Effects of Neotyphodium fungi on Lolium multiflorum seed germination in relation to water availability

BACKGROUND AND AIMS

Temperate endophyte-infected (Neotyphodium sp.) grasses have been shown to exhibit an ecological advantage over endophyte-uninfected grasses under abiotic stressful conditions. It is predicted that endophyte-infected plant populations will display higher rates of germination and proportion of germinated seeds under limiting water conditions.

METHODS

The hydrotime regression model was used to describe the effect of Neotyphodium endophyte on seed germination of Lolium multiflorum at different water potentials. Additionally, seed mortality after water stress exposure was estimated in endophyte-infected and -uninfected seeds.

KEY RESULTS

Endophyte infection inhibited seed germination at all water potentials. The hydrotime model described satisfactorily the germination responses, and revealed that endophyte-free seeds exhibited higher rates of and final percentage germination, probably due to a lower base water potential compared with endophyte-infected seeds. However, Neotyphodium endophyte conferred a higher rate of survival in those seeds that remained ungerminated when exposed to highly water stress conditions.

CONCLUSIONS

Changes produced by Neotyphodium endophyte in L. multiflorum seeds might affect fitness in particular ecological scenarios. For example, the presence of the endophyte may curtail seed germination when water is limiting, reducing the risk of seedling death. Conversely, endophyte-free seeds would display an enhanced germination, ensuring a more rapid seedling establishment if later water conditions do not restrict plant growth.

First Report of White Rust of Arugula Caused by Albugo candida in Argentina

Production of arugula (Eruca sativa) has increased greatly in Argentina. Since 2002, particularly during the fall, a foliar disease has affected commercial crops in Capilla del Señor (northeast of Buenos Aires Province, Argentina). The disease appeared in foci, spreading throughout the whole production field or greenhouse. Severely affected crops were plowed under. Diseased leaves were chlorotic and had white sori that emerged through the abaxial epidermis. Sori corresponded to the white rust agent, Albugo candida (Pers.) Kunze (1). Sporangiophores were hyaline and clavate, and sporangia were globose and hyaline with a mean diameter of 16.2 μm (14.2 to 19.2 μm). Pathogenicity tests were performed by spraying a suspension of 10⁶ zoospores/ml or 5 × 10⁴ sporangia/ml on four healthy 30-day-old arugula plants. Inoculum was prepared by scrapping sporangia from infected leaves. Sporangia were used directly or incubated in sterile distilled water (SDW) for 14 h at 5°C to induce zoospore formation (2). Four additional healthy plants were sprayed with SDW to serve as controls. Plants were kept in plastic bags for 48 h and maintained in the greenhouse thereafter. White rust symptoms, similar to those observed on the original plants from the field, were observed on inoculated plants 10 days after inoculation. To our knowledge, this is the fist report of A. candida on arugula in Argentina. References: (1) K. Mukerji. No. 458 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1975. (2) H. Scheck and S. Koike. Plant Dis. 83:877, 1999.