EFFECT OF MICROCLIMATIC VARIATIONS ON THE ESTIMATE OF RELATIONSHIPS BETWEEN RFLP MARKERS AND LOW HERITABILITY TRAITS IN MAIZE

The photosynthetic capacity of maize (Zea mays L.), estimated ''in viv o'' as CO2 exchange rate (CER) is a low heritability trait that has be en shown to be a significant yield component, at least in restrictive environmental conditions. With regards to this trait, Marker Assisted Selection is theoretically expected to be of greater efficiency than t hat of phenotypic selection. In the paper, 72 hybrid combinations from 48 recombinant inbreds fully genotyped by RFLP markers were compared by means of an experimental field design which allowed the effect of m icro climatic variations to be estimated. CER measurements were taken at pre-anthesis stage and at silking time on the same plants. The asso ciation between markers and CER variability was estimated by means of multiple regression within each linkage group. The results showed that simple strategies for data correction of environmental effects on the detection of marker associated QTLs for CER variability were effectiv e. Moreover RFLP markers having a more stable association with the qua ntitative trait of interest, i.e., less sensitive to environmental eff ects and thus more suitable for MAS experiments, were identified. Fina lly, eight markers gave significant results in both pollen shedding an d pre-anthesis stage, suggesting the existence of ''major'' markers as regards CER variability.