Downy mildew (DM) caused by the fungus Peronosclerospora sorghi is one of the most serious diseases reducing maize (Zea mays L.) production in East Timor. We have conducted three trials of DM resistant (R) and non-DMR source populations in three locations; Loes, Dili and Lospalos. Materials were developed by using DMR-ESR-Y and MO5-5-RUVT-EE (TZEE-Y) (IITA) and Suwan 5 (Thailand). Three sets of random mating, incomplete diallel crosses and parent populations were planted with three replications in one meter row with RCBD. Data assessment of DM infection was rated based on 1 – 9 rating score (1 = highly tolerant and 9 = highly susceptible) from 2 and 4 weeks before flowering. In Comoro, Dili, 32 genotypes exhibited very low DM infection with coefficient of variance and mean 17.2% and 3.9, respectively. BISI-2 (Indonesian hybrid) and TH2 (Timor Hybrid 2 crossed from two DMR OPVs, Indonesian Arjuna and Suwan 5) showed outstanding commercial value (CV). Twelve cultivars of MO5 were varied in CV. At Loes Research Station, genotypes showed high variation in DM infection. Average heterotic effect of 36 F1 crosses for DM tolerance was 29.5%. Mean parent value and F1 indicated negative correlation for DM infection. The result showed that to breed high resistance is difficult. However, breeding for host tolerance with polygenic system with a threshold nature is possible.

Downy mildew (DM) caused by the Peronosclerospora maydis is considered the most damaging disease of maize (Zea mays L.) in South Asia. In East-Timor, it has been widely spread and considered as the major stress of maize production. It was observed at Loes Research Station and farmers’ field since 2004. All materials exhibited high susceptibility to DM infection at the CIMMYT trial. Only Suwan5 (Thailand), LYDMR (CIMMYT) and Arjuna (Indonesia) showed tolerance. Different trials with 900 crosses were tested at 5 locations; Lospalos, Dili, Comoro, Aileu and Loes in 2006/2007 In 2008, high DM infection was observed at Loes. Crosses of Suwan5, NAI, Arjuna and DMR-ESR-Y (IITA)with tropical and temperate germplasm showed tolerance. The International Corn Foundation (ICF)/KNU team with the Ministry of Agriculture have run breeding research three cycles yearly. By 2007, the joint team developed an open-pollinated variety (OPV) with combined tolerance to DM and drought. The Ministry named it "NAI", means "honorable" in national language. Hybrid breeding for both DM and drought are being developed.

The common corn rust caused by Puccinia sorghi Schw. is widely distributed southern regions of temperate zones and sub-tropical regions world wide. It has been reduced corn yield significantly in Texas and Hawaii. The first author has observed incidence of this disease in Korea since ten years ago both in South (Kunwi, Ilsan, Pyungchang) and North Korea (Tongcheon). P. sorghi had very high infection in Jeju Island with over 2000 mm rainfall in 2008 on commercial hybrids from USA (DK 729, Pioneer 3394, P32P75) and Korea. All showed high susceptibility. Genetic tolerance could be the most economic way to control these fungi. The occurrence of this disease in Korea may be caused by environment changes. Pro-environment tolerance breeding with quantitatively inherited genes of host crop can guarantee for the durability and sustainability of crop cultivars under continuous changes of weather and environments.