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United States Department of Agriculture

Agricultural Research Service

Title: Tolerance to Sclerotinia in Wild Sunflower Species

Authors
item Rashid, K - AG & AGRI-FOOD CANADA
item SEILER, GERALD

Submitted to: Proceedings Sunflower Research Workshop
Publication Type: Proceedings
Publication Acceptance Date: March 21, 2001
Publication Date: N/A

Interpretive Summary: There are many pathogens affecting sunflower in North America and worldwide. One fungus, Sclerotinia, is pathogenic on more than 300 plant species with no evidence of resistance in any of the host species. In sunflower, stalk and head rot occur in major production areas. In spite of reports of different levels of susceptibility among sunflower hybrids, there is no evidence of resistance in any commercial hybrids available to producers. Wild ancestors of cultivated sunflower have been a source of genes for tolerance and resistance to sunflower pathogens. The objective of this study was to screen populations of wild perennial sunflower species for resistance/tolerance to Sclerotinia stalk and head rot. A total of 327 populations of wild perennial sunflower were evaluated, 125 Maximilian's sunflower and 202 of Nuttall's sunflower. Populations of these species have been established at the Agriculture and Agri-Food Canada Res. Stn., Morden, Manitoba. The populations were evaluated for stalk rot using an inoculum applied to the soil at seedling stage. For head rot, the inoculum was applied to the head and stems at five different times, starting at early flowering. The fungus applied in the soil infected the plants and gave a good test for stalk rot. In spite of the five artificial inoculations starting at early flowering, head and stem infections were scarce and data did not show any differences between the populations of the two wild perennial species. Of the 125 populations of Maximilian's sunflower, 29 had no sign of infection, 20 had 1-5% infected plants, and 76 had more than 5% infected plants for stalk rot. For 202 populations of Nuttall's sunflower, 66 had no sign of stalk infection, 36 had 1-5% infected plants, and 100 had more than 5% infected plants.

Technical Abstract: Sclerotinia sclerotiorum is a common pathogen affecting sunflower in North America and worldwide. This fungus is pathogenic on more than 300 plant species with no evidence of resistance in any of the host species. In spite of the reports of different levels of susceptibility among sunflower hybrids, there is no evidence of resistance in any of the commercial hybrids available to growers. The objective of this study was to screen populations of wild perennial sunflower species for resistance/tolerance to S. sclerotiorum stalk and head rot. A total of 327 populations of wild perennial sunflower of the species Helianthus maximiliani and H. nuttallii have been established at the Agriculture and Agri-Food Canada Res. Stn., Morden, Manitoba. To inoculate for stalk rot evaluation, infected millet seed and small sclerotia (20% of inoculum) were dried at room temp for a few days. The inoculum was distributed between wild sunflower plants of the individual plots at the seedling stage, and the soil surface was scratched lightly. For head rot evaluation, infected millet seed was ground to a powder, then used to inoculate sunflower heads and stems. Of the 125 populations of H. maximiliani, 29 had no sign of infection, 20 had 1-5% infected plants, and 76 had more than 5% infected plants for stalk rot. In the 202 populations of H. nuttallii, 66 had no sign of Sclerotinia infections, 36 had 1-5% infected plants, and 100 had more than 5% infected plants for stalk rot. In spite of the five artificial inoculations starting at early flowering, head and stem infections were scarce and data did not show any differences between the accessions of the two species of wild sunflower under investigation.

Last Modified: 7/28/2014
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