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United States Department of Agriculture

Agricultural Research Service

Research Project: EVALUATION OF SUNFLOWER HYBRIDS AND GERMPLASM FOR RESISTANCE TO SCLEROTINIA
2012 Annual Report


1a.Objectives (from AD-416):
The overall objective of this project is to identify and determine resistance to sclerotinia among commercial sunflower hybrids and germplasm used in breeding programs. An additional aspect of this project is to develop and refine misting systems that create the environment conducive for sclerotinia. This aspect of the project will not only generate reproducible and reliable data that identifies genetic resistance, but will better identify the environmental onditions necessary for sclerotinia infection and development.


1b.Approach (from AD-416):
Sunflower hybrids and advanced experimental lines with expected resistance or tolerance to sclerotinia head rot will be solicited from sunflower seed companies and breeding programs. Two sets of screening nurseries will be developed, one to screen new hybrid lines that have not been publicly evaluated and another set of hybrids to confirm the resistance that was previously defined. The new hybrid lines will be compiled into the “Initial Screening” which will include about 75 entries and be planted at Carrington, ND, and Morden, Manitoba. The best lines with resistance from previous evaluations will be compiled into the “Repeat Screening” which will include about 25 entries. The “Repeat” test will be planted at Carrington; Morden; Langdon, ND; and Oakes, ND. Each hybrid will be established in plots 1-row (30-inch) wide by 25 ft long and arranged in a randomized complete block with four replications. At the onset of flowering, 15 to 20 individual heads within each plot will be artificially inoculated with ascospores over a period of time to accommodate the differential development within and among hybrids. Misting systems will be constructed and activated before inoculation and remain operational based on the prevailing environment as necessary to favor disease development. Sunflower disease incidence and severity will be scored at a minimum of two timings. Scientists from the USDA-ARS Sunflower Research Unit will provide the ascospores inoculant to be used throughout the sunflower misting systems projects. A large misting system will be assembled and operated at the Carrington REC for the sole purpose of accommodating germplasm and breeding lines from the USDA-ARS Sunflower Research Unit scientists. Sunflower plots will be established by the USDA-ARS team and the disease assessments will be determined by the USDA-ARS scientists. The Carrington REC staff will assemble and manage the misting system and will make the ascospores inoculations as appropriate within this nursery. A separate nursery will be established at Carrington to evaluate sunflower hybrids and germplasm for resistance to sclerotinia stalk rot.

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.


3.Progress Report:

This project was initiated on June 1, 2009, research is ongoing, and the overall objectives of this project are to identify sunflower cultivars which are less susceptible to Sclerotinia head rot and to study chemical and biological control options for managing this disease.

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.


Last Modified: 12/22/2014
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