GROWTH AND DEVELOPMENT OF SPECIES AND HYBRIDS OF POA UNDER CONTROLLED TEMPERATURES

Abstract

A PROGRAM WAS INITIATED in 1943 by the Department of Plant Biology of the C,arnegie Institution for the study of various species and ecologic races of Poa and Poa hybrids in connection with their possible use as range grasses. One sector of this program is concerned with the problem of determining which factors are responsible for the successful growth -and survival of these plants in different kinds of environment. Genetic differences among species, clim,atic races, and individuals of the same species are strikingly evident in Poa. Moreover, the genus has a complex chromosomal structure based on several levels of polyploidy, and many of its species reproduce primarily by apomixis (cf. Akerberg, 1942; Clausen et al., 1947; Nygren, 1950). Although the genetic and cytologic framework of Poa is complex, reasonably well-defined taxonomic species have evolved. Some of these contrast markedly from each other in morphology, in natural distribution, and in their ability to grow in different kinds of environment. By testing species, strains, and interspecific hybrids of Poa in field plantings in contrasting climates in North America -and in Europe, it has been found that their relative performance varies widely. Very little is known concerning the genetically-controlled physiological characteristics that determine growth and development in various environments. A logical step in analyzing these char,acteristics is to study the comparative growth of selected forms under controlled conditions with but a single known external variable. With the completion of the Earhart Laboratory at the California Institute of Technology -at Pasadena in June, 1949, the opportunity to study the growth of plants under controlled environmental conditions on a fairly large scale was for the first time made possible. Through the invitation of its director, Dr. F. W. Went, the writer was privileged during 1950 to conduct the present study in this laboratory. The experiments here reported were limited to the investigation of the effects of various combinations of day and night temperatures on the growth and development of clones of key individuals of Poa which were also at the same time being grown under many contrasting field conditions. For a brief description of the Earhart Laboratory, the reader is referred to Went (1950).