Breeding of maize for silage: Yield components in genotypes with different degrees of improvement --Torrecillas, MG, Broccoli, AM, Bertoia, LM The objectives of this work were: i) To analyze the importance of morphological characters (plant architecture and size) on ear and stover dry matter yield, and ii) to verify if the behavior of such variables is maintained in germplasm with different origin and degree of improvement.

Twelve genotypes of maize (Zea mays L.), representing four groups of different origin and degree of improvement, were evaluated for their aptitude for silage. Trials were carried out in three environments during the 1996/1997 and 1997/1998 growing seasons.

Groups of genotypes were:

G1 = Three commercial hybrids (Three-way hybrids): Cargill Semiden 5, Funk's Tronador and Pioneer 3452.

G2 = Three Argentine Landraces: Accesions 03-056, 14-066 y 16-042.

G3 = Three experimental hybrids (Single hybrids): LZ 2, LZ 14 and LZ 40.

G4 = Three F1 integrated by: subtropical racial composites without any improvement x Synthetic varieties: Composite Cravo x HP3, White Dent composite x SB73 and Yellow Dent composite x SMo17).

The studied variables were:

Leaf number (LN); harvest index (HI) measured as ear dry matter yield : whole plant dry matter yield ratio; stalk diameter (SD), measured in the node of ear insertion; plant height (PH), measured above ground level to basal tassel branch; leaf area (LA); ear dry matter yield (EDMY) and stover dry matter yield (SDMY).

A multiple regression analysis that included LN, HI, SD, PH, LA as independent variables and EDMY, SDMY as dependent variables in the four groups combined among environments was performed.

Absence of multicollinearity among variables was verified. After a stepwise procedure was performed, models with good predictive capacity (adequate values of R2 and cp of Mallows) were selected.

LN and HI were important in all models, explaining EDMY and SDMY. SD was important in G1 explaining EDMY ((4 = 0.61) and SDMY ((4 = 0.06) and in G2 for SDMY ((4 = 0.02). PH contributed significantly ((1 = 0.07) in the model to predict EDMY in G2. The most adequate models that contributed to predict EDMY and SDMY varied according to the involved genetic groups. LA, LN and HI gave models with good predictive behavior, especially for EDMY in three genetic groups (G2, r2 = 0.81; G3, r2 = 0.55; and G4, r2 =0.63). It is important to emphasize that these groups lacked any improvement process defined for grain. Results indicate the feasibility of using leaf area, leaf number and harvest index in selection processes of unadapted germplasm, in order to maximize forage production.

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