Abstract:
Taro (Colocasia esculenta (L) Schott) is an important staple food crop grown throughout many
part of the world for it fleshy corms and nutritious leaves. Suckers are the main planting
materials used in West Africa; therefore, it is traditionally conserved in field collections. This is
not an effective conservation strategy for medium to long term preservation of taro genetic
resources due to extreme climatic conditions, pests and diseases. Tissue culture is one of the in vitro techniques which have in recent years become major agricultural importance in the area of
plant propagation, disease elimination and production of secondary metabolites in-vitro.
However, with tissue or micropropagation conservation, challenges include: High growth rate of
both the local and exotic genotypes of taro which causes sub-culturing in every eight weeks and
also high shoot proliferation and all axillary buds produce shoots, leading to a dense population
competing for limited nutrients in the glass vessel. Taro is a crop that is amenable to tissue
culture.
A study was conducted to optimize rapid multiplication and establish slow growth systems for
Colocasia genotypes in-vitro. Thus, taro genotypes used for the experiment were obtained from
the Taro Breeding Programme at Crop Research Institute which includes SA0 002, CE/MAL/32,
SA0 006 and CE/MAL/ 14, BL/SM/80, KA 019 as corms. The study was carried out at the
Tissue culture labouratory-Crops Research Institute (CRI), Fumesua.
The experiment was categorized into 5 stages thus: In-vitro Rapid Multiplication, In-vitro
Medium-Term Conservation; In-vitro Recovery, Fourier Transform Infra-red analysis for
concentration of Mannitol absorption content in Colocasia genotype and Biochemical analyses.
The genotypes were evaluated in a complete random design. Means were separated using LSD at
5%. Rapid multiplication experiment cultures were maintained at 25±10C at 16hr photoperiod.
Two modes of explant excision (Transverse Section (TS) and Longitudinal Section (LS)) were
used. For the rapid multiplication set up results, the highest number of shoots (26.00) and leaves
(40.00) were produced on the multiplication medium of transverse section (TS) shoot excision
for BL/SM/80 genotype, and lowest number of shoots (24.00) and leaves (39.67) occurred on
medium culture of longitudinal section (LS) shoot excision. However, for KA 019 genotype, the
minimum number of shoots (30.60) and maximum leaves (38.13) were observed in the culture of
LS excision, while the maximum number of shoots (32.00) and minimum leaves (37.40) were
observed on culture of TS of shoot.
The in-vitro cultures were evaluated for their growth, re-growth, mannitol absorption rate and
enzyme activity (Catalase and peroxidase activities) as a response to the conservation conditions
of the in-vitro collection. The four genotypes studied showed a good in-vitro response, when the
mannitol was used as a growth retardant. The medium term conservation cultures were incubated
at 20±10C and 12 hours photoperiod (3000lux) conditions. Explants were subjected to different
concentrations of mannitol (0, 20, 25 and 30g/l) and White medium (which is a supposed low
nutrient as compare to MS basal media). No growth regulators were added to the various media.
Survival rate was high and explants remained almost green and healthy on all mannitol treated
media when conserved for 6 months on conservation medium. However, with White medium,
the growth decreased as the conservation period increased. High number of shoots (6.33) and
leaves (22.67) occurred on medium containing 20 and 25g/l mannitol in genotype SAO 006,
whereas 30g/l mannitol was the best to restrict growth for the entire 6 months period in terms of
shoot height (22.50cm) among all the genotypes conserved. Results regarding recovery and
regrowth showed that regeneration percentage, number of shoots per ex-plant and their length
(cm) decreased with increasing concentration of mannitol from control to 30g/l. Determination
of mannitol absorption rate by the plantlet, enzyme activities were performed by FTIR
spectroscopy and UV/VIS spectrophotometer respectively. The analysis of FTIR and UV
spectroscopy both confirm the rate of absorption of mannitol and enzyme activities after 6
months period of conservation.
This showed that Transverse (TS) section of explants has more axillary and accessory buds
occurring at the base than Longitudinal (LS) section, therefore rapid multiplication can be
achieved, whereas mannitol supplemented culture media could reduce the growth of Colocasia
plantlets especially in stem height. Results showed that conserved explants can be regenerated
after transferring and culturing on recovery medium and incubating under regular usage
conditions.
The osmolite mannitol, at all concentrations tested, did not affect the viability of the whole
explants, probably influenced ROS scavenger system, affecting the antioxidant enzymes activity.
The time of FTIR analysis is considerably reduced compared to the classical methods; this
demonstrates that FTIR analysis of mannitol offers a quick and efficient means of sugar analysis.
Description:
A THESIS IN THE DEPARTMENT OF CROP AND SOIL SCIENCES EDUCATION,
FACULTY OF AGRICULTURE EDUCATION
SUBMITTED TO THE SCHOOL OF GRADUATE STUDIES, UNIVERSITY OF
EDUCATION, WINNEBA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE AWARD OF MASTER OF PHILOSOPHY (M.PHIL) DEGREE IN
AGRONOMY IN THE UNIVERSITY OF EDUCATION, WINNEBA.
JUNE 2016