Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2011
Publication Date: 8/8/2011
Citation: Cruz, C., Bockus, W., Pedley, K.F., Peterson, G.L., Stack, J., Tang, X., Valent, B. 2011. Standardization of protocols to test wheat (Triticum aestivum L.) for reaction to blast in a biocontainment laboratory. Phytopathology. 101:S40. Interpretive Summary:
Technical Abstract: Growth medium, spore age, and inoculum density are essential factors for determining host responses to a plant pathogen. The standardization of these factors is important to obtain adequate and reproducible disease assessments. We are testing US wheat cultivars for reaction to the exotic disease blast, caused by the fungus Magnaporthe oryzae, in a Biological Safety Level 3 (BSL-3) pathogen containment facility. Although several protocols have been published, it was necessary to adapt those to a biocontainment environment. Four culture media (potato dextrose, V8, oat meal, and corn meal agar), three spore ages (7, 14, 21 days), and two levels of spore hydration (non-dried and dried) were used to study their effect on appressoria formation by isolate T-25. Hydrated and then dried spores did not germinate regardless of growth medium or age, and spores from 14- and 21-day-old cultures had low germinability. The highest percentage of appressoria formation was observed for hydrated spores from 7-day-old cultures from V8, oatmeal, and corn meal agar. Hydrated conidia and conidia that had been dried for 1 min., 15 min., 30 min., or 1 hr, before being rehydrated, were tested for infectivity. In general, dried, and then rehydrated conidia lost their germinability and did not infect wheat. The optimum inoculum density and volume was then determined on three cultivars showing different levels of susceptibility. The optimal inoculum density for infection was 20,000 spores per ml with an inoculation volume of 1.0 ml per wheat head. This information will allow for accurate and reproducible screening efforts aimed at identifying US wheat varieties with resistance to blast.