Abstract Abstract: This research aimed to evaluate the genetic variability of 15 Stylosanthes scabra populations (Alfafa do Nordeste) as a result of the adaptation strategy to different environments from the regions: Mata, Agreste and Sertão in the state of Pernambuco. These populations, obtained from representative samples of seeds, were planted in a field trial at Campo Experimental da Empresa Pernambucana de Pesquisa Agropecuária (IPA). This trial served as a base for the study of fractional energy distribution. The energy allocation to the plant parts, described as a dry matter weight function, classified the populations as r and K strategists, evaluated during the 1 st reproductive cycle. The obtained results show that there is a great interpopulational variability for all the evaluated characters. Based on the obtained data, Brejos de altitude target Stylosanthes scabra populations for K strategists. The populations from Sertão behaved as r strategists. Populations with greater reproductive precocity, like that of Itamaracá, Serra Talhada and Santa Cruz da Baixa Verde, were classified as r strategists, directing a higher percentage of energy relative to the reproductive effort. The great variability between populations represents an adaptation strategy to the different environments as a process of genetic maximization in the species evolution.

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