Chitosan seed treatments appear as a cellophane-type coating.
Experimental data indicating the beneficial effects of chitosan
treatments in agriculture [42,43] resulted in the first marketing
of a product, YEA (yield enhancing agent). Recent reviews [2–5]
summarize many of the reported the beneficial uses of chitosan in
crop protection. Successful chitosan treatment can be a function of
the application chemistry. The moisture of soil surrounding treated
seed, maintains some chitosan solubility if the chitosan pH remains
below 7.0. The initial antifungal and anti-bacterial properties of chitosan
are at the seed surface. Subsequently chitosan must penetrate
the seed coat and cell membranes before it can exert its influence
on the cellular metabolism of the plant. Studies using radio-labeled
chitosan indicated that the chitosan applied to the seed is detected
in other parts of the seedling as they develop [44]. Lignin accumulations
following wheat seed treatments raise significantly above
levels in the untreated tissue and may contribute to stem strength
[43]. Chitosan has been applied to a range of plant tissues from succulent
vegetables to woody plants and no one hypothesis relates to
all beneficial modes of action. Correspondingly chitosan treatments
can range from positive to moderately positive, or to an absence of
benefit. Chitosan treatments to wheat seeds designed to counter a
disease called “straw breaker” (Pseudocercosporella herpotrichoides)
had a positive effect and kept the wheat upright through to harvest
[44]. Was the effect due to a direct antifungal action on the
pathogen growth or was it a strengthening of the stem bolstered
by an increase in lignin?