Maize Research Institute, 5635 Knezha, Bulgaria
(Manuscript received 10 Juny 2016; accepted for publication 29 November 2016)
Abstract. This study is conducted in the period 2014 – 2015 in the experimental field of the Maize Institute, Knezha by using an agro technique adopted for the region. For the purposes of the study four maize hybrids Kn 307, Kn 435, Kn 509 and Kn 625М are included at different degree of maturity – FAO 300-399; 400- 499; 500-599 and FAO above 600. The hybrids together with their parental forms are studied in competitive variety trials under conditions without irrigation at three densities of the crop 45000pl/ha; 55000рl/ha and 65000рl/ha. From the presented results obtained based on the data of manifestation of heterosis and the degrees of dominance of the hybrids clearly expressed heterosis is established for the traits grain yield, length of cob and number of grains per row. For the trait number of rows in the cob both presence and absence of heterosis is observed. The degrees of dominance in F1 also vary widely, from intermediate inheritance to incomplete positive dominance and over-dominance.