The effect of Biased Estimate of Parameters on the Location of Quantitative Trairs Loci By Means of Molecular Markers

The photosynthetic capacity of maize {Zea mays L.), estimated "in vivo" as CO2 exchange rate (CER) is a low heritability trait that has been 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 that 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 micro climatic variations to be estimated. CER measurements were taken at pre-anthesis stage and at silking time on the same plants. The association 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 effective. Moreover RFLP markers having a more stable association with the quantita­ tive trait of interest, Le., less sensitive to environmental effects and thus more suitable for MAS experiments, were identified. Finally, eight markers gave significant results in both pollen shedding and pre-anthesis stage, suggesting the existence of "maior" markers as regards CER variabilitv.