ABSTRACT
Seeds of three cultivars of cassava were collected from the
CSIR-Crops Research Institute at Fumesua in the Ashanti Region to
determine the effect of storage periods and seed pre germination treatments
on the germination percentage, physicochemical and health properties of seeds from
the three varieties of cassava. The experiment was conducted under
laboratory conditions and a 3 x 3 x 7 factorial in Completely Randomized Design
(CRD) with three replications was used. The first factor was cultivar at three
levels (Ahwengyanka-1, Ahwengyanka-2 and Aworowa-3); the second factor was
pre-germination treatments at seven levels (hot water, cold water, mechanical
scarification, three concentrations of acid scarification and no treatment as
the control); the third factor was storage period at three levels (no storage,
three months storage and six months storage). The study revealed that seeds of
cassava stored for up to three months produced about 40% germination after
undergoing the various pre-germination treatments. Seeds of the Aworowa-3
cultivar stored for six months produced the highest germination percentage of
61.0%. Seeds mechanically scarified with sand paper produced the highest
germination percentage of 48.9% whereas seeds with no treatment recorded the
least percentage of 34.8%. Seven fungi pathogens were identified on the three
cultivars of cassava seeds irrespective of the cultivar and period of storage.
The study concluded that Aworowa-3 seeds without storage produced a higher
germination percentage than Ahwengyanka-1 and Ahwengyanka-2 seeds without
storage but all the seeds of the three varieties had the highest germination
percentage when stored for six months.
CHAPTER ONE
1.0 INTRODUCTION
Cassava (Manihot esculenta Crantz)
is the most important tropical root crop in many parts of Africa because of its
edible roots (FAO, 2009). It is also cultivated for its leaves and tender
shoots which are rich sources of proteins, vitamins A, B, C, and other minerals
are consumed as vegetable (Fregene et al., 2000; IITA, 2001). In Africa, Ghana
ranks third after Nigeria and the Democratic Republic of Congo as the largest
cassava producing country (FAO, 2009). Cassava in Ghana is grown across all the
agro-ecological zones and contributes 22% to Ghana’s Agricultural Gross
Domestic Product (AGDP) (Parkes, 2009).
Cassava is vegetatively propagated
by mature stem cuttings. This mode of propagation is the most widely used since
cassava does not produce large amounts of sexual seeds; however, the wild
species are naturally propagated through seeds (Teixeira, 1987). The seedlings
that are obtained from cassava seeds are initially smaller than plants that are
developed from vegetative cuttings and they require special care to become
established. The seeds of cassava are oval in shape and have a cross section
that is elliptic or circular. The seeds are approximately 100 mm long and 4 to
6 mm thick (Alves, 2002).
Seeds of cassava can remain viable
when stored under ambient conditions for up to 1 year, although germination
percentages may decline substantially after 6 months (Rajendran et al., 2000)
in some cases. Under cold storage conditions (4°C and 70–80% relative humidity)
cassava seeds can remain dormant for up to 7 years with no loss of germination
thus dormancy is a usual occurrence in cassava seeds. Dormancy in seeds, therefore is known to inhibit the
germination of intact viable seeds under favorable conditions (Bagheri and
Asadi, 2003; Robert, 2003; Finch Savage and Leubner-Metzger, 2006). Germination
of seeds of cassava can be favored by dry heat and complete darkness (Ellis et
al., 1982). Generally, treatments used to break seed dormancy may include
mechanical scarification, chemical scarification (especially sulfuric acid),
cold-wet, hot water, electrasonic waves and stratification (Isvand et al.,
2004; Dehghani, 2005).
Genetically, cassava clones are
highly heterozygous and sexual propagation (propagation through seeds) results
in a wide diversity of phenotypes, which is of interest to breeders (Ceballos et
al., 2004). This discovery has endeared to breeders who have started to use
cassava seeds as the starting material in their breeding programmes. However, a
major problem with freshly harvested cassava seeds is its characteristic
dormancy which is a well documented occurrence in Euphorbiaceae genera (Keleny
and VanHaaren, 1967; Eakle and Garcia, 1977; Lago et al., 1978; Nassar and
Teixeira, 1983). The period of dormancy in cassava seeds could last for a
minimum period of 6-9 months under ambient temperatures (Ellis et al., 1982)
with adverse consequences on breeding programmes. To overcome this problem so
that cassava seed breeding programmes can be undertaken anytime without the
time-related dormancy limitation, development of suitable dormancy-breaking
techniques are of paramount importance. The general aim of the study therefore
was to determine the most suitable pre-germination treatment of seeds for high
germination of cassava seeds for breeding programmes.
Determine the effects of storage
periods and seed pre-germination treatments on the germination percentage,
physicochemical and health properties of seeds from the three varieties of
cassava.
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