The effect of provenance on the response of the recalcitrant seeds of Trichilia dregeana to drying and chilling.
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Date
2011
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Abstract
One of the factors that affect the post-harvest behavior of seeds is provenance. Different
geographical locations are characterised by different environmental conditions, hence,
plant materials harvested from different locations may respond differently to laboratoryinduced
stresses.
The aim of the present study was to assess the role that provenance plays on the degree of
recalcitrance of a single species – a factor that needs to be taken into consideration when
choices are to be made for plant germplasm conservation. In this study, seeds of Trichilia
dregeana, which have been shown to display recalcitrant post-harvest behavior, were
harvested from four locations that were slightly different in climatic conditions: Mtunzini
(MTZN), Durban (DBN), Pietermaritzburg (PMB) and Port Edward (P.ED), all within
the KwaZulu-Natal province of South Africa. Clean seeds, whose aril and seed coat have
been removed, were subjected to different drying and chilling stresses and their responses
to the stresses are examined. Excised embryonic axes of the seeds were also subjected to
flash (very rapid) drying and their responses to the stress are shown.
Although the vegetation of these locations can be categorized as being sub-tropical, the
present study suggests that there may be ‘degrees’ in the sub-tropical nature based on the
rainfall and maximum temperature data. The ‘degree of sub-tropicality’ is suggested to be
in the order MTZN > DBN > P.ED > PMB. Mean seed size assessed as seed length,
width and fresh mass varied significantly across the four regions, with seeds from MTZN
being the smallest and those from P.ED being the largest. The shedding water content of
the embryonic axes of the seeds for 150 min. However, shoot
production, root and shoot length and dry mass accumulation showed that axes of seeds
from MTZN were the most adversely affected by rapid drying while those from PMB
were the least sensitive. When clean whole seeds were dried slowly by burying in silica
gel for 36 h, all seeds of the four provenances still retained more than 50% of their
shedding water. MTZN seeds lost viability completely from the 24 h of slow drying
while seeds from the other three locations retained some viability after 36 h. The order of
survival of slow drying was MTZN < DBN < P.ED = PMB.
Storage of cleaned whole seeds at chilling temperatures (3oC, 6oC and 16oC) caused
increase in the water content of the embryonic axes of the seeds across the four locations.
All seeds of the four provenances had lost more than 50% survival after they had been
stored at 3oC for 10 weeks. Survival was completely lost from the 12th week for MTZN
seeds, from the 14th week for DBN and P.ED seeds and from the 16th week for PMB
seeds. There was no survival recorded for seeds across the four regions at the 18th week.
The seeds were able to tolerate storage at 6oC for a little longer than those stored at 3oC.
Only MTZN seeds completely lost viability at the 18th week; seeds from the other three
locations retained some viability throughout the 18 weeks of storage. Storage at 16oC was
the most tolerable, as all seeds from the four provenances maintained some viability until
the 18th week in storage, with MTZN having the least survival and those from P.ED
having the highest survival.
Phylogenetic analysis of the internal transcribed spacer (ITS) region of the DBN and
PMB samples showed intraspecific levels of genetic variation, and were separated by a
genetic distance of 0.9%, an indicator that differences in storage behavior, chilling and
desiccation sensitivity between seeds obtained from different collection localities may be
genetically based.
This study showed that MTZN seeds were the most sensitive, while seeds from PMB and
P.ED were the most tolerant, to drying and chilling treatments, respectively. The
prevailing climatic conditions may have a bearing on the responses observed in this
study.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.
Keywords
Seeds--Development., Seeds--Storage., Seeds--Harvesting., Trichilia., Meliaceae., Theses--Botany.