GENETIC VARIABILITY OF Rottboellia cochinchinensis POPULATIONS IN SUGARCANE FIELDS

The hypothesis assumed was the existence of biotypes within populations, which has been the cause of difficulties in itchgrass control by farmers. For that, the genetic variability of three populations of Rottboellia cochinchinensis in sugarcane fields in the state of Sao Paulo was investigated by using the Amplified Fragment Length Polymorphism (AFLP) technique. Six primers were used to obtain molecular characterization data. AFLP gels were analyzed based on marker presence (1) and absence (0). Using NTSYs (Numerical Taxonomy and Multivariate Analysis System) software, the genetic similarity was calculated by the Jaccard coefficient and, from that, a dendrogram was built through the UPGMA (Unweighted Pair Group Method Arithmetic averages) method, besides determining the isopolymorphic marks. The average genetic similarities seen in the region was 0.742 for Igarapava, 0.793 for Mococa and 0.808 for Piracicaba. Between regions it was 0.730 (Igarapava vs Mococa), 0.735 (Mococa vs Piracicaba) and 0.694 (Igarapava vs Piracicaba). In line with the dendrogram, it is possible to detect the formation of two groups, one with 8 plants from Igarapava and Mococa and the other with 21 plants from Igarapava, Mococa and Piracicaba, as well as the presence of 1 discriminant individual from Piracicaba. It can be concluded that the genetic similarity among itchgrass populations from the state of Sao Paulo was high (72%), which denotes that the difficulties in chemical management are not only due to different biotypes but also due to other characteristics linked to tolerance of the species to herbicides. However, biotype existence cannot be discarded because of the polymorphic marks generating 22% average genetic variability.