IRRI prioritizes resistant breeding against emerging threats

In 2025, IRRI's scientists confirmed two emerging rice diseases in the Philippines: Rice Yellowing Syndrome and Southern Rice Black Strip Dwarf Virus. This underscores a critical message for farmers: accurate diagnosis and resistant varieties are the first line of defense in safeguarding rice production.

Overlapping symptoms complicate diagnosis

The country’s first documented case of Rice Yellowing Syndrome is caused by co-infection with two viruses, RGSV and RRSV. The highest incidence was recorded in Laguna province, causing severe yield losses in affected wet-season areas.

"Initially, the symptoms were suspected to be tungro or orange leaf disease because of the yellow-orange leaves," explained Dr. Gilda B. Johnson, IRRI pathologist. "However, further investigation revealed a different cause. The overlapping symptoms made field diagnosis more challenging."

Plants infected with the combined viruses exhibit severe stunting, leaf deformation, curling, and aborted panicle initiation. In many cases, the crop fails to produce harvestable grains. In artificially inoculated one-month-old plants, researchers observed significant stunting compared to healthy controls. Some infected plants appeared greener than healthy ones, adding further confusion in visual assessment.

Historically, RGSV and RRSV were observed in the 1970s and 1980s but had not been prevalent in recent decades. The resurgence and particularly the co-infection in a single plant is what scientists now call Rice Yellowing Syndrome. Because the symptoms closely resemble tungro, distinguishing between diseases based solely on field observation is nearly impossible. Similar outbreaks were first reported in China in 2001, followed by Vietnam in 2011 and India in 2022. 

To address this, IRRI relies on molecular diagnostic tools. The protein-based process involves extracting viral RNA from plant samples and using polymerase chain reaction (PCR) techniques in a thermal cycler to amplify and detect specific viral sequences. 

"Accurate disease diagnosis is the key," Dr. Johnson emphasized. "Farmers need identify correctly to find the right management solutions."

Both diseases can cause panicle abortion, meaning farmers cannot harvest anything at all.  According to IRRI experts, beyond diagnosis, proper field sanitation, including management of infected stubble is critical to reduce virus reservoirs. Most importantly, planting resistant rice varieties offers the most sustainable solution.

Breeding for resilience: The power of genetic diversity

Behind IRRI's disease response lies one of the world’s most important agricultural assets: the International Rice Genebank (IRG). Hosted at IRRI headquarters in Los Baños, the IRG is the largest repository of rice genetic diversity globally, conserving more than 132,000 rice accessions from over 130 countries.

The genebank maintains two primary storage systems. The Active Collection supports medium-term preservation for 20-40 years at 2-4°C and supplies seeds to scientists and breeders, while the Base Collection ensures long-term conservation for 50 - 100 years at -18 to -20°C. Safety duplicates are stored at the National Laboratory for Genetic Resource Preservation in the U.S. and at the Svalbard Global Seed Vault in Norway, providing global backup security.

The IRG is one of 10 CGIAR global genebanks and was the first to meet all standards set by the Crop Trust for perpetual funding.

Ms. Anna Kristnal of IRRI explained that seeds distributed from the genebank are provided under a Standard Material Transfer Agreement in line with the International Treaty on Plant Genetic Resources only for food and agriculture. Materials can be used strictly for research, breeding, and training related to food and agriculture. Private companies may also request seeds for breeding programs, but usage is monitored and reported to the FAO.

Importantly, IRRI encourages users to report findings back to the genebank. "If researchers discover that a specific accession shows resistance to pests, high heat tolerance, or other beneficial traits, that information strengthens global knowledge and accelerates breeding progress", she shared. 

IRRI’s breeding programs have already produced tangible results. The institute has developed more than 100 elite lines tolerant to salinity stress. A key genetic region known as Saltol - a quantitative trait locus associated with salt tolerance has been incorporated into popular varieties such as BRRI Dhan 11, 28, and 29 in Bangladesh, as well as several varieties grown in West Africa.

As climate change intensifies abiotic stress and emerging diseases spread across borders, genetic resources stored in genebanks are becoming increasingly valuable. IRRI is also leveraging artificial intelligence to identify promising traits and varieties more efficiently, supported by a $2 million grant from Google. The International Rice Genebank shares small seed samples free of charge to researchers and institutions worldwide, reinforcing its mandate to serve the global public good.

The emergence of diseases on rice raises a question for scientists. Visual symptoms alone are no longer reliable in a landscape of overlapping viral infections. Therefore, precision diagnostics, vigilant monitoring, and resistant varieties are indispensable tools for protecting farmers’ livelihoods.