PLANT GENETIC ADAPTEDNESS TO CLIMATIC AND EDAPHIC ENVIRONMENT

Genetic adaptation implies the shaping of population and species gene pools In response to environmental challenges. The two components of t he abiotic land environment are climate and soil, both of which determ ine much of the evolutionary adaptedness of plants as, besides represe nting a set of surrounding physical, chemical and sometimes limiting t raits, they determine the availability of nutrients and energy, of whi ch they are the immediate source. Ecogeographical distribution of spec ies and ecotypes and different physiological mechanisms and developmen tal patterns are good evidence of plant adaptedness to soil and climat e. However, it is not always easy to determine the underlying genetics of adaptive processes, because 1) environmental factors to which the plants are responding are not always evident and are sometimes too com plex, 2) several genes may be involved in the response to a given envi ronmental factor, and 3) the same gene/s may be involved in different adaptive responses. In particular, data on Avena species and temperatu re as a key environmental factor will be used to illustrate some examp les of climatic and edaphic adaptedness. Temperature affects the genet ic evolution and geographical distribution of all organisms, and a gre at deal of evidence indicates that species and populations are genetic ally adapted to different temperature regimes. Isozymes and other mole cular markers have helped in the understanding of the genetic basis of adaptedness. There are many examples of correlation between isozyme a nd DNA-marker variation and environmental differences. For many popula tion geneticists, isozyme markers are just genetic markers with little or no direct involvement in adaptation. However, metabolic processes are controlled by enzymes, influenced by the environment and used to r eact in response to it. Evidence that isozymes, and perhaps other mole cular polymorphisms, are directly involved in adaptedness will be also presented. Molecular genetic analyses at gene and population levels a re opening the ways to a better understanding of plant genetic adaptat ion.