SELECTION OF MAIZE LINES AND CROSSES BY COMBINING TOP CROSS AND DIALLELIC CROSS TESTS

Abstract

Obtaining competitive commercial maize (Zea mays L.) hybrids requires efficient selection strategies to improve populations and develop elite parents. The objective of this research was to select lines and crosses with high general (GCA) and specific (SCA) combining ability for grain yield (GR) and agronomic characteristics, by combining top crosses (line × tester) and diallel crosses. In the Autumn-Winter 2010-2011 agricultural season, 144 top crosses were formed with S₃ inbred lines from the ST C₂ F₂ subtropical population, and as a tester, the subtropical population PABGT-CE C₉ F₂. Top crosses were evaluated under rainfed conditions in the 2012 Spring-Summer (SS) agricultural season at Tlajomulco and Tepatitlán, Jalisco, Peña del Panal, Michoacán, and Santa María del Oro, Nayarit, covering a range from 1100 to 1900 m of altitude. In this test, nine top crosses were selected by GCA across locations for GY and lodging tolerance. With the remaining seed of lines of the selected top crosses diallel crosses were formed in SS 2015. Crosses were evaluated in SS 2016 in the previous locations and Iguala, Guerrero. Lines ST C₂ F₂-21-2-1 and ST C₂ F₂-29-2-1 stood out in both tests by virtue of their high GCA for GY, but the last one was eliminated because in diallel crosses its GCA and SCA for lodging were positive and significant (P ≤ 0.05). The SCA of the cross ST C₂ F₂-33-1-1 × ST C₂ F₂-49-2-1 for GY was significant (P ≤ 0.05), yet in lodging it was negative but not significant. Associating top cross and diallel cross tests allowed to select in a more rigorous way lines with high GCA and SCA for GY and agronomic characteristics; in addition, it allowed to eliminate lines before forming the synthetic and obtaining single crosses that could be used to develop hybrids with elite progenitors of the other heterotic component.