NATURAL TRIPLOIDS IN THE ORCHARD GRASS,DACTYLIS GLOMERATAL., POLYPLOID COMPLEX AND THEIR SIGNIFICANCE FOR GENE FLOW FROM DIPLOID TO TETRAPLOID LEVELS

Abstract

Diploid and tetraploid forms in sexual polyploid groups have been generally regarded as reproductively completely isolated from one another. Whether this is always the case was already questioned by Zohary (1956) and Stebbins and Zohary (1959). In the following work an attempt is made to examine the genetic relationships between diploid and tetraploid populations of the Orchard Grass, Dactylis glomerata L., in places where such populations come in contact in Israel. This paper reports on a study of the occurrence of natural triploids in contact areas and on the types of progeny such triploids produce under natural conditions. Previous studies (Zohary 1956, Stebbins and Zohary 1959) have established the polytypic group of Orchard Grass (Dactylis glomerata L.) as a large polyploid complex. This complex contains at least ten distinct diploid (2n = 14) subspecies as well as a large, sexual, tetraploid (2n = 28) superstructure. The diploid forms have each a restricted geographical distribution and they are widely separated from one another. Each diploid is characterized also by comparatively narrow and distinct range of variation. In contrast with the diploids, tetraploid Dactylis forms are continuously and widely spread over most of Europe, West Asia and North Africa. The tetraploid level is characterized by a large, continuous range of variation which covers most of the characters found in the various diploids. Cytogenetically all tetraploid forms are interfertile and show typical autopolyploid chromnosome behavior.