2012 Annual Report
Misting systems will be established and managed to create contrasting micro-climates that will be assessed to determine their ability to create conditions favorable for sclerotinia head rot infections and thus the evaluation of sunflower resistance. The contrasting micro-climates will be developed by utilizing different misting timings, misting durations, and mist intensities. The misting systems will be equipped with different emitters, spacing, and risers along with timers to achieve the different environments. Climate and plant canopy sensors tied to data loggers will be used to record the micro-climate variables. A series of known sunflowers hybrids will be planted and inoculated with ascospores in accordance with proven procedures. Assessments of head rot infection will be recorded and compared across the different misting system regimes. The different climatic data that is associated with each misting regime will evaluated to identify those conditions that best promote sclerotinia head rot infections.
Upon project initiation, the breeding for Sclerotinia head rot resistance in sunflower hybrids was in very early stages of development, and it was unknown whether commercial hybrids differed in their susceptibility to Sclerotinia head rot. Over the past several years, the project has documented that significant, repeatable differences exist in the susceptibility of sunflower hybrids to Sclerotinia head rot. The project has assessed the Sclerotinia head rot resistance of new commercial hybrids as those hybrids have been introduced into the market, thereby providing growers with independent data on the Sclerotinia head rot resistance of commercial hybrids. The project has also played a key role in the development of new hybrids with improved Sclerotinia head rot resistance by screening sunflower breeding lines and elite experimental hybrids for their resistance to Sclerotinia head rot. Finally, the project has been successful in developing inoculation procedures and misting systems that reliably lead moderate to high levels of Sclerotinia head rot infection that are needed to identify the relative susceptibility of sunflower hybrids to Sclerotinia head rot. Over the years of this project, both public and private sunflower breeders have been able to effectively screen their hybrids or breeding lines and thereby identify differences in resistance to Sclerotinia head rot. The success of these annual assessments has fostered improvements in the overall resistance to Sclerotinia head rot and the number of hybrids with improved levels of resistance. Sunflower growers now are able to review the results of the field trials associated with the project to identify and select commercial hybrids that have improved resistance to Sclerotinia head rot and stalk rot.
During 2011, Sclerotinia head rot incidence was moderate to high across sites. In the initial screenings, head rot incidence at physiological maturity ranged from 72 to 100% across entries in Carrington, ND and 0 to 29% in Morden, MB. In the repeat screenings, average head rot incidence ranged from 82 to 100% across entries in Carrington, 24 to 94% in Crookston, MN, 21 to 89% in Langdon, ND, 0 to 30% in Morden, 3 to 90% in Oakes, ND, and 32 to 99% in Sidney, MT. For Carrington, data were missing from many entries due to high plant mortality caused by a severe hail storm on July 24.Sclerotinia head rot severity results were significantly correlated between the Carrington, Crookston, Oakes, and Langdon locations, and Sclerotinia head rot incidence results were significantly correlated between the Langdon, Oakes, and Crookston locations. The results from Morden and Sidney were generally not significantly correlated with any other location. The repeatability of the results obtained from Carrington, Crookston, Langdon, and Oakes can be explained by inoculation procedures. In Carrington, Crookston, Langdon, and Oakes, inoculations were conducted over multiple days, and each sunflower head was inoculated once (Oakes) or twice (Carrington, Crookston, and Langdon) during flowering. In Morden and Sidney, all sunflower heads across all entries were inoculated on two fixed dates, and the growth stage at which inoculations were conducted differed across entries. The low repeatability of the disease incidence results between Carrington and the other locations can be explained by the high disease pressure at the Carrington location; in the Carrington nursery, most entries exhibited disease incidence levels near 100%.
Five hybrids and breeding lines with elevated resistance to Sclerotinia head rot were identified in the multi-location analysis of disease severity index and disease incidence data from the ‘repeat’ trials: Seeds 2000 ‘X9856’, Pioneer ‘63N82’, Croplan ‘343 DMR HO’ (resistant check), Genosys ‘8064’, and Pioneer ‘63ME70’. As assessed at physiological maturity, these lines exhibited significantly lower levels of Sclerotinia head rot than the most susceptible lines (Croplan ‘305 DMR NS’, Triumph ‘TRX8343’, CHS ‘HRT10-4’, and Seeds 2000 ‘X5913’). Two additional hybrids and breeding lines with elevated resistance to Sclerotinia head rot were identified in the multi-location analysis of disease incidence data: Seeds2000 ‘X9814’ and Pioneer ‘64HE01’.
Nine hybrids and breeding lines with elevated resistance to Sclerotinia head rot were identified in the ‘initial’ screening trial in Carrington: Croplan ‘343 DMR HO’ (resistant check), Triumph ‘EXPSCL05’, Mycogen ‘E257321’, Triumph ‘EXPSCL06', Syngenta ‘3990 NS/CL/DM’, Genosys ‘1068’, Syngenta ‘3995 NS/SU’, Genosys ‘1068’, Syngenta ‘3995 NS/SU’, Mycogen ‘E378947’, and Croplan ‘EXP1141’. At physiological maturity, these lines exhibited significantly lower levels of Sclerotinia head rot than the most susceptible entries (Red River Commodities ‘8015’ and the susceptible check Croplan ‘305 DMR NS’). The disease severity index (DSI), which combines both disease incidence and severity, was used in the analysis: DSI was chosen for this analysis because this measure produced highly repeatable results in the Carrington ‘repeat’ screening nursery. The ‘initial’ screening nursery conducted in Morden was not informative due to highly variable results across replicates.