What to consider when selecting a sunflower variety
Nowadays, most sunflower seeds in the market are hybrids. In that sense, a farm-saved seed is significantly less productive, and the grower must buy new seeds yearly. This allowed the breeding companies to invest strongly in researching and developing hybrids for different climates with good agronomic traits and resistance to biotic and abiotic stress. Choosing the right hybrid is a key factor for successful sunflower cultivation.
The end product use is the first matter that the farmers need to consider. The vast majority of the commercial sunflower hybrids are oilseed types, while confectionary hybrids retain a niche market. In many cases, sunflower oil production industries publish lists containing their preferred hybrids. A bonus is frequently given for these hybrids. Usually, these are hi-oleic hybrids, which have high levels of monounsaturated fat, a trait sought by the oil-producing industry.
Regarding the cultivation site, the farmer should consider several things for selecting the right hybrid. The area’s climatic conditions will affect every stage of crop cultivation. As a brief description, the cultivation will need an average temperature above 10oC after sowing for good germination and quick growth, no excessive heat, drought during the flowering time for successful pollination, and dry conditions during the desiccation phase up until the harvest. Depending on the timing of these weather conditions, the earliness of the selected hybrid should be decided. Areas closer to the equator tend to select late hybrids, as the warm periods of the year are prolonged. Still, in many regions with higher latitudes, late hybrids will also be chosen, but seed drying after harvest is usually necessary.
Abiotic stress conditions should also be considered when selecting the right hybrid. Sunflower is a well-known drought tolerant plant; however, some hybrids tend to have more stable yields even in very dry years. In areas with a high risk of heavy summer storms, combined with hale or/and strong gusts of wind, shorter hybrids that withstand these conditions should be cultivated. Currently, there are plenty of semi-dwarf hybrids on the market.
Biotic stress conditions are more common in areas where sunflower has been cultivated for many years. Pathogens and parasites overwinter on sunflower residues or the soil and can be spread to fields nearby through agricultural machinery, wind, and water. Fungal diseases such as Phomopsis, Phoma, Sclerotinia, and Plasmopara can negatively affect cultivation and production. In a location with high disease pressure, the selection of hybrids that hold good resistance to the respective pathogen is strongly advised. This should lower the costs of the cultivation since less or no applications of fungicides will be necessary, while it will increase the expected production.
Broomrape (Orobanche cumana) is, economically, the most important parasite of sunflower since it can cause detrimental yield loss. When the sunflower’s seeds germinate, the pathogen attaches to the plant’s underground parts and feeds off the host. Once a field is infested, it is extremely difficult to be cleansed, as the seeds can stay viable in the soil for up to 10 years. Several broomrape races are known (A – H). For each race, a different resistance gene must be present in the genetic background for the hybrid to exhibit the resistance. For this reason, the growers of a region need to know the broomrape race that infests their land to make the right hybrid choice. Although choosing a resistant hybrid often doesn’t eliminate the danger of broomrape appearance, it is an essential part of dealing with an existing infestation. The development of herbicide-resistant and herbicide-tolerant hybrids at the start of the 21st century had a crucial role in broomrape control.
As far as the agricultural practices are concerned, farmers can choose between simple and herbicide-resistant hybrids, which can withstand the application of some non-selective broadleaf and grass herbicides.
There are two types of such resistances in sunflowers. The technology first discovered is called Clearfield®. Plants hold a specific resistance gene derived from a wild relative of Helianthus anuus. The cultivation can withstand the application of any herbicide with the active ingredient imazamox (e.g., Pulsar). The second generation of this technology has been presented in the last decade. Clearfield+® hybrids can withstand a significantly greater dosage of imazamox, offering a better solution in fields that contain difficult-to-control weeds.
The second resistance technology is called ExpressSun® and provides the sunflower hybrids with the resistance to the active ingredient of sulfonylurea herbicides, tribenuron-methyl. The ExpressSun® trademark could be used only by the first company that introduced this technology. Thus, companies producing tribenuron-methyl resistant hybrids started using the word Sulfo as the identifier of this technology.
If a simple hybrid is selected, broad-leaved weeds can be handled using pre-sowing or pre-emergence herbicides. Mechanically, weeds are usually controlled by tilling using a strip-till between rows when the plants have 4 true leaves and onwards. Herbicide-resistant hybrids can offer security to farmers when weeds that are difficult to control appear or the weather conditions aren’t suitable for applying pre-sowing or pre-emergence herbicides. Simple hybrids are a great choice in areas with low or moderate weed pressure, where crop rotation tactics are followed. There are plenty of simple hybrids bred over the last decades with excellent yield potential and resistance to biotic and abiotic stress. It is important to note that Clearfield® and ExpressSun® technologies have the same mode of action, inhibiting the synthesis of acetolactate (ALS inhibitors). Thus, the rotation between hybrids of these two technologies doesn’t remove the risk of the selective pressure that could lead to the appearance of resistant weeds.
- Clearfield® Plus Production System for Sunflower (https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.agricol.co.za/wp-content/uploads/2017/09/Clearfield-Plus-Sunflower.pdf&ved=2ahUKEwj-5rj0uY_4AhXqS_EDHaYEAdwQFnoECAUQAQ&usg=AOvVaw2o9f2rZJBKq1MRlh1vxPNk)
- Imazamox,Massachusetts Department of Agriculture Division of Crop and Pest Services and Massachusetts Department of Environmental Protection Office of Research and Standards, 2014 (https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.mass.gov/doc/imazamox/download&ved=2ahUKEwixubnJxZT4AhVBDewKHXPSA5MQFnoECAMQAQ&usg=AOvVaw3YpxumgGmfon2Kdc_xd1Et
- Gulya T.J., Mathew F., Harveson R., Markell S., Block C. (2016) Diseases of Sunflower. In: McGovern R., Elmer W. (eds) Handbook of Florists’ Crops Diseases. Handbook of Plant Disease Management. Springer, Cham. https://doi.org/10.1007/978-3-319-32374-9_27-1
- Saul, Wolf-Christian et al. (2017), Data from: Assessing patterns in introduction pathways of alien species by linking major invasion databases, Dryad, Dataset, https://doi.org/10.5061/dryad.m93f6
- Louarn, J., Boniface, M. C., Pouilly, N., Velasco, L., Pérez-Vich, B., Vincourt, P., & Muños, S. (2016). Sunflower resistance to broomrape (Orobanche cumana) is controlled by specific QTLs for different parasitism stages. Frontiers in plant science, 7, 590.
Sunflower Variety Selection