Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: January 1, 2004
Publication Date: January 20, 2004
Citation: Gulya Jr, T.J., Miller, J.F., Seiler, G.J. 2004. Sunflower germplasm development with Sclerotinia head and stalk rot resistance. Sclerotinia Initiative Annual Meeting, January 20-22, 2004, Bloomington, MN. Technical Abstract: Several lines of study to develop sunflower germplasm tolerant to Sclerotinia head rot or stalk rot were continued or initiated during 2003. Following successful field tests in 2002, three sunflower inbred lines (RHA 439, RHA 440, HA 441) with high levels of head rot resistance were released in the spring of 2003. USDA breeding material was again evaluated for head rot tolerance at the mist field plots in Carrington, ND. Sclerotinia infection was low with susceptible checks averaging only 36% infected heads and a DSI of 2.7 on a 5-point scale. High winds and hot weather following ascospore inoculation were suspected to be the main factors causing the low disease severity. Modifications for 2004 to improve infection include switching from mist nozzles to micro sprinkler heads, and installing leaf wetness and relative humidity sensors to determine when the mist duration is insufficient. Future modifications may include use of a data logger coupled with the sensors, programmed to activate the mist system instead of a simple time controller. In studies to evaluate wild sunflower germplasm, eight annual Helianthus species were tested for the second year at Carrington, ND. As observed in the first year, the primary response of wild Helianthus species to ascospore inoculation was peduncle necrosis rather than head rot. Only in H. annuus, with the largest heads (approaching 3 cm in diameter) were typical head rot symptoms observed, and then only after cut heads were incubated in moist chambers in the laboratory. Additionally, only 35% of the 500+ transplanted wild sunflowers produced flowers in time for inoculation. The consensus after two years of experience is that evaluation of wild Helianthus species for Sclerotinia resistance would be most efficient after crossing with cultivated sunflower, and testing the F1 interspecific hybrid, which should have agronomic characteristics approaching that of cultivated sunflower. A second mist irrigation nursery at Fargo was initiated to supplement the Carrington site. Sunflower, canola, and dry bean pathologists from North Dakota State University will use the four-acre site cooperatively. A two-year stalk rot inoculation method study at two locations was completed. Sclerotinia grown on either oats or millet and placed in a row-side furrow one month after planting gave consistent and high levels of stalk rot. Sclerotia, in contrast, produced low levels of disease. Twenty commercial hybrids were evaluated at four locations using the oat/Sclerotinia inoculum. Disease incidence across hybrids ranged from 22 to 56% at the four locations, with the resistant check hybrid averaging 17% infection compared to 55% for the susceptible check hybrid. Mechanizing this inoculation procedure by dispensing the inoculum with a granular chemical applicator mounted on a tractor-drawn cultivator should enable us to efficiently test a large number of entries. With artificial inoculation procedures for both head rot and stalk rot, our program should be able to screen for both diseases in our attempt to incorporate resistance to both Sclerotinia diseases in the same germplasm.