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 ...

The Dactylis glomerata L. species complex is a genetically diverse group of naturally occurring diploid (2n = 2x = 14), tetraploid (2n = 4x = 28), and hexaploid (2n = 6x = 42) subspecies. The diploid subspecies tend to be geographically isolated and genetically distinct. Each subspecies probably possesses alleles for adaptation to specific environmental regimes. The objective of this research was to evaluate tetraploid progeny from 2x–4x intersubspecific crosses for forage yield and quality relative to their tetraploid parent. Progeny were developed by two stages of hybridization; intra- and inter-subspecific hybrids were generated from 2x–2x crosses, after which selected diploid progeny were mated, as females, to adapted tetraploid genotypes. From 14 2x–4x crosses, utilizing diploids known to produce 2n eggs, 59 tetraploid progeny were identified. These tetraploid progeny and their parents were vegetatively cloned and established in pots in two greenhouses. Forage was harvested from two replicates of each plant in each greenhouse for a total of six cuttings. Vigor, in vitro dry matter digestibility (IVDMD), and neutral detergent fiber (NDF) were determined. Parent–progeny regressions indicated evidence of heritable variation for vigor and IVDMD, but not for NDF. Favorable heterosis (relative to the tetraploid parent) on a family mean basis was significant only for IVDMD in one family. When selection among progeny within families was possible (in six families), favorable transgressive segregants were observed for all traits in at least one family and in a total of five families. The favorable performance of some tetraploid progeny, combined with the diverse nature of the species, indicate that improvements to cultivated orchard grass are possible. Selection at both the diploid and tetraploid levels will be necessary to achieve these goals.Key words: Dactylis glomerata L., gametic nonreduction, heterosis, heterozygosity, orchard grass, polysomic polyploids.