 18 days earlier than did those grown at above 10°C. The early blooming scapes were shorter and had fewer florets than did the late blooming ones.

Genetic studies on the resistance of winter wheat to speckled snow mould

Speckled snow mould (caused by Typhula ishikariensis) is a potential threat to winter wheat (Triticum aestivum L.) production in eastern Canada. Information on the inheritance of snow mould resistance is needed to develop an effective breeding strategy. In this study, the inheritance of resistance to the speckled snow mould was examined using crosses of a resistant genotype, PI 173438, and four susceptible cultivars, Lennox, Kitami-2, Norin-8 and Ena. The parental lines, and the F1 and F2 populations from each of the four crosses were grown in the field and in an unheated plastic greenhouse and scored for snow mould resistance. Biomass yield, survival, plant height and number of tillers/plant, all expressed as percentage of check plants, were used as indices of snow mould resistance. Generation means analysis, combining data from the field and greenhouse experiments, indicated that snow mould resistance was largely influenced by environmental conditions, and that additive genetic effects were more important than epistatic effects in controlling the expression of the disease. Dominance effects oriented towards susceptibility were detected in only one of the four crosses. Estimates of broad sense heritability in the four F2 populations ranged from 0.62 to 0.96 and from 0.34 to 0.79, respectively, when biomass yield and number of tillers/plant were used as indices of snow mould resistance. When plant height was used as an index of snow mould resistance, the heritability estimates ranged from 0.10 to 0.53. Key words: Wheat (winter), Triticum aestivum, speckled snow mould, Typhula ishikariensis, heritability

Évaluation de trois contenants pour la production de plants d'espèces feuillues de fortes dimensions

Three types of containers of different volumes (Polymos 15, 700 cm3; Polymos 12, 1,000 cm3; Whitcomb®, 3,500 cm3) were tested to produce large hardwood seedlings. Studies of growth and root development of three species, white ash (Fraxinus americana L.), bur oak (Quercus macrocarpa Michx.) and northern red oak (Quercus rubra L.) were used to assess containers after two growing seasons in an unheated plastic shelter. The mean height of seedlings increased with the volume of the containers. The total dry mass of seedlings at 55 cm in height was more important in the larger container; the total root mass and the proportion of secondary roots were higher in the container of greater volume. For the two species of oak, the 3,500 cm3 container produced seedlings with a taproot showing a number of deviations when touching the bottom of the container. White ash, a species with a fibrous root system, showed a higher deviation index in the smaller containers. The openings on the sides of the square-shaped Whitcomb® containers were effective for the air-pruning of secondary lateral roots of species with a taproot and their volume allowed for an important root mass. However, the flat bottom with openings at each of the four corners did not prevent deviation of the primary root. The use of a bottomless square-shaped container with a volume greater than 1,000 cm3 and with adequate lateral openings would optimize the production of large seedlings of hardwood species with taproot. Key words: large containerized seedlings, root development, root deviation, Quercus sp., Fraxinus sp.