Rate of Neotyphodium endophyte vertical transmission imposed by host grass fitness threshold

GUNDEL, PE; GARCIA-PARISI, PA; CASAS, C; OMACINI M; MARTINEZ-GHERSA,MA; GARIBALDI,LA; GHERSA, CM

Lexington, Kentucky

Congreso; Joint Meeting of the Mycological Society of America (MSA) and of the International Symposium on Fungal Endophytes of Grasses (ISFEG); 2010

Sociedad Americana de Micologia

<!-- /* Font Definitions */ @font-face {font-family:Calibri; mso-font-alt:"Century Gothic"; mso-font-charset:0; mso-generic-font-family:swiss; mso-font-pitch:variable; mso-font-signature:-1610611985 1073750139 0 0 159 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin-top:0cm; margin-right:0cm; margin-bottom:10.0pt; margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:Calibri; mso-fareast-font-family:Calibri; mso-bidi-font-family:"Times New Roman"; mso-ansi-language:ES-AR; mso-fareast-language:EN-US;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> The nature of the symbiosis between vertically transmitted Neotyphodium endophytic fungi and grasses may depend on the ecological context. It has been found that the endophyte may depress host fitness under restrictive growth conditions; results that have been interpreted as costs for the host in maintaining the symbiont. It is unknown if these costs may impact the endophyte fitness. Endophyte fitness is determined by host seed production and the proportion of this seeds that are infected (transmission rate). While the former has been widely studied, the latter has been scarcely studied. Here, we explore the relationship between endophyte transmission rate and seed production at individual plant and spike levels. The model of study is the annual grass Lolium multiflorum and the endophyte Neotyphodium occultans. We analyze two matrixes of data. The first one includes the transmission rate and seed production per plant of 94 individual plants. Variability in seed production per plant was obtained by subjecting the plants to different treatments of resources and stress level in different experiments. The second matrix includes the transmission rate and seed production per spike of 94 individual spikes. Variability in seed production per spike was obtained by subjecting monospecific patches to simulated grazing (defoliation and trampling) in one experiment. We found a positive correlation between transmission rate and seed production for both individual plants (rho=0.27, P<0.009) and spikes (rho=0.43, P<0.001). Transmission rate was the highest and invariant in plants or spikes with high seed production. Alternatively, the variability in transmission rate was evident in plants and spikes with low seed production. Our results suggest that there could be a threshold of host fitness value (in terms of seed production) below which the endophyte-grass symbiosis could be harmed.