Diana Pilson University of Nebraska dpilson1@unl.edu

To most people sunflower conjures an image of the domestic cultivar, a plant with a large stalk crowned by a single large inflorescence. Our lab works on wild sunflower, Helianthus annuus, the progenitor of the crop plant. Unlike its domestic progeny, wild sunflower exhibits a branched growing form with numerous inflorescences.

In the Asteraceae, the structure commonly referred to as the flower head is a agglomeration of many small flowers. In sunflowers, the flowers are of two types: each sterile ray flower along the perimeter of the head bears one of the yellow ‘petals’, fertilization of the many concentric whorls of disk flowers that occupy the central ‘eye’ result in the production of achenes (seeds). The diameter of wild sunflower at our study site averages around 0.66 inches or 16.7 mm (ranging from 4.3 to 28.9 mm,) unlike cultivated forms which commonly reach a foot in diameter.

Cultivated sunflower is grown in the center of distribution of its wild progenitor. In the picture at left, wild sunflower is shown growing at the edge of a cultivated sunflower field near Ogallala. Because of their sympatric distributions, insect herbivores and pathogens common on wild plants tend to be common on the crop as well. For this reason, pest and diseases can cause serious economic losses in the Great Plains.

Cultivars are completely interfertile with wild H. annuus. Because crop and wild plants are interfertile, crop genes derived from traditional breeding methods, or potentially in the near future from genetically engineered plants, could escape and persist in wild populations. Of interest are the potential effects of crop genes on wild populations of H. annuus, and also on its insect herbivores.

 

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