Application Of Biocontrol Agents Research Articles

Weapons hidden underneath: bio-control agents and their potentials to activate plant induced systemic resistance in controlling crop Fusarium diseases

Fusarium is a genus among the major pathogens affecting cereals production worldwide. At present, the control of Fusarium diseases in farm largely relies on the use of chemical fungicides, which are persistent in environments and harmful to human health. To reduce the risk of using chemical compounds, it becomes urgent to find an alternative strategy, such as bio-agents to control Fusarium diseases. Beneficial microorganisms underground have been well known for their activity to trigger induced systemic resistance (ISR) against pathogens, existing either in the soil or aboveground. Despite numerous studies suggesting various beneficial microorganisms, also recognized as bio-control agents (BCAs), including Bacillus spp., Trichodema spp., Pseudomomas spp. and others, as capable of suppressing diverse crop diseases, the function and mechanisms underlying ISR triggered by these beneficial microbes in controlling Fusarium diseases remain to be systemically understood. In this review, we summarize the roles of diverse beneficial microbes in limiting crop Fusarium diseases and also discuss the possible involvement of ISR with associated signaling pathways employed in Fusarium disease control. Finally, we consider the practical application of diverse BCAs with ISR activity for ecological and sustainable crop production.

Trichoderma dan Gliocladium untuk Mengendalikan Penyakit Busuk Akar Fusarium pada Bibit Kelapa Sawit

Trichoderma and Gliocladium for Controling Fusarium Root Rot Disease of Oil Palm SeedlingsFusarium spp. have been reported as the causal agent of common spear rot and crown rot diseases on oil palm. An effective strategy to control these diseases is not available yet. This research was aimed to find biocontrol agents for effective control of crown rot disease on oil palm seedlings caused by Fusarium spp. The experiment consisted of 3 parts i.e. pathogenicity test of 3 isolates of Fusarium, identification and in vitro test of biocontrol agents, and in planta test of biocontrol agents against Fusarium spp. In vitro test was done through dual culture test and test for volatile compound produced by the biocontrol agents. In planta test was conducted through inoculation of Fusarium spp. into oil palm seedlings growing on medium containing selected biocontrol agents i.e. Trichoderma harzianum, T. virens, T. inhamatum, and Gliocladium fimbriatum. In vitro test showed that Gliocladium fimbriatum 1 and 2 were inhibited effectively the growth of Fusarium spp. on the dual culture test, whereas T. harzianum Gadingrejo 2 was inhibited effectively the growth of Fusarium spp. on volatile compound test. The application of biocontrol agents was effective to protect oil palm seedlings from Fusarium spp. infection.

Compatibility interactions between the biocontrol agent Penicillium frequentans Pf909 and other existing strategies to brown rot control

BackgroundTo improve efficacies achieved through biocontrol agent application, there has been increasing interest in studying the efficacy of biocontrol agent with other existing technologies like chemicals or different biocontrol agent combinations. The compatibility of Penicillium frequentans (Pf909) with modern inputs in plant protection like fungicides (chemicals and biologicals) and insecticides is a pre-requisite for developing integrated brown rot management strategies. ResultsThe combination of P. frequentans and Bacillus amyloliquefaciens, each with different mechanisms of action, competition and antibiosis, respectively, did not improve the biocontrol of brown rot when each treatment was applied individually. P. frequentans and B. amyloliquefaciens could not be combined together in the same tank, because bacteria inhibited the germination and growth of P. frequentans tubes in suspension. Furthermore, B. amyloliquefaciens also competes with P. frequentans once applied on fruit surfaces. Additionally, bacteria reduced the growth of P. frequentans CFUs on media, at different 25 °C and 30 °C throughout the incubation periods. However, 76% of fungicides and 90% of insecticides commonly used against stone fruit pests are compatible with P. frequentans. ConclusionsResults indicated that the most commercial chemical pesticides could be simultaneously applied with Pf909 in integrated pest control, but not B. amyloliquefaciens.

Supplementing biocontrol agents with botanicals improved growth and yield of coriander (Coriandrum sativum L.) infected with Protomyces macrosporus Unger

This investigation was carried out to examine the effect of some biocontrol agents (Trichoderma viride, T. harzianum, Azotobacter chroococcum, Pseudomonas putida) and botanicals (Melia azedarach, Eucalyptus globulus, Calotropis procera) both alone and in combination on growth, yield and stem gall disease of coriander (Coriandrum sativum L.) caused by Protomyces macrosporus Unger in a pot experiment. Plants inoculated with P. macrosporus caused significant reduction in growth and yield attributes as compared to untreated control. Stem gall intensity was recorded 59% in plants treated with pathogen alone. The results revealed that, application of biocontrol agents / botanicals both alone and in combination caused significant reduction in stem gall intensity (20.33–84.82%) as compared to control. Among the tested biocontrol agents, T. viride was found superior in enhancing the growth and yield as well as reduction in stem gall intensity (44.37%). Application of biocontrol agents in soil supplemented with botanicals was found more beneficial in enhancing plant growth and yield attributes as well as reducing stem gall intensity (52.54–84.82%). Among various combinations tested T. viride + Melia azedarach and T. viride + E. globulus caused greater increase in plant growth and yield characters both in pathogen inoculated as well as uninoculated plants.

Expression of defense-related genes in mung bean varieties in response to Trichoderma virens alone and in the presence of Rhizoctonia solani infection.

Web blight/wet root rot caused by Rhizoctonia solani is one of the major constraints for mung bean (Vigna radiata) production. Growing of resistant varieties and use of biocontrol agents are the feasible options available to manage the disease. The present study was conducted to determine the variation in the expression of various defense-related genes in susceptible and resistant mung bean varieties in response to biocontrol agent Trichoderma virens and R. solani interactions. The primers were designed using sequences of defense-related genes, namely PR 10, epoxide hydrolase (EH), catalase and calmodulin available in NCBI database and evaluated against cDNA obtained from both susceptible and resistant mung bean plants at 1-4days post-inoculation (dpi) with the test pathogen R. solani and biocontrol agent T. virens using conventional PCR and qPCR analyses. R. solani inoculation upregulated the mean expression of PR 10 and calmodulin in susceptible and resistant varieties, respectively, whereas downregulated in the rest of the treatments. Quantitative PCR analysis showed that except catalase in the susceptible variety, which is downregulated, the expression of PR 10, EH, catalase and calmodulin was upregulated in both resistant and susceptible varieties in response to T. virens alone and in the presence of R. solani. In general, the expression of PR 10 and calmodulin was highest at 1dpi whereas EH and catalase expression were maximum at 4dpi. The application of T. virens suppressed the development of disease in the presence of R. solani in both susceptible and resistant varieties with more pronounced effect in resistant variety. Thus, the application of biocontrol agent T. virens upregulated the expression of defense-related genes and reduced disease development.

Effect of increased CO2 and temperature on plant diseases: a critical appraisal of results obtained in studies carried out under controlled environment facilities

Increases in carbon dioxide (CO2) and temperature are expected to induce complex effects on plant pathogens. The results of studies on the effects of climate change on a number of pathosystems, such as the downy and powdery mildew of grapevines, and on several pathogens of vegetable crops, such as rocket, basil, beet and zucchini, have been analysed in this review. In the reviewed works, plants were grown in controlled environment facilities (phytotrons) under six different simulated climatic conditions: a standard CO2 concentration (400–450 ppm) with a standard (ranging from 18 to 22/24 °C) and elevated temperature (5 °C higher than standard), and elevated CO2 (800–850 ppm) under a standard and elevated temperature. When the CO2 level and the temperature were increased, an increase was observed of powdery mildew on zucchini, Alternaria leaf spot on rocket salad, black spot and downy mildew on basil, Allophoma tropica on lettuce and Phoma leaf spot on garden beet. Variable effects were instead observed when individual climate parameters were taken into consideration. The effects of changed environmental values on some physiological parameters on the production of mycotoxins as well as on disease management were also considered on selected pathosystems. CO2 concentration and temperature proved to influence disease severity and mycotoxin production in different ways. As far as the application of biocontrol agents is concerned, the efficacy of Ampelomyces quisqualis against zucchini powdery mildew was found to be improved under higher temperature and CO2 conditions. The results obtained with different host/pathogen combinations will allow to develop adaptation strategies for disease management and to provide the seed industry with useful information in order to develop new cultivars that will be more adapted/adaptable to the changing conditions. The usefulness and limitations of studies carried out under controlled environment conditions are critically discussed.

A Ready-to-Use Single- and Duplex-TaqMan-qPCR Assay to Detect and Quantify the Biocontrol Agents Trichoderma asperellum and Trichoderma gamsii.

Trichoderma asperellum strain icc012 and Trichoderma gamsii strain icc080, the microbial active ingredients of RemedierTM (ISAGRO, Novara, Italy), are biocontrol agents (BCAs) employable for crop protection against a wide range of fungal pathogens, including soil-borne pathogens and fungi involved in grapevine trunk disease. In this study, single and duplex real-time quantitative PCR (qPCR) methods to detect and quantify T. asperellum and T. gamsii were developed. Primers/probe sets were designed on the T. asperellum and T. gamsii rpb2 genes and tested for specificity on a panel of microorganisms commonly associated with grape wood and soil. No differences were observed comparing single- and duplex-qPCR assays on different BCAs, 1 pg of target DNA was detected approximately at Cq = 34. R2-values and the efficiency were always equal to 0.99 and >80%, respectively. The detection limit of the duplex-qPCR assay on artificially inoculated samples was 2 × 103 and 4 × 104 conidia g-1 of grape wood tissue and soil, respectively. The methods will be useful to better schedule BCA application in the field and in grapevine nurseries, as well as for investigating the dynamic of BCA populations.

Assessing synergism of combined applications of Trichoderma harzianum and Pseudomonas fluorescens to control blast and bacterial leaf blight of rice

Combined application of biocontrol agents (BCAs) have been used to exploit their synergistic potential. But the analysis of additive, synergistic and antagonistic effects of BCAs has rarely been explored for the biocontrol of plant diseases. This study was conducted to evaluate in vitro and in vivo biocontrol potential of the combined application of Trichoderma harzianum strain Th3 and Pseudomonas fluorescens strain RRb11, and the fungicide carbendazim against the rice blast (RB) pathogen, Magnaporthe oryzae, and the bacterial leaf blight (BLB) pathogen, Xanthomonas oryzae pv. oryzae. Combined application of T. harzianum Th3 and P. fluorescens RRb11 synergistically reduced severity of RB by 69.5% in comparison to the untreated control, displaying a synergy factor (SF) of 1.29. P. fluorescens RRb 11 alone and in combination with T. harzianum Th3 and the mixture of T. harzianum Th3 + carbendazim was antagonistic (SF = 0.71 and 0.45, respectively). The combined application of T. harzianum Th3 and P. fluorescens RRb 11 also enhanced several rice plant growth and yield parameters. Additive, synergistic or antagonistic effects among the two BCAs were assessed by applying the numerical hypothesis of ‘Bliss Independence’ which suggested that the combined application of the two BCAs was synergistic in reducing RB but antagonistic with respect to BLB. Out of the six combined application interactions for both the diseases only one interaction (T. harzianum Th3 and P. fluorescens RRb11) was synergistic against RB, which suggested that synergism is a rare event in combined use of BCAs.

Effect of prey and pollen on interactions between Typhlodromus bagdasarjani and Phytoseiulus persimilis (Acari: Phytoseiidae) on cucumber (Cucurbitaceae)

AbstractIntraguild predation is a notable factor to proper application of biocontrol agents to reduce pest populations. Intraguild predation was studied between Typhlodromus bagdasarjani Wainstein and Arutunjan (Acari: Phytoseiidae) and Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) in presence and absence of Tetranychus urticae Koch (Acari: Tetranychidae) as well as pollen. Intraguild predation between two predators was bidirectional. The highest and the lowest predation rates of both predators in absence and presence of T. urticae as well as in the pollen treatments were on heterospecific eggs and deutonymphs, respectively. Typhlodromus bagdasarjani consumed more heterospecific eggs compared with P. persimilis. When pollen was added, predation of T. bagdasarjani significantly reduced on heterospecific eggs and deutonymphs in absence and presence of T. urticae treatments, respectively. However, predation rate of P. persimilis on heterospecific stages was not significantly affected by pollen addition. Oviposition of both predators was higher in presence of T. urticae than in its absence and oviposition of P. persimilis was significantly higher on heterospecific stages than T. bagdasarjani. Pollen addition had a significant effect on increasing the oviposition rate of T. bagdasarjani. Extraguild prey presence had a nonsignificant effect on the consumption rate of intraguild prey by the intraguild predators. However, presence of extraguild prey led to a significant increase in oviposition rate of both predators.

Streptomyces globosus UAE1, a Potential Effective Biocontrol Agent for Black Scorch Disease in Date Palm Plantations.

Many fungal diseases affect date palm causing considerable losses in date production worldwide. We found that the fungicide Cidely® Top inhibited the mycelial growth of the soil-borne pathogenic fungus Thielaviopsis punctulata, the causal agent of black scorch disease of date palm, both in vitro and in vivo. Because the use of biocontrol agents (BCAs) can minimize the impact of pathogen control on economic and environmental concerns related to chemical control, we aimed at testing local actinomycete strains isolated from the rhizosphere soil of healthy date palm cultivated in the United Arab Emirates (UAE) against T. punctulata. The selected isolate can thus be used as a potential agent for integrated disease management programs. In general, the BCA showed antagonism in vitro and in greenhouse experiments against this pathogen. The most promising actinomycete isolate screened showed the highest efficacy against the black scorch disease when applied before or at the same time of inoculation with T. punctulata, compared with BCA or fungicide application after inoculation. The nucleotide sequence and phylogenetic analyses using the 16S ribosomal RNA gene with other Streptomyces spp. in addition to morphological and cultural characteristics revealed that the isolated UAE strain belongs to Streptomyces globosus UAE1. The antagonistic activity of S. globosus against T. punctulata, was associated with the production by this strain of diffusible antifungal metabolites i.e., metabolites that can inhibit mycelial growth of the pathogen. This was evident in the responses of the vegetative growth of pure cultures of the pathogen when exposed to the culture filtrates of the BCA. Altogether, the pathogenicity tests, disease severity indices and mode of action tests confirmed that the BCA was not only capable of suppressing black scorch disease symptoms, but also could prevent the spread of the pathogen, as a potential practical method to improve disease management in the palm plantations. This is the first report of an actinomycete, naturally occurring in the UAE with the potential for use as a BCA in the management of the black scorch disease of date palms in the region.

Photochemistry of Luffa cylindrica (L.) Roem under fungal biocontrol interaction

The aim of this study was to evaluate the photochemistry of Luffa cylindrica (L.) Roem in fungal biocontrol interacting treatments. Healthy plants were infected with Pythium aphanidermatum before the biocontrol application. Biocontrol agents were selected in preliminary Petri-plate experiment evaluation against causative agent P. aphanidermatum. Photosynthetic performance traits were studied. We found that P. aphanidermatum infection caused significant reduction in photosynthetic performance, pigments, and in maximum quantum yield of primary photochemistry, photochemical quenching, and electron transport rate with increase in nonphotochemical quenching as compared with non-infected control. However, application of biocontrol agents substantially improved maximum quantum yield of PSII, performance index, and total content of photosynthetic pigments in infected plants. The fluorescence intensity was used for quantifying the antagonist effect of biocontrol agents on infected plant leaves.

Comparison of Prokaryotic and Eukaryotic Communities in Soil Samples with and without Tomato Bacterial Wilt Collected from Different Fields.

Biocontrol agents (BCA) effectively suppress soil-borne disease symptoms using natural antagonistic prokaryotes or eukaryotes. The main issue associated with the application of BCA is that disease reduction effects are unstable under different field conditions. In order to identify potentially effective BCA among several fields, we compared prokaryotic and eukaryotic communities in soil with and without tomato bacterial wilt from three different fields, each of which had the same field management and similar soil characteristics. Soil samples were collected from three fields and two depths because bacterial wilt pathogens were present in soil at a depth greater than 40 cm. We classified soil samples based on the presence or absence of the bacterial phcA gene, a key gene for bacterial wilt pathogenicity and tomato disease symptoms. Pyrosequencing of the prokaryotic 16S rRNA gene and eukaryotic internal transcribed spacer region sequences showed that the diversity and richness of the communities mostly did not correlate with disease symptoms. Prokaryotic and eukaryotic community structures were affected more by regional differences than the appearance of disease. Several prokaryotes and eukaryotes were more abundant in soil that lacked disease symptoms, and eight prokaryotes and one eukaryote of this group were commonly detected among the three fields. Some of these taxa were not previously found in disease-suppressive soil. Our results suggest that several prokaryotes and eukaryotes control plant disease symptoms.

Status of maize stalk rot complex in western belts of Nepal and its integrated management

Maize stalk rot complex is becoming a serious threat for maize growing areas of Nepal. A field monitoring for maize stalk rot complex was done during crop season (August, 2016) covering 10 farmers field each of Surkhet, Banke, Dang, Chitwan and Nawalparasi districts. Maize crop showed highly susceptible reaction to the disease at western belts of Dang and susceptible reaction was marked in Chitwan and Nawalparasi districts while the disease effect was mild at Banke and Surkhet district. Most of the plant diseases managed successfully through the application of bio-control agents, host resistance, chemicals and other different cultural control methods. The result of field experiment conducted at Dang showed that all the treatments had significant (P≤0.05) effect on percent disease index (PDI) and crop yield over farmers practice to control maize stalk rot. The higher percent disease control (52.36%) and yield increase (40.29%) were recorded from the plot sprayed with streptocyclin @ 2 g L-1 and insecticide (cypermethrin + chloropyrifos @ 2.5 ml L-1 of water during knee height and subsequent spray after 15 days interval as compared to farmers practice. Out of 30 genotypes, Rampur composit, Arun 2, Rampur 34, RamS03F08, TLBRS07F16 and Rampur 24 were found resistant against stalk rot complex with higher yield at Rampur Chitwan.

English

The novel technologies in all areas of agriculture have improved agricultural production, but some modern practices affect the environment. The recent challenge faced by advanced farming is to achieve higher yields in environment-friendly manner. Thus, there is an immediate need to find eco-friendly solutions such as wider application of biocontrol agents. Among various types of species being used as biocontrol agents, including fungi and bacteria, fungal genus Trichoderma produces different kinds of enzymes which play a major role in biocontrol activity like degradation of cell wall, tolerance to biotic or abiotic stresses, hyphal growth etc. The understanding of filamentous fungi belonging to the genus Trichoderma has continuously evolved since last two decades, from the simple concepts of biocontrol agents to their recently established role as symbionts with different beneficial effects to the plants. Recent findings from structural and functional genomics approaches suggest the additional use of these microbes as model to study mechanisms involved in multiple player interactions that is, microbes-microbes-plant-environment. In this work, historical development of Trichoderma spp., mode of action against different biological agents, potential applications and recent mass production techniques are summarized and discussed in detail with updated advances with their application in the agriculture and sustainable environment. Key words: Biocontrol agent, mycoparasitism, induced resistance, endophyte, mass production, bioremediation, bioreactors, agrochemicals

Biological control of Phomopsis leaf blight of brinjal (Solanum melongena L.) with combining phylloplane and rhizosphere colonizing beneficial bacteria

Beneficial phylloplane colonizing bacteria (PCB) and rhizosphere colonizing bacteria (RCB) were evaluated individually and in combinations for plant growth promotion and control of Phomopsis leaf blight of brinjal (Solanum melongena L.). Bacteria from the leaf surface of brinjal plants were isolated and screened, and four PCBs were selected based on their ability to colonize phylloplane and inhibit the growth of Phomopsis vexans. All PCB and RCB strains were characterized for their beneficial traits and their leaf and root colonizing ability were confirmed through SEM. Under greenhouse conditions, individual applications such as seed treatment with Pseudomonas putida Has-1/c (RCB) and foliar application of Bacillus subtilis Br/ph-33 (PCB) significantly increased the plant growth and leaf surface area, respectively. Among 16 combinations of PCB and RCB tested, seed treatment with Pseudomonas fluorescens 2apa-pf followed by foliar application of B. subtilis Br/ph-33 significantly increased root length (6.3cm) and shoot length (23.2cm), fresh weight (2.51g) and dry weight (0.373g) of seedling. Individual application of PCB strains recorded significant decrease in disease incidence and severity over control. Among various combinations tested, Has-1/c+Br/ph-11 significantly reduced the disease incidence (18.0%) and severity (0.54) in comparison with distilled water treated control (91% and 6.0). The results suggested that combined application of biocontrol agents is more efficient in improving plant growth and controlling the disease over their individual application. The research findings could be beneficial in replacing agrochemicals in brinjal cultivation and also promising in suppressing leaf blight disease caused by P. vexans in brinjal.

The effect of locust bean gum (LBG)-based edible coatings carrying biocontrol yeasts against Penicillium digitatum and Penicillium italicum causal agents of postharvest decay of mandarin fruit

Strains belonging to Wickerhamomyces anomalus, Metschnikowia pulcherrima and Aureobasidium pullulans species were tested in vitro as biocontrol agents (BCAs) against the post-harvest pathogenic molds Penicillium digitatum and Penicillium italicum. Moreover, studies aimed at screening the antifungal activity of selected yeast strains in vivo conditions against P. digitatum and P. italicum, and investigated the efficacy of a polysaccharidic matrix, locust bean gum (LBG), enriched with the tested BCAs, in controlling postharvest decays in artificially inoculated mandarins. The population dynamics of BCAs on wounds and the magnitude of peroxidase (POD) and superoxide dismutase (SOD) in fruit tissues were also investigated after treatments of mandarins with antagonistic yeasts.W. anomalus BS91, M. pulcherrima MPR3 and A. pullulans PI1 provided excellent control of postharvest decays caused by P. digitatum and P. italicum on mandarins, both when the yeasts were used alone and in combination with LBG, which enhanced the yeast cell viability over time.Finally, the increased activity of POD and lower decrease in SOD activity in response to BCAs application in mandarin fruits confirmed their involvement in the biocontrol mechanism.

Identification and application of biocontrol agents against Cotton leaf curl virus disease in Gossypium hirsutum under greenhouse conditions

ABSTRACTBiological control is a novel approach in crop protection. Bacteria, such as Bacillus spp. and Pseudomonas spp., are reported for this purpose and some of their products are already commercially available. In this study, the rhizosphere and phyllosphere of healthy cotton plants were used as a source of bacterial isolates with properties of potential biocontrol agents. The isolates were screened for phosphate solubilization activity, indole acetic acid (IAA) production and antifungal activity. Two isolates, S1HL3 and S1HL4, showed phosphate solubilization and IAA production simultaneously, while another two, JS2HR4 and JS3HR2, demonstrated potential to inhibit fungal pathogens. These bacteria were identified as Pseudomonas aeruginosa (S1HL3), Burkholderia sp. (S1HL4) and Bacillus sp. (JS2HR4 and JS3HR2) based on biochemical and molecular characteristics. The isolates were tested against Cotton leaf curl virus (CLCuV) in greenhouse conditions, both as individual bacterial isolates and consortia. Treated plants were healthy as compared to control plants, where up to 74% of the plants were symptomatic for CLCuV infection. Maximum inhibition of CLCuV was observed in the plants treated with a mixture of bacterial isolates: the viral load in the treated plants was only 0.4% vs. up to 74% in controls. This treatment consortium included P. aeruginosa S1HL3, Burkholderia sp. S1HL4 and Bacillus spp. isolates, JS2HR4 and JS3HR2. The principal-component biplot showed a highly significant correlation between the viral load percentage and the disease incidence.

Bioefficacy of Bacillus subtilis against root knot nematode Meloidogyne incognita (Kofoid and White) Chitwood in tomato

An investigation was conducted for the management of root knot nematode Meloidogyne incognita (Kofoid and White) Chitwood infesting tomato through the application of bio-control agent like Bacillus subtilis, Trichoderma harzianum and Pseudomonas fluorescens. Experiment result revealed that minimum no. of galls/25seedlings (17.50) and maximum seedling height (27.6cm) were observed in Bacillus subtilis @50g/m2 in nursery bed + B. subtilis @ 5kg along with 2.5 tons of FYM/ ha. The highest weight/25seedlings (69.50g) was noticed in the B. subtilis @50g/m2 in nursery bed + B. subtilis 2.5kg along with 2.5 tons of FYM/ha. The highest growth of the plant at 45 DAT (49.2cm) and at harvest (81.2cm) and maximum fresh (711.3g) and dry weight (265g) was found in B. subtilis @50g/m2 in nursery bed + B. subtilis 2.5kg along with 2.5 tons of FYM/ha. B. subtilis @50g/m2 in nursery bed + B. subtilis 2.5kg along with 2.5 tons of FYM/ha exhibited lowest gall index (1.2/plant) and highest reduction of nematode population and provided highest yield of tomato fruits (335.75q/ha).

Hot-spot application of biocontrol agents to replace pesticides in large scale commercial rose farms in Kenya

Rose (Rosa hybrida L.) is the most important ornamental crop in Kenya, with huge investments in pest management. We provide the first full-scale, replicated experiment comparing cost and yield of conventional two-spotted spider mite (Tetranychus urticae Koch) control with hot-spot applications of the predatory mite Phytoseiulus persimilis (Acari: Phytoseidae) in large commercial rose greenhouses. Hot-spot treatments replaced acaricides except at high infestations and the two treatments were applied in seven greenhouses each. With the conventional treatment, acaricides were applied when T. urticae populations exceeded 250 motile individuals per plant based on scouting. Treatments with acaricides and P. persimilis were guided by weekly scouting and hot-spot treated greenhouses with infestations exceeding 1000 individuals m−2 (calculated as average mites/leaflet × average leaflets per plant) were first blanket-treated with an acaricide to decrease infestations. Roses subjected to the hot-spot treatment had significantly lower T. urticae infestations compared with conventionally treated roses. In addition, significantly fewer high spider mite infestations were recorded in roses with the hot-spot treatment. The cost of pest management was significantly lower in the hot-spot-treated greenhouses than in the conventional treatment. However, there was no significant difference in the number of harvested stems from the two treatments. It can therefore be concluded that acaricides can be replaced by P. persimilis hot-spot treatments in commercial cut rose production, effectively reducing pest management costs with no loss in crop yield.

Genetic approaches for mitigating losses caused by bacterial wilt of tomato in tropical islands

Bacterial wilt, caused by Ralstonia solanacearum (Smith, US Department of Agriculture, 12, 1–28, 1986) Yabuuchi et al. (Microbiology and Immunology, 39, 897–904, 1995) (formerly Pseudomonas solanacearum), causes 35–90 % yield loss in tomato production in hot-humid tropical regions. Commonly used strategies for minimizing incidence of bacterial wilt include choosing resistant varieties, cocopith based growing media, chemical methods, grafting on resistant rootstocks, application of biocontrol agents and field management practices. The cultivation of resistant varieties is the most appropriate and eco-friendly way to manage the soil borne diseases in crops but the same is not fitting well with bacterial wilt in tomato. In this review, a systematic analysis has been made on reaction of 526 genotypes of tomato to R. solanacearum pathogen tested over a 30 year period in Andaman Islands and identified 37 genotypes as highly resistant (HR), 58 as resistant (R) and 151 as moderate resistant (MR). None of the claimed resistant genotypes exhibited stable and durable resistance against this pathogen and no single genotype reported in HR category (after 2002) except only two genotypes in R category. The period for a genotype to shift from resistance to susceptible is very short because of pathogen evolution hence, it is necessary to constantly develop new resistant varieties in tomato against R. solanacearum. The review also suggests breeding strategies for rapid development of bacterial wilt resistant varieties in tomato in order to minimize the yield losses especially in the tropical conditions.