Proceedings of the XLV Italian Society of Agricultural Genetics - SIGA Annual Congress

Salsomaggiore Terme, Italy - 26/29 September, 2001

ISBN 88-900622-1-5

Abstracts of posters

ALLELIC FREQUENCY CHANGES AT RFLP LOCI ASSOCIATED WITH RECURRENT SELECTION FOR TISSUE CULTURE REGENERATION IN MAIZE

SALVI S., FRASCAROLI E., CHIAPPETTA L., LANDI P.

Dipartimento di Scienze e Tecnologie Agroambientali, Via F. Re 6, 40126, Bologna

salvi@agrsci.unibo.it

directional selection, molecular markers, random genetic drift, in vitro culture, Zea mays

Molecular markers are powerful tools for detecting the chromosome regions that have been affected by selection processes. In a previous study we conducted three cycles of recurrent selection for tissue culture regeneration in the maize double cross (A188 × W64A) × (A634 × B79). Then, the source and selected populations were compared and sizeable selection responses were found.

This study was conducted with the objective of identifying the chromosome regions that were preferentially retained during the recurrent selection, by means of RFLP analysis. DNA was extracted from the four parental inbreds and the three selected populations (C1 to C3) and digested with three restriction enzymes (BamHI, EcoRI and HindIII). Nineteen probes, which were polymorphic among the parental lines, were hybridized to membranes containing the digested DNA samples of the three populations. For each marker locus, the allelic frequency changes throughout selection were analyzed following a chi-square statistical procedure considering, as null hypothesis, that changes are due to random genetic drift acting alone. The analysis also considers a linear component due to changes of allelic frequencies caused by directional selection. Calculations take into account the effective population size determined at selection (8 S₁ families to develop C1, 11 for C2 and 14 for C3) and the size of the samples used for estimating the allelic frequencies (40 plants were randomly sampled within each population).

Data analysis pointed out that for eight of the 19 polymorphic loci there was a significant deviation from the null hypothesis at least for one allele. For four of such loci the significance of the deviation was due to the residual component, suggesting the action of erratic factors. The linear component was significant for the other four loci, implying that directional selection affected their allelic frequency changes. In particular the linear trend was significant for loci umc128 (chromosome 1), csu109 (chr. 2), umc65 (chr. 6), and csu13 (chr. 7). The allele showing a significant frequency increase was provided by A634 for umc128, by W64A for csu109, and by B79 and/or by W64A for csu13; for umc65 there was a significant decline of the allele provided by A634 and/or by B79.

These results suggest that close to the four mentioned RFLP loci there are genes controlling the selected trait and that the favorable alleles are not provided by only one parent. This is consistent with the findings of a previous investigation, which showed that within each population (especially C3) there was an upward transgressive segregation with respect to the best parent (i.e., A188). The identification of the chromosome regions affected by selection can represent a valuable information for undertaking studies of marker assisted selections and studies on the mechanisms underlying the expression of the trait.