Endophyte incidence and growth promoting in Bromus setifolius from Santa Cruz, Argentina

NOVAS, M:V:; GENTILE, A.; CABRAL, D.

Córdoba, Argentina

Congreso; Fifth International PGPR Workshop; 2000

J. Kloepper, Editor

Endophytes are fungi related to aerial tissues of plants. They are widely distributed among vascular plants, algae and bryophytes. A particular group is that of grasses where endophytes develop an intercellular systemic infection throughout the aerial tissues involving a substantial fungal biomass. They are clavicipitaceous (Balansiae, Clavicipitaceae) fungi, most of them in their Neotyphodium anamorphic state, are always transmitted by seeds and never show external signs of infection or symptoms of disease. While some grass species appear to be ubiquitously infected, others are not known as hosts; indeed, many other species fall between these extremes. The presence of endophytes in grasses is of considerable agronomic and veterinary interest. Fescue toxicosis is a serious problem of animals that graze on infected tall fescue. Endophytes produce a variety of alkaloids responsible for poisoning of cattle. Neotyphodium/ grass symbiosis, on the other hand, is known to improve abiotic and biotic stress resistance in their hosts. Among the benefits of these relationships for the plant is the increased resistance to herbivores, pathogens, and nematodes, as well as better competitive ability and drought tolerance. Increased shoot mass and tillering, decreased seed depredation, greater seed germination and enhanced growth and survival, have also been observed. This association is known as constitutive mutualism. Most of the above mentioned studies were performed on the widespread, commercially cultivated Festuca arundinacea Schreb. and Lolium perenne L. However, the persistence of an association in nature depends solely upon the advantages of the symbiosis between plants and microorganism. Therefore, more information on the effect of endophytes in host plant fitness can be best studied from natural populations than from genetically manipulated ones. Distribution of natural infected (E+) and uninfected (E-) populations of the same grass species, their significance as well as the advantage to the hosts far from toxic effects, have been poorly studied. During the last years, a screening of native grass associations with endophytes has been carried out in Argentina. More than 30 species of hosts have been recognised. Some of them show particular distribution of E+ and E- populations as well as incidence percentage. The aim of this study was to evaluate the distribution of E+ and E- population of a single grass over a great extension area and also to analyse the incidence and the biology of seeds and seedlings on infected and uninfected populations. Bromus setifolius J. Presl., a perennial non toxic widespread grass, was selected for this study. From Southeast to Northwest in Southern Patagonia (Santa Cruz province) plants and seeds from 23 populations were sampled. Also soil samples were taken in most of them. Latitude, longitude, altitude and clime characteristics were recorded. J. Presl., a perennial non toxic widespread grass, was selected for this study. From Southeast to Northwest in Southern Patagonia (Santa Cruz province) plants and seeds from 23 populations were sampled. Also soil samples were taken in most of them. Latitude, longitude, altitude and clime characteristics were recorded. To analyse the infection level, tissues of 20 plants of each population were examined under the microscope. As a preliminary study of the biology of seeds the weight, timing and percentage of germination was performed. Growth parameters of the seedlings such as height and dry weight were also recorded. Both assays were carried out under controlled environmental conditions, using seeds from two nearby populations previously characterised as E+ and E-. Two hundred seeds of each population were weighted. Germination was carried out by planting 100 seeds of each population in two different pots. Emergent seedlings were counted daily for 30 days. Growth comparisons of seedlings were conducted in twelve plants of each population at 1, 2 and 3 months after germination. Preliminary results show differences of incidence between Bromus setifolius populations, which is confirmed by Kruskal-Wallis non-parametric test. The groups of populations conformed by this analysis consist of distinct plant communities. Although we observed a tendency of higher infection in areas with greater precipitation rates, it is still not clear which parameters are associated with infection incidence. One-way analysis of variance was used to compare seed weight. The weight of seeds from infected plants was over twice that from uninfected plants, a highly significant difference (p<0.0001). Infected seeds show higher germination than uninfected ones. Early observations reveal differences in above ground biomass produced by infected and uninfected individuals, the infected ones being the highest and strongest. Growth comparisons among seedlings are still in course and all of them will be statistical analysed.