Focus
   Breeding Barley for resistance to Fusarium Head Blight
By
Flavio Capettini
The Fusarium Head Blight fungus ruins both the quality and yield of barley crops, which has caused multi-million dollar losses to the food, feed, and malting industries around the world. ICARDA and CIMMYT scientists are trying to breed varieties of barley with resistance to the onslaught of this destructive disease.

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Researchers inoculate barley spikes to test their susceptibility to Fusarium Head Blight.
he Fusarium fungus responds to the coming of spring and the increased warmth and humidity by releasing hundreds of miniscule, crescent-shaped spores. Rain and wind carry the spores across fields until they settle on exposed parts of small grain crops, such as barley. As the fungal infection progresses, only some of the damage – such as shriveled, lightweight, discolored grain, or black or salmon-colored fungal growth on the hull – becomes evident. The most serious effect of Fusarium Head Blight, or FHB, remains invisible to the eye. The fungus produces a mycotoxin called deoxynivalenol, which is toxic to humans, and causes excessive vomiting, hormonal disorders, and even cancer in animals. High levels of the mycotoxin can ruin a potentially profitable barley crop and render it useless for food, feed, and brewing.

FHB causes serious difficulties in the commercialization, export, and processing of commercial grade barley. Epidemic outbreaks of FHB have caused serious losses worldwide. In the US, the economic losses caused by the fungus from 1998 to 2000 represent as much as 25.7% of the commercial value; in 2000, the losses represented almost 36% of the total sale of the crop. In 2001, the fungus caused Uruguay’s barley yield to drop from the 2500 kg/ha estimated before harvest to 800 kg/ha. Most of the harvested grain was contaminated with the mycotoxin. The obvious, though not necessarily the simplest, solution is to breed disease-resistant barley.

Fusarium Head Blight testing nursery in Toluca, Mexico.
Breeding Strategy
Complete immunity to FHB has not been identified in barley, which is why mitigating the impact of this disease is an extremely challenging and critical research objective. When the ICARDA/CIMMYT barley breeding program started looking for sources of FHB resistance in 1986, only 23 barley accessions out of a total of 5000 screened were found to be partially resistant. These were used extensively in crosses to introduce resistance genes into the main breeding program. Sources of FHB resistance were also shared with other breeding programs worldwide after epidemics.

 After identifying the sources of FHB resistance, researchers carried out various crosses in an attempt to enhance the resistance in successive generations. The ICARDA/CIMMYT program discovered two forms of resistance (Type I and Type II) to FHB in barley, which were previously described only in wheat. Type I is resistance to the penetration of the fungus in the spike and Type II is resistance to the spread of the fungus within the spike. Researchers crossed Type I and Type II resistant plants to combine the resistance. The resulting lines were evaluated at the Toluca Experiment Station in Mexico where environmental conditions are ideal for the spread of the Fusarium fungus. Researchers also collaborated with barley breeding programs in Brazil, Canada, China, Ecuador, Uruguay and the United States.
Resistant (left) and susceptible barley at the Toluca Experimental Station, Mexico.

The breeding strategy proved to be effective. Researchers achieved enhanced levels of protection from FHB when they combined 1-3 sources of resistance. They also observed that the improved lines were resistant in a variety of geographical areas. “Since FHB infection is highly influenced by environmental conditions, it is very important that the resistance is expressed in several different environments and crop growing conditions worldwide,” says Dr William Erskine, ICARDA’s Assistant Director General (Research). The barley bred for resistance in Mexico showed resistance and low levels of the mycotoxin when grown in Canada, China, Latin America and the United States.

In 1998, the ICARDA/CIMMYT breeding program released ‘Gobernadora,’ a 2-row barley variety with enhanced levels of resistance. “Gobernadora represents one of the most important results of the program, mainly because it reached a sizeable commercial planted area in China,” says Erskine. ‘Gobernadora’ was released in Shanghai, China, with the new name of ‘Zhenmai-1,’ and was grown on more than 100,000 hectares in three provinces in the lower basin of the Yangtze River where FHB is endemic. Today ‘Gobernadora’ is commonly used as a source of resistance for germplasm enhancement and in research studies.

Collaborative Projects
Tailor-made Solutions
The problem of breeding for FHB resistance is further complicated by the number of species of Fusarium fungus in a given location. Graduate thesis work carried out in Mexico found 14 species of Fusarium in the main barley commercial area of the Mexican Highlands. When researchers artificially inoculated the most commonly grown barley cultivar with fungal samples collected in the field, several produced mycotoxins, though they did not reduce yield. The results revealed that the most frequently occurring species of Fusarium in the Mexican Highlands was F. avenaceum, rather than F. graminearum, which is usually the case. When researchers evaluated genotypes from different programs in Latin America, Mexico and the United States for Type I and Type II resistance, they found that resistance varied with the species. This means that barley varieties released in Mexico should be resistant to F. avenaceum, not just F. graminearum, and that breeding efforts need to be specifically tailored to species and location.
For the past four years, ICARDA/ CIMMYT’s barley breeding program has been working with Busch Agricultural Resources Inc. to produce FHB-resistant germplasm for brewing using commercial US sources. The project is also producing F7 advanced lines with high levels of FHB resistance and enhanced resistance to Stripe, Stem and Leaf Rust, Barley Yellow Dwarf Virus, and Net and Spot Blotch. Researchers plan to test for malting quality lines in the future.

Barley breeders have also been working with the US Wheat and Barley Scab Initiative (USWBSI) for four years to introgress FHB-resistant elite lines and cultivars from the US into the ICARDA/CIMMYT program and vice-versa. This special breeding program is expected to increase the chance of finding FHB-resistant lines that are adapted to a specific target area. The program also aims to enhance malting quality in barley and has incorporated genetic material from Australia, Europe, South America, as well as the United States into the main breeding pool. Augmenting malting quality of barley will further enhance the contribution the program is making to help the poor farmers in the region by capturing opportunities for worldwide
collaboration.

Dr Flavio Capettini (f.capettini@CGIAR.ORG) is the Head of the ICARDA/CIMMYT Barley Breeding Program at ICARDA’s Latin America Regional Program, based at CIMMYT in Mexico.
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