The potential of hot water treatments for curtailing seed-associated mycoflora.
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Date
1995
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Abstract
The consequences of toxigenic fungi associated with stored seed have stimulated these
investigations aimed at developing treatments to minimise this mycoflora, without
significantly reducing seed quality or viability. The effects of immersion in water at 55, 57
and 60 QC for durations of 5 to 60 min were assessed for maize (Zea mays L.) seed in terms
of fungal status, water uptake, electrolyte leakage, germination and seedling establishment.
These assessments were conducted immediately after treatment, after re-dehydration for 2
days in an ambient air stream, and following a 1 month storage period under either cold (4
QC) or ambient (25 QC) conditions (33% and 91% RH, respectively). In all cases, the results
are compared with those of control seeds and seeds pre-imbibed for 4 h at ambient
temperature.
The level of internal contamination, represented almost entirely by Fusarium moniliforme
Sheldon, declined significantly when assessed immediately after treatment, the efficacy of
which increased with increasing temperature and duration of treatment. Seeds immersed in
water at 55 QC for a duration of 15 min exhibited an 85% reduction in infection levels, when
compared with those of the control, while those treated at 57 and 60 QC (same duration) were
uninfected. Immersing seeds in hot water, however, resulted in a lag in germination rate and
drop in germination totality, the degree of which was enhanced by increasing duration and
temperature of treatment, suggesting the status of the manipulation to be an accelerated ageing
treatment. The electrolyte leakage studies indicated that the reduced germination performance
of these seeds was not due to plasmalemma disorganisation. These deleterious effects,
however, were counter-balanced as seeds treated at 55, 57 and 60 QC for durations up to 60,
30 and 10 min, respectively, produced plants of superior quality than those of the control,
which is ascribed to the reduction of systemically transmitted pathogens. The efficacy of the
hot water treatment in reducing the levels of seed infection and improving seedling quality
was enhanced by subsequent re-dehydration. The reduction in seed-associated mycoflora was
maintained following storage for 1 month at both 4 QC (33% RH) and 25 QC (91% RH).
However, both seed and seedling quality were adversely affected following storage even under
cold, dry conditions, which may be a consequence of the pre-treatment history of the seeds,
which had been cold-stored for two years prior to the experiments. Applied as a pre-sowing
treatment, therefore, hot water treatment shows promise for producing a crop of superior
quality, less prone to fusarial pathogenesis. This treatment may be of particular importance
to Third-World subsistence communities.
Description
Thesis (M.Sc.)-University of Natal, 1995.
Keywords
Theses--Botany., Maize--Seeds., Seeds--Viability., Fusarium Moniliforme., Fungi--Morphology.