A healthy aversion to smut
Head smut disease, caused by the fungus Ustilago kamerunensis, has a devastating impact on Napier grass, turning vigorous, impenetrable clumps of valuable livestock feed into thin, shrivelled stems. First reports of the disease from central Kenya some ten years ago, have since been followed by others from Tanzania, Uganda, Rwanda and the Congo. The problem is currently confined to relatively small areas, but the risk of spread throughout the region has made finding a solution a matter of urgency.
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Credit: J Hanson, ILRI |
For smallholder dairy farmers in East Africa the threat posed by head smut is potentially very serious. Being able to provide enough good quality feed is by far the most important factor in achieving high milk quality and yield. A well fed animal produces two or three times more milk than an averagely fed one, and so long as a farmer has access to a reliable market, dairying can be a highly profitable activity. In some countries, such as Kenya, it remains the single most important rural enterprise in terms of contribution to household income and employment. Eighty percent of the country's marketed milk is produced by smallholders, and in the central region nearly three quarters of farming families keep dairy cattle. Most feed their animals through a cut-and-carry system, with Napier grass the most popular form of feed; crops of Napier are deliberately cultivated by farmers for the purpose. The demand for feed is so high, in fact, that some Kenyan coffee farmers, struggling to make money against the tide of falling prices, have found that they can earn more per hectare growing Napier for cattle. Even some landless farmers are benefiting, planting the grass along road verges to cut and sell.
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Credit: D Miano Mwangi |
Finding resistance
Disease control is expensive, beyond the means of most smallholders. Hence the hope among scientists in the region that by identifying smut-resistant varieties of Napier they may be able to develop a more sustainable solution. Since 1992, scientists from the Kenyan Agricultural Research Institute (KARI) and the International Livestock Research Institute (ILRI) have been collaborating in trials of Napier varieties, and KARI have discovered two smut-resistant types that flourish in Kenyan conditions. The varieties, Kakamega 1 and 2, which were sourced from ILRI's field genebank in Ethiopia, are not as productive as the best of Kenya's local varieties, but have nevertheless proved extremely popular in smut-affected areas. In 2001 KARI's Muguga research station received numerous requests for Kakamega root splits, and some schools in the area are, at the request of parents, using school gardens to multiply the material.
Increasing variety
Despite this success there remain some major hurdles to be overcome. An important one is the danger posed by the dependence on just two varieties. Napier grass is clonally propagated: new plants are genetically identical to the parent. With all the smut-resistant stock based on just two clones, the chances of that resistance being broken down are high. KARI and ILRI staff are therefore continuing to search their genebanks for other Napier lines that show smut-resistance potential. Their aim is to both increase the number of varieties that can be distributed, and also identify plants that combine both smut-resistance and high yields. Farmers are also continuing to use the Kakamega lines in their fields, and institute staff will experiment with different dissemination techniques. The hope is that the successful 'pathways' can then be used to spread new varieties as they become available.
Work on the smut problem has highlighted some important issues, both for farmers and for the scientific community. For farmers, it emphasises the potential of Napier grass. In future this potential may be enjoyed by many millions of livestock keepers in areas where Napier has never been grown before. Multi-locational trials in southern and eastern Africa, for example, have already identified several cold-tolerant varieties of Napier. Four lines being tested by the Ethiopian Agricultural Research Organisation have outperformed local grasses in fields as high as 2400m, and have substantially reduced feed costs. For the scientists, the success of the Napier trials has confirmed the importance of plant genebanks in helping to meet the challenges faced by resource-poor farmers, an importance further underlined, in terms of funding, by the establishment of the Global Conservation Trust in Johannesburg last year.
