Aluminium packs, which have zero water vapour permeability,
limit the moisture vapour flux between seeds and the surrounding
atmosphere under fluctuating storage conditions (Walters 2007).
However, a non-significant moisture gain was recorded in noncoated
seeds, which could be attributed to their periodic exposure
to laboratory atmosphere during sampling for the moisture test.
This effect was not observed for coated seeds, which may be due to
the combined countering effect of the package and polymer seed
coat against moisture exchange. Similarly, under LTLH storage conditions,
moisture gain in coated seeds that were stored either in
paper or aluminium packs was non significant due to the combined
countering effects of polymer coating, low temperature and low RH.
This non-significant moisture gain limited the rate of seed deterioration,
resulting in non-significant decrease in germination percent
and vigour of stored seeds.
It is well established that the differences in seed deterioration
as a result of ageing leads to differences in seed vigour status
among different seed lots (Matthews and Khajeh-hosseini, 2007).
This has been demonstrated in maize, where seeds stored at lower
equilibrium moisture content under the humid tropical conditions
maintained higher vigour in comparison to those stored at higher
equilibrium moisture content due to lesser deterioration process
during storage (Abba and Lovato 1999). In the present study, the
hydrophilic polymer film coat acted as a physical barrier for absorption
of moisture in the vapour phase. Therefore, under ambient
conditions, the film coated seeds remained effectively protected from equilibration with fluctuating relative humidity, in a manner
comparable with storage in hermetic containers. Considering this
fact, we propose that the polymer film coat in itself acts as a microcontainer
for seed and thereby facilitates safe seed storage for an
extended length of time.