Seed-borne diseases to consider before using saved seed
Wheat harvest is winding down in most of Missouri and some producers may be thinking of saving seed to use for planting this fall. This is a year when it would be wise to consider the possibility of seed-borne diseases and how they might impact seed quality and stand establishment. The Septoria/Stagonospora complex and bacterial leaf streak/black chaff both came on late in the season causing some head discoloration. After head emergence there were more questions than usual about loose smut. Finally Fusarium head blight or scab was fairly widespread in Missouri this season. All of these pathogens can be carried on or in the wheat seed, reducing germination, causing seedling blights or causing disease problems the next season. If any of these diseases were present at significant levels in a field, it would be best not to use seed from that field for planting this fall. If wheat is going to be saved for seed, this is certainly a year to pay careful attention to the quality of seed being saved.
Lesions of Septoria leaf blotch begin as light yellow flecks or streaks. These flecks expand into yellow to reddish-brown, irregularly shaped blotches. Dark brown specks (fruiting bodies or pycnida of the causal fungus, Septoria tritici) may be scattered within the centers of mature lesions. Lesions may coalesce killing larger areas of leaf tissue. Stagonospora glume blotch (formerly called Septoria glume blotch) may also begin as light yellow flecks or streaks on leaves. The lesions also turn yellow to reddish-brown but usually have a more oval to lens shaped appearance than those of Septoria leaf blotch. Again, the dark brown specks or fungal fruiting bodies of the causal fungus Stagonospora nodorum may be evident within the lesions. Symptoms of Stagonospora glume blotch are more common on heads than foliage of wheat. Infected heads will have dark blotches on the glumes. Stagonospora is more likely to be seed-borne than is Septoria. Seed lots infected with Stagonospora may have a greater risk for stand establishment problems as the fungus can cause seedling blight under a range of soil temperatures.
Bacterial streak and black chaff are names for the same bacterial disease which produces symptoms on both leaves and heads. Water-soaked lesions may develop on young leaves. These develop into reddish brown to brownish black streaks on the leaves. Glumes and awns show brown-black blotches or streaks. Black chaff may be confused with glume blotch. Symptoms may not be evident on individual kernels but the bacterial pathogen can be seedborne. Since seed treatment fungicides are not effective against this bacterial pathogen, seed from fields which had bacterial streak and black chaff should not be used for planting.
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