Nodulation patterns of actinorhizal plants in the family rosaceae

Abstract

Patterns of nodulation, growth, and Frankia -host specificity have not been well characterized for the actinorhizal genera in the family Rosaceae because of the scarcity of Frankia isolates from these taxa. Furthermore, the few isolates available from actinorhizal Rosaceae have consistently failed to nodulate plants from the host genus. indicating nitrogenase activity for these nodulated plants. These data suggest that a similar microsymbiont infects the actinorhizal genera in the family Rosaceae.

Ecology Of Actinorhizal Plants

“…However, infective Frankia can be found in a variety of soils both within and outside the immediate influence of actinorhizal hosts as well as outside of the native range of actinorhizal plant species (Burleigh and Dawson, 1994;Lawrence et al, 1967;Maunuksela et al, 1999Maunuksela et al, , 2000Paschke and Dawson, 1992a;Zimpfer et al, 1997). Frankia able to nodulate Alnus, Myrica, Dryas and Elaeagnus are found widespread outside the native range of their host plants, suggesting that they have the capacity to persist as a saprophyte (Kohls et al, 1994;Maunuksela et al, 1999;2000;Nickel et al, 1999;2000).…”

“…nodulate readily either outside their native ranges or with soils and nodule inocula obtained from locations distant from their native ranges (Kohls et al, 1994;Paschke et al, 1994). The explanation generally offered for this capacity is that the host species are promiscuous and can consort symbiotically with a heterogeneous mix of widespread microsymbiont genotypes.…”

Evolution Of Actinorhizal Host Plants And Frankia Endosymbionts

“…Frankia enter the roots of compatible plants either by root hair infection (RHI) or by direct intercellular penetration (IP; see chapter by Berry and Wall in this volume). Group 1 strains infect via RHI (Berry and Torrey, 1983;Berry et al, 1986;Callaham et al, 1979;Torrey, 1976); Group 3 strains infect either by IP or RHI depending on the plant being infected (Bosco et al, 1992;Cournoyer et al, 1993;Miller and Baker, 1986;Racette and Torrey, 1989b); and Group 2 strains infect hosts by IP (Berry and Sunell, 1990;Kohls et al, 1994;Liu and Berry, 1991;Miller and Baker, 1985;Valverde and Wall, 1999).…”

“…They have not yet been isolated in pure culture. Consequently, little is known concerning the host range of individual members of Group 2, although crossinoculation studies using crushed nodules suggest that symbionts from Dryas, Ceanothus, Datisca, and Coriaria are in the same cross-inoculation group ( Kohls et al, 1994;Torrey, 1990). Group 2 is characterized by low variability among the reported 16S-rRNA gene sequences, a situation that may indicate either a bottleneck in their evolutionary development or simply insufficient sampling compared to other actinorhizal species.…”

“…Swensen (1996) addressed the question of homology of the symbioses in the four different actinorhizal groups by mapping anatomical and morphological features of root nodules onto the rbcL tree. These data included the number and shape of Frankia symbiotic vesicles (Baker and Schwintzer, 1990;Lalonde, 1979;Murray et al, 1985;Zhang et al, 1984), the location of Frankia vesicles within infected cells (Akkermans and van Dijk, 1981;Silvester and Harris, 1989), the location of infected cells within the nodule (Akkermans et al, 1983;Calvert et al, 1979;Newcomb and Pankhurst, 1982), evidence for gaseous diffusion barriers in the nodule and hemoglobin concentration (Tjepkema 1978;, and the mode of infection of the host plants (Berry et al, 1986;Berry and Sunell 1990; 1979; Kohls et al, 1994;Liu and Berry 1991;Miller and Baker, 1985;Racette and Torrey 1989a). There were clear differences in these characters in actinorhizal species belonging to each of the four groups, suggesting that groups B-E were the result of different symbiotic origins and that actinorhizal symbioses originated at least four times in the evolution of flowering plants.…”