Plant disease resistance and other useful information

Farm Forum

I spent a fair amount of yesterday and this morning taking counts of sunflower plants that were infested with the fungal disease, phomopsis, in the SDSU Sunflower CPT plot near Presho. Phomopsis overwinters in infected plant debris, and during the summer, ascospores are wind-blown or water splashed onto lower sunflower leaves. Infection moves in the leaf, to the petiole and then the stem, damages the pith in the stalk and makes the plant prone to lodging.

After identifying the hybrids in the treatments that had the highest incidence of phomopsis, the same names kept coming up. The same was true for the treatments that had little or no infestation of the disease. This was no great surprise as crop rotation and resistant hybrids are the best tools in managing the pathogen. Of the sunflower hybrids in the plot, the incidence of phomopsis ranged from little or none, to as high as 50% of the plants in some of the treatments. Fortunately, not all of the lesions were large, and many of the plants will likely stand long enough to reach maturity and until they are harvested. In years that are ideal for the disease however, lodging can be a major problem and severely reduce yields.

With many crop diseases, resistance is an important tool, as fungicides are often not labeled for, or effective in controlling them. The challenge plant breeders face is incorporating as many of the desirable characteristics as possible into a variety or hybrid so that it will perform. One of the challenges farmers face is selecting one or more varieties or hybrids that will work well in their operation. They may need to determine if there are weaknesses in a variety or hybrid they can correct with management, and how best to go about doing so.

Whenever one hears or reads about the process of plant breeding, there is likely reference to the number of crosses that are made, the number of experimental lines that are evaluated, the number of traits that are being considered, etc. During the process, numbers continue to be important as the various traits and characteristics are evaluated in their value and importance. That became starkly apparent as I was walking up and down sunflower rows, counting plants containing phomopsis lesions. Since the plot contains 46 hybrids, each repeated 4 times throughout the trial, and the protocol was to count the plants infected with the disease in 10 plants in each of 4 rows per plot, the rating process involved looking at no less than 7,360 sunflower plants.

The good news is that this information should be highly valuable to sunflower growers, as is the yield and other information that will be listed for each hybrid when the report comes out. I know if I was a sunflower grower, in addition to yield, I would definitely want to plant hybrids that have a reasonable level of resistance to phomopsis. And of course there is similar research work conducted and available for all of the major crops grown in South Dakota. To access the SDSU Crop Performance Testing results, visit: