Effect of plant growth regulators and other selected compounds on the growth of Acremonium coenophialum in vitro

A mutualistic relationship exists between the endophyte Acremonium coenophialum (Morgan, Jones and Gams) and tall fescue Festuca arundenacea (Shreb). The host, tall fescue, provides protection, a source of nutrients and a means of dissemination for the endophyte. The endophyte protects tall fescue from adverse environmental conditions, overgrazing by herbivores and insect and pathogen attack. Changes in the physiology of the fescue plant causes changes to occur in the growth of the endophyte. The purpose of this study was to examine plant growth regulators and carbohydrates to determine their effect on the growth of the endophyte.

In liquid and solid media, the synthetic auxins 2,4-D (2,4-dichloro Phenoxyacetic acid) and dicamba (3,6-dichloro 2- methoxybenzoic acid), had no observable effect on growth of A. coenophialum. Abscisic acid also had no observable effect on growth of the endophyte. When A. coenophialum was exposed to an ethylene atmosphere of 9ppm, no observable difference in growth was observed when compared with the control. Gibberellic acid (GA3) had no observable effect on growth of the endophyte after 4 weeks. However, at 6 weeks, a reduction of 40 percent was observed on solid media. In liquid M102 media (Bacon et al. 1988) , growth was consistent with that of the control at concentrations of 0.1, 1 and 10μM; however, 100 percent reduction was observed at 100 μM. The synthetic cytokinin, kinetin, reduced the growth of A. coenophialum at each concentration examined. Growth reductions ranged from 20 percent at 20 μM to 100 percent at 100 μM. Zeatin also reduced the growth of the endophyte. A 50 percent growth reduction was observed at 100 μM. In liquid M102 media, no reduction in growth of the endophyte occurred at 0.1, 1, and 10 μM kinetin, but at 100 μM kinetin, growth was reduced by 95 percent.

Growth of A. coenophialum on media containing various carbon sources was investigated. Radial growth was higher on sucrose than on other carbon sources tested. A morphological change was noted on media containing sucrose. The endophyte grown on media containing sucrose exhibited a mucoid-like appearance, while the endophyte grown on the xylose-substituted media had a cottony appearance.

In summary, none of the plant growth regulators (PGRs) examined had a stimulatory effect on the endophyte. However, a reduction in growth was noted with cytokinins and GA3. Sucrose was a better carbon source than xylose, but changes in the morphology of the endophyte occurred when grown on media supplemented with sucrose in M102 media. The endophyte took on a mucoid-like appearance when grown on M102 media supplemented with sucrose, while cultures grown on M102 media supplemented with xylose had a white cottony appearance.