Tray Plants Research Articles

First Report of Berkeleyomyces basicola Causing Black Shoot Rot of Raspberry in Nursery Production in the United States and Worldwide.

Commercial production of raspberry (Rubus ideaus) transplants is almost exclusively accomplished through clonal propagation. One system involves forcing young shoots to grow from roots. The shoots are cut and rooted in propagation trays and referred to as tray plants. Sanitation is important during tray plant production as this method carries some risk due to contamination by substrate pathogens. In May 2021, a new disease was observed on raspberry tray plant cuttings at one nursery location in California, and observed again in 2022 and 2023 but at a much lesser extent. Multiple cultivars were affected; however, up to 70% mortality was observed on cv. RH740.1. In less affected cultivars, mortality ranged from 5-20%. Symptoms included chlorotic leaves, lack of rooting, and blackening at the basal end of shoots, followed by death of the cutting. Affected propagation trays had inconsistent foliage and patchy growth. Chains of chlamydospores (two to eight spores in each chain) similar in morphology to Thielaviopsis species (Shew and Meyer 1992) were observed at the cut end of symptomatic tray plants using a microscope. Isolates were retrieved by incubating tissue on surface-disinfested (1% NaOCl) carrot discs in a humid chamber for 5 days until greyish black mycelium was observed (Yarwood 1946). Mycelium was transferred to acidified potato dextrose agar and formed a gray to black compact mycelial colony with both endoconidia and chlamydospores. Endoconidia were catenulate, single-celled with slightly rounded ends, colorless, and 10-20 µm x 3-5 µm in size; dark-colored chlamydospores were 10-15 µm x 5-8 µm in size. The ITS region of isolates 21-006 and 22-024 was amplified with ITS5 and ITS4 primers using a 48°C annealing temperature (White et al. 1990), Sanger sequenced (GenBank accession OQ359100) and yielded 100% match to Berkeleyomyces basicola accession MH855452. Pathogenicity was confirmed by dipping 80 grams of roots of cv. RH740.1 into a suspension of 106 conidia/mL of isolate 21-006 for 15 min. For the non-inoculated control, 80 grams of roots were dipped in water. Roots were then planted into trays of coir (Berger, Watsonville, CA). Six weeks after inoculation, twenty-four shoots were harvested from each treatment, stuck into propagation trays filled with coir and maintained in a humid chamber for 14-days to induce rooting. Tray plants were then harvested and assessed for root development, black basal shoot tips, and presence of chlamydospores. Forty-two percent of cuttings from the inoculated treatment had rotten basal tips and failed to root, in comparison to 8% of the cuttings from the non-inoculated control. Chlamydospores were visualized only on shoots that emerged from inoculated roots and B. basicola was isolated only from cuttings originating from inoculated roots. Post-inoculation isolates were confirmed as B. basicola using methods described above. To our knowledge, this is the first report of B. basicola infecting raspberry. Confirmation of this pathogen on tray plants is significant because of the potential impact this disease may have in commercial nursery production worldwide. In 2021, the value of the harvested raspberry crop in the U.S. totaled $531 M, of which California represented $421 M (USDA 2022). The value of the 2021 crop was highest in the U.S. ($531 M), followed by Russia ($512 M), Spain ($405 M) and Mexico ($332 M) (FAO 2021).

Efficiency of Strawberry Cultivation under the Effect of Different Types of Plants in a Soilless System in the High-Altitude Regions of Southern Brazil

By analyzing the growth and development of different types of strawberry plants, the researchers were able to evaluate the interference with the horticultural potential of the cultivar ‘Albion’. The five treatments that have been studied corresponded to different types of strawberry plants: mini plants in trays with young roots, plants in trays with mature roots and an initial reduction of fertigation, plants in trays with mature roots, plants with bare roots, and plants in trays with mature roots preserved by the cold. In bags containing coconut fiber, the experiment was laid out in a randomized block design with three replications. The attributes evaluated were the total yield per plant, the total yield per plant with fruits above 10 g, the total yield per hectare, the total yield per hectare with fruits above 10 g, the average plant diameter, the average number of buds per plant, and the average number of stolons per plant. There were no significant effects among the plant types concerning yield production. Plants in cold-preserved trays with mature roots showed a higher number of buds than plants in trays with mature roots. Cold-preserved tray plants with mature roots produced the highest number of stolons, followed by bare-root plants. It is concluded that the types of strawberry seedlings did not influence the productive performance of the strawberry ‘Albion’ cultivar. However, cold-preserved tray plants with mature roots showed better vegetative performance, with a yield of a higher number of buds and stolons. However, the results were influenced by the agroclimatic conditions of the producing region; due to climatic interference in the behaviour of the plants about the factors studied, it is recommended to repeat the experiment for a better understanding of the objectives.

Wood Fiber from Norway Spruce—A Stand-Alone Growing Medium for Hydroponic Strawberry Production

There is an increased interest in the hydroponic production of strawberries in protected cultivation systems, and it is, therefore, urgent to develop new, more sustainable growing media alternatives. This study investigated the physical properties of wood fiber produced from Norway spruce (Picea abies (L.) H. Karst.) and peat:wood fiber substrate blends as well as the performance of the wood fiber in comparison to the industry standards, i.e., peat and coconut coir in the cultivation of hydroponic strawberry. Tray plants of the June-bearing strawberry (Fragaria × ananassa Duch.) cultivar ‘Malling Centenary’ were transplanted into five different growing media: a peat (80%) and perlite (20%) mixture, stand-alone (100%) coconut coir and three stand-alone (100%) Norway spruce wood fiber substrates (including coarse textured fibers with compact and loose packing density and compacted fine-textured fibers). Ripe strawberries were harvested and registered throughout the production season. The overall marketable yield was comparable across all the tested growing media; however, after 4 weeks of harvest, both coarse wood fiber and fine wood fiber showed better fruiting performance than the peat-perlite mixture. A trend for earlier berry maturation was observed for all wood fiber-based substrates. Plant parameters recorded after the end of production showed that plant height, number of leaves, and biomass production were higher in coarse wood fiber than in the peat-perlite mixture. Moreover, plants grown in wood fiber-based substrates had less unripe berries and flowers not harvested in comparison to both the peat and coir treatments.

The influence of chilling hours on root starch content, growth and yield of strawberry tray plants

The chilling requirements of two strawberry cultivars (‘Sonata’, ‘Albion’) were assessed by evaluating the starch accumulation levels in the tray plants’ root system and their subsequent growth and yielding. The research was conducted in an experimental orchard and a greenhouse of the National Institute of Horticultural Research in Skierniewice, Poland, in 2017–2019 (2 cycles of obtaining planting material and growing plants). The tray plants (rooted tips) were grown in the natural field conditions until they were transferred in batches to a cold store (–2°C) on five different dates: 12 Oct., 30 Oct., 20 Nov., 11 Dec., and 3 Jan. (of the following year). The number of accumulated chilling hours less than 7°C was recorded for each transfer date, and the roots were analysed for starch content at the time of transfer. After the end of cold storage (3 months, standardised for all treatments), the plants were planted in pots and transferred to a greenhouse to assess growth and plant yielding. The obtained results indicate that chilling induces changes in the extent of starch accumulation. The highest starch accumulation in ‘Sonata’ roots was recorded when the plants received about 500 h of chilling (under Polish conditions accumulated in November/December). In the ‘Albion’ strawberry case, the maximum was found at the lower chilling level – about 300 h (middle of November). The highest fruit yields were produced by ‘Sonata’ plants, for which the number of chilling hours (0–7°C) was 500–800 h. In the case of ‘Albion’, the values were 2–3 times lower. A more extended period of keeping tray plants in field conditions (over 1000 h of chilling) resulted in a deterioration in fruit yield.

Steam thermotherapy strongly reduces Botrytis in strawberry transplants with no or minor negative effects on plant growth and yield

The effect of steam thermotherapy on Botrytis spp. populations in strawberry transplants was evaluated. Tray plants rooted in 0.2 L peat plugs of seasonal flowering cvs. Falco, Sonsation, and Soprano, and everbearing cvs. Favori and Murano were pre-treated with steam at 37 °C for 1 h, followed by 1 h at ambient temperature and air humidity, and then 2 or 4 h steam treatment at 44 °C. Except for one cultivar with a slight reduction in yield, there were no negative effects on plant performance. Compared to untreated transplants, mean incidence of Botrytis on the five cultivars was reduced by 43 and 86% with the 2 and 4 h treatments, respectively. Within cultivars the reduction was significant in 2 and 3 experiments following the 2 and 4 h treatments, respectively. Sclerotia from four different isolates of Botrytis were subjected to treatment including 4 h of steam thermotherapy and subsequently tested for viability. Following 14 days of incubation, 90 to 100% (mean 97%) of treated sclerotia failed to produce mycelial growth compared with untreated sclerotia, which all germinated and produced mycelia. Botrytis isolates recovered from both treated and untreated strawberry transplants were tested for resistance to seven fungicides, including boscalid, fenhexamid, fludioxonil, fluopyram, pyraclostrobin, pyrimethanil and thiophanate-methyl. Multiple fungicide resistance was common; 35.5% of isolates were resistant to fungicides from at least three FRAC groups. Results indicate that steam thermotherapy treatment strongly reduces populations of Botrytis spp., including fungicide-resistant strains, in strawberry transplants with negligible negative impacts on the transplants.

Effects of Temperature and Photoperiod on the Flower Potential in Everbearing Strawberry as Evaluated by Meristem Dissection

The growing interest in using everbearing (EB) strawberry cultivars to extend the cultivation period has faced some challenges. These include poor runner production due to its perpetual flowering nature; irregular flowering behavior and extended periods of high temperature have caused floral inhibition and reduced yield. As flowering is an interplay between temperature and photoperiod, it is important to investigate the effects of this interaction on the cultivation. Therefore, this study used meristem dissection as a tool to study the effect of temperature and photoperiod on meristem development. Tray plants of two EB strawberry cultivars ‘Florentina’ and ‘Favori’ were grown at 20 °C, 25 °C, and 30 °C under short day (SD) conditions, and subsequently at 20 °C under long day (LD) conditions. The meristem development was analysed every 6 weeks for a 15-week period in SD and for 14 weeks in LD conditions using meristem dissection. The plants showed similar flowering patterns to previously studied everbearing cultivars, which was qualitative LD plants at high temperatures and quantitative LD plants at lower temperatures. Our results show that meristem dissection can be used to determine the temperature and photoperiodic effect on meristem development, and for the occurrence of cropping peaks, and can therefore be used to decide the environmental input and to evaluate yield potential.

Crecimiento en campo de Pinus patula Schltdl. & Cham. como efecto de la poda radicular y los contenedores utilizados en vivero

Introduction: The production of seedlings in containers implies the risk of deforming the root. This damage persists and increases after outplanting causing negative effects on the plants. Objective: To evaluate outplanting performance of Pinus patula Schltdl. & Cham. as an effect of root pruning and containers used in the nursery. Materials and methods: Nine-month-old seedlings were grown in three 170 cc containers: plastic tray, polystyrene tray and grid with containers with 54, 77 and 42 cavities, respectively. The cavities were impregnated with copper hydroxide to encourage chemical root pruning; additionally, an aerial root pruning treatment was included (containers with lateral openings). Survival and growth of P. patula were evaluated under field conditions during two years in 72 plants per treatment, randomly distributed in six blocks or replications. Results and discussion: Pruned and unpruned plants showed significant differences (P ≤ 0.05) in survival (89 vs. 79 %), height (154.0 vs. 147.1 cm) and relative annual growth rates of diameter (0.97 vs. 0.93 cm·cm-1·year-1) and height (0.97 vs. 0.92 cm·cm-1·year-1). Plants in plastic containers and polystyrene trays had the best growth and survival rates. The interaction container*pruning was not significant. In spite of starting with the lowest sizes, the plants in containers designed for aerial root pruning had similar characteristics to those grown in the same containers with and without chemical root pruning. Conclusion: Root pruning favored survival and growth of P. patula after outplanting and had a greater effect than the type of container used.

Propagation and Floral Induction of Transplant for Forcing Long-term Production of Seasonal Flowering Strawberries in Japan

In Japan, over 95% of the acreage is covered with plastic to force June-bearing (seasonal flowering, SF) strawberry cultivars to produce fruit from late fall to early summer. During the late 1960s, a forcing technique was developed that advanced flower bud initiation to late summer and prevented the transplants from becoming dormant during winter. This new forcing technique involved nitrogen starvation of nursery plants to induce floral initiation. Until about 1980, strawberry growers in Japan used runner plants produced in waiting beds, but most transplants are now produced in plastic pots under rain shelters to avoid soil-borne diseases. Recently, the use of tray plants produced from hanging runner cuttings has become popular. To induce early floral initiation, the following artificial low temperature (LT) treatments have been established: (1) “Yarei”, a combination of a short day with solar radiation and LT under darkness in cooling facilities (Yarei-ko); (2) “Kaburei”, continuous dark-LT with refrigeration facilities including industrial warehouses; and (3) “Kanketsu-reizo”, intermittent LT storage. An overview of the technologies applied to plant propagation and the control of floral initiation of Japanese SF cultivars is provided in this review.

Sawdust and bark-based substrates for tray plants strawberry production under greenhouse conditions

Sawdust and bark-based substrates for tray plants strawberry production under greenhouse conditions

'ELEGANCE' AND 'VIBRANT', TWO NEW STRAWBERRY CULTIVARS FOR PROGRAMMED CROPPING IN NORTHERN EUROPE

Programmed cropping with short-day cultivars, also known as the 60-day system, is common in the United Kingdom and other countries in northern Europe. Three types of plants are used: graded cold-stored runners (Frigo plants), waiting bed plants or tray plants. The crop is produced approximately 60 days after planting and the system can be used in either soil or substrate. The cultivars most widely used in this system are 'Elsanta' and 'Sonata', which both perform well, but most other European short day cultivars are poorly adapted. At East Malling Research (EMR) we have studied the inheritance of traits associated with good performance in the 60-day system and focussed on developing cultivars that are well adapted. Two recent releases, 'Elegance' and 'Vibrant' have been specifically bred for the 60-day system and perform well from all three plant types. 'Elegance' is adapted for open field or tunnel production and the 60-day yield potential is higher than 'Elsanta' from plants of the equivalent size and type. 'Elegance' is also very productive as a mature plant (maincrop), and at EMR has produced higher yields and larger berries than 'Elsanta' in five trials in different years. The fruit of 'Elegance' is very attractive, with large, firm, berries of uniform conical shape, glossy skin and a bright, orange/red colour. Brix levels and sensory flavour scores have been similar to 'Elsanta'. 'Vibrant' has an earlier season than 'Elegance' and is approximately seven days before 'Elsanta' in the maincrop season. It is suitable for tunnel production in soil or substrate and in trials at EMR the average 60-day yield has exceeded 'Elsanta'. If 'Vibrant' plants are forced into production early, they will flower again and produce a second crop later in the summer. The yield of this second crop varies between years, depending on the weather conditions. The berries of 'Vibrant' are firm with a very uniform conical shape and strong red colour. Sensory flavour scores and Brix levels have been similar to 'Elsanta'.

YIELD PERFORMANCE ASSAY AND FRUIT QUALITY OF STRAWBERRY GENOTYPES TOLERANT AND SUSCEPTIBLE TO FUSARIUM OXYSPORUM AND TO A VIRAL COMPLEX

Root and crown rot produced by Fusarium oxysporum and by a viral complex consisting of at least five viruses has been affecting the region of Irapuato, Guanajuato, Mexico, causing serious damage to the strawberry production. For this reason, 14 years ago two Mexican organizations, INIFAP (the National Institute for Forestry, Agriculture, and Livestock Research) and CINVESTAV (the Centre for Research and Advanced Studies, of the National Polytechnic Institute) started a breeding program to produce cultivars tolerant to both kinds of pathogens, using Fragaria chiloensis, from the central coast of California, USA, as source of resistance. During the season 2010-2011 a group of five clones, (07.4, 07.35, 07.61, 07.89 and 07.90), carrying 12.5% of F. chiloensis genetic information, were evaluated on untreated soil planted with tray plants under macrotunel, vs. a group of nine clones of Fragaria x ananassa, and the cultivar 'Camino Real', which was used as a control, to estimate the progress in the genetic program for characteristics such as productivity and fruit quality in this group of clones. Clone 07.35 exhibited the highest early production and total yield, namely 20.1 and 69.2 t.ha-1 respectively, outperforming all other cultivars, including 'Nikte' and 'Camino Real', although these two had higher fruit weight and firmness. During the assay, the presence of virus was evaluated through monitoring by means of UC-4 virus indicator plants. Most of the clones carrying F. chiloensis genes tested, were more tolerant to the viral complex than cultivars of F. x ananassa, and at least two of the clones tested (07.4 and 07.35), exhibit tolerance to both pathogens, and have the potential to outperform those of commercial cultivars. Nine of the 14 genotypes were susceptible to one or both pathogens.

Strawberry Production in Japan: History and Progress in Production Technology and Cultivar Development

In Japan, there are more than 25,000 strawberry farms totaling 6360 ha. Over 95% of the acreage is in an annual hill culture system and covered with polyethylene plastic to force June-bearing cultivars, such as Tochiotome and Saga-honoka to produce fruit from late fall to early summer. In the late 1960s, a forcing technique was developed that advanced flower bud initiation to late summer and prevented the transplants from becoming dormant in the winter. The new forcing technique involved nitrogen starvation of nursery plants, growing the transplants in walk-in tunnels with no chilling and a long-day photoperiod condition, and applying gibberellic acid before the onset of endodormancy. Until about 1970, strawberry growers in Japan used runner plants produced in waiting-beds, but now most of the transplants are produced in plastic pots to avoid soil-borne diseases. Recently, the use of tray plants produced from hanging runner cuttings has become popular. Most of the strawberries in Japan are grown in soil using the annual hill culture system. To offer better working conditions for plant management and fruit picking, low cost substrate culture systems and bench-top production systems are now used by over 1,800 farmers throughout Japan totaling over 470 ha in production.

Flower Initiation in June-bearing Strawberry as Affected by Crown Depth, Age, and Size of Tray Plants

The use of tray grown transplants is becoming popular for substrate strawberry production. Although tray plant production with hanging runner cuttings is a laborsaving propagation procedure for forcing of June-bearing strawberries, the tray grown plants are inferior to pot grown plants in terms of earliness and uniformity of flowering. The crowns of rooted tray plants are often deeply drawn into medium by their own roots. The effect of crown depth, age, and size of tray plants on flowering of June-bearing strawberry (Fragaria × ananassa Duch. ‘Nyoho’) were investigated. Tissue temperature around the apical meristem was lower, and earlier and more uniform flower bud differentiation was obtained in the crown stripped or shallow-grown plants compared to deeply embedded plants. Flowering was later in young and small tray plants compared to aged large plants. By applying crown stripping, early and uniform flowering could be obtained even in the young and small tray plants. The variation in the depth of crown was clarified to be a cause of poor flowering performance of the tray grown strawberry plants. To obtain productive tray grown transplants, crown stripping would be an efficient procedure in practice.

THE EFFECTS OF RUNNER GRADE, HARVEST DATE AND PEAT GROWING MEDIA ON STRAWBERRY TRAY PLANT FRUIT PRODUCTION

Strawberry plugs are quickly replacing traditional bare-root transplants in Ireland. This is particularly the case for soilless culture in glasshouse and polythene tunnel production. The aim of this experiment was to study the effect of runner size, date of runner harvest and two peat types on subsequent fruit yield characteristics from the 'tray plants' grown. Runner tips were harvested from 'super elite' strawberry mother plants cv. 'Elsanta' and planted into peat modules and grown in a non-heated glasshouse. Runner tips were harvested on the 5 th and the 19 of July 2005. On both dates they were graded into small, medium and large sizes. These were rooted in one type of propagation tray and two different types of peat substrate. The final strawberry crown diameter ranged from 14.3 to 15.69 mm at harvest. The root score ranged from 3.55 to 4.36 out of a total score of five. There was no significant difference between the total yields recorded in either season one or two for any of the treatments. The lowest and highest average yield recorded over the two seasons was 11.33 and 12.73 kg per m 2 respectively. The average fruit weight was higher from plants propagated from large runners and when grown in the finer peat substrate. However, when large runners were used later in the season, the average fruit weight is lower. Strawberry crown dissection showed the regular pattern of flower formation throughout the growing season. The stage of flower development was closer for the three runner grades that were harvested later.

'ELSANTA' AUTUMN CROP PERFORMANCE USING DIFFERENT PLANT TYPES AND PLANTING DATES

To evaluate the crop performance of 'Elsanta' strawberry plants grown in a soilless culture and under polyethylene tunnels for autumn production, a field experiment was established with different plant types and planting dates. Four types of cold stored plants, bare-rooted plants (A, A + and waiting bed - WB) and tray plants, and three planting dates, 28 September, 10 October and 17 October were compared. Tray, WB and A + plants had higher initial fresh plant weight, crown number and diameter than A plants. Cropping performance was more affected with plant type rather than with planting date. However, delaying planting date induced plants to produce in December and January with increasing proportion of unmarketable yield. The highest productivity was obtained with tray plants followed by WB and A plants that performed squally. Fruit quality did not vary between plant types. In general, plants of the 2 nd planting date showed higher TSS values. Although yields were not affected by planting dates, earlier plantings should be considered to achieve most profitable autumn production with fruits of good quality.

QUALITY AND PERFORMANCE OF STRAWBERRY TRAY PLANTS IN HIGH LATITUDE CONDITIONS

The aim of a series of experiments was to examine nursery production of strawberry (Fragaria × ananassa) plants for an extended harvest season in the northern European conditions. Different pre-culture treatments were applied, and the yielding potential of transplants potential was tested in fruit production trials. The quantity and composition of the carbohydrate reserves in the crowns and roots of the plants were studied in order to assess the transplant quality. The carbohydrate reserves varied according to the cultivar and the plant type. The total carbohydrate concentration was higher in the crowns and roots of tray plants than in those of bare-rooted waiting bed plants. Leaf removal prior to cold storing enhanced the cropping potential of waiting bed plants. A period of short-day treatment prior to the natural short-day season increased flower initiation, but not the fruit yield. After transplanting, the carbohydrate reserves in the crowns and roots of cold-stored tray plants reduced strongly. This reduction was smaller if white mulch instead of black mulch was used. Fruit yield was, however, not affected in terms of quantity.

INFLUENCE OF THE GENOTYPE, TYPE OF PLANT AND POPULATION DENSITY ON STRAWBERRY PRODUCTIVITY AND FRUIT QUALITY UNDER MACROTUNNEL

In an experimental assay with 12 strawberry genotypes, without protection and under macrotunnel, there was no interaction of the genotype x the production system for none of the parameters evaluated. Macrotunnel increased 12% in average the early production with respect to the former, however both production systems had a similar production for the full cycle. Macrotunnel promoted higher weight, better appearance and less percentage of deformed fruits. In another experiment using two genotypes, two types of plants, at 100, 150 and 200 thousand plants ha -1 , 'Festival' was more precocious than '01.165', however both exhibited the same total productivity. Tray plants survived better to the transplant and had higher early production than bare root plants, but both showed similar total yield at the end of the cycle. The maximum early production and total yield for both genotypes and type of plant was with 150,000 plants ha -1 , where '01.165' had lower percentage of deformed fruits, higher weight and better appearance than 'Festival'. Bare root plants had less percentage of deformed fruits and higher mean weight for both periods. Population density had no influence on quality parameters.

SCREENING PLANT RESISTANCE TO PHYTOPHTHORA CACTORUM WITH THE DIPPING TEST

Resistance of strawberry cultivars to crown rot (Phytophthora cactorum) has been evaluated at MTT Agrifood Research Finland since 1993 using the crown test and the NFT test. The crown test is quick and reliable and the test with running irrigation water gives results as quickly as the crown test. The NFT system is, however, expensive and the viability of Phytophthora zoospores can be reduced or completely lost if the hydroponic environment contains substances that are harmful to them. Inoculation by dipping the tray plants in P. cactorum inoculum was investigated to solve this problem. The inoculum concentration was the same as previously used in the NFT test. Inoculation in Vefi pots seemed to give the same result as addition of sporangia to circulating irrigation water, but symptom expression was delayed during the first two test weeks. Crown rot developed within 4 weeks and a longer test time did not change the level of infection. According to the tests on cultivars 'Jonsok', 'Kimberly' and 'Polka', inoculation in Vefi pots with zoospores is effective and can save costs in the greenhouse environment.

Dimerization Controls the Activity of Fungal Elicitors That Trigger Systemic Resistance in Plants

The soilborne fungus Trichoderma virens secretes a small protein (Sm1) that induces local and systemic defenses in plants. This protein belongs to the ceratoplatanin protein family and is mainly present as a monomer in culture filtrates. However, Hypocrea atroviride (the telomorph form of Trichoderma atroviride) secretes an Sm1-homologous protein, Epl1, with high levels of dimerization. Nonetheless, the molecular mechanisms involved in recognition and the signaling pathways involved in the induction of systemic resistance in plants are still unclear. In this report, we demonstrate that Sm1 and Epl1 are mainly produced as monomer and a dimer, respectively, in the presence of maize seedlings. The results presented show that the ability to induce plant defenses reside only in the monomeric form of both Sm1 and Epl1, and we demonstrate for the first time that the monomeric form of Epl1, likewise Sm1, induces defenses in maize plants. Biochemical analyses indicate that monomeric Sm1 is produced as a glycoprotein, but the glycosyl moiety is missing from its dimeric form, and Epl1 is produced as a nonglycosylated protein. Moreover, for Sm1 homologues in various fungal strains, there is a negative correlation between the presence of the glycosylation site and their ability to aggregate. We propose a subdivision in the ceratoplatanin protein family according to the presence of the glycosylation site and the ability of the proteins to aggregate. The data presented suggest that the elicitor's aggregation may control the Trichoderma-plant molecular dialogue and block the activation of induced systemic resistance in plants.

Cold Storage of Strawberry Plants

Cold storage has not only been a good method to overwinter strawberry plants safely and to compensate for the lack of natural chilling. Initially cold stored plants were used for early spring cropping only. Meanwhile this technique has become a normal commercial practice among growers in central Europe and has given them the opportunity to extend the strawberry production season from July until January. Cold stored waiting bed plants have been used since the early seventies in The Netherlands and Belgium and currently represent an important part of strawberry production. These sixty-day-plants are planted mainly outdoors in the soil for a production from July until September. More recently waiting bed plants have gained popularity in the UK, Germany and northern Italy to extend the season. Alternatively in France and Germany cold stored runner (A+) plants are traditionally being used for a summer production outdoors followed by a spring crop. During the last decade module or tray plants have gained popularity for autumn cropping on substrate culture in plastic tunnels and greenhouses. During the most recent years the programmed “out of season” production of strawberries has become more important in several European countries. Intensive research has been going on concerning the improvement of the growing techniques and quality of plant material and cold Storage conditions.