Performance of Bt maize event MON810 in controlling maize stem borers Chilo partellus and Busseola fusca in Uganda

Stem borers are major insect pests of maize in Uganda. A study was conducted in 2014–2016 to assess the performance of Bt hybrids expressing Cry1Ab (event MON810) against the two major stem borer species in Uganda – the African stem borer (Busseola fusca) and the spotted stem borer (Chilo partellus) – under artificial infestation. The study comprised 14 non-commercialized hybrids, including seven pairs of Bt and non-Bt hybrids (isolines), three non-Bt commercial hybrids and a conventional stem borer resistant check. All stem borer damage parameters (leaf damage, number of internodes tunneled and tunnel length) were generally significantly lower in Bt hybrids than in their isolines, the conventionally resistant hybrid, and local commercial hybrids. Mean yields were significantly higher by 29.4–80.5% in the Bt hybrids than in the other three categories of non-Bt hybrids. This study demonstrated that Bt maize expressing Cry1Ab protects against leaf damage and can limit entry of stem borers into the stems of maize plants, resulting in higher yield than in the non-transgenic hybrids. Thus, Bt maize has potential to contribute to the overall management package of stem borers in Uganda

Detection of sister-species in invasive populations of the fall armyworm <i>Spodoptera frugiperda</i> (Lepidoptera: Noctuidae) from Uganda

<div><p>The fall armyworm (FAW) <i>Spodoptera frugiperda</i> (J. E. Smith) is a species native to the Americas. This polyphagous lepidopteran pest was first reported in Nigeria and the Democratic Republic of São Tomé and Principe in 2016, but its presence in eastern Africa has not been confirmed via molecular characterisation. In this study, FAW specimens from western and central Uganda were identified based on the partial mtDNA COI gene sequences, with mtDNA COI haplotypes matching those identified in Nigeria and São Tomé. In this study, we sequence an additional partial mtDNA Cyt <i>b</i> gene and also the partial mtDNA COIII gene in Ugandan FAW samples. We detected identical mitochondrial DNA haplotypes for both the mtDNA Cyt <i>b</i> and COI partial genes, while combining the mtDNA COI/Cyt <i>b</i> haplotypes and mtDNA COIII haplotypes enabled a new maternal lineage in the Ugandan corn-preferred FAW samples to be identified. Our results suggested that the African incursions of <i>S</i>. <i>frugiperda</i> involved at least three maternal lineages. Recent full genome, phylogenetic and microsatellite analyses provided evidence to support <i>S</i>. <i>frugiperda</i> as likely consisted of two sympatric sister species known as the corn-preferred and rice-preferred strains. In our Ugandan FAW populations, we identified the presence of mtDNA haplotypes representative of both sister species. It is not known if both FAW sister species were originally introduced together or separately, and whether they have since spread as a single population. Further analyses of additional specimens originally collected from São Tomé, Nigeria and throughout Africa would be required to clarify this issue. Importantly, our finding showed that the genetic diversity of the African corn-preferred FAW species is higher than previously reported. This potentially contributed to the success of FAW establishment in Africa. Furthermore, with the additional maternal lineages detected, there is likely an increase in paternal lineages, thereby increasing the diversity of the African FAW population. Knowledge of the FAW genetic diversity will be needed to assess the risks of introducing Bt-resistance traits and to understand the FAW incursion pathways into the Old World and its potential onward spread. The agricultural implications of the presence of two evolutionary divergent FAW lineages (the corn and the rice lineage) in the African continent are further considered and discussed.</p></div

Phylogenetic analysis of <i>Spodoptera frugiperda</i> selected partial mitochondrial DNA COI (mtDNA COI) sequences obtained from publicly available DNA database, including Corn-REF and Rice-REF (see ) haplotypes, and haplotypes identified in this study (MF197867, indicated by blue coloured arrow; MF197868, indicated by red coloured arrow).

<p>Rice-preferred and corn-preferred mtDNA COI haplotypes were confidently clustered into sister clades at 74.9% and 96.4%, respectively. The partial mtDNA COI haplotype KF854210 identified also as <i>S</i>. <i>frugiperda</i> (isolate GK424, [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0194571#pone.0194571.ref038" target="_blank">38</a>] was inferred to be basal to the <i>S</i>. <i>frugiperda</i> rice and corn sister clades. The out groups species were <i>S</i>. <i>exigua</i> (JX316220) and <i>S</i>. <i>litura</i> (JQ647918).</p

Multigene phylogeny (i.e., from concatenation of partial mitochondrial DNA (mtDNA) COI, COIII, Cyt <i>b</i> genes) of the rice-preferred and corn-preferred Ugandan <i>Spodoptera frugiperda</i> sister species.

<p>Partial mtDNA COI, COIII and Cyt <i>b</i> gene sequences were obtained from full mtDNA genomes of <i>Spodoptera</i> species (<i>S</i>. <i>exigua</i> JX316220; <i>S</i>. <i>litura</i> JQ647918; <i>S</i>. <i>frugiperda</i> KM362176; <i>S</i>. <i>frugiperda</i> KU877172, and <i>S</i>. <i>frugiperda</i> ‘Corn’ and ‘Rice’ reference mitogenomes (i.e., Corn-REF, Rice-REF, <<a href="http://bipaa.genouest.org/data/public/sfrudb/FAW_mitochondrial_genomes.fa" target="_blank">http://bipaa.genouest.org/data/public/sfrudb/FAW_mitochondrial_genomes.fa</a>>, see [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0194571#pone.0194571.ref040" target="_blank">40</a>]) and from sequences generated through this study (MF197867, MF197873, MF197869 (i.e., Uganda ‘Rice’ maternal lineage); MF197868, MF197871, MF197870 (i.e., Uganda ‘Corn’ maternal lineage 1); MF197868, MF197872, MF197870 (i.e., Uganda ‘Corn’ maternal lineage 2)). The multigene phylogeny provided strong bootstrap support values (1,000 replications) for the existence of two closely related monophyletic <i>S</i>. <i>frugiperda</i> sister clades. The rice-preferred <i>S</i>. <i>frugiperda</i> clade is made up of two individuals (i.e., published [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0194571#pone.0194571.ref040" target="_blank">40</a>]; and ‘Uganda ‘Rice’ maternal lineage’ (this study)). The corn-preferred clade has five individuals, of which two (i.e., Uganda ‘Corn’ maternal lineage 1; Uganda ‘Corn’ maternal lineage 2) are from this study. The remaining three ‘Corn’ maternal lineages are from published sequences (i.e., [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0194571#pone.0194571.ref040" target="_blank">40</a>]; KM362176; KU877172). Out group species are <i>S</i>. <i>exigua</i> and <i>S</i>. <i>litura</i>.</p

Estimates of evolutionary divergence (<i>p</i>-distance method) between concatenated partial mtDNA COI, COIII and Cyt <i>b</i> sequences of the two closely related <i>Helicoverpa</i> sister species of <i>H</i>. <i>armigera</i> (GU188273) and <i>H</i>. <i>zea</i> (KJ930516) and between the two distinct <i>Helicoverpa</i> species, i.e., <i>H</i>. <i>punctigera</i> (KF977797) and <i>H</i>. <i>armigera</i> (GU188273).

<p>Estimates of evolutionary divergence (<i>p</i>-distance method) between concatenated partial mtDNA COI, COIII and Cyt <i>b</i> sequences of the two closely related <i>Helicoverpa</i> sister species of <i>H</i>. <i>armigera</i> (GU188273) and <i>H</i>. <i>zea</i> (KJ930516) and between the two distinct <i>Helicoverpa</i> species, i.e., <i>H</i>. <i>punctigera</i> (KF977797) and <i>H</i>. <i>armigera</i> (GU188273).</p

Estimates of evolutionary divergence (based on <i>p</i>-distance method) between concatenated partial mtDNA COI, COIII and Cyt <i>b</i> sequences of rice-preferred (COI-COIII-CYTB Rice-REF; Uganda 'Rice' maternal lineage) and corn-preferred (KM362176; KU877172; COI-COIII-CYTB Corn-REF; Uganda 'Corn' maternal lineage 1, Uganda 'Corn' maternal lineage 2) <i>S</i>. <i>frugiperda</i> individuals.

<p>Estimates of evolutionary divergence (based on <i>p</i>-distance method) between concatenated partial mtDNA COI, COIII and Cyt <i>b</i> sequences of rice-preferred (COI-COIII-CYTB Rice-REF; Uganda 'Rice' maternal lineage) and corn-preferred (KM362176; KU877172; COI-COIII-CYTB Corn-REF; Uganda 'Corn' maternal lineage 1, Uganda 'Corn' maternal lineage 2) <i>S</i>. <i>frugiperda</i> individuals.</p