ANSWERING QUESTIONS ABOUT TARO LEAF BLIGHT

News Release

American Samoa Community College Pago Pago, American Samoa

September 29, 2003

According to a recent survey done for the Community & Natural Resources (CNR) Program at the American Samoa Community College, many local farmers have expressed concern, and in some cases confusion about the taro leaf blight disease (Lega) in American Samoa. In the interest of helping the public better understand this common problem, Dr. Fred Brooks, CNR Plant Pathologist, offered the following answers to some basic questions about taro leaf blight disease:

What is it?

Lega is a disease that attacks taro. It eats the leaves and can cause the corm to rot. Leaves of a healthy taro plant live for about 40 days, and a plant may have six or seven leaves at a time. Leaves of taro infected with Lega last only 10-20 days, and there may only be two or three leaves on a plant. Infected plants use all their energy to survive; no energy is stored in the corm as starch, so corms are small. Taro with weak defenses against the disease, like "Taro Niue," may eventually die. Lega is more severe during cool, rainy weather than during hot, dry periods.

How does it spread?

It spreads from plant to plant and from field to field via splashing rain, or rain carried by the wind. Most long distance movement, however, takes place when farmers plant infected tiapula. Lega can live on tiapula, at the base of leaf stalks, for up to three weeks.

Are other plants affected by it?

Colocasia-type taro ("Taro Niue," Palau Taro, etc.) is most at risk from Lega. Occasionally you can find leaf spots on ta’amu.

What is the scientific name of the organism causing taro leaf blight disease?

Phytophthora colocasiae. The name Phytophthora in Latin means "Plant Destroyer". Colocasiae is from the name of the taro grown throughout the Pacific region: Colocasia esculenta.

How do you control it?

If there are only a few spots of Lega on leaves, the spots or leaves can be removed and burned. If too many leaves are removed, however, this may do more damage than the Lega. Several chemicals can reduce the disease, but they are expensive and do not work well in this climate. The best control is to plant taro with strong defenses against Lega, such as Palau Taro or "Taro Fili".

What are Palau Taro and "Taro Fili"?

These are taro varieties with a high resistance to Lega. Resistance is the ability of a plant to protect itself from a disease. A plant variety with high resistance, like "Taro Fili" (it is from the Philippines) has fewer spots on its leaves and can store its extra energy in large corms. Taro from Palau is also resistant to Lega, and some of the Palau varieties were tested at the University of Hawaii. During testing, the varieties were numbered: P1, P2, P3, etc. Palau Taro varieties with the highest resistance to Lega were sent to American Samoa in 1997, and are still known by their experimental numbers.

Can "Taro Niue" be grown in American Samoa in the future?

Probably not. If no colocasia-type taro or ta’amu were grown in the territory for several years, the Lega might die from lack of food. However, it would be impossible to completely eradicate all the colocasia-type taro and ta’amu already here, so the disease will most likely remain and attack "Taro Niue" if it is planted. There may be some remote areas of American Samoa, however, where little or no Lega is present, and some "Taro Niue" plants may be able to grow there.

What about a taro breeding program?

Several countries, such as Papua New Guinea and the independent state of Samoa, breed taro to improve its characteristics. Samoa has been breeding taro for resistance to Lega since 1996. Two highly resistant parents, P10 and "Taro Fili," have been mated, as have several others. Of the thousands of offspring produced, only a small number have been found acceptable and released for sale. Plant breeding takes time, experience, patience and funding. A program coordinator in Samoa said they would like to mate P10 with "Taro Niue," but funds for this project are due to end this year. Offspring from a P10/Niue mating would supposedly have both the taste of "Taro Niue" and the disease resistance of P10. However, until scientists can successfully produce such a hybrid taro, farmers are better off cultivating Palau Taro and "Taro Fili," which we already know have a high resistance to infection by Lega.

If you would like more information about the taro blight disease than is provided here, please contact Dr. Fred Brooks at (684) 699-1575 or (684) 699-1394.

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