1. INTRODUCTION
Radio-sensitivity of selected cowpea (Vigna unguiculata) genotypes to varying gamma irradiation doses
L. Horn1,2 and H. Shimelis2
1. Directorate of Research and Training, Plant Production Research, Ministry of Agriculture, Water and Forestry, Private Bag 13184, Windhoek, Namibia
2.School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, Pietermaritzburg, South Africa
Cowpea (Vigna unguiculata L. Walp., 2n=2x=22) is an important component of the traditional cropping systems in the semi-arid tropics
About 95% of farmers in northern Namibia grow cowpea
Cowpea productivity is generally low at 250 to 350 kg/ha in Namibia
Mutation breeding is useful in crop improvement and functional genomics
A collaborative research between the International Atomic Energy Agency (IAEA) and the Government of the Republic of Namibia was initiated during 2009 to improve food security crops using mutation breeding
Exposure of plant propagules including seeds, tissues and organs to an appropriate dose of gamma radiation induces genetic variation for breeding (Mba et al., 2010)
The objective of this study was to determine an ideal dose of gamma radiation to induce genetic variation in three cowpea genotypes widely grown in Nambia.
INDRODUCTION
Fig. 2 A CO60 source
SHINDIMBA
BIRA
NAKARE
Cowpea genotypes (Fig. 1) Nakare (IT81D-985), Shindimba (IT89KD-245-1) and Bira (IT87D-453-2) were used for the study
Thirty seeds per genotype were gamma irradiated in three replications at seven irradiation doses (0, 100, 200, 300, 400, 500 and 600 Gy) were applied using a CO60 source Gamma cell (Fig. 2) at the IAEA as illustrated in Fig. 3
Data collected included germination %, hypocotyl and epicotyl lengths measured in cm
Fig. 1 Cowpea genotypes used in the study
MATERIALS & METHODS
RESULTS AND DISCUSSION
A significant (P<0.01) interaction was detected between genotypes
and irradiation doses (Table 1)
Germination % decreased drastically in all the three varieties with increased radiation doses (Fig. 4, Table 2)
There was no germination observed for Nakare and Shindimba above 300 and 400 Gy, respectively
Genotype Bira could withstand the radiation doses of up to 600 Gy and displayed 47% germination at this dose (Table 2, Fig. 5)
Fig. 3 Gamma irradiation and mutation generations for selection.
Irradiate to produce M1 seeds
M1 plants
M2 plants
M2 seeds
M3 seeds
Planting and Selection continues until desired traits are attained
Table 1. Analysis of variance on percent germination, epicotyl and hypocotyl lengths between cowpea genotypes, radiation dose and their interaction
Varied doses of gamma radiation applied on three different cowpea genotypes influenced germination, arly growth and development differently
LD50 for genotypes Nakare, Shindimba and Bira were achieved at , and Gy, respectively (Fig. 4)
The selected dose of the gamma radiation may help as a generic treatment dose to induce large scale mutagenesis in cowpea e
Irradiation doses leading to an average of 50% damage (LD50) to seed germination in genotypes Nakare, Shindimba and Bira varieties were determined.
The result demonstrated that cowpea genotypes required specific irradiation dose before large-scale mutagenesis is undertaken
Induced mutations are random events and as such published radiation conditions might not result in the same mutation events for different genotypes
CONCLUSIONS
Fig. 4 Germination responses of Nakare, Shindimba and Bira against gamma radiation doses
Fig. 5 Cowpea genotype Bira Irradiated at 600 Gy and M1 seedlings.
Table 2. Mean and standard deviation on percent germination, epicotyl and hypocoyl lengths among three cowpea genotypes tested using seven irradiation doses.
The IAEA is acknowledged for funding the study through the TC project in collaboration with the Government of the Republic of Namibia
The IAEA research team at the Joint FAO/IAEA Agriculture and Biotechnology Laboratory Seibersdorf, Vienna, Austria are thanked for research support
AKNOWLEDGEMENTS
REFERENCES
Mba C, Afza R, Jain SM (2010). Induced mutagenesis in plants using physical and chemical agents. Joint FAO/IAEA. Programme, Vienna, Austria, pp