Rate of photosynthesis is expected to be directly related to yield potential and to be a major physiological component of yield in maize. On the contrary, available information generally shows an absence of association between photosynthetic variability and yield components. In fact the rate of photosynthesis may not be a limiting factor in a non-restrictive environment; moreover the photosynthetic activity must be estimated in a large number of samples with good precision and in the correlation analysis linkage effects must be distinguished from pleiotropic ones.

For these reasons we have analyzed physiological components of maize yield and their relevance by means of an appropriate population structure and by growing plants in normal and restrictive conditions. As regards the population structure, a set of random pure lines was extracted from the BSLE population and tested in 1984. Hybrid combinations were obtained from them according to an incomplete diallel crossing design (circulant diallel) and tested in 1985. In both cases two field conditions were used: normal (spring sowing) and restrictive condition (summer sowing) with light and temperature as a limiting factor in the last part of the vegetative cycle. The rate of photosynthesis was estimated as CER by means of an original apparatus based on ¹⁴CO₂ photosynthetic fixation, that ensures high repeatability of the data in a large number of samples.

The correlation coefficients between CER and yield components were (significant coefficients are underlined):

The results, interpreted also by means of multivariate statistical techniques, show that, as regards pure lines, CER can be a relevant component of the yield level especially in restrictive conditions. Hybrids are less sensitive to the environmental conditions. For these reasons the relevance of physiological parameters seems to be not independent from the genetic constitution of the material and this fact should be considered in breeding programs based on components of yield.

Table.

A. Camussi, E. Ottaviano, B. Basso and E. Pirillo
 
 

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