Efficacy of mon 89034 bt trait in conferring fall armyworm resistance in high yielding three-way and single-cross maize hybrids.
Chingombe, Pretty Nyaradzo.
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Maize production, especially in tropical sub-Saharan Africa, is hampered by the fall armyworm (FAW) posing a serious threat to food security and livelihoods. Many methods of control including pesticide use have been tried against FAW but without sustainable success. The main objective of this study was to investigate whether or not the Bt trait (MON89034) could be successfully integrated in high yielding tropical hybrids and confer effective resistance to FAW when deployed in three-way and single cross hybrids. The study was conducted under natural FAW hotspot conditions and under field conditions representative of farmer’s situation. Conventional non-genetically modified (non-GM) tropical single cross hybrids and inbred lines were crossed to four WEMA Bt lines. The resultant three-way and single cross hybrids were evaluated at three sites, in South Africa. The results indicated adequate discrimination of hybrids according to FAW resistance and grain yield, under both FAW infestation and at two other sites with limited FAW pressure. The experimental Bt hybrids displayed high yields exceeding 5 t/ha and higher FAW resistance, which was comparable to standard genetically modified (GM) control hybrids. In sharp contrast, the conventional non-GM control hybrids recorded yield as low as 0 t/ha, under FAW infestation. They were highly susceptible to FAW which was indicated by high damage scores. Therefore, the event MON89034 was effective in conferring FAW resistance in both three-way and single cross hybrids. Although the environment main effects were highly significant (P<0.001) for grain yield, the three-way cross hybrids were relatively stable and showed non-significant (P>0.05) genotype x environment interaction (GxE) effects. In sharp contrast, GxE effects were highly significant (P<0.001) for grain yield of single cross hybrids, indicating that they were less stable than their three-way counterparts. New Bt hybrids with high cultivar superiority index and combining high yield potential and FAW resistance were identified. These included (H3WX3167Bt) (HSX5054Bt), (HSX5368Bt) and (H3WX3194Bt). The three-way experimental hybrid (H3WX3167Bt) had yield advantage of 64% above WEMA GM checks, 33% above local GM hybrid checks and 22% above conventional non-GM checks. The single cross experimental hybrid (HSX5368Bt) exhibited yield advantage of 127% above mean of conventional non-GM checks, 100% above mean of WEMA checks and 99% above mean of local GM checks, under FAW infestation. In addition, secondary traits, such as ear prolificacy and number of ears harvested per plot, which had significant direct and indirect effects for grain yield under FAW infestation were identified for use in construction of a viable selection index. Overall, the study was successful and showed efficacy of the Bt trait (MON89034) in conferring FAW resistance when deployed in tropical high yielding three-way and single cross hybrids. The best performing experimental Bt hybrids with high yield and high FAW resistance, and out-yielded both GM and non-GM standard commercial hybrids, would be advanced in the breeding program that targets the GM market segment in tropical Africa. A survey of the literature has not revealed prior studies on evaluation of FAW resistance in three-way cross hybrids. The trait is deployed predominantly in single cross hybrids, in the GM maize production lead countries, such as Argentina, Brazil, China, South Africa and USA. Therefore, this study formed a significant baseline for revealing useful information on the efficacy of the Bt trait in conferring FAW resistance in three-way cross hybrids which are predominantly deployed to smallholder farmers in tropical Africa.