Endophyte infection may affect the competitive ability of tall fescue grown with red clover

Cool-season grasses infected with Neotyphodium endophytes may be more persi stent and competitive than noninfected plants. In a greenhouse experiment, two tall fescue (Festuca arundinacea Schreb.) cloned genotypes (DN2 and DN1 1) with different growth characteristics and endophyte status (E -, non-inf ected; E +, infected) were grown in monocultures and in full competition wi th red clover (Trifolium pratense L.) cv. Reddy Red for 20 weeks. When grow n in monoculture, endophyte infection reduced the root dry matter (DM) of D N2 (16 %) and DN11 (5 %) when compared to E - plants, while shoot DM was no t affected. In full competition with red clover, root and shoot DM of tall fescue were not influenced by endophytes, but cumulative herbage DM yield w as less in Ef than in E - plants. Root growth of red clover was significant ly depressed (22 %) in competition with E+ plants of DN2 compared to E- pla nts, but was not affected when plants were grown in competition with DN11. The relative yield total (RYT) did not differ from 1.0 in red clover mixtur es with E- plants of DN2 and DN11, and with Ef plants of DN11, indicating c ompetition between the competitors for the same resources. In contrast, RYT was less than 1.0 in the red clover/DN2 E+ mixture, suggesting a negative interaction between the competitors. Endophyte infection increased the comp etitive ability of DN2 but reduced that of DN11 when compared to E- plants. Because the concentration of pyrrolizidine alkaloids in roots of E+ plants of DN2 was twice that found in roots of DN11 (1083 and 536 mu g g(-1), res pectively), we suggest that pyrrolizidine alkaloids might influence the com petitive ability of some endophyte-tall fescue associations through a possi ble allelopathic effect on companion species.