Endophytic Undifilum oxytropis (Q. Wang, Nagao & Kakish) Pryor, Creamer, Shoemaker, McLain-Romero, & Hambleton found within toxic locoweeds ( Astragalus and Oxytropis spp.) produces the alkaloid swainsonine, which is responsible for locoism in grazing animals. We sought to determine the location of U. oxytropis within locoweed seed, develop endophyte free plants, and assess the influence of environmental stresses on locoweed and endophyte cultures. Undifilum was identified within the parenchyma layers in seeds of Astragalus lentiginosus M.E. Jones using light microscopy and polymerase chain reaction. Astragalus lentiginosus and Oxytropis sericea Nutt. seedlings produced in embryo culture without seed coats did not contain swainsonine or fungus. Plants produced from whole seed contained U. oxytropis in both foliage and root tissues. When the in-vitro cultured plants of O. sericea and U. oxytropis cultures were subjected to environmental stresses including high temperature, low and high pH media, nutrient deficient media, and polyethylene glycol (PEG) amended media to simulate water deficit, both dry mass and swainsonine levels were affected. Swainsonine levels were greatest for O. sericea and Undifilum cultures in PEG or hydrochloric acid amended media. Plants grown in PEG-amended media had significantly greater dry mass, while Undifilum grown in PEG-amended media had lower dry mass than other treatments.

Onions are an important crop for New Mexico with 7,700 acres (3,116 ha) harvested in the state in 2003 (3). In 2002, onions of several cultivars were first noticed with diamond-shaped chlorotic or bleached lesions on seed stalks or leaves, typical of those reported for Iris yellow spot virus (IYSV). A more widespread survey of breeding stocks and commercial onion fields revealed similar symptoms on thrips-infested onions in Dona Ana and Rio Arriba counties. Incidence of disease symptoms ranged from <0.5 to nearly 30%. Symptomatic leaves were assayed for the presence of IYSV using enzyme-linked immunosorbent assay (ELISA; Agdia, Elkhart, IN) and antisera acquired from Agdia. Symptomatic leaves from breeding and commercial fields tested positive for IYSV. The virus was transmitted by Thrips tabaci from symptomatic onions to three onion cvs. New Mex Mesa, New Mex Vado, and New Mex Cryspy in growth chamber tests. All three cultivars showed symptoms of IYSV and tested positive for the disease using ELISA. However, New Mex Vado and New Mex Cryspy cultivars each showed 24% infection (4 infected plants of 17 tested) compared with 59% infection (10 infected plants of 17 tested) for New Mex Mesa, suggesting that not all cultivars are equally susceptible to the virus. To our knowledge, this is the first report of IYSV in onions in New Mexico, which has also been reported in the western United States in Idaho, Oregon, Colorado, and Washington (1,2,4). References: (1) L. J. du Toit et al. Plant Dis. 88:222, 2004. (2) J. M. Hall et al. Plant Dis. 77:952, 1993. (3) National Agricultural Statistics Service, On-line publication. USDA, 2004. (4) H. F. Schwartz et al. Plant Dis. 86:560, 2002.