A study to determine the genetic basis of photosynthesis and its relationship to morphological traits and yield determinants is in progress. For this purpose, lines of the flint type maize grown in Argentina are used. The first crosses were made using three inbred lines developed by the Institute which differed in photosynthetic activity measured by polarography (MNL 58, 1984). These lines, their F1 hybrids, backcrosses and F2 were tested in a trial with four repetitions in which several traits were measured, among them apparent photosynthesis and canopy traits. Apparent photosynthesis was measured by polarography at Hanway's stage 2.5 (AP-1) on the 6th leaf from the plant base, and at stage 5.0 (AP-2) on the 3rd leaf from the top. Leaf orientation values were estimated on the 3rd leaf from the top (LOV3), the leaf above (LOVA) and the leaf below (LOVB) the ear; values were calculated by Pepper's formula (Crosbie, Pearce and Mock, Crop Sci. 18:87-90, 1978). The leaf area index (LAI) was calculated considering as estimator for the leaf area, for all the leaves, the product length x maximum width x 0.75.
Phenotypic correlations between these characters for inbred lines (IL) and their F1 are shown in the table.
The results indicate that: (1) There are negative correlations between apparent photosynthesis measurements and traits related to canopy. Upright leaves and high leaf area index correspond to low photosynthetic activity per fresh weight. (2) LAI shows a positive correlation with LOV measured on leaves placed above the ear. More erect upper leaves are supposed to contribute to more efficient use of light energy, inducing more vegetative growth. (3) It is observed, with few exceptions, that there is a general correspondence between the phenotypic coefficient values of inbreds and those of their F1. This should be of practical value for prediction of F1 features based on inbred measures.
Jaime R. Jatimliansky, Francisco J. Babinec and Miguel J. Arturi
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