Occurrence of rice blast (Magnaporthe oryzae) and identification of potential resistance sources in Uganda

• Rice blast affects 54% of the cultivated rice area in Uganda.
• Magnaporthe oryzae causes mean grain yield losses of 42% in Uganda, with high incidence in the late season.
• Transplanting rice minimizes yield losses caused by M. oryzae compared to broadcasting.
• The R genes, Pi9, Piz-t, Piz-5, Pi19 and the cultivar Tetep, are resistant to M. oryzae in Uganda.

Rice blast caused by Magnaporthe oryzae continues to be the most destructive disease of rice worldwide, and is a number one disease of rice in Uganda. We present the footprints of M. oryzae importance, distribution, incidence and severity in the rice growing agro-ecologies of Uganda for 2009/2010, and the potential mitigation measures. Our data show that rice blast affects more than 50% of the cultivated rice area on average, and ranks as the most important disease encountered in the field. Between and within agroecologies, both incidence and severity varied (P < 0.05) reflecting the contribution of different cropping practices on rice blast epiphytotics. The highest blast incidence and severities were recorded in Bugiri, Butaleja, Mbale and Lira farmlands, which are the ancestral rice cultivation areas in Uganda. These areas showed mean yield reductions of >30% relative to other locations, suggesting that rice production history played a significant role in rice blast outbreaks. Broadcasting and drill seeding yielded 42.4% less than transplanted rice. Growing two rice crops per year is one of the methods suggested to increase rice production in Uganda, but there was a higher disease incidence in the late season than in the early season, indicating the need for improved resistant varieties. Four blast resistance genes (Pi9, Piz-t, Pi19 and Piz-5) and the cultivar Tetep had the lowest (≤4) blast severity scores in all the test locations. It could be suggested that these genes are potential resistance sources for developing varieties, which would be more relevant for the double cropping systems.