Effects of Temperature and Light Variations on Seed Germination in Sunflower(Helianthus)Species

Some genetic and physiological aspects of seed germination of wild and weedy sunflowers were investigated in order to analyze their population differentiation in seed characteristics. Seed germination of six populations classified on the basis of morphology asHelianthus exilisGray,H. exilis-bolanderihybrids, andH. bolanderiGray was studied under red light at 20 C. The average germination of the three groups respectively were 56, 63, and 42%. Germinability of individual plant progenies derived from populations ofH. bolanderiandH. exiliswas studied under red and far-red light combined with the pretreatments at two temperatures (10 and 20 C). Average germination per progeny reached a maximum of 59% with red light and 10 C inH. bolanderi. Far-red light promoted germination ofH. bolanderibut was ineffective withH. exilis. The homogeneity of populations within each taxon and the fact that germinability differences among theH. bolanderiprogenies were consistent over replications, suggest a genetic component of variation. However, progenies obtained by crossing selected individuals that germinated under certain light and temperature treatments, were not significantly correlated in germinability with that of their parents. Inheritance of germination characteristics appears to be complex and highly dependent on the environmental conditions.