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Microbes Inside Rootcrops May Cure Ubi Anthracnose, Other Plant Diseases

Researchers at the Philippine Rootcrop Research and Training Center (PhilRootcrops) of the Visayas State University (VSU) in Baybay, Leyte have unveiled what could become the next potential biological control for anthracnose in purple yam and other plant diseases.

Julie D. Tan, Evelyn B. Taboada, May V. Tampus, Jilly B. Regis, and Rodney H. Perez have isolated and tested the endophytic microorganisms found in sweetpotato, which are recognized as sources of secondary metabolites useful in biotechnology and agriculture. And initial results confirmed that these endophytes produce antimicrobial compounds that inhibit the growth of pathogenic microorganisms in plants.

In their study titled “Antimicrobial evaluation and effects of fermentation process conditions of bioactive compounds produced by endophytic Bacillus sp. against some selected food and plant pathogens”, the researchers screened isolates of endophytes from rootcrop-based products and other related fermented food products for their abilities to inhibit the growth of some selected food pathogens. They also determined the effects of fermentation on the productivity and activity of the biocontrol compound.

Endophytes are microorganisms that inhabit the interior portion of plant, especially leaves, branches and stems without harming it. Fungi and bacteria are the most common microbes existing as endophytes. They are valuable to agriculture as they improve crop performance due to their capability to colonize and grow inside the host tissues and eventually produce useful products such as natural preservatives, antibiotics, enzymes and other novel compounds for industrial and biotechnological applications.

In the study, the researchers isolated from stem cuttings of local sweetpotato varieties the endophytic bacterium Ba cillus subtilis among the 21 isolates (12 bacteria and 9 fungi) chosen from 96 endophytic microorganisms screened that possessed inhibitory activity against eight plant and food pathogens. These pathogens included Bacillus subtilis, Colletotrichum gloeosporioides, Lasiodiplodia theobromae, Diplodia natalensis, B. subtilis AHU 1035, Aspergillus flavus var. esper AHU 7051, Alternaria sp. S-1, and Candida albicans CA14.

As one of the most important microorganisms used in microbial technology, B. subtilis can control many plant pathogens since it is a known producer of a wide spectrum of antimicrobial compounds. This valuable characteristic of endophytic B. subtillis prompted the researchers to investigate its antimicrobial activity against fungus Colletotrichum gloeosporiodes, the pathogenic microorganism that causes purple yam anthracnose.

Purple yam anthrachnose, also called dieback, is a serious problem in yam production worldwide because this disease reduces yield as well as the quality of tubers. The disease results in the production of several small tubers that are unmarketable. Oftentimes, severe infestation occurs that results in significant yield loss.

Experts at PhilRootcrops said that aside from planting resistant varieties and disease-free setts, there is currently no concrete control measure for yam anthracnose and previous measures were not able to eradicate it. Right now the Center is testing a concoction of indigenous microorganisms as an alternative control for anthracnose.

The results of the study suggest that controlled fermentation conditions (30°C, 89% dissolved oxygen saturation, 500 rpm, and pH 6.8) favored higher antimicrobial activity of compound produced by B. subtilis against C. gloesporioides than when it is grown under uncontrolled pH.

With these results, the researchers recommended coming up with a practical preparation that can be applied in the field. Tan said that future studies shall focus on the production of compound either in crude or concentrate form that can be diluted with water and sprayed on affected plants at the seedling stage. “But first we have to screen suitable medium (preferably a rootcrop) for the reproduction of antimicrobial compound,” she added.

Aside from B. subtilis, the researchers are also set to study other endophytic microorganisms that they have isolated as each of them has a potential for various applications such as food preservation, as secondary product synthesis, and as a control agent for pathogenic microorganisms.

This research won 3rd place in the research category of the National Symposium on Agriculture and Resources Research and Development conducted by the Philippine Council for Agriculture, Forestry and Natural Resources Research and Development (PCARRD) during its 37th anniversary on November 9, 2009 at the PCARRD Headquarters in Los Banos, Laguna.

By Melpha M. Abello