1991. Identification and frequency of tetraploid progeny from 2x-4x and 4x-2x crosses in Dactylis. Genome, 34: 273-278. The utilization of diploid germ plasm in the improvement of tetraploid orchard grass (Dactylis glomerata L. ssp. glomerata Hayek) requires some means of polyploidization. Studies in several different crop species have shown that sexual polyploidization has the advantage of transmitting a large proportion of heterozygosity from the parent to the offspring. In tetrasomic tetraploids, maximum heterozygosity is a necessary requirement for maximum heterosis. The objective of this research was to investigate the occurrence of 2n eggs and 2n pollen in several sources of wild diploid germ plasm, by quantifying the frequency of 4x genotypes among the progeny of interploidy crosses. Pollen diameter was determined in 110 diploid genotypes. These genotypes were then ranked for five descriptive statistics based on diameter (maximum, 75th percentile, median, arithmetic mean, mode). The eight top-ranking genotypes in four of the five categories were crossed to male-sterile 4x seed parents. Randomly selected diploid genotypes were also crossed as seed parents to 4x genotypes. Tetraploid progeny were recovered from both types of crosses. Of 57 2x genotypes, 15 produced 2n eggs. Of the 8 large pollen diameter genotypes, 6 produced 4x progeny in relative frequencies of 3-100070. The success of recovery was dependent on the genotype of the pollen parent as well as the seed parent. Of the 6 genotypes producing 2n pollen, 2 also produced 2n eggs, resulting in the recovery of tetraploids from selfed progeny. VAN SANTEN, E., HUGESSEN, P. M., et CASLER, M. D. 1991. Identification and frequency of tetraploid progeny from 2x-4x and 4x-2x crosses in Dactylis. Genome, 34 : 273-278. L'utilisation de plasma germinal diploi'de pour l'amklioration du Dactyle peletonne tktraploi'de (Dactylis glomerata L. ssp. glomerata Hayek) nkcessite le recours a certains moyens de polyploi'disation. Des Ctudes chez plusieurs espkcescultivkes diffkrentes ont montrC que la polyploi'disation sexuke a l'avantage de transmettre une large part de I'hCtCrozy-gositC des parents aux descendants. Chez des tCtraploi'des tCtrasomiques, un maximum d'hCtCrozygositC est nkcessaire pour l'obtention d'un maximum d'hetkrosis. L'objectif de cette recherche a Ct C : d'investiguer l'occurrence d'oosphkres 2n et de pollen 2n chez plusieurs sources indigknes de plasma germinal diploi'de par quantifier la frkquence de gCnotypes 4x chez les descendants de croisements entre deux ploi'dies. Le diamktre des grains de pollen a Ct C dktermink chez 110 gCnotypes diploi'des. Ces gknotypes ont ensuite Ct C classCs selon cinq catkgories statistiques baskes sur le diamktre : le maximum, le 75' percentile, la mCdiane, la moyenne arithmktique et le mode. Les huit gCnotypes qui se sont classCs premiers pour quatre des cinq catkgories statistiques ont Ct C croisCs avec des parents miiles stkriles, producteurs de grains 4x. Des descandants tCtraploi'des ont kt6 recouvrks chez les ...