EFFECT OF ENVIRONMENT UPON CHROMOSOMAL PAIRING OF SOME SPECIES AND HYBRIDS OF POA

Abstract

WHILE THE PAIRING of chromosomes reflects the affinities of the genes contained within them, the expression of this phenomenon, like every other genetical character, is subject to both genetic and environmental influences. In order to measure the degree of pairing within a given or hybrid, it is necessary that the effects of the more common environmental variations be evaluated. This is especially important for many of the genus Poa in which high polyploid-y and inter-specific hybridizations, coupled with apomixis, have resulted in the formation of species which normally show irregularit'es in chromosomal pairing. Pairing studies in this genus are not concerned with distinguishing normal as opposed to irregular pairing, but with comparing plants all of which show irregularities, though in differing degrees. Moreover, even within the same anther there is variability of chromosome pairing from cell to cell, and consequently the observations must be made on a statistical basis. In the present investigation the effects of several environmental influences were studied as a necessary first step in a program of investigation requiring the interpretation of chromosome pairing in many and hybrids of Poa. MATERIALS AND METHODS.-The plants used were individuals of two of Poa and a few interspecific hybrids. They are part of a study of the evolution and breeding potentialities of the bluegrasses begun in 1943 by Clausen, Keck, and Hiesey in cooperation with the United States Soil Conservation Service. All the forms used were high polyploids ranging from hexaploids with 2n 42 to 14-ploids having approximately 2n 98 chromosomes. The included Poa ampla Merr., P. nevadensis Vasey, and several different combinations of the hybrids P. ampla X pratensis, and P. ampla X compressa. These hybrids, being results of intersectional crosses, represent combinations of widely divergent genomes.