Commercial Greenhouse Conditions Research Articles

The sky is not the limit: Successful foliar application of Steinernema spp. entomopathogenic nematodes to control Lepidopteran caterpillars

Entomopathogenic nematodes (EPNs) are ubiquitous soil-thriving organisms that use chemical cues to seek and infect soil-dwelling arthropods, yielding various levels of biological control. Going beyond soil application, scientists and practitioners started exploring the option of applying EPNs onto the foliage of crops in attempts to manage leaf-dwelling insect pests as well. Despite some success, particularly with protective formulations, it remains uncertain whether EPNs could indeed survive the phyllospheric environment, and successfully control foliar insect pests. In this context, we tested the potential of commercially produced Steinernema feltiae and S. carpocapsae, two of the most commonly used EPNs in the field of biological control, in controlling Lepidopteran foliar pests of economic importance, i.e. Tuta absoluta and Spodoptera spp. caterpillars as models. We first tested the survival and efficacy of both EPN species against the Lepidopteran caterpillars when applied onto tomato, sweet pepper and lettuce leaves, under controlled conditions and in commercial greenhouse conditions, respectively. Subsequently, we explored the behavioural responses of the EPNs to environmental cues typically encountered in the phyllosphere, and analysed plant volatile organic compounds (VOCs). Our results show that both S. feltiae and S. carpocapsae successfully survived and infected the foliar caterpillars, reaching similar level of control to a standard chemical pesticide in commercial practices. Remarkably, both EPN species survived and remained effective up to four days in the phyllosphere, and needed only a few hours to successfully penetrate the caterpillars. Interestingly, S. feltiae was attracted to VOCs from tomato plants, and tended to prefer those from caterpillar-induced plants, suggesting that the nematodes may actively forage toward its host, although it has never been exposed to leaf-borne volatiles during its evolution. The present study shows the high potential of steinernematids in managing major foliar pests in greenhouses and in becoming a key player in foliar biological control. In particular, the discovery that EPNs use foliar VOCs to locate caterpillar hosts opens up new opportunities in terms of application techniques and affordable effective doses.

Single amino acid change in tomato brown rugose fruit virus breaks virus-specific resistance in new resistant tomato cultivar.

Tomato cultivation across the world is severely affected by emerging plant viruses. An effective method for protection of commercial crops against viral threats is the use of cultivars harboring resistance genes. Tomato brown rugose fruit virus (ToBRFV), a recently emerged tobamovirus, is able to overcome the dominant Tm-22 resistance that is present in the majority of commercial tomato cultivars. In an effort to alleviate the severe consequences of ToBRFV on tomato production, tomato breeding companies are developing new cultivars with varying levels of resistance against ToBRFV. In the present study, cultivars with a new resistant phenotype against ToBRFV were screened against a wild-type isolate of ToBRFV, and subsequently, their performance under commercial greenhouse conditions was monitored. Following the identification of ToBRFV symptoms in a commercial greenhouse-where both new resistant and susceptible cultivars were interplanted-these cultivars were more closely examined. The presence of ToBRFV was molecularly confirmed on both cultivar types suggesting that the new resistance had been broken. High-throughput sequencing (HTS) was used to study the complete genomes of viral isolates present in the two cultivar types. The analysis revealed a single amino acid change at position 82 of the movement protein of ToBRFV in the isolate present in the new resistant cultivar compared with the isolate identified in the susceptible cultivar. A screening bioassay, that was performed to compare the infectivity of the two ToBRFV isolates, confirmed that only the isolate with this specific amino acid change could successfully infect the resistant cultivar, overcoming the new resistance against ToBRFV.

Automated and non-destructive estimation of soluble solid content of tomatoes on the plant under variable light conditions

In this study, a method is proposed to deal with the variable light conditions in a greenhouse to non-destructively predict the soluble solid content (SSC) of tomatoes on the plant. It was investigated how well the SSC – measured as °Brix – of tomatoes could be predicted based on spectral data in the range of 470–900 nm, where data acquired in situ (in the greenhouse) was compared to post-harvest data captured under controlled laboratory conditions. To deal with the variation in illumination in the greenhouse, a dynamic-calibration method is proposed, using a grey reference in the image. Ground-truth SSC data of the tomatoes was acquired using a refractometer. Data was collected of three different types of truss tomatoes with a wide range of SSC. Different PLS regression models were then trained on the spectral data in relation to the refractometer values. Trained and tested on all types, the in situ measurements showed a predicted coefficient of determination on the test set, Q2, of 0.95 with a Root Mean Squared Error of Prediction (RMSEP) of 0.29 °Brix using the dynamic calibration, and a Q2 of 0.93 with RMSEP of 0.35 °Brix without using the dynamic-calibration method. The post-harvest measurements resulted in a Q2 of 0.95 with RMSEP of 0.31 °Brix. The results show that spectral imaging using dynamic calibration is applicable for in situ non-destructive prediction of SSC. This method enables high-throughput and non-destructive quality estimation of fruits on the plant in commercial greenhouse conditions.

Optimizing Crop Water Productivity in Greenhouse Pepper

Although advanced production systems have been developed in the last 20 years, water scarcity is still a growing problem in agriculture. This study aims to evaluate the effect of different strategies that combine the application of seaweed and microbial biostimulants with regulated deficit irrigation (RDI) strategies on the irrigation water productivity (WPI), fruit quality parameters and soil enzymatic activity in pepper plants (Capsicum annum sp.) under two commercial greenhouse conditions. In each trial, two treatments were applied: (i) irrigation according to Farmer criteria without biostimulant applications and (ii) a combined treatment of RDI and the same biostimulation program, composed of Bacillus paralicheniformis and Ascophillum nodosum extracts. RDI was applied in different phenological stages in each greenhouse after the establishment until the 1st harvest in trial 1 or during the ripening and harvest period in trial 2. On average, the irrigation was reduced by 600 m3 ha−1 compared to the Farmer irrigation schedule. In both trials, biostimulation promoted an increase in fruit numbers, punctually in trial 1, leading to yield precocity, or generally in trial 2, obtaining a higher yield. Globally, WPI was increased when RDI was combined with biostimulation. This combined treatment also enhanced the root water absorption and improved the soil enzymatic activity in both greenhouses, suggesting that nutrients in the soil would become more available to plants. Thus, the combined action of biostimulation under different RDI strategies has been proved to be a useful strategy to improve agricultural sustainability.

Distance‐dependent attraction of the generalist aphid parasitoid Aphidius colemani towards synthetic volatile organic compounds under greenhouse conditions

AbstractManipulation of insect foraging may provide the basis for effective insect pest control strategies. Recent laboratory and small‐scale greenhouse experiments have shown that a blend of styrene and benzaldehyde is attractive to some Aphidius parasitoids, making it a good candidate for attracting and retaining these natural enemies in cropping systems. However, an appropriate dispenser type and appropriate dose for field application and its attraction range have yet to be identified. In this study, we performed experiments to determine an appropriate dispenser type – Omnilure® vs. low‐density polyethylene (LDPE) bags – and the most suitable dose to attract Aphidius colemani Viereck (Hymenoptera: Braconidae) under commercial greenhouse conditions and to determine the maximum distance of attraction. A mixture of 10 mg styrene and 100 μg benzaldehyde was the most attractive dose for A. colemani when provided by the dispensers under greenhouse conditions. The highest percentage of parasitoids was attracted when insects were released at a distance of 0.5 m from the Omnilure dispensers. Nevertheless, compared to the solvent control the blend of styrene and benzaldehyde remained attractive over a distance of up to 5 m. The potential application of these results in novel augmentation biocontrol strategies is discussed.

Evaluation of a guardian plant system to suppress Frankliniella occidentalis (Thysanoptera: Thripidae) in greenhouse ornamentals.

Western flower thrips (WFT), Franklinella occidentalis (Pergande), is an economically damaging pest of greenhouse ornamentals. A 'guardian plant system' (GPS) that targeted WFT was evaluated under controlled and commercial greenhouse conditions. This system used mycotized millet grains with the entomopathogenic fungus Beauveria bassiana (Balsamo-Crivelli) Vuillemin applied to soil of potted marigolds, Tagetes patula (L.), combined with the foliar-dwelling predatory mite Neoseiulus (=Amblyseius) cucumeris (Oudemans) in slow-release sachets under controlled greenhouse conditions, and with the addition of a pheromone lure under commercial settings. Significantly fewer WFT and less foliar damage on GPS was observed over the 10 and 12 weeks experimental periods compared to the untreated controls. Predatory mites were maintained up to 10 weeks with one release under controlled greenhouse conditions and 12 weeks with two releases in commercial greenhouses. In commercial greenhouses, greater numbers of WFT were found on marigolds than on crop plants within 1 m of the system. Fungal granules persisted for 12 weeks up to 2.5 × 105 CFU g-1 in the GPS soil. The use of biological control agents to suppress WFT within a GPS could be a useful IPM strategy for greenhouse production. The marigold GPS attracted WFT which were suppressed primarily through predation by foliar-dwelling predatory mites and to a lesser extent, infection from conidia produced by the granular fungal formulation in the soil. Further investigations into system deployment and fungal granular application rates and new fungal formulations are suggested to improve system efficacy. © 2023 Society of Chemical Industry.

Biological Control of Downy Mildew and Yield Enhancement of Cucumber Plants by Trichoderma harzianum and Bacillus subtilis (Ehrenberg) under Greenhouse Conditions

The downy mildew disease of cucurbits is considered the most economically damaging disease of Cucurbitaceae worldwide. The causal agent, Pseudoperonospora cubensis (Berkeley & Curtis), may cause complete crop losses of cucurbits. Few commercial cucurbit cultivars are resistant to this disease. Commercially, P. cubensis is controlled primarily with synthetic fungicides that inhibit or eliminate the pathogen. Several biological agents have also been identified that provide some level of control. In our study, foliar applications of three strains of Trichoderma harzianum and two native strains of Bacillus subtilis were evaluated for the control of the disease on cucumber plants grown under commercial greenhouse conditions. The study was conducted using a completely randomized design with six individual treatments during two production cycles: fall 2015 and spring 2016. The response variables included disease incidence and severity, plant height, total yield, fruit quality, and weight. B. subtilis provided the best control over the incidence and severity of the disease in both production cycles. Interestingly, while T. harzianum was less effective at controlling the disease, it enhanced plant growth and productivity, and produced a higher number of better-quality fruits per plot. This increased yield with higher quality fruits may result in higher profit for the growers.

The Amount of the Rare Sugar Tagatose on Tomato Leaves Decreases after Spray Application under Greenhouse Conditions.

Tagatose is a rare sugar that suppresses plant diseases, such as late blight of tomato, caused by Phytophthora infestans. Tagatose can be metabolized by some microorganisms and no information is available on its persistence on tomato leaves. The aim of this study was to assess the persistence of tagatose on tomato leaves under commercial greenhouse conditions. The amount of tagatose on tomato leaves and the inhibitory activity against P. infestans decreased seven days after spray application in the absence of rain wash-off. Potential tagatose-degrading bacteria were isolated from tomato leaves, and they belonged to Acinetobacter sp., Bacillus sp., Comamonas sp., Enterobacter sp., Methylobacterium sp., Microbacterium sp., Pantoea sp., Plantibacter sp., Pseudomonas sp., Ralstonia sp., Rhodococcus sp., Sphingobium sp., and Sphingomonas sp. Thus, indigenous phyllosphere microorganisms could partially metabolize tagatose laid on plant leaves after spray application, reducing the persistence of this fungal inhibitor on tomato leaves.

Streptomyces strains can improve the quality properties and antifungal bioactivities of tomato fruits by impacting WRKY70 transcription factor gene and nitrate accumulation

The current study evaluated the effect of plant growth-promoting (PGP) strains of Streptomyces on yield, quality, and nitrate content of fruits, plant-microbe responses, and antifungal effect against blight disease caused by fungus pathogen Alternaria solani on tomato fruits in commercial greenhouse conditions. Greenhouse trials were done with four treatments including strains Y28, IC10, IT25, and commercial bio-fertilizer (Barvar NPK®) on tomato plants. In PGP treatments, the number of infected fruits significantly reduced (60%) compared to Barvar and control. Strain Y28 improved the quality of tomatoes more than other treatments. All three PGP treatments contained a higher level of total sugar concentration and antioxidant enzyme activities than Barvar and control. In contrast, PGP strains, especially Y28, significantly reduced nitrate accumulation (25%) compared to Barvar and control tomatoes. Streptomyces treatments induced more than a 20-fold increase in UDP and WRKY70 transcription factor gene expression relative to the control (P < 0.01). Based on the results, microbe-dependent plant defense induced by these strains is positively correlated to WRKY70 expression and nitrate reduction in commercial greenhouse conditions. These findings suggest that the commercial application of specific strains not only can illustrate an eco-friendly solution to induce resistance against fungal pathogens but also improve the quality properties of food plants with lower nitrate content.

Streptomyces consortium improved quality attributes of bell pepper fruits, induced plant defense priming, and changed microbial communities of rhizosphere under commercial greenhouse conditions

Although many studies have shown the positive effect of PGPRs on the yield and quality characteristics of crops, only a few are successful in commercial greenhouses. This study aimed to evaluate the efficiency of PGP-Streptomyces in commercial greenhouse conditions. Greenhouse trials were done with four treatments including strains SS12, Y17, an effective combination of strains SS14 and IT20, and a commercially available bio-fertilizer (Barvar NPK®) on two cultivars of bell pepper. Treatment with strain SS12 improved the yield of green (26%) and orange (5%) bell pepper compared to the control while SS14 + IT20 increased only the yield of green pepper (23%). The score value of overall acceptance obtained from the sensory evaluation of orange bell peppers treated with SS14+ IT20 was the highest, following the higher score values of quality properties including appearance, flavor, smell, and juiciness. Treatments of Barvar and SS14+ IT20 reduced the nitrate content of both cultivars by about 32–41% and based on the analysis of variances, SS14+ IT20 was more effective than Barvar. Lower concentrations of fruit sugar without affecting its acceptance and higher levels of micronutrients Ca, Zn, and Fe indicate the higher nutritional value of SS14+ IT20 -treated peppers. Increased expression of defense genes ERF and PR1 and higher activity of antioxidant enzymes in SS14+ IT20 and Barvar showed that treated plants are ready to deal with possible pathogens that cause damage in commercial greenhouses. The results of this study showed for the first time that PGP-Streptomyces can be effective in commercial bell pepper greenhouses.

Isolation and identification of Amycolatopsis sp. strain 1119 with potential to improve cucumber fruit yield and induce plant defense responses in commercial greenhouse

The application of chemical fungicides is the first strategy to control plant fungal diseases. This approach is highly polluting for the environment and affects human health. The artificial introduction of beneficial rhizobacteria into the soil can be an economical and practical way to control phytopathogenic fungi in commercial greenhouses. Here, we recount the travel of a rare Actinomycete (Amycolatopsis strain 1119) from a maize field to a commercial cucumber greenhouse. Culturable bacteria from rhizosphere and bulk soils of dicot and monocot crops were isolated and screened. About 20% of the representative colonies showed Actinobacteria appearance. 106 Actinobacteria that had antagonistic activity against Phytophthora capsici and were able to produce IAA-like molecules were selected for further analysis. Two Streptomyces strains (432 and 615) and 2 Amycolatopsis strains (3513 and 1119) that showed a positive effect on plant growth in greenhouse conditions were selected to evaluate the biocontrol potential. Strains 432, 3513, 615 and 1119 controlled incidence of the damping-off by 65%, 42%, 83% and 100% respectively. Application of strain 1119 under commercial greenhouse conditions resulted in an increase in fruit yield (20%) and a decrease in fruit nitrate content (70%). Increased antioxidant enzymes activity and increased LOX and APX transcription and also, increased expression of two genes PR1-1a and GLU (SAR genes) showed that strain 1119 could induce both ISR and SAR in cucumber without pathogen exposure. Our results demonstrate that the Amycolatopsis strain 1119 has a great potential to be used as an active principle for bio-inoculant development because of the ability to improve cucumber fruit yield and induce plant defense responses in a commercial greenhouse.

Several Pythium species cause crown and root rot on cannabis (Cannabis sativa L., marijuana) plants grown under commercial greenhouse conditions

Cannabis (Cannabis sativa L., marijuana) plants with symptoms of crown rot, root decay, wilting and plant death were sampled during 2018 and 2019 from seven production greenhouses. Affected tissues from 140 diseased plants were surface-sterilized and plated onto potato dextrose agar. Ninety-five isolates morphologically resembling Pythium species were subcultured and subjected to PCR of the ITS1-5.8-ITS2 region of ribosomal DNA. The following species were identified based on >99% sequence identity to reference isolates in GenBank: P. myriotylum (43 isolates), P. dissotocum (35 isolates), P. aphanidermatum (3 isolates) and Globisporangium ultimum (syn. P. ultimum) (2 isolates). A fifth species – P. catenulatum (12 isolates), was distinguished from P. rhizo-oryzae using the cytochrome oxidase c subunit I (COI) sequence. Cannabis licensed production facilities in British Columbia had all five species present, while P. dissotocum was found in two facilities in Ontario, and P. myriotylum was present in one facility in northern California. Isolates selected to represent each Pythium species were grown on potato dextrose agar at 25 oC and they all showed comparable colony growth after 6 days. The same isolates caused root browning, decay and stunting of cannabis plants grown in a coco: perlite potting medium. Plant mortality was similar after 21 days but rates of disease progression varied depending on the isolate tested. Wounding of roots and prolonged periods of saturation enhanced disease development. These results demonstrate for the first time that crown and root rot on greenhouse grown cannabis plants can be caused by up to five Pythium species.

Effects of Calcium, Magnesium and Potassium on Sweet Basil Downy Mildew (Peronospora belbahrii)

Downy mildew (Peronospora belbahrii) is a major disease of sweet basil (Ocimum basilicum). We examined the effects of potassium, calcium and magnesium, individually and in combination, on sweet basil downy mildew (SBDM) in potted plants and under commercial-greenhouse conditions over six growing seasons. An increased K concentration in the fertigation solution increased SBDM severity, whereas foliar-applied KCl and K2SO4 suppressed SBDM. The application of higher concentrations of those salts increased the K concentrations in the shoots and significantly alleviated SBDM. Increased concentrations of Ca or Mg in the fertigation solution decreased SBDM severity, as did foliar-applied CaCl2. However, the combination of Ca and Mg did not have any synergistic effect. Foliar-applied K2SO4 provided better disease suppression than some of these treatments. The 3.3 mM Mg + fungicide treatment and the 5.0 mM Mg + fungicide treatment each provided synergistic disease control in one of two experiments. SBDM severity was significantly reduced by MgCl2 and MgSO4 (both 3.3 mM Mg), as compared with the basic Mg fertigation (1.6 mM), with MgCl2 providing better control. The combined Mg salts + fungicide treatments reduced SBDM better than any of those treatments alone. These results demonstrate that macro-elements can contribute to SBDM control.

Plant exposure to herbivore-induced plant volatiles: a sustainable approach through eliciting plant defenses

Modern agricultural policies across the globe are committed to a significant reduction in chemical pesticide dependency; however, pest management strategies are still based on the use of synthetic pesticides. There is an urgent need to find new, sustainable and biorational tools for pest management programs. Plants communicate with each other and activate defense mechanisms against pests using herbivore-induced plant volatiles (HIPVs). The use of such HIPVs could be an ecologically sustainable alternative. However, as of now, there have been no comprehensive studies on HIPVs, from selection to practical use in industry production. Here, we describe the first case of an HIPV successfully implemented for pest control under commercial greenhouse conditions. In this research, tomato plants induced with (Z)-3-hexenyl propanoate [(Z)-3-HP] were less susceptible to the attack of economically important tomato pests. We designed and calibrated polymeric dispensers for the constant release of (Z)-3-HP. These dispensers maintained commercial tomato plant defenses activated for more than two months reducing herbivore pest damage without reducing plant productivity. Transcriptomic and metabolomic analyses of plants induced with (Z)-3-HP confirmed that genes involved in specialized anti-herbivore defense were up-regulated, resulting in an increased production of fatty acid-derived compounds, activation of the lipoxygenase pathway and accumulation of specific defense compounds. Our work demonstrates under commercial greenhouse conditions how the release of HIPVs as elicitors of plant defenses via designed polymeric dispensers can be successfully integrated as a new biorational and sustainable tool for pest control.

Pseudomonas putida P3-57 induces cucumber (Cucumis sativus L.) defense responses and improves fruit quality characteristics under commercial greenhouse conditions

The possibility of chemical fertilizer residues in cucumber has raised concerns about the consumption of this beneficial fruit. Although very good studies have been reported on the effect of growth-promoting bacteria on increasing the health of cucumber plants, their performance in commercial greenhouse conditions has been less studied. A two-year study was conducted to evaluate the effect of P. putida strain P3-57 with 100 % or 70 % of the recommended amount of NPK fertilizers on cucumber fruit yield and quality compared to Barvar NPK® commercial biofertilizer under commercial greenhouse conditions. The 30 % reduction in chemical fertilizers reduced yield and overall fruit acceptance score in the sensory evaluation test. Plant treatment with P3-57 or Barvar had no significant effect on yield but when 70 % of chemical fertilizers were used, they increased the quality of cucumber due to the increase in the score of some sensory traits. P3-57-100% had the highest overall acceptance score, which was associated with increased aroma, flavor and fruit juice, and the lowest levels of nitrate, Zn, Mg, Mo, Sr, Ba and Li. Also, the concentration of protein and CAT activity of fruits was higher compared to control-100 % and Barvar-100 %. Evaluation of CAT, APX and POX activity and expression of PR1-1a, GLU, APX, CHIT, LOX and PAL showed that P3-57-100 % and Barvar-100 % stimulate plant immune system through ISR/SAR and SAR pathways respectively. Based on the results of this study, strain P3-57, as a bio-stimulator that increases cucumber quality, has great potential to enter the market.

Role of Trichoderma aggressivum f. europaeum as Plant-Growth Promoter in Horticulture

The main objective of this study was to determine the capacity of Trichoderma aggressivum f. europaeum to promote pepper and tomato seedling growth compared to that of T. saturnisporum, a species recently characterised as a biostimulant. Consequently, in vitro seed germination and seedling growth tests were performed under commercial plant nursery conditions. Additionally, the effects of different doses and a mixture of both species on seedling growth under plant nursery and subsequently under greenhouse conditions were determined. Furthermore, mass production of spores was determined in different substrates, and their siderophore and indole acetic acid production and phosphate (P) solubilisation capacity were also determined. Direct application of Trichoderma aggressivum f. europaeum to seeds in vitro neither increases the percentage of pepper and tomato seed germination nor improves their vigour index. However, substrate irrigation using different doses under commercial plant nursery conditions increases the quality of tomato and pepper seedlings. Tomato roots increased by 66.66% at doses of 106 spores per plant. Applying T. aggressivum f. europaeum or T. saturnisporum under plant nursery conditions added value to seedlings because their growth-promoting effect is maintained under greenhouse conditions up to three months after transplantation. The combined application of the two species had no beneficial effect in relation to that of the control. The present study demonstrates the biostimulant capacity of T. aggressivum f. europaeum in pepper and tomato plants under commercial plant nursery and greenhouse conditions.

The Use of a Tomato Landrace as Rootstock Improves the Response of Commercial Tomato under Water Deficit Conditions

Grafting onto drought tolerant rootstocks has been proposed as a useful strategy to overcome future water scarcity periods. The ‘de Ramellet’ tomato is a drought tolerant landrace selected under semiarid Mediterranean summer conditions under rain-fed or low irrigation. In this manuscript, the responses of a commercial hybrid ‘de Ramellet’ genotype grafted onto a traditional ‘de Ramellet’ (RL) and a commercial Maxifort (Mx) tomato rootstocks under commercial greenhouse conditions are studied. Non-grafted (NON) and self-grafted (SELF) plants were used as controls. Two water regimes were established: well-watered (WW, covering plant water demands) and water deficit (WD, reducing 50% irrigation as compared to WW). The results confirm an improvement in agronomic performance of Mx as compared to NON, but also show a similar improving effect of RL. Grafting enhanced plant growth regardless of the rootstock under WW conditions. Similarly, water-use efficiency (assessed as leaf carbon isotope composition) increased in grafted plants under WD treatment as compared to NON. Despite the lack of significant differences, RL tended to promote higher fruit production and fruit number than Mx, irrespective of the water treatment, whereas RL was the single graft combination with higher fruit production than NON under WD. In conclusion, the results uncover the potential of drought-adapted landraces to be used as rootstocks in order to increase plant growth and fruit production under both well-watered and water deficit cultivation conditions.

Paecilomyces variotii as A Plant-Growth Promoter in Horticulture

In the present study, P. variotii, an endophytic fungus isolated from plant roots from the Cabo de Gata Natural Park (Parque Nacional Cabo de Gata—Spain), was tested to determine the effect on the growth promotion of tomato and pepper seeds and seedlings. For these purposes, germination trials in a laboratory and two experiments in a commercial nursery and greenhouse conditions were performed. The P. variotii isolate has shown a high ability to produce siderophores and IAA, but low ability to solubilize P. High values for germination percentage, seedling vigor, root and shoot length were obtained by P. variotii on tomato and pepper against control. P. variotii applications resulted in improved most of the growth parameters evaluated, for both horticultural crops, with the best results in the development of pepper seedlings. The application of a higher dose of P. variotii improved most of the morphological parameters and the Dickson quality index (DQI) value in tomato in seedlings and plants. The establishment of the endophytic fungus at the root enabled its biostimulant effects to persist after transplantation without any additional application. Few studies have analyzed this species as a biostimulant. The positive results from the tests showed its high potential. The application of this isolate can be of enormous benefit to horticultural crops for its high reproductive and establishment capacity.

Biological control of symphylid pests in a commercial chrysanthemum (Dendranthema grandiflora) crop using the fungus Purpureocillium lilacinum, strain UdeA0106

The symphylids, also known as garden centipedes or pseudocentipedes, are soil-dwelling arthropods of the class Symphyla. They affect diverse crops worldwide due to the consumption of young roots and seedlings. This study presents the effectiveness of the fungus Purpureocillium lilacinum (strain UdeA0106) to reduce the symphylid population under commercial greenhouse conditions. The results showed that this fungus strain could reduce symphylid density by 70.6%. It also demonstrated that a high concentration of strain UdeA0106 helped to recover chrysanthemum (Dendranthema grandifIora) crops infested with symphylid. The results shown in this paper are the first evidence of effective biological control of symphylids pest in a commercial fIower plantation, representing the potential of P. lilacinum strain UdeA0106 as a biological control agent.

Efficacy of a Lebanese isolate of Beauveria sp. for the biocontrol of Bemisia tabaci

The sweetpotato/cotton whitefly, Bemisia tabaci(Gennadius) is a major pest of several crops worldwide. In addition to the direct damage induced, it has the ability to transmit some of the most dangerous plant viruses rendering it a very critical pest.The development of whitefly resistance to several groups of pesticides forced farmers and researchers to adopt integrated pest management strategies and to look for alternative control measures. Studies using molecular markersshowed the coexistence in Lebanon oftwo species, the “Middle East-Asia Minor 1 species” also known as biotype B and the “Mediterranean species”also known as biotype Q. In greenhouse trials, the Beauveriapseudobassianaisolated in Lebanon wasfound to be quite efficient for themanagement ofB. tabaci. Sprays containing spore suspensions of 107spores/mL caused around75% mortality of the early growth stages: egg, crawler,second and third instar larvae. The addition of a surfactant such as corn oil improved the mortality level thatreached 98% in the egg /crawler stage and 84% in the second and third instar larvae at a spore concentration as low as 105conidia/mL. In view of the promising results, further medium size trials under commercial greenhouse conditions are planned.