Testing seed is important in order to prevent low-quality seed from being planted, to alert the grower of diseases to be aware of during the growing season, and to provide an opportunity to manage seedborne fungal plant diseases using seed treatment fungicides.

Fungal Pathogens:

Ascochyta complex. A complex of fungal species causes the disease known as ‘Ascochyta blight.’ These pathogens cause lesions on all parts of the plant and disease can lead to defoliation, stem breakage, empty pods, shrunken and discolored seeds, etc., yield loss and poor seed quality. Chickpea is the most susceptible pulse crop to Ascochyta blight. 1Click here for more.

Botrytis species. This pathogen causes grey mold. The pathogen can be long-lived in residue and soil.

Collectotrichum species. This pathogen causes a disease known as anthracnose. This disease is similar to Ascochyta blight but tends to infect at higher temperatures. Lentil varieties can be very susceptible.

Fusarium  species. This pathogen can cause different diseases based on the species and where it infects the plant. Some species cause (fusarium) wilt, others cause root rot.

Sclerotinia  species. This fungal species causes white mold and stem rot. Lentils are very susceptible to this disease. Pathogen is very long-lived in soil.

Stemphylium  species. This pathogen causes a leaf blight late in the season. The disease can decrease seed quality.

Rhizoctonia  species. Causes seedling rot if weather conditions are favorable.

Alternaria  species. This is a species complex which causes a leaf blight on all pulse crops. The impact of the disease on pulses is unknown but high levels of infected seed indicate it may be a problem species. Disease severity is likely lower than Ascochyta blight, and research is underway to answer many of our questions about the disease.

For more information on the above fungal pathogens, click on 2Article 1, and 3Article 2. Also, see the table on page 7 for the levels of fungal pathogens detected in 2015 and 2016 seedlots.

Bacterial Pathogens

Bacterial blight agents (Pseudomonas syringae pv pisi, and pv syringae (field pea and lentil), and Xanthomonascampestris pv cassia (chickpea). These bacterial pathogens cause water-soaked lesions on stems and lower leaves. Lesion can girdle stem and lead to lodging of above plants, reduced yield and seed quality. Symptoms most often occur following hail or wind-driven rain. Click on 4Article 3 and 3Article 2 for more information on bacterial blight.

Viral pathogens

Pea seedborne mosaic virus (5PSbMV). Causes banding of seeds, cracking of seed coat, reduced seed size, stunting of plants, poor seed quality and yield reduction.

Pea enation mosaic virus (6PEMV). Causes pod distortion and splitting, plants are stunted and leaves show enations (blister-like structures). Leads to yield loss and reductions in seed quality.

Although there are other seedborne viruses, the above are the common ones. Others we are monitoring include Bean yellow mosaic virus (7BYMV),Cucumber mosaic virus (8CMV), andAlfalfa mosaic virus (9AMV). All of these viruses cause mosaic symptoms which reduce the ability of the plants photosynthesize and thus reduce seed yield. They are vectored by insects, especially aphids, which spread the virus.

For more information on these viruses, click Article

Nematodes

Ditylenchus species (10stem and bulb nematodes) and 11pea cyst nematodes (Heterodera spp).

Pulse seeds for export to India and other countries requires seed to be tested for these seedborne or seed-contaminating nematodes. Seed lots must have a phytosanitary certificate prior to receipt by the country. If you have questions about the phytosanitary process, contact your Department of Agriculture. Information on exports in Montana can be found at: https://agr.mt.gov/Topics/Export.

a) Ascochyta-Plus Package. This is the minimum test package we recommend. It which includes tests for the fungal pathogens listed in Section 2a, above.

b) Smart Package. If you have observed mosaic or yellowing symptoms on your plants in your fields during the growing season, we recommend the ‘Smart package” test. The Smart Package includes all the fungal tests in the Ascochyta Package and the most important and common viruses: Pea seedborne mosaic virus (PSbMV) and Pea enation mosaic virus (PEMV).c) Comprehensive Package. If you had observed mosaic symptoms on your plants, had hail damage, or you want most information of the health status of your seed, we recommend the “Comprehensive Package”. In this package, we test for all the seedborne fungi (as in Ascochyta-Plus), two viruses (PSbMV and PEMV), and bacterial blight agents.

f) Nematode test. If you are exporting pulse crops to India, ask for Nematode test.

g) Individual pathogen test. We also test for individual pathogens on request.

For more information, Regional Pulse Crop Diagnostic Laboratory website (http://plantsciences.montana.edu/pulsecropdiagnosticlab/).

The test takes from 7 days to 12 days for Ascochyta-Plus and Smart Package. Some fungi growing slowly and at 5-7 days the slow-growing ones are hard to identify. Attempts at identifying them less than 10 days may lead to errors. However, results could be ready within 7 days if the seeds are free of fungal pathogens. Collectorichum species is a pathogen causing anthracnose. It is slow-growing and may need at least 10 days to identify.

Comprehensive Package test takes 2 weeks because it involves tests for fungal pathogens, two viruses and causal agents for bacterial blights. Test for bacterial blight agents could take 2 weeks.

A list of registered seed treatment fungicides (See table on page 8) and 12foliar fungicides are available as part of a collaborative effort of the Western Region and Northcentral Region Integrated Pest Management Center’s Pulse Crop Working Groups.  The Table of seed treatment fungicides is on the next page.

There are no chemical treatments for bacterial, viral, or nematode pathogen management. List will be regularly updates as more fungicides become registered. If any company has a list of registered fungicides for the treatment of seedborne fungi of pulse crop not in the list, please contact:

Mary Burrows,

MSU Extension Plant Pathologist

Tel: 406-994-7766

E-mail: mburrows@montana.edu

See the next page for the list of registered fungicide.

A ‘threshold’ is a term used when a certain amount of damage can be sustained by a crop with no observable yield losses. When a pest (insect, disease, and weed) exceeds that ‘threshold’ a treatment decision needs to be made. This decision is made based on the goals of the producer including economics, agronomic management practice options, pesticide availability, pesticide efficacy, etc. (Burrows et al, 2016). Thresholds are commonly used for insect damage and include the number of insects observed, measurement of loss of leaf area due to feeding damage, etc.

For plant diseases, threshold values are complicated by a number of factors including the strain of the pathogen, its aggressiveness on the host or susceptibility of the host to the pathogen, and, most importantly, the environment during the growing season. ‘Rule of thumb’ thresholds are well established for Ascochyta blight, but even these thresholds are based on limited field data. Any observed disease level must also consider the host and environment before a treatment decision is made. For example, a seed lot may contain high levels of Ascochyta blight above the recommended threshold but no disease may be observed during the field season if the environmental conditions are not conducive to disease development (and vice versa). In addition, the crop host and timing of symptom development may influence your treatment decisions. For example, in chickpeas any identification of Ascochyta must be quickly acted upon due to the high susceptibility of most varieties; in pea and lentil treatment may not be needed based on the timing relative to crop maturity, host resistance and weather when the disease is observed.

When you receive your seed test and it is positive for a fungal pathogen, learn more about that pathogen using resources available [insert more links to resources below]. Learn how to recognize that disease in case it may be an issue in your field during the field season, and get the disease accurately identified before choosing your best management strategy. Always use a fungicide seed treatment as a best management practice, and ensure the product you choose is labelled for management of the disease carried on your seed to reduce the chance of seed to seedling transmission.

Due to the high demand for threshold values and lack of supporting research data, we hesitate to recommend any threshold for the use of seed. However, recommended ‘action’ thresholds have been published from 13Canadian source. If % of pathogen infection of your seed exceed that of the thresholds in the table below, treat seed with appropriate fungicides (for fungal infection). There are no seed treatments for bacterial or virus pathogens. The best management practice is to assess your risk and planting situation before making a planting decision, and to monitor for these diseases during the field season.

 

Pathogen Test

Pathogen Threshold for Pulses

 

Alternaria (Alternaria blight)

Not available.(C, L, P). Suggestion: 15%

Fungi

Ascochyta (Ascochyta blight)

C = 0%; L & P = 5%

Botrytis (gray mold)

0.5% Low risk areas ; 0.1% high risk areas (C, L, P)

Colletrotrichum (Anthracnose)

Not available. (C, L, P): Suggestion: 0.5%

Fusarium (wilt and root rot)

Not available. Suggestion: 5%  (C, L, P)

Sclerotina (white mold)

Not available. Suggestion: 0.5% (C, L, P)

Stemphylium (Stemphylium blight)

Not available. Suggestion:  5% (C, L, P)

Viruses

Pea enation mosaic virus (PEMV)

0.5% Low risk areas ; 0.1% high risk areas (C, L, P)

Pea seeborne mosaic virus (PSbMV)

0.5% Low risk areas ; 0.1% high risk areas (C, L, P)

Bacteria

Pseudomonas syringae pv pisi & P.s. pv syringae

0.1% Low risk areas ; 0% high risk areas (L, F)

 

Xanthomonas campestris pv. cassiae

0.1% Low risk areas; 0% high risk areas (C.)

If your samples contain pathogens two times or more above thresholds (if available), the decision to treat seeds or use pathogen-free seeds is left to the growers. Consider the costs of seed treatments, fungicide efficacy deficiencies, and getting pathogen-free seeds before making such decision.

 Given the difficulty in setting threshold values for plant diseases, it is hard to give recommendations about ‘what percent is too high’ when planting Ascochyta blight (AB) infected seed. If a seed lot contains AB pathogens above the threshold, it can still be planted with a seed treatment effective on AB, but the crop must be monitored for disease symptoms and action taken if needed. In the case of infected seed, two corners of the disease triangle, susceptible host and pathogen, are present, but that third corner, the ‘environment’ will determine whether disease develops or not. The exception to this case is that chickpea cannot be sold as seed if there is any AB pathogen found due to the high susceptibility of the host. This is an industry regulation.
 Seedborne pathogens are those inside the seed: below the seed coat or in the embryo or cotyledons of the seed itself. They are passed from the parent plant into seeds. Washing and surface-disinfecting the seeds do not remove seedborne pathogens. Soilborne pathogens are present in the soil prior to planting. These can infect seeds or plants. As a precautionary step, seeds are usually treated with fungicides to protect against soilborne pathogens. We advise you treat your seeds for both soilborne pathogens and specific seedborne pathogens of your seed.
 
  • Schutter Diagnostic Laboratory

Montana State University, Bozeman, MT

Tel: 406-994-5150;

E-mail: diagnostics@montana.edu

Web: http://diagnostics.montana.edu

MSU Extension Plant Pathology Specialist:  Jessica Rupp, 406-994-5572, jessica.rupp@montana.edu
 

Contact Bright Agindotan, the Regional Pulse Crop Diagnostic Laboratory, Manager and Diagnostician.

E-mail: bright.agindotan@montana.edu.

Phone: 406-994-7738.

Phone: 406-994-4267