The potential of hot water treatments for curtailing seed-associated mycoflora.

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.