What is the diﬀerence between Systemic Acquired Resistance (SAR) and Induced Systemic Resistance (ISR)?
ISR is usually initiated as a result of beneﬁcial microbes applied to the roots of the plant and increases the level of jasmonic acid in the plant tissues. Beneﬁcial microbes that are applied to the canopy usually induce SAR and it tends to increase the level of salicylic acid in leaf tissue.
Are biopesticides protective or curative?
Biopesticides are more eﬀective when used in a prophylactic preventative programme, not dependent on thresholds or scouting. The colonization of the rhizosphere by beneﬁcial microbes in advance of the attack by pathogens and pests will reduce the living space on the roots where the pathogens might attempt to colonise. Beneﬁcial microbes will secrete substances, which can slow down the growth of the competing pathogenic microbes or kill them. This will reduce the level of disease or pest attack on the plant.
How does Trichoderma control root knot nematodes?
Real IPM Trichoderma is Registered in Kenya and Ethiopia for the control of root knot nematode. Its probable mode of action is the excretion of a chitinase enzyme, which destroys the egg masses of nematodes on the outside of the plant roots.
A root gall contains one large single female nematode. She extrudes eggs masses on the outside of the root and then dies. The gall will not disappear and remains as historical evidence of rkn presence. If Trichoderma is applied regularly with the irrigation water, the number of new galls should decrease.
How does Trichoderma control downy mildews?
Trichoderma is an endophyte and needs to be applied to re-growth of rose plants (red leaves) after ﬂushing or pruning. Downy mildews are also systemic which makes them diﬃcult to control because they are not exposed to control agents. Systemic fungicides are more prone to resistance occurring and Trichoderma should be tank mixed when systemic fungicides are applied – as part of a resistance management programme. Weekly foliar applications of Trichoderma have provided good control of downy mildews in roses and onions. Do not spray to ‘run-oﬀ’.
How do plants ‘use’ the Bacillus subtilis applied to the soil to help protect the plant canopy from attack by diseases?
Scientists have measured a peculiar interaction between a plant under attack from a disease in the canopy. Root colonization by Bacillus subtilis increases (below right). The increased level of Bacillus subtilis on the root system sends signals to the plants own chemical pathways that produce abscisic acid and salicylic acid which are involved in controlling the closure of stomata. When stomata close they reduce the entry points for the disease into the plant.
How does Bacillus subtilis control powdery mildew if sprayed in the canopy?
Bacillus subtilis is known to produce lipopeptides, which destroy the cell membrane of powdery mildew spores on the leaf surface. (ref AgraQuest).
These substances are produced by Bacillus during the manufacturing process and are present in the total fermented product. The live bacterium itself is less important than the substances in the liquid culture. Applications should not be made to ‘run-oﬀ’ so that the natural active ingredients remain in contact with the leaf surface and prevent powdery mildew spores form germinating.
Are any of Real IPM’s biopesticides also endophytes?
Real Trichoderma and Real Bacillus subtilis are endophytes. Real IPM is currently inves-tigating the endophytic attributes of its EPFs (Metarhizium and Beauveria).
What is the diﬀerence between and phytopathogen and an endophyte?
Phytopathogens are bacteria or fungi, often with part of their life cycle in the soil, which cause harm to the plant. Diseases are caused by phytopathogens. Endophytes colonize an ecological niche similar to that of phytopathogens, which makes them suitable as bio-control agents
What is an endophyte?
An endophyte is a bacterium or fungi able colonize the internal tissue of a plant without causing a disease or any harm to the plant. Of the nearly 300,000 plant species that exist on the earth, each individual plant is host to one or more endophytes.
What is a bioﬁlm?
Rhizobacteria can form bioﬁlms on root surfaces; a continuous colony of bacteria bound together by polysaccharides. This helps the bacteria bind to the root surface and makes it more diﬃcult for other rhizobacteria to establish on the root. Bioﬁlm formation is enhanced by the presence of malic acid, which is excreted by plant roots.
How do green manures work?
Green manure crops act mainly as soil acidifying matter to decrease the alkalinity pH of alkali soils by generating humic and acetic acids. Incorporation of cover crops into the soil allows the nutrients held within the green manure to be released and made available to the succeeding crops. This results immediately from an increase in abundance of soil microor-ganisms from the degradation of plant material that aid in the decomposition of this fresh material. Microbial activity from incorporation of cover crops into the soil leads to the formation of fungal mycelium and viscous materials, which beneﬁt the health of the soil by increasing its soil structure by aggregation. The increased percentage of organic matter improves water inﬁltration and retention, aeration, and other soil characteristics
What is a green manure?
Green manure crops uprooted or mown crop parts, which are left to wither on a ﬁeld so that they serve as a mulch and soil amendment. Plants used for green manure are often cover crops grown which are ploughed under and incorporated into the soil while green or shortly after ﬂowering. Green manure is commonly associated with organic farming and can play an important role in sustainable annual cropping systems
Are mycorrhizae compatible with Trichoderma and Bacillus subtilis?
The mycorrhizae network in the soil may provide a physical structure for the Trichoderma and Bacillus to grown on. Mycorrhizae are usually only applied once at plant establishment and both Trichoderma and Bacillus are applied regularly as crop protection agents and bio-fertilisers.
What are the diﬀerent modes of action of mycorrhizae and Trichoderma and Bacillus subtilis?
Mycorrhizae are an extension of the plant’s root system and the Trichoderma and Bacil-lus subtilis solubilise phosphate, create a larger physical plant root with more branches and are antagonistic against plant pathogens and pests.
Are phosphorous levels too high in hydroponics for mycorrhizae to invade plant roots?
Mycorrhizae spores remain dormant if phosphorous levels are above 70 ppm, however if you establish your mycorrhizae colony early on when phosphorous levels in the nutrient solution are lower, they may continue to grow later in the cycle when P levels are higher.
What’s the diﬀerence between ecto-mycorrhizae (VAM) and endo-mycorrhizae?
Ecto-mycorrhizae form a sheath around the plant roots and mainly colonise conifers and oaks. Endo -mycorrhizae (vesicular arbuscular mycorrhizae – VAM) will penetrate the root with a structure that enable exchanges to take place between the mycorrhizal network and the plant. Most vegetables, grasses, ﬂowers, shrubs, fruit trees and ornamentals associate with VAM.
How do mycorrhizae work?
Mycorrhizal fungi attach to the surface of the root and penetrate in or around the inside of the root cells. Filaments (called mycelium) extend into the surrounding soil, eﬀectively extending the plant’s roots and root absorbing capacity for nutrients and water, from ten to several thousand times. In return, the mycorrhizae receive from the plant roots sugars and other compounds.
The mycorrhizal mycelium release enzymes that dissolve tightly bound minerals like phosphorus, sulphur, iron and all the major and minor nutrients used by plants. The nutrients are organically assimilated by the mycorrhizae and become readily available for use by the plants.
The fungal ﬁlaments also bind soil particles into larger aggregates with organic glues such as humic com-pounds; the resulting soil structure allows air and water movement into the soil, encouraging root growth and distribution.
How can root knot nematode galls and Rhizobium nodules be distinguished on the roots of legumes?
The galls of rkn are swellings within the root, which cannot be rubbed oﬀ by hand (below right) and Rhizobium nodules are external balls which can be rubbed oﬀ by hand (below left). If the Rhizobium nodules are actively ﬁxing nitrogen they will be pink in colour when dissected.