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

Salsomaggiore Terme, Italy - 26/29 September, 2001

ISBN 88-900622-1-5

Poster Abstract

INHERITANCE OF MOLECULAR MARKERS IN TETRAPLOID SALIX ALBA X S. FRAGILIS PROGENIES AND INFERENCE ON CHROMOSOME MEIOTIC BEHAVIOUR AND GENOME ORGANIZATION

MENEGHETTI S.*, PAIERO P.**, LUCCHIN M.*

* Dipartimento di Agronomia Ambientale e Produzioni Vegetali, Università di Padova – Agripolis, Via Romea 16, 35020 Legnaro, Padova, Italy

margherita.lucchin@unipd.it

** Dipartimento Territorio e Sistemi Agroforestali, Università di Padova – Agripolis, Via Romea 16, 35020 Legnaro, Padova, Italy

Salix alba, S. fragilis, AFLP, linkage map, allopolyploidy

Willow species are known to be important landscape features and essential components of a well-balanced ecosystem; they have a primary role in soil protection, erosion control, maintenance of ground water quality, preservation of biodiversity and can be a valuable economic asset.

The study of genetic variability at different levels, between species, between and within populations, in terms of allele diversity, allele frequency (presence/absence of common and/or rare alleles), level of heterozygosity and genetic structure of populations, is a crucial step for the correct taxonomic classification of the critical populations and for identifying the most appropriate sources of individuals to use in waste land reclamation. Salix alba L. and S. fragilis L. are tetraploid (2n=4x=76), dioecious , closely related species with a wide distribution troughout Europe. In many cases the two species coexist in mixed stands and interspecific hybridization can occur, so intermediate morphological forms largely dominate on the field. Clonal propagation however is very common as known for most polyploid species. As a consequence, most of the phenotypic features have low diagnostic value for identifying the taxa and their interspecific hybrids, and for assessing introgression patterns and defining genetic variation structure.

Multiplex PCR-derivate molecular markers (AFLP and SAMPL) can be usefully employed for studying the amount and the partition of genetic variability within and among willow species. This approach can be improved by the development of a genetic map of willow that should allow the unequivocal identification of species and populations. A strategy of two-way pseudo-testcross has been used to construct a first linkage map for white willow. The success of such a strategy in tetraploid species depends on the identification of marker alleles present in one parent and absent in the other one. Only 1:1 segregation ratios were considered in the F₁ mapping population. A total of 135 out of 331 polymorphic markers were scored in 69 F₁ progenies from both the controlled interspecific cross S. alba x S. fragilis and reciprocal. In particular for white willow, a total of 33 paternal (6 SAMPLs and 27 AFLPs) and 59 maternal (12 SAMPLs and 47 AFLPs) single-dose markers, tested to be linked in coupling phase, were mapped. The observed segregation ratio of markers was tested by chi-square analysis for goodness of fit the expected segregation ratios, as well as by the Mather test to assess the linkage phase. Grouping of the markers at a minimum LOD score of 3 resulted in 19 and 14 linkage groups consisting of 91 and 44 markers covering 546 cM and 323 cM for the S. alba female and male parent respectively. The pattern of segregation showed by single marker alleles and the coupling phase assayed by linked marker loci suggest a disomic inheritance and so an allopolyploid nature of the willow genome.