The effect of four new Frankia isolates on growth and nitrogenase activity in clones of Alnusrubra and Alnussinuata

Abstract

Two clones of red alder (Alnusrubra Bong) and two clones of Sitka alder (Alnussinuata (Regel) Rydb) were inoculated with four new Frankia isolates. The endophytes included a red and a Sitka alder isolate from Vancouver Island, British Columbia, and a red and a Sitka alder isolate from Mount Hood National Forest, Oregon. All inoculated ramets were well nodulated and had an active nitrogenase system as measured by the acetylene reduction assay. For the inoculated red alder clones, host genotype had a significant effect on stem height and root weight. None of the growth parameters was affected by endophyte strain or by clone–endophyte interaction. For Sitka alder clones, host genotype affected all growth variables. While endophyte strain had no effect on plant growth, clone–endophyte interaction occurred with stem height and leaf weight. Conversely, acetylene reduction values were not affected by clone or clone–endophyte interaction in either species. In red alder, acetylene reduction values were significantly affected by endophyte strain showing both inter- and intra-species variations. In Sitka alder, endophyte strain did not affect acetylene reduction values. The results indicate that both host genotype and endophyte may affect the efficiency of host–endophyte symbioses.