NONCONFIRMATION OF NODULATION IN ARTEMISIA LUDOVICIANA

Abstract

Reports of nodulation and nitrogen fixation specifically associated with or insect galls of Artemisia ludoviciana were not confirmed. REPORTS (Farnsworth and Hammond, 1968a; Farnsworth, Romney and Wallace, 1976) of nitrogen fixation in Artemisia ludoviciana claim that nodules, with a Rhizobium-like endophyte, are the site of fixation. Nevertheless, another paper (Farnsworth, 1975) strongly implies that these are probably insect galls. However, this is not explicitly stated in the latter report nor has the reported fixation been confirmed. During the months of April, May and June in the years 1977 through 1980 we made extensive observations for and insect galls on Artemisia ludoviciana growing in the vicinity of the original study area near Morgan, Utah (Farnsworth, 1975; Farnsworth and Hammond, 1968a). Sometimes we found insect galls associated with underground stems of some plants (Fig. 1), but failed to observe any or galls (Farnsworth, 1975) at any time. Although the external appearance of the galls might seem to resemble nodules, their internal appearance is unequivocally that of insect galls (Fig. 2). Since, externally, the galls (Fig. 1) closely resemble the root nodules (Farnsworth, 1975; Farnsworth and Hammond, 1968a), we would suggest that the root nodules (Farnsworth, 1975; Farnsworth and Hammond, 1968a) are in fact insect galls developed on underground stems. In view of the above reports we tested the galls for nitrogenase activity, and report here negative results obtained for June 1980 which are representative of assays made during the aforementioned years. 1 Received for publication 18 November 1980; revision accepted 4 February 1981. We thank S. A. Pratt for electron microscopy and R. Young for photography. w:~~~~~~~~Sk * ; i