Use of Imidazolinone Resistant (IR) maize to assess the potential effect of transgenic maize in Uganda
Purple witchweed (Striga hermonthica) is a parasitic weed that attacks cereals particularly maize, causing up to 80% yield loss. The main objective of this study was to evaluate the efficacy of non-transgenic imidazolinone resistant maize (IR-maize) against S. hermonthica, using it as a model for impact assessment of transgenic herbicide resistant maize in Uganda. Experiments were carried out in the first and second rain seasons of 2006 and during the first rains of 2007 (hereafter referred to as 2006A, 2006B and 2007A, respectively). Field experiments to evaluate the efficacy of IR-maize in controlling S. hermonthica (here after referred to as Striga) were set up in Bugiri district in Eastern Uganda. In 2006A, 50 lines of IR-maize were evaluated for efficacy against Striga using maize variety, Longe 5 as a control. In 2006B and 2007A, Ua kayongo, a line of IR-maize was used against Longe 5 as a control. There was variability among IR-maize lines with respect to both Striga control and maize yield. The best performing lines with respect to Striga control were lines 18 and 3 whereas the best in terms of yield were 40 and 3. On the other hand, the worst performing IR-maize lines with respect to Striga control were 44 and 32. There was a positive relationship (r=0.285) between maize yield and the numbers of Striga plants that emerged in the plots. In 2006B and 2007A, maize varieties, Ua Kayongo and Longe 5, differed with respect to number of Striga plants that emerged in the plots (P<0.05). There was no difference between maize grain yield of various lines under test in 2006A and B. Another experiment to evaluate the effect of IR-maize on weed species other than Striga was also conducted; IR-maize and Longe 5 fields were established at the same location in each season. There were differences in weed numbers in IR-maize and Longe 5 over three seasons for Digitalia velutina, Kyllinga erecta, Mitracarpus villosus, Cyperus grandbulbosus and Eleusine indica (P<0.05) of which Digitalia velutina, Cyperus grandbulbosus and Eleusine indica had increased numbers in IR-maize. In the third experiment, geneflow levels from IR-maize to Longe 5 were determined at the Makerere University Agricultural Research Institute, Kabanyolo. In this experiment, the crossing frequency between IR-maize and Longe 5 was between 74-100%. In conclusion, IR-maize is very effective in controlling Striga, has no significant effect on other weeds and is cross-compatible with Longe 5 giving viable hybrids. Based on the findings of this study, IR-maize can be recommended to farmers for Striga management since it is effective and has no effect on other weed species. However, IR-maize is cross- compatible with Longe 5 and the resulting hybrids are herbicide resistant. Considering the farmer’s practice of saving seed for the next season, this may pose a risk of contamination. This may also imply that if transgenic crops were to be grown by farmers, they would contaminate the existing crop varieties and their landraces which may have serious consequences in the long run.