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| Pocket rots have been a mysterious and highly destructive problem for taro growers for many years. In the past year, an important step in combating this problem was accomplished when pocket rot was reproduced for the first time. This success was achieved using a new species of Phytophthora isolated from taro with pocket rot. The work, done in the laboratory of Dr. Janice Uchida in the Department of Plant and Environmental Protection Sciences, has come as a culmination of years of diligent detective work, commitment to community improvement, and a multidisciplinary problem-solving approach. For growers who have suffered from heavy damage by pocket rots for years, a big mystery has been solved. |
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Front Left to Right: Roy Yamakawa, Kauai CES; Wayne Tanji, Taro Farmer; Lance Santo, HARC; Dr. James Silva, UH TPSS.
Back: Desmond Ogata and Julana Jang, UH ADSC.
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| The success was based on solid scientific procedures: |
- Many field observations were made, and microorganisms from diseased taro were repeatedly collected.
- A series of symptom changes in taro corms leading to pocket rot formation were identified and characterized; pocket rots were found to be the end-product of active infections of the corm that occurred many months before a typical pocket was observed.
- New isolation procedures were developed to culture the elusive pathogen.
- New aseptic culture procedures were formulated to grow the new organism.
- Confirmation experiments demonstrated that many commonly isolated fungi do not cause pocket rots.
- Other experiments repeatedly confirmed that pocket rots are reproduced when the new Phytophthora is added to healthy taro.
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Establishing that pocket rots were the end-products of a series of corm infection stages was crucial to identifying the new pathogen. The earliest stages of corm rot are small rots near the base of the petiole. When rots are washed and placed on isolation agar, the new Phytophthora only grows from these early symptoms. The great difficulty of observing and isolating this new Phytophthora has been a large part of the mystery of this disease.
From all other corm rot stages, the new Phytophthora is absent or has not been cultured. It grows extremely slowly and will not emerge from infected tissue pieces if surface disinfestants are used. Use of surface disinfestants is a standard procedure for the isolation of pathogens from diseased tissue. The presence of this new Phytophthora can be confirmed in early stages of infection, as the mycelium is present in diseased tissue. Phytophthora colocasiae, the cause of taro leaf blight, and other microbes in the soil may also cause pocket rots, and these organisms are being investigated.
The new Phytophthora species is homothallic (self fertile). It produces sexual spores that have a thickened wall, which permits it to survive in the paddy for long periods. This allows the pathogen to accumulate in the soil, and the disease frequency can potentially increase with every crop. CTAHR researchers recommend that taro growers fallow their fields or grow a short-term cover crop to reduce the number of surviving pathogen spores.
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Left to right: Chad Koide, Raymond Uchida, UH ADSC; Robin Shimabukuro, Maui CES; Isaac Kanoa, Taro Farmer; Robert, Maui CES; Kyle, former UH UDSC student help. |
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Good relationships have developed between taro farmers throughout Hawaii and CTAHR’s research and extension programs. This collaboration continues to raise the level of good will toward CTAHR and the University of Hawaii. The success of our efforts is tied to the dedication of the growers who allow the use of their fields and donate taro huli (starters). It also is built on the perseverance of CTAHR Cooperative Extension Service county agents and the interdisciplinary CTAHR team.
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Core CTAHR team:
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| Plant and Environmental Protection Sciences (PEPS) |
Janice Uchida
Chris Kadooka
Jeri Ooka |
| Tropical Plant and Soil Sciences (TPSS) |
Jim Silva |
| CTAHR Agricultural Diagnostic Service Center |
Ray Uchida
Desmond Ogata
Julana Jang |
| Hawaii Agricultural Research Center |
Lance Santo |
| Kauai CES |
Roy Yamakawa (TPSS) |
| Maui CES |
Robin Shimabuku (PEPS) |
| Oahu CES |
Randy Hamasaki (PEPS) |
| Oahu CES |
Steve Fukuda (TPSS) |
| Maui/Molokai CES |
Alton Arakaki (TPSS) |
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Growers:
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Kauai
Christine Kobayashi
Dimi Rivera
Michael Bino Fitzgerald
Wayne Tanji
Clarence Kaona
Rodney Haraguchi
Alex Diego
Charles Spencer
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Maui
Gladys and Isaac Kanoa
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Oahu
Ernest Tottori
Ka’ala Cultural Learning Center (Eric Enos, Project Director; Butch Detroye, Farm Manager; Hailama Bright, Jonathan Deenik)
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Posted April 17, 2002
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