Maize Genetics Cooperation Newsletter vol 81 2007
Kyungpook National University and the International Corn Foundation
Downy mildew (Perosclerospora sorghi) is still considered the most damaging disease of maize (Zea mays L.) in South Asia. Since the early 1990s, downy mildew (DM) has been a minor problem in Thailand, Indonesia, the Philippines and Taiwan. Breeding for resistance materials and the uses of chemicals such as Ridomil have played a catalytic role in reducing the spread of the disease in the region. However, the same disease has produced epidemics in Cambodia, East Timor and Vietnam, recently. A study of DM was carried out in East Timor and Ben Tre Province in Vietnam for three years, and at the ICF/Cambodia Banteay Dek Agricultural Research Station, for two years (2005-2006). This paper reports the results of DM infections at the station and farmers� fields.
In East Timor, severe infections of DM were observed in farmers� fields and the Lapos station of the CIMMYT/Australia maize trials in February 2003. DMR lines evaluated include: a Thailand open-pollinated variety (OPV), Suwan 1, and lines from IITA, Nigeria and CIMMYT, Mexico. Among the IITA DMR materials, TZDMR-ESR-Y appears to be the best. Using Suwan 5, Kalinga (Indonesia), TZDMR-ESR, the project has developed several DMR variety crosses. Both OPV and variety crosses are being tested at research stations and in farmers� fields. DMR materials will be recommended to East Timor.
In Ben Tre Province of Vietnam (the first province of the Mekong Delta), DMR materials from IITA and Thailand have been tested for three years (October, 2002) with the assumption that DM would be the key biotic constraint of maize cultivation in the country. However, DM was observed in March 2006 to be widely present in the country. Waxy hybrids introduced from Thailand and locally bred field corn hybrids were found to be highly susceptible. Five DMR OPVs were selected. The best known DMR OPV, Suwan 1 showed an unknown black ear rot. Maize programs in Vietnam must focus on DMR breeding to block further spread of DM nation wide.
In Cambodia, DM is the number 1 production constraint for maize cultivation. Severe epidemics of DM infection were observed from several farmers� fields in the Phnom Penh area in August, 2005. The program has focused on DMR materials for Cambodia. Ten different plantings have been made to screen DMR and segregating materials using the ICF/Cambodia Banteay Dek Agricultural Research Station. The station was established by the Government of Hungary 15 years ago. Among the 50 materials tested, four DMR OPVs showed an acceptable level of tolerance. They are Suwan 5 (coded as KC35), Suwan 1 (coded as KC6) from Thailand and TZDMR-ESR-Y (coded as KC25) and TZDMR-LSR-Y (coded as KC4) from IITA. A CIMMYT DMR conversion, EV28-DMR, and several other DMR materials segregate for resistance. DMR genes are being incorporated into farmers� preferred local waxy materials.
Please Note: Notes submitted to the Maize Genetics Cooperation
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