Blast disease eats into rice yields, BRRI looks for resilient varieties

Around 1% of the country's total four crore tonnes of annual rice production is damaged by blast diseases as there are no resistant and tolerant rice varieties, according to the Bangladesh Rice Research Institute (BRRI).

BRRI is currently trying to develop rice varieties resistant to blast diseases. Experimental cultivation of the new variety is taking place in farmers' fields during the ongoing Boro season, say researchers.

If the experiment is successful, the variety will undergo the final approval process from the National Seed Board, they added.

Researchers say blast diseases pose a common threat to the country's two primary crops, rice and wheat. However, the damage has been notably mitigated in wheat through the development of tolerant varieties.

They say blast is a fungal disease and can appear in favourable weather, from seedlings to the ripening stage. It can attack rice leaves, necks, panicles, collars and other parts of the plant.

As per BRRI, the peak incidence of blast diseases in Bangladesh occurred between 2015 and 2017, attributed to the effects of climate change. Despite not manifesting on a large scale since then, the disease continues to inflict damage on crops annually, with its impact gradually escalating.

Researchers say the disease primarily targets aromatic rice during the Aman season in November, when the country produces over 1.5 crore tonnes of rice.

Besides, during the Boro season, the predominant period for rice production, the disease affects high-yielding and fine rice varieties, as well as early and aromatic rice varieties. 

Currently, its impact is substantial across various varieties, including BRRI rice-28, 29, 50, 63, 81, 84, and 88.

BRRI reports that the highest incidence of this disease is observed in the Cumilla, Gazipur, and Rangpur regions. Researchers say in years with March rainfall, the prevalence of the disease increases, leading to more substantial damage to early rice varieties.

According to them, this poses a significant challenge as the country's rice production stability has been achieved primarily through high-yielding varieties.

Dr Mohammad Ashik Iqbal Khan, principal scientific officer at the Plant Pathology Division of BRRI, told TBS, "Rice blast diseases can be mitigated with appropriate medication at different stages, utilising the right medicine in specific doses. However, the most effective solution lies in developing resistant varieties."

He added, "We are currently in the final stages of the process for developing such a variety."

The researcher further noted that on a national scale, the impact may not be significantly felt since less than 1% of rice production is damaged each year. However, in areas severely affected by blast attacks, the damage can reach 100%, making its intensity truly devastating.

The disease targets rice when the temperature ranges between 25-28 degrees Celsius, coupled with high humidity in the air. Under these conditions, its occurrence can also be noted in fields with a substantial amount of urea fertiliser.

On the other hand, the favourable temperature for blast disease in wheat is 20-22 degrees Celsius, and it also attacks in high humidity conditions. Wheat production season primarily occurs during winter, according to researchers.

Blast resistant wheat

Despite the prevalence of the disease in rice, Bangladesh Wheat and Maize Research Institute reports a reduced impact on wheat production.

Researchers attribute this success solely to the development of wheat varieties resistant to blast diseases.

The cultivation of these resistant varieties prevents the disease from damaging the plants. At present, the country produces 11 to 12 lakh tonnes of wheat annually.

Blast-resistant wheat varieties, such as Bari-33 and BWMRI-Gom 3, have been developed alongside several tolerant varieties, including BWMRI-Gom 1 & 5, Bari Gom 30, and 32. These varieties were introduced following the damage caused by the disease in the 2016-17 wheat production season, as reported by researchers.

Dr Md Abu Zaman Sarker, chief scientific officer at the Plant Pathology Division of the Bangladesh Wheat and Maize Research Institute, told TBS, "The incidence and impact of this disease in wheat are now low, primarily attributed to the availability of several blast disease-resistant and tolerant wheat varieties."