The loss of organic material from the roots provides the energy for the development of active microbial populations in the rhizosphere around the root. Generally, saproptrophs or biotrophs such as mycorrhizal fungi grow in the rhizosphere in response to this carbon loss, but plant pathogens may also develop and infect a susceptible host, resulting in disease. This review examines the microbial interactions that can take place in the rhizosphere and that are involved in biological disease control. The interactions of bacteria used as biocontrol agents of bacterial and fungal plant pathogens, and fungi used as biocontrol agents of protozoan, bacterial and fungal plant pathogens are considered. Whenever possible, modes of action involved in each type of interaction are assessed with particular emphasis on antibiosis, competition, parasitism, and induced resistance. The significance of plant growth promotion and rhizosphere competence in biocontrol is also considered. Multiple microbial interactions involving bacteria and fungi in the rhizosphere are shown to provide enhanced biocontrol in many cases in comparison with biocontrol agents used singly. The extreme complexity of interactions that can occur in the rhizosphere is highlighted and some potential areas for future research in this area are discussed briefly.

/pdf/microbial-interactions-and-biocontrol-in-the-rhizosphere-1erj9kqzek.pdf

Microbial interactions and biocontrol in the rhizosphere

Although the number of biocontrol products is increasing, these products still represent only about 1% of agricultural chemical sales. Yet these are important contributions because biocontrol agents offer disease management alternatives with different mechanisms of action than chemical pesticides. Trends in research include the increased use of biorational screening processes to identify microorganisms with potential for biocontrol, increased testing under semicommercial and commercial production conditions, increased emphasis on combining biocontrol strains with each other and with other control methods, integrating biocontrol into an overall system.

Commercialization and Implementation of Biocontrol 1

Herbs, spices and their active components as natural antimicrobials in foods Effect of natural antioxidants in herbs and spices on shelf life of foods Ajowan Aniseed Asafoetida Allspice Capers and caperberries Caraway Celery Chervil Fennel and fennel seed Galangal Kaffir lime leaf Lavender Lemongrass Lovage Nigella Oregano Poppy Sesame Star anise Tarragon Tamarind Other significant herbs and spices.

Handbook of Herbs and Spices

Plant growth-promoting rhizobacteria (PGPR) strains INR7 (Bacillus pumilus), GB03 (Bacillus subtilis), and ME1 (Curtobacterium flaccumfaciens) were tested singly and in combinations for biological control against multiple cucumber pathogens. Investigations under greenhouse conditions were conducted with three cucumber pathogens-Colletotrichum orbiculare (causing anthracnose), Pseudomonas syringae pv. lachrymans (causing angular leaf spot), and Erwinia tracheiphila(causing cucurbit wilt disease)-inoculated singly and in all possible combinations. There was a general trend across all experiments toward greater suppression and enhanced consistency against multiple cucumber pathogens using strain mixtures. The same three PGPR strains were evaluated as seed treatments in two field trials over two seasons, and two strains, IN26 (Burkholderia gladioli) and INR7 also were tested as foliar sprays in one of the trials. In the field trials, the efficacy of induced systemic resistance activity was determined against introduced cucumber pathogens naturally spread within plots through placement of infected plants into the field to provide the pathogen inoculum. PGPR-mediated disease suppression was observed against angular leaf spot in 1996 and against a mixed infection of angular leaf spot and anthracnose in 1997. The three-way mixture of PGPR strains (INR7 plus ME1 plus GB03) as a seed treatment showed intensive plant growth promotion and disease reduction to a level statistically equivalent to the synthetic elicitor Actigard applied as a spray.

https://apsjournals.apsnet.org/doi/pdfplus/10.1094/PHYTO.1998.88.11.1158

Mixtures of Plant Growth-Promoting Rhizobacteria Enhance Biological Control of Multiple Cucumber Pathogens

Whether modern agriculture without conventional pesticides will be possible or not is a matter of debate. The debate is meaningful within the context of rising health and environmental awareness on one hand, and the global challenge of feeding a steadily growing human population on the other. Conventional pesticide use has come under pressure in many countries, and some European Union (EU) Member States have adopted policies for risk reduction following Directive 2009/128/EC, the sustainable use of pesticides. Highly diverse crop production systems across Europe, having varied geographic and climatic conditions, increase the complexity of European crop protection. The economic competitiveness of European agriculture is challenged by the current legislation, which banned the use of many previously authorized pesticides that are still available and applied in other parts of the world. This challenge could place EU agricultural production at a disadvantage, so EU farmers are seeking help from the research community to foster and support integrated pest management (IPM). Ensuring stable crop yields and quality while reducing the reliance on pesticides is a challenge facing the farming community is today. Considering this, we focus on several diverse situations in European agriculture in general and in European crop protection in particular. We emphasize that the marked biophysical and socio-economic differences across Europe have led to a situation where a meaningful reduction in pesticide use can hardly be achieved. Nevertheless, improvements and/or adoption of the knowledge and technologies of IPM can still achieve large gains in pesticide reduction. In this overview, the current pest problems and their integrated management are discussed in the context of specific geographic regions of Europe, with a particular emphasis on reduced pesticide use. We conclude that there are opportunities for reduction in many parts of Europe without significant losses in crop yields.

https://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS-05-15-0574-FE

Toward a Reduced Reliance on Conventional Pesticides in European Agriculture

Damicone, J. P., Edelson, J. V., Sherwood, J. L., Myers, L. D., and Motes, J. E. 2007. Effects of border crops and intercrops on control of cucurbit virus diseases. Plant Dis. 91:509-516. In five field trials over 3 years, control of aphid-transmitted, nonpersistent virus diseases on pumpkin, caused mostly by the potyviruses Watermelon mosaic virus (WMV) and Papaya ringspot virus type-W (PRSV-W), was achieved by intercropping with grain sorghum, as opposed to clean tillage. Reductions in disease incidence ranged from 43 to 96% (P ≤ 0.05). Surrounding pumpkin plots with borders of peanut, soybean, or corn was not effective. Borders of grain sorghum were effective, but disease control was generally less than for the intercrop treatment. Intercropping soybean and peanut with pumpkin reduced disease incidence by 27 to 60% (P ≤ 0.05), but disease control generally was less than for grain sorghum. Peak periods of alate aphid immigration generally preceded virus disease outbreaks by 7 to 14 days. However, alate landing rates, as measured in green tile traps, did not differ among treatments. Marketable yield was not increased by the intercrop treatments, and yield was reduced by up to 50% for the intercrop treatment with grain sorghum in two trials. The use of grass-selective herbicide applied along pumpkin rows, reduced seeding rates of the intercrops, or mowing did not alleviate the adverse effects of competition between pumpkin and the grain sorghum intercrop on yield.

https://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS-91-5-0509

Effects of Border Crops and Intercrops on Control of Cucurbit Virus Diseases.

Aerial blight, caused by Rhizoctonia solani AG-4, was identified as a major disease of greenhouse mist-produced rosemary cuttings. An isolate of the biocontrol fungus Laetisaria arvalis, selected for tolerance to the experimental fungicide CGA 173506, was used as an amendment to potting soil. Combined treatment of rosemary with L. arvalis and a foliar spray of the fungicide at one-half the recommended rate reduced disease more than treatment with either the fungus or fungicide alone. Similar synergism was not observed for combinations of Trichoderma harzianum as a soil amendment and a foliar spray of the fungicide iprodione applied at the labeled rate.

https://apsjournals.apsnet.org/doi/pdfplus/10.1094/PDIS.1997.81.7.795

Integration of biological and chemical controls for Rhizoctonia aerial blight and root rot of rosemary

Within-row spacing effects on traits of importance to mechanical harvest in paprika-type peppers

Nontreated seed, primed seed, and transplants were compared for effects on stand establishment, plant morphology, and yield of paprika pepper ( Capsicum annuum L.). Nontreated seed was satisfactory for stand establishment, although primed seed had the potential to provide greater initial stands. When populations were made equal by thinning, there were few differences in stem and leaf dry weight, fruit yield, or plant morphology attributed to seed treatment. Generally, morphology of plants established by direct seeding was favorable for mechanical harvest. Using transplants did not result in higher marketable fruit yields than direct seeding in 2 of 3 years. When compared to plants established by direct seeding, three trends were consistent across all 3 years for plants established by transplanting: 1) they were more massive, 2) they had larger vertical fruiting planes, and 3) they had more branches. These traits increase the difficulty of mechanical harvest and create the potential for more leaves and stems (trash) in the harvested product. Thus, transplanting is not recommended for stand establishment of paprika pepper intended for mechanical harvest.

/pdf/plant-morphology-and-yield-of-paprika-pepper-in-response-to-1g1ue8syzc.pdf

Plant Morphology and Yield of Paprika Pepper in Response to Method of Stand Establishment

Ethephon has increased yields of red fruit, but its use as a pepper (Capsicum annuum L.) fruit ripening agent has been limited by premature fruit abscission and defoliation. We tested ethephon solutions of 0, 1500, 3000, 4500, and 6000 μl.liter -1 with or without 0.1 M Ca(OH) 2 as a onetime foliar application to field-grown paprika pepper in southwestern Oklahoma. There was a linear increase in fruit abscission with increasing ethephon rates in 2 of 3 years, with or without added Ca. Marketable fruit as a percentage of total harvested fruit weight was improved by ethephon at 6000 μl.liter -1 in 2 of 3 years, primarily due to a decrease in weight of harvested green fruit [...]

/pdf/calcium-and-ethephon-effects-on-paprika-pepper-fruit-524q0qc8fr.pdf

James E. Motes

Papers

Effects of Border Crops and Intercrops on Control of Cucurbit Virus Diseases.

Integration of biological and chemical controls for Rhizoctonia aerial blight and root rot of rosemary

Within-row spacing effects on traits of importance to mechanical harvest in paprika-type peppers

Plant Morphology and Yield of Paprika Pepper in Response to Method of Stand Establishment

Calcium and Ethephon Effects on Paprika Pepper Fruit Retention and Fruit Color Development