COMPARISON OF MORPHOLOGICAL AND GENETIC-TRAITS OF PEDUNCULATE OAK (QUERCUS-ROBUR L) AND SESSILE OAK (Q-PETRAEA (MATT) LIEBL)

Morphological and genetic traits are compared for pedunculate oak (Que rcus robur L.) and sessile oak (Quercus petraea (MATT.) LIEBL.) by mea ns Of controlled crosses and 2 mixed stands. The existence of hybrids as morphological intermediate forms and of disjunctive characters for distinction between the 2 taxonomic species was tested. It was shown t hat the leaf morphology of the juvenile and the adult trees differ fro m each other. On the level of single individuals a recognition of spec ies' hybrids is not possible by means of an intermediate morphology. O n the level of families it is sometimes possible using statistical bes ts. Morphological, isoenzymatic and DNA-analytic methods are compared for their different abilities to detect a differentiation between pedu nculate and sessile oak. 111 trees of a German stand, were divided int o groups as well by means of discriminant functions as by the direct c omparison of density distributions (VERGA, 1995), which derived from t he measurements of the characters. None of the characters has disjunct ive expressions. The 2 methods of species' discrimination, using morph ological traits, differ in respect of their selectivity between Q. rob ur and Q. petraea and their classification of individuals with interme diate morphology. Phenotypic and genetic parameters were calculated fo r the groups derived from VERGA's method. Eight RAPD fragments whose d ominant Mendelian inheritance was proven were used for DNA analysis. T he total phenotypic differentiation (delta(TP)), based on the RAPD ana lysis, is 0.30 for the ''robur type'' and 0.44 for the ''petraea type' '. On the basis of 10 enzyme loci the genetic parameters were calculat ed according to Gregorius. The mean number of alleles is 2.9 for the ' 'robur type'' resp. 3.1 for the ''petraea type''. The observed heteroz ygosity is 26.7% for the ''robur type'' and 20.6% for the ''petraea ty pe'' (the conditional heterozygosities are 59.9% resp. 55.5%), the tot al differentiation of the collective (delta(T)) is 0.25 for the ''robu r type'' and 0.28 for the ''petraea type''. The distances between the types are: morphological distance (d(m)) 0.45, phenotypic distance (d( OP)) 0.22 and genic distance (d(o)) 0.14. The values of the German sta nd are compared to those of a French stand. The characters which contr ibute to the discrimination between the types within a stand are the s ame for both stands. The geographically separated groups of one type a re differentiated above all because of differences of their leaf lengt h and leaf width. The distance between the same types in different loc ations is small compared to the distance between different types withi n one stand. The ''petraea type'' of the German stand is more variable for all traits analysed than the ''robur type''. Due to the possibili ty of a hybridization between Q. robur and Q. petraea, their different ecological requirements and because of the lack of characters' disjun ctive expressions between the different types, it seems to be appropri ate to state that sessile and pedunculate oak belong to the same biolo gical species for which they represent different ecotypes.