Abstract
Legumes have been used as food by indigenous people of Africa yet their full potential as food sources has not been completely realized. With modern technologies such as marker-assisted selection and mutational breeding, there is scope for rapid improvement of germplasm in these underutilized species. One approach is to induce genetic mutations through irradiation of plant tissues with neutrons or gamma rays generating molecular changes. The irradiation leaves residual radiation in the exposed tissues creating offspring with new features. Genetic mutations in plants can improve their performance, germination, quality, size and disease resistance. The effects of radiation applied to marama bean (Tylosema esculentum) were explored. The aim of this study was to screen individuals of T. esculentum derived from seeds irradiated with gammarays using microsatellite markers. There were two irradiation treatments -50 and 100 gamma ray irradiations that were compared to non-irradiated seeds as controls. For each treatment, seeds were imbibed and germinated. Seed emergence rates and percentages were ascertained. Each set of seeds was genotyped using a SSR marker - MARA039, located in a sub-unit of a polygalacturonase – an enzyme that mainly regulates seed germination. In regard to emergence, significant differences between the irradiated seeds and non-irradiated counterparts were noted. Irradiated seeds germinated faster and in adosage-dependent manner compared to non-irradiated counterparts (p>0.05). Genotyping revealed that the total number of AGA repeats in the microsatellite region shifted from its original five in the controls to between four and seven in the irradiated seeds. Furthermore, there were several point mutations in the irradiated seeds as compared to the controls. The study findings, suggest that irradiation may induce beneficial mutational changes such as faster germination rate of the marama bean, considering that the mutated microsatellite repeat region is located in gene encoding the enzyme regulating seed germination in plants. Key words: Marama bean, Tylosema esculentum, mutational breeding, irradiation, seed cycle, SSR.
Highlights
Legumes have been used by the indigenous peoples of Africa for centuries, their full potential as sources of food has never been realized
Seeds for this study were collected from a wild population of a Namibian marama bean plant, and the irradiation process was done by the International Atomic Energy Agency (IAEA) Laboratories in Vienna (Austria) prior to germination with normalization of seed moisture content
There were three experimental groups in this study: 50 seeds irradiated with 50 gamma rays (50Gy), 50 seeds irradiated with 100 gamma rays (100Gy), and 50 non-irradiated seeds
Summary
Legumes have been used by the indigenous peoples of Africa for centuries, their full potential as sources of food has never been realized. Legumes ( known as pulses or food legumes) rank third in the world production behind cereals and oilseeds, and constitute an important dietary constituent for both humans and animals especially where dietary protein is an expensive commodity. Grain legumes play a crucial role in the sustainability of agricultural systems and in food protein supplies in the developing world. The production of cereals dominates world food production while pulses play an often under estimated role as a break crop that fixes nitrogen (Popelka et al, 2004). Genetic transformation could help provide solutions to certain constraints, and improving food security in developing countries (Popelka et al, 2004). The yield potential of crop plants has to be significantly increased in order to combat this worsening food security situation
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