Keep wheat diseases at bay: 11th annual training on stem rust note taking and germplasm evaluation at KALRO Njoro, Kenya

by Jerome Bossuet

As part of the Delivering Genetic Gain in Wheat (DGGW) project, the International Maize and Wheat Improvement Center (CIMMYT) in collaboration with Kenya Agricultural & Livestock Research Organization (KALRO) and Cornell University recently trained 24 researchers (8 women & 16 men) from 9 countries across the world on wheat rust disease diagnosis and germplasm evaluation. The training took place on October 5-13, 2019 at the KALRO research station in Njoro, Kenya, where CIMMYT’s wheat breeding and rust screening facility is located.

Hands-on skills for efficient breeding and disease control

CIMMYT has held such hands-on trainings annually since 2009, benefitting over 220 scientists, mostly wheat breeders and pathologists from national programs of developing countries worldwide.

“These trainings aim at nurturing the next generation of wheat scientists in the different wheat growing areas, harmonizing cost-effective wheat breeding techniques and building a global community of practice, so important for our future food security,’’ said training coordinator, Mandeep Randhawa, Wheat Breeder and Wheat Rust Pathologist based at CIMMYT Kenya. Dr. Randhawa manages overall activities of the stem rust phenotyping platform Njoro.

The training focuses particularly on studying resistance to rapidly evolving fungal diseases like black (stem), yellow (stripe) and brown (leaf) rusts. CIMMYT’s Global Wheat Program in Africa uses such trainings to establish new partnerships and continue efforts in wheat breeding and combating emerging challenges across the different farming regions.

The participants learned how to record stem rust field notes to identify different types and levels of resistance, and the interaction with  wheat experts helped them better understand how wheat rust pathogens keep evolving. Continuous breeding of wheat varieties with not-only high yield potential but with resistance to rust and non-rust diseases was emphasized.    

An important skill the trainees gained during the course was to visually identify and score stem rust symptoms accurately. The percentage of rust coverage on the stem is used to score plants’ susceptibility, e.g. moderately susceptible (MS) or moderately resistant (MR) host reactions to infection.

“Harmonizing the way wheat breeders score stem rust severity in different countries like Ethiopia or Bangladesh is very important, so we could compare research data in any global breeding program like DGGW and for disease surveillance systems,’’ explained Emeritus Professor Robert McIntosh, one of the trainers from the Plant Breeding Institute-Cobbitty, University of Sydney, Australia.

Despite its importance to the global food and nutrition security, wheat remains susceptible to very destructive rust diseases. Rusts can lead to total crop failure when the climate conditions are favorable for the fungus and varieties grown by farmers are susceptible. The wheat scientific community has to remain vigilant on rust outbreaks globally as these pathogens evolve quickly. The stem rust race Ug99, reported for the first time in Uganda in 1999, was able to overcome the stem rust resistance gene Sr31 present in many popular varieties planted by farmers in the region. In 2013-14, wheat variety Digalu in Ethiopia and Robin in Kenya became susceptible to a new stem rust race with virulence to gene Srtmp. By 2019, fourteen different races in Ug99 lineage have been identified across Eastern and Southern Africa.

“You can train someone for one year to score for rust resistance, but you learn all your life,’’ added McIntosh. “In the era of molecular breeding, it is remarkable to see that visual phenotyping recognition still plays a strong role in safeguarding one of the most important cereal.”

“This is the first time I am doing this rust scoring. This will be important for my job of certifying new rust resistant wheat varieties, to know how to rank one wheat variety from other popular check,’’ noted seed health inspector, Philip Chemeltorit from the Kenya Plant Health Inspectorate Services (KEPHIS) Nakuru. A durum wheat breeder, Ms. Divya Ambati from Indore, India learned how the rust symptoms vary between durum and bread wheat germplasm, while wheat scientists, Ms. Sourour Ayed and Ms. Rifka Hammami, from Tunisia were more interested in how to tackle Septoria, another fungal disease prevalent in their country.

“This training course is a great opportunity for national programs to have first-hand information on the performance of their varieties and advanced lines evaluated at the phenotyping platform from respective countries. It is important to understand the different types of resistance that can be used in breeding. Strategies of combining different race specific and adult plant resistance (APR) genes is important for researchers to develop varieties with durable resistance,” said Sridhar Bhavani, Head of Wheat Rust Pathology at CIMMYT Mexico.

Back to the breeder’s equation

Developing and distributing rust resistant wheat varieties is regarded as the most cost-effective and eco-friendly control measure, especially in developing countries, where the majority are resource-poor smallholder farmers with limited access to fungicides to control the disease.

Ravi Singh, Head of Wheat Improvement at CIMMYT Mexico explained the new wheat breeding priorities, where breeders should focus on cost-effectiveness:

‘’Wheat scientists must go back to the blackboard how to increase genetic gains in a cost-effective way. What new methods and tools would increase the number of lines screened (intensity), with good accuracy and shorter breeding cycles?’’

CIMMYT Mexico for instance has just invested in a new large field greenhouse in Toluca research station to produce four generations of wheat annually, instead of two currently. The global wheat program will be more responsive to new pests and disease like the recent wheat blast outbreak that affected Bangladesh.

‘’But not all is about speed breeding,’’ warned Singh. “The wheat research should remain holistic and continue asking the right questions to well capture farmers and wheat processors’ needs when defining future breeding targets or product profiles. Wheat yield potential remain very important, but you have to ‘package other traits like water-use efficiency, disease resistance, nutrition, profitability etc.’’’

Godwin Macharia, Centre Director and Wheat Breeder of the KALRO- Njoro Centre discussed progress in wheat improvement through CIMMYT-KALRO partnership:

 “Wheat varieties Kenya Kasuku and Kenya Jacana with significant yield advantage over current commercial varieties and moderate levels of resistance to stem rust were released by KEPHIS in 2019. Moreover, several high-yielding rust resistant wheat lines are in the national performance testing towards identification and release of suitable varieties for commercialization in Kenya growing environments. Seed multiplication is in process with enough volumes of breeder seed of the new varieties available for further bulking and distribution to growers for cultivation in the 2020 season.’’