Be Ware, You May Loose Your Entire Crop

Throughout the late 1970s to early 1990s stem rust disease had been controlled in Kenya through the development of resistant varieties by Karlo Njoro. In the late 1990s, a new race called ug99, highly virulent to most commercial varieties emerged. This race that was initially detected in Uganda in 1999 quickly spread to Kenya causing devastating crop losses in fields planted to popular commercial varieties then including Duma, Kenya Heroe, Chozi, Kenya Yombi. For Instance, total crop losses attributable to stem rust were reported by many farmers in Narok in 2007.

Following renewed threat posed by emerging races of stem rust including UG99, an alarm was raised led by, among others, the Nobel Laureate Dr. Norman Borlaug for a concerted global effort to combat the threat. This effort culminated in the creation of the Borlaug Global Rust Initiative (BGRI), which brought together many international institutions including Karlo (Then KARI) with the objective of systematically reducing the world’s vulnerability to stem, yellow, and leaf rust of wheat and facilitating the evolution of a sustainable international system to contain the threat of wheat rusts.

An international screening site for rust disease resistance was established at KARLO Njoro. The organization works with other collaborators to combat the stem rust disease menace that remains a key deterrent to wheat productivity in the country and the region.

The Cereal Disease Laboratory (CDL) at the University of Minnesota has partnered with KARLO to profile the local stem rust pathogen populations to inform variety development and deployment processes. Each growing season KARLO researchers collect isolates of the pathogen in wheat fields and dispatches those to CDL for analysis. Results both from KARLO’s own research and those from CDL have helped identify the stem rust race change. Accordingly, this joint research has established that beside the original Ug99 stem rust race discovered in the region over a decade ago, there are other similar races that infect specific wheat varieties. Evidence from rust disease survey activities carried out across by KARLO scientists in the country have been informative and helping advice farmers on what varieties to grow across the wheat zones.

Varieties developed jointly with The International Maize and Wheat Improvement Centre, commonly known by its Spanish acronym, CIMMYT, and released by KARLO includes Eagle10, Kenya Kingbird and Kenya Korongo. They are not only high yielding and of good grain quality, but also possess moderate to high stem rust resistance, depending on seasonal rust pressure.

These are suitable candidates for many wheat growing areas in the country under an integrated host resistance, chemical, and cultural management approach. Notably, Eagle10 and Kenya Kingbird are suitable for lower altitude regions such as lower Narok and some parts of Laikipia whereas Kenya Karongo is best suited for medium to high altitude zones.

The latest international project, “ Delivering Genetic Gain in Wheat”, presently underway at KARLO Njoro continues to spearhead discovery of new genetically superior wheat material, and many such promising wheat varieties are in the pipeline.

Beyond establishing infrastructural capacities to combat wheat rusts diseases in the country and beyond, a key focus has been on training of the next generation of plant scientists especially with regard to cereal rust diseases and breeding for resistance. Many graduate students are being trained between KARLO-Njoro and Egerton Universitiy, and a few have proceeded to Cereal Disease Lab and the University of Minnesota, USA for short term training and for doctorate level courses. A similar engagement is in place between KARLO and CIMMYT, Mexico.

An integrated disease management approach would be the most feasible in environments, which favour stem rust disease proliferation. Such an approach spans critical cultural practices, appropriate chemical use, coupled with growing seed of less susceptible varieties.

Some of the cultural practices that farmers need to employ are proper land preparation prior to establishing new wheat crops in a bid to getting rid of any volunteer wheat plants that may be holding the disease. This might also involve rotation of wheat with a suitable crop, say canola, a well as clearing bushes around the wheat fields which too could be harbouring growing wheat plants from previous crops that are likely sources of initial stem rust disease spread in new crops. Moreover, in some instances early or timely planting helps a crop mature in time before disease epidemics build up. Neighbouring farmers can plan to plant their crops at nearly the same date and implement other operations like spraying concurrently. This might reduce accumulation of stem rust inoculum and contribute to managing the rigours of the disease.

Appropriate chemical used entails, firstly choosing the right fungicide among manythat might be in the market, applying the recommended rates , spraying at the right crop growth stage when the plants are likely prone to initial attack.

Chemical intervention is also helped by systematic scouting for early symptoms of the stem rust disease, which before spreading to other parts of the plant manifests as reddish pustules or lesions on wheat stems. Considering that stem rust can lead to 100% yield loss if it landed on a susceptible variety only 3-4 weeks to harvest, close monitoring and scouting for the disease is a highly recommended practice so that immediate action is taken. In combination with proper cultural and chemical application regimes, farmers are highly encouraged to use certified seeds of moderately to highly resistant varieties available at KARLO-Njoro, for example Eagle10, Kenya Kingbird, and Kenya Korongo.

Planting seed of unknown identity puts the farmer at the risk of establishing a rust susceptible crop, with the possibility of total yield losses, build-up of the disease inoculum that spreads to other fields, and the undesirable events of the stem rust disease changing rapidly to give rise to new virulent races, a sort of a vicious cycle.