Fighting cassava witches’ broom disease

MANILA, Philippines - Cassava is an important crop in the Philippines because of its many uses.  In addition to rice and corn, cassava is a staple food among Filipinos particularly those in Mindanao. It is also used for feed and fuel.

In fact, according to the Philippine Rural Development Program report of 2014, the biggest chunk of cassava production in the country goes to the production of livestock feeds – the biggest taker of cassava produce. 

Before, cassava was considered as a subsistence crop only. But with the advent of a huge feed milling industry and the flurry of investments from the private sector, cassava production in the country is steadily taking off. But, given its promising demand, the country still lags behind when it comes to cassava production.

According to Erlinda Vasquez, director of the Leyte-based Philippine Root Crop Research and Training Center (PhilRootcrops), the Philippines is one of the lowest producers of cassava in Southeast Asia. It has around 300,000 hectares, which is relatively small in comparison with other countries like Thailand with 1.6 million hectares and Vietnam (0.6 million). New comers, Cambodia and Laos are already producing more than 400,000 hectares each.

Vasquez revealed that even though the Philippines has been planting cassava for a long time, “the production area has remained at the 300,000-hectare level.”

From subsistence to commercial crop

“One of the biggest challenges to cassava production is the occurrence of pests and diseases. This is because we are creating a condition that becomes very conducive to pest and disease development,” Vasquez said.

She said the incidence of pests and diseases was not a problem before because cassava was grown as a backyard crop. But since it is now being produced in a commercial scale, growers are encountering problems that have mainly resulted from a monoculture system of cassava growing.

With the high demand for cassava comes the matter of expansion in terms of production area to meet the supply requirement. Unfortunately, the local produce is not even enough to meet the domestic demand. “We are exporting some cassava products, like starch. Now that cassava is utilized, not only as feeds but also as starch, creating thousands of products from it in the process, this adds more demand to produce cassava,” Vasquez said.

Phytoplasma, a menacing cassava disease

“It was in 2007 that I first saw a high infestation of Cassava Phytoplasma Disease (CPD). Commonly, they referred to it as the Cassava Witch’s Broom disease, particularly in the Southeast Asian region. But there is a problem if we refer to it mainly as witch’s broom as it is only one of the many symptoms of CPD,” Vasquez noted.

“There are instances wherein you cannot see the witch’s broom manifestation – only the yellowing, bunchy top, stunted growth, and sometimes proliferation of its auxiliary buds.  Now, when there is proliferation of auxiliary buds, you can call it a witch’s broom because the plant manifests the branching effect.  But in many cases, you cannot see it, just the yellowing. It also depends on the strain because, based on our study, we have found out at least seven strains of Phytoplasma,” she said.

“We have gone to a number of places all over the country interviewing farmers, as old as 70 to 80 years old, and they told us that the disease has been in the country for quite a long time.  But at that earlier time, there was no problem about this disease because people plant cassava on a subsistence level or backyard production only. Now with the commercialization and importation of planting materials, and without thorough selection, we are having the problem of diseases,” she added. 

There are a number of pests and diseases attacking cassava, but at the moment, CPD is considered as the most challenging and rigorous one. 

Vasquez explained that when the plant is infected, there are no symptoms at all. It depends on the variety, season, age, elevation, temperature, soil nutrition, management, and interplay of other factors.

“With CPD, if the manifestations or the symptoms appear as early as two to three months, then you’ll have 100 percent loss as there will be no more production of roots. Now, if the symptoms appear at the later stages like five to six months or onward, you can expect reduction in yield of up to 40 percent,” she said.

With CPD, the losses are not only on the yield, but also on the quality of starch. “When cassava is infected, both the yield and the quality of the starch are affected. Starch is an important by-product of cassava for processed food. An infected cassava has high hydrocyanic acid content making the flour bitter and therefore inedible,” she said.         

Abating the problem through Streptomycin

The research project, “Management of Cassava Phytoplasma Disease: Survey, Diagnosis, Characterization, and Control”, is being implemented by PhilRootcrops in collaboration with the Bureau of Plant Industry and various regions of the Department of Agriculture.

This P2.9 million research initiative, which was funded by the Bureau of Agricultural Research (BAR) through its cassava R&D program, has three components: nationwide survey to map out the distribution and occurrence of the disease, PCR-based diagnosis and characterization,  and control of phytoplasma disease.