Submitted to: Helia
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/5/2006
Publication Date: 12/15/2006
Citation: Vischi, M., Cagiotti, M.E., Cenci, C.A., Seiler, G.J., Olivieri, A.M. 2006. Dispersal of wild sunflower by seed and persistant basal stalks in some areas of central Italy. Helia. 29(45):89-94. Interpretive Summary: Since 1986 some crop areas of Central Italy have been severely infested by wild sunflower, particularly where the sunflower crop has been grown for a number of years. Because of the long sunflower production tradition and its importance in Italy, we observed this new weedy relative to find out how it was dispersed and to attempt to ascertain its origin. Wild plants grow scattered at the moist edges of arable fields where tillage and herbicide treatments are very limited or absent. Plants also grew spontaneously along the ditches and at the edges of main roads and motorways. Sometime they form naturalized populations with plants of different ages due to the non-uniform seed germination, typical of wild species. Almost all plants were branched with red pigmentation, usually observed on stems and branches and sometime up to the main leaf veins. In any case, at maturity, the plants also had considerable pubescence and floral traits, such as phyllaries and pales, which would be classified them as wild Helianthus annuus. Most plants observed had rhizome-like roots with an almost perennial structure, shaped differently, and emerging from deep in the soil. However, this trait is not associated with wild H. annuus which is annual. Only a few heads (less than 5% out of the sampled plants) had complete seed retention. Seed shattering is a trait of wild sunflower species. Concerning the origin of such material, we believe that a cultivated crop variety was introgressed with genes from a foreign species, possibly a perennial species. We can not rule out the possibility of a mutation and/or the recombination of H. annuus with adventitious roots. In the future, molecular markers may be able to help us understand the origin of this sunflower.
Technical Abstract: Wild sunflowers are spreading from the marginal areas into the field crops in some areas of Central Italy. Crops like maize, tomato, tobacco, alfalfa are often infested with wild sunflowers. Cultivated hybrid sunflower crops are also being infested with wild sunflower. Plants and populations of this ruderal sunflower also spontaneously grow at the edge of the fields, and along the ditches and roads. We have observed that this ruderal wild sunflower is dispersed partially by its seed, but possibly can be propagated vegetatively by its perennial basal stalk when it survives the mild winter seasons. We have evidence that the seed maintains germination for years when they are plowed into the soil. The ruderal wild sunflower phenotypically resembles H. annuus, but the strong root system is not usual for an annual sunflower species. Concerning its origin, we observed variations indicating naturalization by either an introgression process involving wild species or a segregation of a hybrid variety and the incorporation of genes conferring seed dispersion and root persistence. It is possible that a similar process occurred a few centuries ago when sunflower was introduced into Europe and escaped botanical gardens and began to colonize Eastern European ruderal areas.