Plant Disease Incidence Research Articles

Multispectral radiometric monitoring of bacterial blight of coffee

Bacterial blight of coffee caused by Pseudomonas syringae pv. garcae shows great destructive potential in the main coffee producing regions in Brazil and worldwide. Remote sensing technologies can be used as an inexpensive and effective method to identify and monitor the disease. This study evaluated the potential of the Landsat 8 OLI/TIRS multispectral sensor for the spatial and temporal monitoring of coffee (Coffea arabica) affected by the bacterial blight. In a commercial coffee field in Minas Gerais State, Brazil, samples were collected from a grid of 85 points spaced from 35 to 50 m apart. Each sampling point consisted of five plants, being four plants distributed surrounding a central plant. The analyzes of the plant foliage, disease incidence, and disease severity were performed from January to December 2014 and correlated with 15 vegetation indices derived from a time series of 11 multispectral images. The brightness temperature of these images was calculated in order to indicate the area of the field more favorable to the occurrence of the bacterial blight of coffee. Vegetation indices were highly correlated with the incidence (r = 0.76) and severity (r = 0.52) of the disease. The brightness temperature aided in the mapping of areas with optimal temperature conditions for the occurrence of the disease. In general, the study demonstrated the potential of Landsat 8 OLI/TIRS images to identify and monitor crops affected by the bacterial blight of coffee.

Stem inoculation with bacterial strains Bacillus amyloliquefaciens (GB03) and Microbacterium imperiale (MAIIF2a) mitigates Fusarium root rot in cassava

Cassava (Manihot esculenta), a major staple food in the developing world provides a starch-based carbohydrate diet for over half-a-billion people living in the tropics. Despite the plant’s resistance to most local insect pests and bacterial pathogens, cassava is susceptible to root rot caused by Fusarium solani. With the recent identification that the beneficial soil bacterium Bacillus amyloliquefaciens (GB03) increases iron accumulation in cassava, the question arises as to whether plant growth-promoting rhizobacteria (PGPR) also induces plant resistance to fungal infection and in turn, ameliorate cassava disease symptoms. Phytopathological analyses reveal that shoot-propagated cassava, inoculated with Bacillus amyloliquefaciens (GB03) or Microbacterium imperiale (MAIIF2a) induces increased shoot and root growth by over 100% compared to un-inoculated controls. Moreover, PGPR inoculation lowered disease incidence in greenhouse-grown plants by over half compared to media treated controls and reduced mycelial growth and fungal colonization with in vitro cassava-plant assays. These results demonstrate the integrated role beneficial bacteria play to increase plant growth and protect against pathogen infection in a starch crop that is cultivated on a global scale.

Using Support Vector Machines classification to differentiate spectral signatures of potato plants infected with Potato Virus Y

Potato Virus Y (Potyviridae, PVY) has resulted in significant economic harm to potato (Solanum tuberosum) farmers and has disrupted seed supplies to commercial growers, especially in varieties with beneficial processing and marketing attributes but high disease susceptibility such as Russet Burbank and Russet Norkotah varieties. Commercial growers rely entirely on seed producers and certification systems to get disease-free seed as they have no recourse to mitigate seed-borne PVY after the seed is planted. Potato seed stock producers currently utilize intensive pesticide applications to suppress insect vectors and human-resource intensive activities where workers visually inspect and remove suspect infected plants during the growing season. Industry stakeholders also depend upon extensive field and tuber sampling coupled with off-season growouts and laboratory testing to ascertain infection levels within certification programs. Despite these efforts, seed producers and certification agencies are currently unable to control PVY infection in the industry’s seed pipeline, and this has a significant impact on commercial markets and regional economies. The industry also lacks a consistent, scalable, accurate, and robust detection system capable of assessing every plant within the seed potato production agro-ecosystem during the production season. Remote sensing technologies coupled with machine learning classifiers are a significant leap forward in the detection and differentiation of plant disease incidence. The continuing advancement of unmanned aerial systems (UAS) and unmanned ground vehicles provide access to high spatial, temporal, and spectral resolution instrumentation with which to monitor dynamic agricultural production systems at a leaf-scale resolution. In this study, we demonstrate PVY-infected potato plants in an agricultural production field produce different spectral reflectance profiles in comparison to neighboring non-infected plants. The Support Vector Machines (SVM) classifier differentiated spectral reflectance curves of PVY-infected and non-infected plants at an accuracy of 89.8% using near infrared and shortwave infrared wavelengths. The classification accuracy dropped to 46.9% using red, green, and blue wavelengths that the industry currently utilizes to detect diseased plants visually. This research shows that remote sensing and machine learning classifiers outperform current industry standards and have the potential to greatly enhance PVY detection efforts resulting in improved potato seed stock quality necessary to maximize yields.

Biochar chemistry defined by 13C-CPMAS NMR explains opposite effects on soilborne microbes and crop plants

Numerous recent studies have demonstrated that biochar may significantly reduce the incidence of plant diseases caused by airborne and soilborne pathogens, although contrasting results have also been reported. In this work, we investigated how biochar affects crop plant and soilborne microbe growth. Aims of this study were: i) to analyze the chemical changes occurring in four organic feedstocks (e.g. wood chips, organic urban waste, Zea mays residues, and Medicago sativa hay) when pyrolyzed at 300 °C and 550 °C by using 13C NMR spectroscopy and SEM (Scanning Electron Microscopy); ii) to assess how biochar affects growth of five bacteria, nine fungi, and three crop plants; and iii) clarify the relationships between biochar chemistry and its effect on target species.As pyrolyzation temperature increased, organic matter chemistry of all products changed significantly, with a progressive loss of O-alkyl C, di-O-alkyl C, and methoxyl and N-alkyl C, coupled with an enrichment in aromatic C types. Untreated urban waste and Medicago hay severely inhibited Lepidium, Lactuca and Solanum root growth, whereas no inhibitory effects were found for the other feedstocks. However, these phytotoxic effects largely decreased after pyrolyzation. In contrast to the crop plants, fungi and bacteria thrive on most of the unprocessed organic materials but showed reduced growth and development or complete growth inhibition on biochars obtained at 300 °C and 550 °C. Soilborne microbes demonstrated remarkably similar correlation patterns between their growth to the organic feedstock and biochar chemical components. This work demonstrates that defining organic matter quality by 13C NMR extends our understanding of the impact of biochar on crop plants and key components of the soil food-web.

Responses of Insect Pests and Plant Diseases to Changing and Variable Climate: A Review

Natural and anthropogenic factors have resulted in altered environmental conditions that influence changes in abundance and diversity of insect pests. Global climate change projections focus on crop yields and adaptation strategies to declining yields and ignore the likely impact of a changing climate on insect pests and plant diseases. In this research paper, we review the effects of climate variables namely temperature, carbon dioxide (CO2), precipitation and extreme weather events on insect pests and plant diseases incidence. Elevated temperatures, CO2 and extreme weather events have been shown to alter the distribution, reproductive potential, the incidence and abundance of plant insects and diseases in temperate regions because of the dependence of insects and diseases on environmental conditions. There is limited information on the influence of temperature and carbon dioxide as well as their interaction on the incidence and severity of insect pests, bacterial and viral diseases in the tropical regions. Information on the influence of altered precipitation patterns is also limited but could be of importance in insect distribution studies in a changing climate. Some tropical insects pests are most likely to suffer from extreme heat, resulting in death and hence pest extinction. Future research should focus on the interaction of elevated temperature and CO2, determine the influence of supra optimal summer temperatures, temperature variability, precipitation variability and the corresponding viral and bacterial diseases.

Inventory and incidence of plant diseases affecting vegetables in selected areas in the Visayas and Mindanao

The identification of different vegetable diseases in a particular area is key to managing them. An inventory of diseases affecting important vegetables was conducted in selected areas in the Visayas, and Mindanao. The vegetable diseases were documented in Leyte, Samar, Biliran, Bohol and Claveria Misamis Oriental. Disease surveys were conducted and samples were brought to the laboratory for diagnosis. Pathogenicity tests were conducted for uncommon diseases and PCR and nest PCR assays were done for suspected Phytoplasma diseases. The most common and major disease that affect vegetables in Eastern Visayas is bacterial wilt caused by Ralstonia solanacearum which attacked tomato, pepper, eggplant, bittergourd and was also detected in a wilt infected lettuce. Downy mildew is another which affected bittergourd and pechay. Cercospora diseases were found to commonly affect pepper, eggplant, tomato and bittergourd. Phytophthora diseases were common in tomato, eggplant, pepper and pechay. Fusarium wilt had affected tomato and pepper in Claveria Misamis Oriental, but not common in Eastern Visayas. Emerging diseases were recorded such as Phytoplasma and Corynespora cassiicola which affected tomato and bittergourd, bacterial canker, bacterial speck, target spot, Septoria leaf spot and pith necroses were also found affecting tomato. Information gained from the inventory informed the production of extension materials aimed at farmers and farm extension officers.

Biosynthesised silver and copper nanoformulation as foliar spray to control bird's eye spot disease in tea plantations.

Tea leaves have economic importance in preparation of the popular beverage of the world "tea". Bird's eye spot disease of tea leaves creates significant revenue loss in tea trade of many tea plant cultivating countries. Management of this disease by silver (AgNps) and copper (CuNps) nanoparticles that are biosynthesised by efficient antagonists was studied. The biocontrol agents like Pseudomonas fluorescens, Trichoderma atroviride and Streptomyces sannanensis were evaluated for nanoparticle synthesis against Cercospora theae isolates namely KC10, MC24 and VC38. Initially, the freshly prepared extracellular AgNps showed high disease control (59.42 - 79.76%), but the stability of antagonistic property in stored nanoparticles were significantly high in CuNps (58.71 - 73.81%). Greenhouse studies on various treatments imposed also showed reduced disease incidence percentage of 13.4, 7.57 and 10.11% when treated with CuNps synthesized by P. fluorescens, T. atroviride and S. sannanensis respectively. Various treatment schedule in fields suggested the use of Bionanocopper@1.5 ppm for highest yield (3743 kg/ha) with 66.1% disease prevention. The results suggest the use of biosynthesised CuNps using Streptomyces sannanensis for controlling the tea plant pathogens causing foliar disease with higher stability in releasing the antagonistic activity during sporadic disease incidence of bird's eye spot disease in tea plants.

Soil fertility regulates invasive herbivore performance and top-down control in tropical agroecosystems of Southeast Asia

Abstract In terrestrial ecosystems, changes in soil nutrient availability, plant growth or natural enemies can generate important shifts in abundance of organisms at various trophic levels. In agroecosystems the performance of (invasive) herbivores and their impacts on crops is of particular concern. Scientists are presently challenged with making reliable inferences on invader success, natural enemy performance and efficacy of biological control, particularly in tropical agroecosystems. In this study, we assess how trophic regulatory forces (bottom-up vs. top down) influence the success of three globally important pests of cassava. We examine the mealybug species (Hemiptera: Pseudococcidae) of differing host breadth and invasion history: Phenacoccus manihoti, Paracoccus marginatus, and Pseudococcus jackbeardsleyi. Potted plant fertilizer trials were combined with a regional survey in Vietnam, Laos and Cambodia of 65 cassava fields of similar size and age, but with varying soil fertility. Relative abundance of each mealybug invader was mapped along a soil fertility gradient, and contrasted with site-specific measures of parasitism. Potted plant trials revealed strong bottom-up effects for P. manihoti, such that impacts of nitrogen and potassium additions were propagated through to higher trophic levels and substantially boost development and fitness of its specialist parasitoid, Anagyrus lopezi (Hymenoptera: Encyrtidae). Field surveys indicate that mealybug performance is highly species-specific and context-dependent. For example, field-level abundance of P. jackbeardsleyi and P. marginatus, was related to measures of soil fertility parameters, soil texture and plant disease incidence. Furthermore, for P. manihoti, in-field abundance is equally associated with soil texture (i.e., silt content). Principal component analysis (PCA) and regression suggested that P. manihoti and P. marginatus are disproportionately favored in low-fertility conditions, while P. jackbeardsleyi prospers in settings with high organic carbon and phosphorus. Parasitism of P. manihoti by A. lopezi varied greatly with field and soil fertility conditions, and was highest in soils with intermediate fertility levels and where management practices include the addition of fertilizer supplements. Our characterization of the relative performance of invasive mealybugs and strength of parasitism across variable soil fertility conditions will help guide parasitoid release programs and soil management practices that enhance mealybug biological control.

Different mechanisms of Trichoderma virens-mediated resistance in tomato against Fusarium wilt involve the jasmonic and salicylic acid pathways.

In the present study, we investigated the role of Trichoderma virens (TriV_JSB100) spores or cell-free culture filtrate in the regulation of growth and activation of the defence responses of tomato (Solanum lycopersicum) plants against Fusarium oxysporum f. sp. lycopersici by the development of a biocontrol-plant-pathogen interaction system. Two-week-old tomato seedlings primed with TriV_JSB100 spores cultured on barley grains (BGS) or with cell-free culture filtrate (CF) were inoculated with Fusarium pathogen under glasshouse conditions; this resulted in significantly lower disease incidence in tomato Oogata-Fukuju plants treated with BGS than in those treated with CF. To dissect the pathways associated with this response, jasmonic acid (JA) and salicylic acid (SA) signalling in BGS- and CF-induced resistance was evaluated using JA- and SA-impaired tomato lines. We observed that JA-deficient mutant def1 plants were susceptible to Fusarium pathogen when they were treated with BGS. However, wild-type (WT) BGS-treated tomato plants showed a higher JA level and significantly lower disease incidence. SA-deficient mutant NahG plants treated with CF were also found to be susceptible to Fusarium pathogen and displayed low SA levels, whereas WT CF-treated tomato plants exhibited moderately lower disease levels and substantially higher SA levels. Expression of the JA-responsive defensin gene PDF1 was induced in WT tomato plants treated with BGS, whereas the SA-inducible pathogenesis-related protein 1 acidic (PR1a) gene was up-regulated in WT tomato plants treated with CF. These results suggest that TriV_JSB100 BGS and CF differentially induce JA and SA signalling cascades for the elicitation of Fusarium oxysporum resistance in tomato.

The c-Jun N-terminal kinase pathway of a vector insect is activated by virus capsid protein and promotes viral replication.

No evidence has shown whether insect-borne viruses manipulate the c-Jun N-terminal kinase (JNK) signaling pathway of vector insects. Using a system comprising the plant virus Rice stripe virus (RSV) and its vector insect, the small brown planthopper, we have studied the response of the vector insect's JNK pathway to plant virus infection. We found that RSV increased the level of Tumor Necrosis Factor-α and decreased the level of G protein Pathway Suppressor 2 (GPS2) in the insect vector. The virus capsid protein competitively bound GPS2 to release it from inhibiting the JNK activation machinery. We confirmed that JNK activation promoted RSV replication in the vector, whereas JNK inhibition caused a significant reduction in virus production and thus delayed the disease incidence of plants. These findings suggest that inhibition of insect vector JNK may be a useful strategy for controling the transmission of plant viruses.

Variability of Effective Micro-organisms (EM) in bokashi and soil and effects on soil-borne plant pathogens

The microbial inoculant ‘Effective Microorganisms’ (EM) has been used to promote soil fertility and plant growth in agriculture. We tested effects of commercial EM products on suppression of soil-borne diseases, microbial activity and bacterial composition in organically managed sandy soils. EM was supplied as microbial stock suspension and fermented organic matter (EM-bokashi). Bioassays for soil-borne disease incidence were conducted with a naturally infested soil and inoculated disease-free organically managed nonamended soils or the same soils amended with EM-bokashi or sterilized EM-bokashi. Soil respiration analysis and denaturing gradient gel electrophoresis (DGGE) were performed to determine microbial activity, and bacterial composition and diversity. Disease incidence of cucumber plants was not affected by EM-bokashi but reduced by sterilized bokashi compared to the control in naturally infested soil. Pythium ultimum damping-off of cucumber in inoculated soil was enhanced by EM-bokashi and sterilized bokashi compared to the control. In one of three soils, infection of carrot by Rhizoctonia solani was reduced by EM-bokashi compared with sterilized bokashi. Soil respiration increased one week after soil amendment with EM-bokashi and sterilized EM-bokashi compared to the control, but not seven weeks later. DGGE showed that two batches of EM products had different microbial communities and soil amendment with EM-bokashi or sterilized EM-bokashi did not change the bacterial community and diversity in two soils. The added microorganisms in EM were possibly outcompeted and did not affect the existing bacterial community. We conclude that EM did not consistently suppress soil-borne diseases or change microbial activity and bacterial composition and diversity.

Stimulation of Defense Enzymes in Tomato (Solanum lycopersicum L.) and Chilli (Capsicum annuum L.) in Response to Exogenous Application of Different Chemical Elicitors

The objective of this study was to evaluate the response to exogenous application of different chemical elicitors on the stimulation of defense enzymes such as chitinase, peroxidase, phenylalanine ammonialyase (PAL) and polyphenoloxidase (PPO) in tomato and chilli plants leaves tissues. Chemical elicitors are compounds, which activate chemical defense systems in plants. Various biosynthetic pathways are activated by chemical elicitors in plants depending on the elicitors used. Two times exogenous application of 200 ppm of salicylic acid (SA), ascorbic acid (AA), jasmonic acid (JA) and H2O2 and ethanol (1 mL of 95% ethanol in 1 L distilled water) induced the four defense enzymes production in chilli and tomato plants leaves tissues and significantly reduced viral disease incidence in chilli plants compared to control. SA at 200 ppm enhanced significantly chitinase, peroxidase, PAL and PPO enzymes in leaves tissues of tomato plants. Tomato plants treated with chemical elicitors and control did not show any disease symptoms.

A control package revolving around the removal of single diseased banana stems is effective for the restoration of Xanthomonas wilt infected fields

Xanthomonas campestris pv. musacearum, the causal agent of Xanthomonas wilt of banana (XW), does not infect or cause symptom development in all physically attached shoots in an infected mat. Incomplete/partial systemicity and latent infections often occur. The single diseased stem removal (SDSR, the removal of only symptomatic plants) technique depends on these observations. The SDSR technique, as an alternative or complementary practice to complete mat uprooting (CMU) for XW control, was evaluated at eight XW pilot sites in eastern Democratic Republic of Congo as a novel control option. This technique is low-cost, simple and easily applicable. Within one month, XW plant incidence at the experimental sites declined to below 10%, while within three and 10 months declined to below 2% and 1%, respectively. Restoration of banana plots was observed even in plots that initially had over 80% plant disease incidence. CMU removes a larger portion of the inoculum in a field but is very tedious, time consuming and costly in terms of labour and lost production, due to the premature cutting of symptomless plants that potentially could bear a bunch. CMU can potentially prevent further spread when XW appears for the first time on a farm or location. The choice of CMU relative to SDSR also depends largely on farming objectives. CMU can be carried out in intensive and market-oriented production systems, whose ultimate target is eradication, for example, in South-Western Uganda. In contrast, SDSR is more appealing to subsistence-oriented production, such as in eastern DR Congo, Burundi or central Uganda, whose target is more oriented towards management/control. SDSR can be suggested where access to clean planting material is difficult, thus could be recommended to a very large percentage of small-scale farmers in the currently affected banana-based production systems in east and central Africa.

Isolation and identification of fungi responsible for leaf spots disease of mango (<i>Mangifera indica linneaus</i>) in Sokoto state, Nigeria

A survey was carried out to investigate the incidence of fungal leaf spots disease of mango (Mangifera indica) in Sokoto metropolis using random sampling methods. Field survey was carried out in six mango growing areas; Arkilla, Dambuwa, Gagi, Illela, More and permanent site of the Usmanu Danfodiyo University, Sokoto. Diseased plant leaves were identified using disease symptoms. A total of 125 healthy and diseased leaves were collected using detached leaf technique. The diseased plant leaves were taken to the laboratory for culture, isolation, and identification of pathogens. Plant disease incidence was determined using disease index and severity scale of 0-4 rating. Eleven fungal pathogens were isolated and identified. These included; Alternaria longipes, Aspergillus fumigatus, Aspergillus niger, Colletotrichum gloesporioides, Fusarium oxysporum, Fusarium mangifera, Pestalotiopsis mangiferae, Phoma mangiferae, Phomopsis mangiferae, Pseudofusicoccum spp. and Rhizopus oryzae. The incidence of leaf blight was high in Usmanu Danfodiyo University, Sokoto with percentage frequency of (56.75%), followed by Dambuwa (45.50%), More (44.48%), lllela (37.00%), Gagi (34.15%) and Arkilla (31.65%). Leaf spots intensity was more influenced by environmental conditions and cultural practices rather than climatic factors in the areas. Also, programs aimed at enlightening the farmers on proper cultural practices and boosting mango yield and reducing pathogen invasion are recommended.Keywords: Incidence, Fungi, Leaf spot, disease, Mango, Sokoto.

Induced systemic resistance and symbiotic performance of peanut plants challenged with fungal pathogens and co-inoculated with the biocontrol agent Bacillus sp. CHEP5 and Bradyrhizobium sp. SEMIA6144

Synergism between beneficial rhizobacteria and fungal pathogens is poorly understood. Therefore, evaluation of co-inoculation of bacteria that promote plant growth by different mechanisms in pathogen challenged plants would contribute to increase the knowledge about how plants manage interactions with different microorganisms. The goals of this work were a) to elucidate, in greenhouse experiments, the effect of co-inoculation of peanut with Bradyrhizobium sp. SEMIA6144 and the biocontrol agent Bacillus sp. CHEP5 on growth and symbiotic performance of Sclerotium rolfsii challenged plants, and b) to evaluate field performance of these bacteria in co-inoculated peanut plants. The capacity of Bacillus sp. CHEP5 to induce systemic resistance against S. rolfsii was not affected by the inoculation of Bradyrhizobium sp. SEMIA6144. This microsymbiont, protected peanut plants from the S. rolfsii detrimental effect, reducing the stem wilt incidence. However, disease incidence in plants inoculated with the isogenic mutant Bradyrhizobium sp. SEMIA6144 V2 (unable to produce Nod factors) was as high as in pathogen challenged plants. Therefore, Bradyrhizobium sp. SEMIA6144 Nod factors play a role in the systemic resistance against S. rolfsii. Bacillus sp. CHEP5 enhanced Bradyrhizobium sp. SEMIA6144 root surface colonization and improved its symbiotic behavior, even in S. rolfsii challenged plants. Results of field trials confirmed the Bacillus sp. CHEP5 ability to protect against fungal pathogens and to improve the yield of extra-large peanut seeds from 2.15% (in Río Cuarto) to 16.69% (in Las Vertientes), indicating that co-inoculation of beneficial rhizobacteria could be a useful strategy for the peanut production under sustainable agriculture system.

Disease-reducing effects of aqueous leaf extracts of annona glabra and wedelia calendulacea on fusarium basal rot of shallot caused by fusarium oxysporum

Fusarium basal rot (Fusarium oxysporum) of shallot is a destructive disease, which constrains the production and quality of this crop in Vinh Chau (Soc Trang, Vietnam). This study aims at screening wild plants with antimicrobial activities to bio-control the disease. Among aqueous extracts of 49 commonly found plant species in Vietnam, the 4% (w/v) leaf extracts of Annona glabra and Wedelia calendulacea exhibited strongest inhibitory effects on the mycelial growth of F. oxysporum (up to 35.3% and 25.7%, respectively) in disc diffusion assays. Furthermore, incubating the conidia in A. glabra extract (4%) resulted in a significant suppression in germination (up to 95.3%). Under net house conditions, soil drenching of both extracts at 4% and 5% concentrations showed an equivalent reducing effects on both disease incidence and severity in shallot plants compared to the chemical treatment. Thus, A. glabra and W. calendulacea show their potentials for large-scale applications to sustainably control Fusarium basal rot of shallot.

Mycorrhiza consortia suppress the fusarium root rot (Fusarium solani f. sp. Phaseoli) in common bean (Phaseolus vulgaris L.)

The ability of Arbuscular Mycorrhizal Fungi (AMF) to alleviate the lethal effects incited by root pathogens in a range of plant hosts has been demonstrated. Accumulated evidence also shows that multiple rather than single AMF species exhibit greater potential against pathogens and could mimic natural systems. Nevertheless, it is well established that the effectiveness of a consortium of beneficial organisms is function of interaction among the partners and the involved host. In the present study, four AMF formulations made up of three strains each (1:1:1 w/w) from propagated units of selected AMF strains, Glomus intraradices, Glomus hoi, Gigaspora margarita, and Scutellospora gigantea were evaluated in enhancing common bean (Phaseolus vulgaris L.) growth and biocontrol vis-à-vis Fusariumsolani under greenhouse conditions. The results revealed that all the mycorrhizal preparations significantly reduced the levels of disease severity and incidence in infected bean plants. The biocontrol efficiency of AMF was a function of genera diversity. Though, either neutral or significantly increased growth parameters were recorded upon mycorrhizal colonization. The rhyzospheric competence (root colonization and spore density) of the mycorrhizal formulations was negatively affected upon Fusarium solani inoculation. Moreover, the total soluble phenols and flavonoids contents as well as the specific activity of Phenylalanine Ammonia Lyase (PAL) were boosted after mycorrhizal colonization, indicating the strengthening of plant immune system against the pathogen. Further studies should confirm our formulations after open field assays as alternatives to agrochemicals.

EFFECT OF PLANT EXTRACTS AND GROWTH SUBSTRATES ON CONTROLLING DAMPING-OFF IN PINUS TECUNUMANII SEEDLINGS

ABSTRACT Damping-off is considered one of the most limiting phytosanitary problems in conifer seedling production because it may cause massive damage or total plant death in short time periods. This pathology is caused by a complex of microorganisms, the most common of which are Fusarium spp. and Rhizoctonia spp. This study evaluated the effect of growth substrates and plant extracts at different concentrations on germination and incidence of disease in Pinus tecunumanii plants. The plants were inoculated with the damping-off pathogen Fusarium oxysporum and treatments were applied in a completely randomized design with a factorial arrangement of 4x2x3. This corresponded to four substrates (pine bark, rice hull, coconut husk and sandy soil (4:1)); two plant extracts (Matricaria chamomilla and Datura stramonium), and three concentrations of each extract (Control concentration: 0%, Concentration 1: 50 % and Concentration 2: Undiluted). Each treatment had three repetitions, with 25 plants per repetition. The growth substrates affected germination; the most effective of these were sandy soil (4:1) and pine bark, with 90% and 92% germination at day 20, respectively. No significant difference was observed between the germination obtained with these substrates and that obtained with coconut husk after day 19. Meanwhile, all of the extracts had a significant effect on controlling the disease when they were combined with the substrates, with the exception of coconut husk. With this last substrate the incidence of disease was lower than 4% without the application of plant extracts; this indicates that coconut husk discourages the development of the disease on its own.

Applying weather index insurance to agricultural pest and disease risks

ABSTRACTIn this paper, we explore the application of weather index insurance to plant pest and disease management strategies using two distinct models: (1) insuring crop loss due to disease incidence (“Crop Insurance”) and (2) insuring the use of pesticides (“Pesticide Insurance”). We find that despite the seeming ease of applying weather-based pest incidence models to an insurance product, insuring plant disease incidence models is presently unsuitable for the insurance market for both scientific and behavioral reasons. However, derivative-like applications of weather index insurance to insure pesticide use offer a means to introduce financial leverage into pesticide usage decisions. Risk management with weather index insurance would thus function as a complement to existing risk management strategies using pesticides, and offer a market-based mechanism for pesticide abatement. We conclude that more interdisciplinary collaboration is needed to develop weather index insurance for remuneration of losses due to plant pests and diseases, but weather index insurance offers a potential mechanism to reduce inefficiencies and negative externalities in agricultural markets if pesticide expenditures are insured instead of crop losses.

Defense responses in plants of Eucalyptus elicited by Streptomyces and challenged with Botrytis cinerea.

Elicitation of E. grandis plants with Streptomyces PM9 reduced the gray-mold disease, through increasing the levels of enzymes directly related to the induction of plant defense responses, and accumulation of specific phenolic compounds. Members of Eucalyptus are economically important woody species, especially as a raw material in many industrial sectors. Species of this genus are susceptible to pathogens such as Botrytis cinerea (gray mold). Biological control of plant diseases using rhizobacteria is one alternative to reduce the use of pesticides and pathogen attack. This study evaluated the metabolic and phenotypic responses of Eucalyptus grandis and E. globulus plants treated with Streptomyces sp. PM9 and challenged with the pathogenic fungus B. cinerea. Metabolic responses were evaluated by assessing the activities of the enzymes polyphenol oxidase and peroxidase as well as the levels of phenolic compounds and flavonoids. The incidence and progression of the fungal disease in PM9-treated plants and challenged with B. cinerea were evaluated. Treatment with Streptomyces sp. PM9 and challenge with B. cinerea led to changes in the activities of polyphenol oxidase and peroxidase as well as in the levels of phenolic compounds in the plants at different time points. Alterations in enzymes of PM9-treated plants were related to early defense responses in E. grandis. Gallic and chlorogenic acids were on average more abundant, although caffeic acid, benzoic acid and catechin were induced at specific time points during the culture period. Treatment with Streptomyces sp. PM9 significantly delayed the establishment of gray mold in E. grandis plants. These results demonstrate the action of Streptomyces sp. PM9 in inducing plant responses against B. cinerea, making this organism a potential candidate for biological control in Eucalyptus.