Efficacy and dose–response relationship in biocontrol of Fusarium disease in maize by Streptomyces spp.

Two isolates of Streptomyces spp. DAUFPE 11470 and DAUFPE 14632 were evaluated to determine the antagonist–pathogen inoculum concentration relationship under greenhouse conditions. Pathogen and antagonist concentration, significantly (P < 0.05) affected development of Fusarium disease in maize with a significant interaction between pathogen and antagonist concentration. Dose–response relationship also differed significantly (P < 0.05) between the two isolates, but both isolates demonstrated effective control of Fusarium disease, regardless of pathogen concentration. The isolate DAUFPE 11470 provided the most effective control. The lowest value for disease incidence occurred at low pathogen (10³ chlamydospore g⁻¹ soil) and high antagonist concentration (10⁶ cfu ml⁻¹) for both isolates. The disease incidence for control plants ranged from 19% to 76%. However, in relation to control the lowest disease reduction occurred at low pathogen (10³ chlamydospore g⁻¹ soil) and high antagonist concentrations (10⁶ cfu ml⁻¹). These reductions were 10.6% and 13% for DAUFPE 14632 and DAUFPE 11470, respectively. The highest disease reductions, in relation to control plants, occurred at high pathogen (10⁶ chlamydospore g⁻¹ soil) and antagonist (10⁶ cfu ml⁻¹) concentrations for both isolates. These values were 55% and 62.2% for DAUFPE 14632 and DAUFPE 11470, respectively. The chlamydospore germination of Fusarium moniliforme was affected by glucose addition, antagonist isolates and type of inoculum. The lowest chlamydospore germination was observed with bacterial suspensions of the isolates, for all glucose additions. The results suggested that both Streptomyces spp. isolates were effective at different doses as biocontrol agents against F. moniliforme. Also, there was evidence for at least two mechanisms of biocontrol and that apparently, both isolates showed the same mechanisms of biocontrol action related to production of bioactive compounds and competition for carbon. Further studies will be developed to improve the level and effectiveness of control by these isolates.     

Decline as a disease category: is it helpful?

Many, but not all, forest pathologists use "decline" to describe forest tree diseases of complex etiology. We contend that this distinction from abiotic or biotic diseases is completely arbitrary, has caused undue confusion, and provides no practical insights for forest managers. All diseases are complex and can be characterized within the conceptual framework of the disease triangle. Why do we use a simple label ("decline") to describe disease situations of complex abiotic and biotic origin when we need to know which damaging agents are present, whether the environment is conducive for disease progression, and host susceptibility over time to understand the origins and management of disease? We propose that forest pathologists discontinue the use of "decline" as a distinct category of disease. Furthermore, we suggest that new diseases should be named based on the affected host, characteristic symptom, and, once known, major determinant. We believe that clearer communication in describing complex diseases is a prerequisite to finding effective management options.     

Benefits of a maize–bean–weeds mixed cropping system in Urubamba Valley,Peruvian Andes

Abstract

In the Urubamba Valley, Peruvian Andes, we evaluated the abundance of insect pests and natural enemies in experimental plots where maize was grown either as monoculture, intercropped with beans, or intercropped with beans plus associated weeds. We also assessed the consequences of the cropping system for maize yield. The main insect pests recorded were Diabrotica spp. (Coleoptera: Chrysomelidae), Carpophilus sp. (Coleoptera: Nitidulidae) and Pagiocerus frontalis (Coleoptera: Scolytidae), and their overall abundance did not differ among crop diversity treatments. However, there was a significant adverse effect of crop diversity on the maximum abundance of both Carpophilus and Pagiocerus. The main beneficial arthropods were Paratriphleps sp. (Hemiptera: Anthocoridae), ladybirds and spiders, and their density did not differ among treatments. Maize yield did not decrease with increasing plant diversity. The reported benefits of intercropping, together with the associated efficiency in land use, make this traditional agricultural practice a valuable alternative to the use of pesticides, particularly for resource-poor Andean farmers.     

Are herbicides a once in a century method of weed control?

The efficacy of any pesticide is an exhaustible resource that can be depleted over time. For decades, the dominant paradigm – that weed mobility is low relative to insect pests and pathogens, that there is an ample stream of new weed control technologies in the commercial pipeline, and that technology suppliers have sufficient economic incentives and market power to delay resistance – supported a laissez faire approach to herbicide resistance management. Earlier market data bolstered the belief that private incentives and voluntary actions were sufficient to manage resistance. Yet, there has been a steady growth in resistant weeds, while no new commercial herbicide modes of action (MOAs) have been discovered in 30 years. Industry has introduced new herbicide tolerant crops to increase the applicability of older MOAs. Yet, many weed species are already resistant to these compounds. Recent trends suggest a paradigm shift whereby herbicide resistance may impose greater costs to farmers, the environment, and taxpayers than earlier believed. In developed countries, herbicides have been the dominant method of weed control for half a century. Over the next half‐century, will widespread resistance to multiple MOAs render herbicides obsolete for many major cropping systems? We suggest it would be prudent to consider the implications of such a low‐probability, but high‐cost development. © 2017 Society of Chemical Industry     

Detection and characterization of a phytoplasma associated with witches’-broom disease of Salvadora persica in India

Salvadora persica trees with symptoms of witches’-broom, little leaf and severe leaf curling were observed in the Biodiversity Park, North Delhi (India) during February 2010. Using a nested-PCR assay targeting two phytoplasma specific loci (16S ribosomal RNA and the ribosomal protein gene) and sequence analysis of the amplified products, we identified the associated phytopathogen as a phytoplasma of group 16SrI. RFLP-mediated characterization revealed that the phytoplasma belongs to subgroup 16SrI-B. Phylogenetic reconstruction also grouped the phytoplasma within group 16SrI. The study reports a new host of phytoplasma in India and worldwide.     

The profitability of maize–haricot bean intercropping techniques to control maize stem borers under low pest densities in Ethiopia

Lepidopteran stem borers are the main pests of cereals in Ethiopia. In recent years, habitat management techniques, which aim at increasing plant biodiversity through mixed cropping, have gained increased attention in stem borer control. In the present study, the profitability of mixed cropping of maize with haricot beans at different ratios and the effect on infestation of maize by stem borers, yield and borer parasitism were studied in Melkassa and Mieso, Ethiopia, in a field experiment under natural infestation. In Melkassa, pest infestations were too low for the cropping system to affect pests, plant damage and yields significantly, whereas in Mieso, where the pest densities were high, intercropping of maize with beans at ratios of 1:1 to 2:1 significantly decreased borer densities compared with pure maize stands. Chilo partellus (Swinhoe) and Cotesia flavipes. (Cameron) were the major stem borer and parasitoid species, respectively, recorded both at Melkassa and Mieso. Borer parasitism was higher at Mieso than at Melkassa and tended to increase with the increase of the haricot bean ratio in the intercropping system. Land equivalent ratios of >1 indicated higher land use efficiency in mixed compared with sole cropping, even if pest densities were low.     

Plant and veterinary disease diagnosis: a generic approach to the development of field tools for rapid decision making?

Rapid and accurate diagnostic tests make an important contribution to programmes to monitor and eradicate infectious diseases that impact animal and plant health. Using foot-and-mouth disease (FMD) and sudden oak death as examples, this review outlines recent progress to develop new field tools for detection of the infectious agents that cause high-impact livestock and plant diseases. The principal driver for this work is to develop tools that can be used locally to assist in decision making. Advances in this area have developed simple-to-use lateral-flow devices for the detection of FMD virus and the genus Phytophthora (including Phytophthora ramorum , the causal agent of sudden oak death and the related pathogen P. kernoviae ), as well as new hardware platforms to allow PCR testing for these agents by non-specialists in the field. Although developed for different diseases, the user requirements for rapid diagnostic tools for FMD and sudden oak death share many similarities. Using generic solutions to these challenging problems, it is now possible to imagine a new paradigm for how the collection and testing of samples to monitor the spread of important livestock and plant diseases might be achieved.     

Xanthomonas arboricola pv. fragariae: what's in a name?

Polyphasic analysis exposed important heterogeneity between bacterial strains catalogued as Xanthomonas arboricola pv. fragariae (Xaf) from different culture collections. Two draft whole‐genome sequences revealed pathogenicity related genes of the type‐three secretion system in strain LMG 19146, whereas none were found in the Xaf pathotype strain LMG 19145. Also, considerable sequence divergence was observed in the phylogenetic marker genes gyrB, rpoD, dnaK and fyuA. Further study of 16 Xaf culture‐collection strains showed that co‐classification is not justified. Partial 16S rRNA gene and gyrB sequencing demonstrated that 12 strains belonged to X. arboricola, but that they did not form one homogeneous group within the species. The four remaining strains were identified as Xanthomonas fragariae and Xanthomonas sp. All sequence‐based identifications were confirmed by MALDI‐TOF MS fingerprinting. Also, the pathogenicity genes hrcQ and avrBs2 were detected in only three of the 12 analysed X. arboricola strains. The X. arboricola and Xanthomonas sp. strains showed pectolytic activity, and upon inoculation in strawberry none of the strains reproduced the leaf blight symptoms reported for Xaf. This study demonstrates that (i) no clear criteria exist for the identification of strains as Xaf, (ii) the name Xaf is currently used for a genetically diverse assortment of strains, and (iii) the species X. arboricola holds many undetermined plant‐associated bacteria besides the described pathovars.     

Occurrence of boscalid resistance in cucumber powdery mildew in Japan and molecular characterization of the iron–sulfur protein of succinate dehydrogenase of the causal fungus

A total of 74 mass isolates of cucumber powdery mildew fungus (Podosphaera xanthii) were collected from commercial greenhouses with a history of boscalid use in Ibaraki Prefecture, Japan, and tested in a leaf disk assay for their sensitivity to boscalid. The mildew development of 40 of 74 isolates and five sensitive reference isolates on the disks was completely suppressed at 5 μg boscalid/ml. The minimum inhibitory concentrations (MIC) for the remaining 34 isolates were 50 μg/ml or higher, and 21 of these isolates also grew well at 500 μg/ml. Six single-spore isolates were resistant to boscalid with MIC values higher than 500 μg/ml; four of these were moderately resistant (MR), and two were very highly resistant (VHR) isolates. The growth of MR isolates was almost completely suppressed at 500 μg/ml, whereas two VHR isolates grew vigorously at 500 μg/ml. In foliar inoculation tests of potted cucumber plants, the efficacy of boscalid (500 μg/ml) against both MR and VHR isolates was very low. Partial DNA fragment of the iron–sulphur protein subunit (SdhB) gene of succinate dehydrogenase was PCR-amplified from five sensitive and five resistant isolates and directly sequenced, revealing that VHR isolates possess a substitution from a highly conserved histidine (CAT) to tyrosine (TAT) in a third cysteine-rich center of a putative SdhB, whereas MR isolates so far have not been found to have such substitution in SdhB.     

Current progress in studying blackleg disease (Leptosphaeria maculans and L. biglobosa) of canola in Iran: Where do we stand now?

Blackleg, caused by a complex of Leptosphaeria species (L. maculans and L. biglobosa), is a fungal disease on Brassica species, especially important in canola (Brassica napus). Since the first report of L. biglobosa in Iran in 2007 and L. maculans in 2008, both species are now of major importance in Iran affecting 10 provinces and 30 regions, with a higher prevalence in the northern provinces of Mazandaran and Golestan. Despite the rapid progression of the disease and the emergence of new Leptosphaeria races in Iran, the research into this pathogen has not progressed at the same rate and is limited to phenotypic characterization studies, pathogenicity research, and to a lesser extent, disease management research. Given the rapid increase in canola cultivation in Iran and changes in the genetic diversity of the pathogen populations, it is likely that blackleg disease will increasingly become a severe threat to Iran’s canola production. Therefore, systematic and prospective studies, along with fundamental research on the pathogen's biology, epidemiology, and genetic diversity, would provide critical information for the development of disease management strategies. Here, we review the research that has been carried out to date on blackleg disease in Iran and describe the extent of progress towards disease control, especially in disease-prone regions.     

First record of the impact of the parasitism of Cecidochares connexa (Diptera: Tephritidae) by a solitary larval ectoparasitoid in West Africa: Cause for concern?

Journal of Plant Diseases and Protection - Cecidochares connexa is currently the only effective biological control agent of Chromolaena odorata an invasive weed in West Africa. Recently, an...     

Occurrence of Raoiella indica Hirst (Acari,Tenuipalpidae) in the Southeast region of the state of Pará, Brazil

Journal of Plant Diseases and Protection - The red palm mite Raoiella indica Hirst attacks coconut, banana and açai trees. In 2007, the mite was recorded for the first time in South America....     

Three years of banning neonicotinoid insecticides based on sub‐lethal effects: can we expect to see effects on bees?

The 2013 EU ban of three neonicotinoids used in seed coating of pollinator attractive crops was put in place because of concern about declining wild pollinator populations and numbers of honeybee colonies. It was also concluded that there is an urgent need for good field data to fill knowledge gaps. In the meantime such data have been generated. Based on recent literature we question the existence of recent pollinator declines and their possible link with the use of neonicotinoids. Because of temporal non‐coincidence we conclude that declines of wild pollinators and of honeybees are not likely caused by neonicotinoids. Even if bee decline does occur and if there is a causal relationship with the use of neonicotinoids, we argue that it is not possible on such short term to evaluate the effects of the 2013 ban. In order to supply future debate with realistic (field) data and to discourage extrapolating the effects of studies using overdoses that are not of environmental relevance, we propose – in addition to field studies performed by the chemical industry – to use the ‘semi‐field worst case’ treated artificial diet studies approach to free flying colonies in the field. This kind of study may provide realistic estimates for risk and be useful to study realistic interactions with non‐pesticide stressors. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.