For anybody who may be interested... Here is a great read from a university on chitosan. This is a copy/paste of the section that concerns agricultural uses, and I think it's pretty interesting. Whether you believe duds are caused by nematodes, fusarium sp, or other pathogen or virus, chitosan could be gold. And like I mentioned in my previous post, I do know somebody that was getting dudded, starting applying chitosan and hasn't seen a dud since.
It's a bit of a long read, but worth it. Discusses use as a fertilizer, soil conditioner, biopesticide, bioinsecticide, bionematicide, as well as boosting plant defense systems, and its' effectiveness against virus and pathogens.
Is Chitosan a New Panacea? Areas of Application
Susana P. Miranda Castro and Eva G. Lizárraga Paulín
38. Chitosan in agriculture
Due to the antifungal, antibacterial and antiviral properties of chitosan, it has been used
successfully in agriculture in recent years: in plant protection, like growth promoter, in soil
correction, enhancer of secondary metabolites production, and activator of defense
mechanisms to mention a few.
39. Seed coating
Chitosan application can be done by different ways: in the seed, in the soil or by foliar way.
In seeds, it has been used as a coating material for cereals, nuts, fruits and vegetables [206-
208]. It has been shown that this way of application alters permeability of the seed plasma
membrane, increasing the concentrations of sugars and proline, and enhancing peroxidase
(POD), catalase (CAT), phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase
(TAL) activities [207,209]. By this way, germination rates increases significantly [ 210] and
seedlings germinate quicker, better, and vigorously [211-214]. Chitosan is used not only in
seed coatings, but also in fruits and vegetables, because it gives more firmness and it
promotes diminution of the normal microbiological charge [215] increasing the product life.
40. Leaf coating
Chitosan foliar application increases stomatal conductance and reduces transpiration,
without affecting plant height, root length, leaf area or plant biomass [216]. When chitosan is
sprayed in leaves, abscisic acid (ABA) content increases [217]. It promotes the activation of
defense mechanisms which allow plants to deal with stress and to defend against diseases
due to the antiviral, antifungal and antibacterial nature of chitosan [218,219].
41. Fertilizer
By applying chitosan in soil, it has been demonstrated that it stops plant wilting because it
acts as a potent fertilizer due to the high concentration of nitrogen content in its molecular
structure [220,221]. Also, it has been used as a soil amendment, controlling diseases caused
by fungal species like Fusarium acuminatum, Fusarium sp, Cylindrocladium floridanum and
Aspergillus flavus [208, 218, 222].
42. Plants growth promoter
Chitosan acts as plant growth promoter in some crops like Faba bean plant, radish,
passion fruit, potato, gerbera, cabbage, soybean and other crops when it is incorporated in
solution, increasing plant production and protecting plants against pathogens too.
Chitosan has a significant effect on growth rates of roots, shoots, flowering, and number
of flowers [219, 223].
43. Plant self defense
Plants react naturally against most of biological and environmental adverse conditions, but
sometimes defense has to be induced in order to fight against harder threats. It has been
reported that chitosan is a great biopolymer used for this purpose, because it induces
defense reactions in some plants, sensitizing them in order to increase their responses
against pathogens attack. Some substances that get favored due to the presence of chitin and
chitosan are phytoalexines, pathogenesis related proteins (PR), protein inhibitors, chitinases
and glucanases, as well as Reactive Oxygen Species (ROS) and
hydrogen peroxide
generation [224]. This is because chitosan interacts with cellular DNA generating multiple
biochemical reactions in the plant, generating a rapid response in the plant against
pathogens attack. For this reason, chitosan has been considered as an elicitor, namely a
defense mechanism activator in plants, generating a process at cellular level in which plant
cells get and transduce biological signals in order to activate defense responses [225]. There
are some specific elicitor-binding proteins which act like physiological receptors in signal
transduction cascades, varying their specificity depending on the studied system, which
allows researchers to find the molecular bases that origin the signal interchanges between
host plants and microbial pathogens [225-227].
Not only at biochemical level but also at microbiological level, chitosan is effective on
plant protection. It has been found that application of chitosan in plants by the ways
mentioned in sections above reduces visibly the damages caused in the plants by
pathogenic fungi because of the antibiotic nature of chitosan [215, 218]. Because of being
a polysaccharide, chitosan acts as a bioremediator molecule that stimulates the activity of
beneficial microorganisms in the soil such as Bacillus, fluorescent, Pseudomonas,
Actinomycetes, Mycorrhiza and Rhizobacteria [228-233], which alter the microbial
equilibrium in the rhizosphere disadvantaging plant pathogens, making them able to
compete through mechanisms such as parasitism, antibiosis, and induced resistance
[234,235].
44. Bioinsecticide
Chitosan research has been focused principally in controlling bacterial and fungal burden;
nevertheless there are some investigations about the use of chitosan as bioinseciticide. One
of the first findings was that chitosan is active against some insects like lepidopterous and
homopterous, with a mortality of 80%, and this percentage increases when increasing oligochitosan
concentration too [236].
Not only chitosan, but also its derivates (as N-acetyl (NAC) and N-benzyl (NBC)
chitosan derivatives) had shown significant insecticidal activities superior to those of
chitosan itself, particularly against species like Spodoptera littoralis, an important
destructive pest of subtropical and tropical agriculture in northern Europe, affecting
cotton, vegetable and ornamental crops [237]. Some other insects have been successfully
attacked by chitosan derivates, like Helicoverpa armigera (H¨ubn), Plutella xylostella (L),
Aphis gossypii (Glover), Metopolophium dirhodum (Walker), Hyalopterus pruni
(Geoffroy), Rhopalosiphum padi L, Sitobium avenae (Fabricius) and Myzus persicae
(Sulzer) [238].
Active chitinases from chitosan are relevant enzymes for biopesticide control mechanisms,
being the hydrolysis of chitin-containing media a common practice to evaluate the efficiency
of bioinsecticide organisms. It has been considered to add chitin derivatives to formulations
The Complex World of Polysaccharides
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containing these microorganisms to increase biopesticide effectiveness, to provide a
favorable developmental environment and resistance against adverse conditions [239]. New
chitosan derivatives with insecticidal or fungicidal properties may thus serve as good
alternatives for broad-spectrum and highly persistent pesticides because they are non-toxic
to vertebrates and humans, and have a biodegradable matrix.
45. Biopesticide
Tricoderma sp. and Bacilus sp. are microorganisms which often increase chitin and chitosan
production, enhancing its efficiency to control pathogenic microorganisms and pests [238].
Native populations of biocontrol microorganisms became increased by adding chitin in soils
infected with pathogenic agents. Thereafter, these endogenous control strains can be
isolated, cultured and potentially used as biological controls. It has also been demonstrated
a significant increase in chitinolytic microorganisms even in very infertile soils like in dunes,
improving soil microbiota and its properties [239, 241].
46. Bionematicide
Nematodes proliferation can be controlled when chitosan is applied in soil, because
chitinolytic microorganisms proliferate destroying nematode eggs and degrading the chitincontaining
cuticle of young nematodes [240]. Because of the high content of nitrogen in
chitosan and chitin molecules, concentrations of ammonia emissions increase turning toxic
to nematodes which principally affect plant roots and shoots [239, 243].
Further research is still required to find more applications of chitosan in agriculture, but
nowadays this polymer means to be a cheap and easy material to deal with crop problems
pre-harvest, harvest and post-harvest level.