| Summary: | The International Seed Testing Association and the Association of Official
Seed analysts define seed vigour as the ability of a seed lot to perform during
the germination process and crop stand establishment under a wide range of
environmental conditions. There are many ways to determine seed vigour, but
few satisfy the requirements of being simple, inexpensive and reproducible,
among others, to permit the seed industry to adopt seed vigour as an indicator
of seed quality when they sell seeds. Hence, the standard germination test,
which is performed under uniform and favourable conditions, is generally used
to indicate seed quality when seeds are marketed. The objective of this study
was to determine the performance of tomato and pepper seeds in response to
pre-germination hydration and dehydration relative humidities (12%, 49% and
75% RH). Before hydration, seeds were hydrated at three temperatures
(10°C, 20°C and 30°C). Hydration was performed by imbibing pre-weighed
pepper ('Santarini' and 'California Wonder'), Chilli and tomato ('Heinz',
'Marondera' and 'Roma') seeds for 2 h in 10 ml of distilled H(2)0 per 100 seeds
at 10°C, 20°C and 30°C. Dehydration was performed by change in seed mass
determined during a 72-hour dehydration at 12%, 49% and 75% RH. Seed
performance in response to imbibition and dehydration was determined by
leakage of electrolytes from seeds during imbibition, laboratory germination
capacity and seedling emergence under simulated shadehouse nursery
conditions. A pot experiment was conducted to determine the effects of seed
treatments on yield. Seed mass increased by about 50% during the 2-hour of
hydration. Dehydration was hastened by decreasing the RH, and 12% RH
significantly (P < 0.05) reduced the post-imbibition seed moisture content
compared with 49% and 75% RH. The latter two relative humidities reduced
the seed moisture content to about 10% and 15%, respectively, for all
cultivars, irrespective of imbibition temperature. Low imbibition temperature
(10°C) significantly (P < 0.01) increased electrolyte leakage, compared with
high imbibition temperatures (20°C and 30°C), which were not significantly
different from each other. At all hydration temperatures, low RH (12%) caused
a significant (P < 0.01) decrease in seed germination whereas 49% RH and
75% RH apparently had a priming effect on seeds. There was no significant
difference between imbibition temperatures, with respect to seed germination,
but 100G caused a significant decrease in germination index, a measure of
seed vigour. Seedling emergence was significantly (P < 0.01) reduced by both
low imbibition temperature (10oG) and low dehydration relative humidity (12%
RH). The negative effects of low imbibition temperature and rapid dehydration
at 12% RH were also observed as stunted seedling growth.
Principal component analysis and linear regression were used to determine a
statistical model to predict seedling emergence from germination percentage.
The model predicted emergence consistently, but it overestimated it by about
2% to 3%. It is concluded that low imbibition temperature and rapid
dehydration can be used to simulate stress to determine seed performance in
pepper and tomato. === Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
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