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Maize landraces are important genetic resources for maize breeding. Many of these landrace varieties have not yet been properly studied in order to be distinguished from the others. In this study, multivariate statistical methods were used, beyond the analysis of variance, for estimating genetic dissimilarity among 27 maize landrace accessions. Principal component analysis and clustering analysis were performed using 16 evaluated quantitative characters. The ANOVA results reported the existence of significant differences among the tested accessions for 14 evaluated characters. Two principal components almost explained 49% of found experimental variance. Four different clusters were formed by the used clustering analysis, whose results were plotted into a dendrogram. The graphical integration of this dendrogram with the PCA allowed to conclude that the variation found may be due to the genotypic distinctions existing among the four groups of accesses determined in this study.
Spodoptera frugiperda is a major pest of maize and plants expressing insecticide proteins from Bacillus thuringiensis. Control programs based on Bt maize events have increased inefficacy for this pest, often demanding insecticide sprays as a complementary measure. The aim of this work was to evaluate larval mortality in two S. frugiperda populations submitted to different insecticide sprays and modes of entry into the insect’s body. Experimental design was completely randomized with a factorial scheme 4×2×2, plus one check. Four insecticides [azadirachtin (12 g a.i. L-1), lambda-cyhalothrin (50 g a.i. L-1), teflubenzuron (150 g a.i. L-1), flubendiamide (480 g a.i. L-1)], two modes of entry for each insecticide (topic contact and ingestion) and two S. frugiperda populations (from Constantina and Sertão) were tested. The mortality of individuals was assessed daily for 15 days after treatment spraying. The insecticides teflubenzuron and flubendiamide presented the highest mortality levels of S. frugiperda, disregarding the differences between tested populations and modes of entry. Contamination by ingestion resulted in higher mortality, especially for teflubenzuron and flubendiamide. The results suggest that S. frugiperda from Constantina are less susceptible to the insecticides evaluated.
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