ARS | Publication request: AN INOCULATION METHOD TO INDUCE SCLEROTINIA STALK ROT IN FIELD-GROWN SUNFLOWERS

Submitted to: American Phytopathological Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: May 28, 2004
Publication Date: December 6, 2004
Citation: Gulya Jr, T.J., Draper, M., Henson, R. 2004. An inoculation method to induce sclerotinia stalk rot in field-grown sunflowers [abstract]. American Phytopathological Society Abstracts. Available: http://apsnet.org/meetings/div/nc04abs.asp

Interpretive Summary: The fungus Sclerotinia sclerotiorum causes both a stalk rot and a head rot on sunflower, and is the most serious disease of sunflower in the United States and worldwide. Testing sunflower cultivars for resistance to Sclerotinia stalk rot must be done on adult plants in the field. Relying upon natural infection has produced erratic results. We have developed a method to artificially induce the disease which can distinguish different levels of tolerance to this disease. The method simply entails growing the fungus on cooked grain (oats or millet) and placing the fungal-colonized grain in a furrow beside the developing plant. Initial trials relied on manual inouculations that limited screening potential based on available labor. This method has been adapted to a mechanized, automated, tractor-drawn implement that allows inoculation of many more rows per day for screening.

Technical Abstract: The efficacy of Sclerotinia sclerotiorum sclerotia or mycelia (grown on either oats or millet) to induce Sclerotinia stalk rot in field-grown sunflower plants was tested in a two-year study at two locations. Grain-based inoculum was superior to sclerotia in inducing disease at all inoculation dates. The lowest rate of grain/mycelia inoculum (40 g/ 6 m row) produced significantly more disease (37%) than even the highest rate of sclerotia (80/row), which produced 12% stalk rot. The optimal inoculation technique consisted of digging a 4 cm deep furrow 15 cm from the plants at the V-6 stage and uniformly placing the mycelial-colonized grain in the furrow. Using the millet/mycelia inoculum, twenty hybrids were evaluated at four locations for tolerance to Sclerotinia stalk rot.Rankings were similar at all four locations, despite differences in climate and disease severity at each location. Averaged over four locations, stalk rot reaction ranged from a low of 17% to a high of 53%.