ABSTRACT
ABSTRACT Epichloë typhina perennially and systemically infects grass plants, causing choke disease in which maturation of host inflorescences is suppressed. In seedling-inoculation tests, isolate E8 from perennial ryegrass established and maintained infection in this host but not in orchardgrass. In contrast, isolates E469, E2466, and E2467 from orchardgrass varied in infection frequency and stability in orchardgrass, but all were unable to establish stable infections in perennial ryegrass. To investigate the genetics of host specificity, isolate E8 was crossed with each of the isolates from orchardgrass. Seedlings of parental host species were inoculated with F(1) progeny, and the frequencies of seedling infection and stability in adult plants were assessed. In the E8 x E2466 cross, the F(1) progeny exhibited a wide range of infection frequency and stability in each parental host. In crosses E8 x E469 and E8 x E2467, where the orchardgrass-derived parents infected 5 to 13% of inoculated perennial ryegrass seedlings, the distributions of infection frequencies for the F(1) progeny wereskewed toward levels comparable to that of the parent from perennial ryegrass. In all crosses, most progeny had low frequencies of infection in orchardgrass. However, transgression was evident in a cross of E8 with E469, an isolate that infected orchardgrass seedlings at a low frequency (2 to 3%). The E8 x E469 cross had a few F(1) progeny that infected orchardgrass at high efficiency (up to 81%). A Spearman rank correlation applied to the E8 x E2466 progeny indicated a significant negative correlation between infection frequencies in perennial ryegrass and orchardgrass. Also, there was a significant correlation of infection frequency and stability in perennial ryegrass but not in orchardgrass. To test whether only a few genes governed infection frequency in perennial ryegrass, an E8 x E2466 F(1) progeny (designated E386.04), which had intermediate compatibility with this host, was backcrossed to E8. The progeny of this backcross exhibited a distribution of infection frequencies in perennial ryegrass between that of E386.04 and the backcross parent, suggesting that multiple genes may determine compatibility at the seedling infection stage. The results of these experiments indicated multiple genetic determinants of compatibility or incompatibility with each host, with intermediate or high heritability.
ABSTRACT
Many cool-season grasses (subfamily Pooideae) possess maternally transmitted fungal symbionts which cause no known pathology and often enhance the ecological fitness and biochemical capabilities of the grass hosts. The most commonly described endophytes are the Acremonium section Albo-lanosa spp. (Acremonium endophytes), which are conidial anamorphs (strictly asexual forms) of Epichloë typhina. Other endophytes which have been noted are a Gliocladium-like fungus in perennial ryegrass (Lolium perenne L.) and a Phialophora-like fungus in tall fescue (Festuca arundinacea Schreb.). Here, we report the identification of additional non-Acremonium sp. endophytes (herein designated p-endophytes) in three more grass species: Festuca gigantea, Festuca arizonica, and Festuca pratensis. In each grass species, the p-endophyte was cosymbiotic with an Acremonium endophyte. Serological analysis and sequence determinations of variable portions of their rRNA genes indicated that the two previously identified non-Acremonium endophytes are closely related to each other and to the newly identified p-endophytes. Therefore, the p-endophytes represent a second group of widely distributed grass symbionts.
