BAR TODAY || Official Quarterly Publication of the Bureau of Agricultural Research

Researchers from the Leyte State University (LSU) have recently identified sweet potato varieties that are resistant to feathery mottle virus disease.

Adaptability trials under the project "Interdisciplinary management of sweet potato feathery mottle virus (SPFMV)," revealed that V27-2, V27-5, and V28-2 are the most resistant varieties to the virus under Tarlac conditions. The researchers, led by Dr. Manuel Palomar of LSU, found that these varieties have the most desirable qualities preferred by farmers and consumers. They also identified the variety kinampay as the most resistant to SPFMV under Bataan conditions.

Plant with SPFMV (Taken from the International Photo Center at www.cipotato.org)

Through surveys in the major sweet potato growing areas of Tarlac and Bataan, researchers learned that the virus was already in the fields even during the 1950s. However, it was not until the late 1980s and early 1990s that the disease reached epidemic levels.

The researchers likewise discovered that SPFMV practically wiped out the most popular sweet potato variety called Bureau in Tarlac at that time. A more resistant variety, VSP6, which the locals dubbed as Super Bureau, replaced the wiped out variety. However, it only took the virus 10 years to make a comeback. An outbreak again occurred in 1997-98 after the El Niño phenomenon, and even the Super Bureau succumbed to it.

Researchers characterized the symptoms of the SPFMV disease into two types. The first symptom, exhibits vein clearing of leaves, followed by the production of chlorotic spots. These are yellow marks on the leaves resulting from the reduced levels of chlorophyll, the green pigment in leaves of plants.

In other cultivars, the virus causes the enhanced production of anthocyanin - the pigment that produces blue, violet, and red colors in plants resulting to purple rings surrounding the chlorotic spots, then followed by vein feathering. Another symptom induces mottling, or formation of an irregular pattern of patches or spots of different colors, chlorotic spots, and reduced leaf size.

The SPFMV is known to significantly reduce growers' harvest and income yearly. Previous surveys on SPFMV-infested areas in Central Luzon confirmed this. Farmers here lamented that prior to the spread of this disease, sweet potato production was a lucrative business, especially during periods when rice could not be grown due to lack of irrigation. Farmers here plant sweet potato to about 10,000 hectares each year.

To date, all sweet potato fields in Tarlac and Bataan are SPFMV-infected, with every locality varying only in the degree of infection, the study reported. The highest SPFMV incidence was noted in Capas, Paniqui, Tarlac, Balanga, and Bagac.

Researchers are now inputting all survey data to complete a geographical information systems map to facilitate easier monitoring of these SPFMV-infested areas. They are also working on the characterization, identification of vectors or disease carriers, and epidemiological studies, the study of causes, origin, and development, of SPFMV. Further adaptability trials and evaluation of other resistant and high-yielding varieties are also being sought.

Source: "Interdisciplinary management of sweet potato feathery mottle virus disease in Central Luzon" by Dr. Manuel Palomar, LSU, Baybay, Leyte