Plant mutation breeding enhance crop productivity and food security in drought-prone environments in Namibia
Agriculture is a major contributor to the Namibian economy and is highly correlated to growth and development. The country has semi-arid and arid climatic condition regions and is one of the driest countries of sub-Saharan Africa, consequently crop yields are severely limited by drought. Since 2013, pearl millet or Mahangu as it is locally known, has been grown by subsistence farmers in many parts of northern Namibia where yields are extremely low because of unreliable and poor rainfall patterns (Figure 1).
Most of the crops are grown under rain fed conditions and the land is prone to severe soil degradation. Namibia has low and erratic annual rainfall between 300-700 mm within and between years. This situation has not only affected crops but also livestock production as there is a lack of grazing lands and feed. Desperate farmers have been taking grass from their thatched huts to feed their cattle and goats.
Pearl millet (Pennisetum glaucum), followed by cowpea (Vigna unguiculata [L.] Walp) are major staple food crops for people living in northern Namibia. Sorghum (Sorghum bicolour) is ranked third in economic importance. Cowpea is a nitrogen fixer and is inter-cropped with pearl millet and sorghum as it provides organic nitrogen fertiliser to the other crops. However, average yields of these crops are extremely low ranging from 250 to 350 kg/ha for cowpea to 800-920 kg/ha for pear millet. Yields are particularly low when drought spells occur. Existing varieties are no longer meeting farmer’s requirements as they are prone to pests and diseases, produce poor yields and are susceptible to changing climatic conditions such as drought and extreme heat stress. The Namibia Agricultural Research Plan (NARP) classified research projects on local and staple food crops such as cowpea, pearl millet and sorghum as priority areas for research and development.
The project: “Using Mutation Breeding and Integrated Soil Plant Management Techniques to Develop Sustainable, High Yielding and Drought Resistant Crops of Pearl Millet, Sorghum and Cowpea” was set up in 2008 as a collaboration between the Government of the Republic of Namibia through the Ministry of Agriculture, Water and Forestry and the International Atomic Energy Agency (IAEA), with the support of the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture.
The objective of the project was to apply plant mutation breeding and soil management techniques to develop new mutant lines/varieties with high yield potential and enhanced tolerance to drought conditions for drought affected farms. Seed of local varieties of cowpea, sorghum and millet were treated with gamma rays at the FAO/IAEA’s Laboratories, Seibersdorf, Austria.
The treated seeds were shipped back to Namibia and planted, and a mutation breeding programme was initiated by the Ministry of Agriculture, Water and Forestry. Three crop research stations have been involved in developing new improved mutant varieties: Omahenene in the North West, Mannheim in the North Central and Bagani Research in the North East of Namibia. The R&D effort in Namibia was supported by the Joint FAO/IAEA Division in 2009 in the form of a fellowship training programme in plant mutation breeding at FAO/IAEA laboratories, Seibersdorf, Austria.
In subsequent years, a number of the young scientists (8 in plant breeding and 8 in soil and water management) have been trained in nuclear techniques applied in plant mutation breeding and soil and water management. The training targeted techniques that produce desired mutants and those that could be used in developing and advancing selected mutant lines for field performance trials in Namibia for drought tolerance, in cowpea, sorghum and pearl millet.
The outputs of the project
Ten years from the initiation of the project, Namibia now has several advanced mutant lines in cowpea (14), sorghum (11) and pearl millet (11) with better yield (10-20% higher than local varieties), better seed shape, large and different coloured seed, early maturity and drought tolerance. These promising lines are now being prepared for testing prior to being released to farmers.
1. Straight pods
One major achievement is the development of a semi-coiled and straight cowpea pod mutants of the local variety Shindimba (Figure 3).
Most farmer’s prefer a straight pod to the highly coiled pods of Shindimba, and farmers are now happy with to have an improved semi-coiled – straight pod “Shindimba” mutant.
2. Drought tolerant and early maturing mutant lines developed
Early maturing (a drought avoidance trait), drought tolerant and better yielding mutant cowpea lines have been developed and introduced to farmers during 2015/16 season for performance testing in farmer’s fields.
These mutants are well adapted and performed well under local farm management conditions. The local farmers themselves demonstrated that the advanced mutant lines performed better than local varieties without supplementary irrigation under severe water stress.
Drought tolerant mutant lines will enable farmers to protect their harvest minimizing losses during severe drought and help them to cope with climate change.
3. Different seed colour, shapes and sizes in cowpea.
The common seed colour of cowpea is white, however variation in seed colour was produced and developed as farmer’s have different preferences for seed colour and most would like to plant all the seed colour types when they become available (Figure 5, 6 and 7).
Improved mutant lines, with different seed colour, will enable farmers to grow and harvest consumer-preferred cowpea varieties that will increase their income.
Source: Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture