Seed-borne Fusarium and Seed Quality

Prepare for the season by ensuring the performance of your seed.

Allison Friesen M.Sc.

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As you prepare for the upcoming season there are numerous decisions to make: crop rotations, fertilizer orders, re-crop restrictions… and the list goes on. However, there is one decision that should be at the forefront of everyone’s mind this season, and that is seed quality.

Throughout the last year we have experienced significant environmental challenges that not only affected our seed quality and yield in 2014, but will also have a major influence on our 2015 crop. The prevalence of Fusarium Head Blight (FHB) in cereal crops across Western Canada was as high as 89% in the trials surveyed in 2014, while seed infection levels were up to 47% (Biovision Seed Labs). This is of large concern for the 2015 season, as the planting of Fusarium-infected seed may result in lower seedling emergence and vigour. It may also spread disease to unaffected fields and contribute to the build-up of inoculum in already infested fields.

Seed-borne Fusarium thrives in wet, warm environments but is capable of infecting under all conditions. The host range that Fusarium infects is wide and includes cereals, oilseeds and pulses. Seed-borne Fusarium is the cause of multiple seed and seedling diseases including:

  1. Seed Rot - death and decay of the seed prior to germination and emergence
  2. Seedling Blight – entire seedling infection that leads to reductions in plant stand
  3. Root Rot - discoloration and decay of the roots, aerial portions of plant appear otherwise normal
  4. Pre- and Post-Damping Off - rotting of the stem at soil level and eventual collapse of the plant

Figure A: Seed Rot

Figure B: Seedling Blight

Figure C: Root Rot

Figure D: Pre- and Post- Damping Off

Although this pathogen is primarily spread via infected seed, it is capable of surviving in the soil as well. Infected seed or soil can cause the development of infected seedlings, resulting in reduced vigour and plant stand in that season. It is also important to note that Fusarium-infected seed will NOT lead to FHB in the same season, as the pathogen only has one infection cycle per season. Instead, the cause of FHB is from the production of spores originating from previous crop residues on the soil surface that can then infect the head of cereals during flowering. However, planting infected seed without proper control mechanisms does lead to a build-up of inoculum in the soil (due to development of infected seedlings), so if not managed correctly it can result in FHB infections in future seasons.

To ensure a healthy seed lot and to prevent the buildup and spread of Fusarium by infected seed you should always have your seed tested in an accredited seed lab where they assess the three major components of seed quality:

  1. Germination test - provides you with a measure of the percentage of seed that are capable of germinating under ideal conditions
  2. Vigour test - determines the proportion of seed that will germinate and be durable enough to survive the stresses associated with emergence and poor planting conditions
  3. Pathogen analyses - reports how many seeds are infested with a specific pathogen (total Fusarium spp., Fusarium graminearum, Cochliobolus etc.)

For seed-borne Fusarium two commonly used pathogen analyses are:

  • Total Fusarium - a measure of the percent seed in a specific seed lot that tests positive for all 5 fungal species responsible for Fusarium infection: F. graminearum, F. culmorum, F. avenaceum, F. poae, and Microdochium nivale
  • Total F. graminearum - a seed test that reports the amount of this specific species in a seed lot

Fusarium graminearum is the most aggressive species and leads to the largest amounts of deoxynivalenol or DON (a.k.a vomitoxin). The increased production of DON is a large concern for growers who use their seed as feed for livestock. Ingestion of this toxin can lead to reduced feeding and gastrointestinal problems such as vomiting, resulting in lower weight gain or reduced milk and egg production.

After analyzing your seed, you will want to assess your seed test results carefully as poor germination and vigour or high levels of disease may require you to select an alternative seed source. Some recommendations to follow are:

  • A seed lot with high germination and low vigour (e.g. vigour < 90%) should only be used if no other seed source is available; seed lots with germination and vigour counts >90% are the most ideal
  • Seed that tests >14% Total Fusarium or Cochliobolus should be discarded
  • Seed that tests > 5% F. graminearum should be discarded

If either the Total Fusarium or F. graminearum numbers are exceeded in a sample, one should always err on the side of caution and use a different seed source if available, regardless of germination or vigour ratings. At these high levels even premium seed treatments may not have enough activity to manage the disease. Also, if your seed has tested positive for a seed-borne disease or the field you are seeding into has a history of disease, the use of a fungicide seed treatment like Insure® Cereal is highly recommended. If not controlled or if a seed lot with lower disease levels is not used, reductions in plant stand may occur and you may contribute to the buildup of disease inoculum in the field. (For more information on how to better understand your seed test results click here).

Although the spread of Fusarium is of growing concern there are numerous integrated crop management practices that can help control seed-borne Fusarium including:

  • The use of clean disease-free seed to prevent spread and build up of inoculum
  • Crop rotation - even though seed-borne Fusarium has a large host range, few crops are susceptible above ground (i.e. pulses vs. cereals)
  • The use of cereal varieties that are less susceptible to Fusarium
  • The use of foliar fungicides, like Caramba®, at flowering to reduce the risk associated with FHB
  • Testing your seed to ensure good germination, vigour and low disease levels
  • The use of an appropriate seed treatment, like Insure Cereal

Insure Cereal Fungicide seed treatment uses three active ingredients to provide broad-spectrum protection against seed-borne and soil-borne diseases, including Fusarium spp. The majority of the premium seed treatments on the market are designed to provide control of seed-borne and soil-borne diseases; however, Insure Cereal is the only fungicide seed treatment that also has the added benefits of AgCelence® (Fig. 1). These benefits include increased seedling vigour, both above and below ground, a more consistent and increased emergence, including under cool conditions, and the enhanced ability to help the crop manage exposure to stresses, such as frost (Fig. 2).

Figure 1: Enhanced seedling and vigour benefits of AgCelence in a seed treatment.

Figure 2: Frost tolerance benefits of AgCelence when wheat seed was exposed to -13°C for 2 hrs.

When using seed treatments it is also important to remember to always use full label rates and choose products with true multiple modes of action to help the sustainable use of these products. Unlike foliar fungicides, seed treatments have a much lower risk of building up resistance due to the low rates of active ingredients required for control and the slow reproductive rates of the pathogens themselves. However, it is still very important to be aware of the risk of resistance and to always follow sustainable and integrated pest management practices to maintain the effectiveness of seed treatments.

While using bin-run seed from the year before could cause some problems with seedling disease and vigour, making sure you take the proper steps to minimize those risks are essential to managing seed-borne and soil-borne diseases. Using a premium fungicide seed treatment like Insure Cereal can give your crop the best chance to a great start in the spring and set up your crop for a successful growing season.

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