Seed separation to control barley loose smut (Ustilago nuda)

Summary in the original language of the document

The main control of loose smut is the selection of varieties that flower with a closed flower. Seed lots infected by loose smut can be treated with fungicides, and this is regularly used in conventional agriculture. Environmental concern has focused on the use of pesticides for seed treatment, and in organic farming pesticides cannot be used at all. Hence, there is a growing demand for non-chemical measures to control seed borne pathogens like loose smut.
The flowers in the top of the barley head normally flowers more openly than the flowers in the centre or the bottom of the head, and the seed developed in these flowers are statistically smaller. It is also possible that the presence of mycelium in the embryo reduces the filling of the seed. Removal of the smallest fraction of the barley seed from a seed lot will hence reduce the infection level of loose smut.
Previous studies on the effect of seed separation on the infection level of loose smut have only investigated the effect of seed size in terms of the width of the seed. However, it is possible that other characters of the seed development are affected, e.g. the density of the seed.
The aim of this experiment is to investigate the effect of different seed separation techniques on the infection level of loose smut in infected seed lots.
Materials and methods
Seed samples of barley were collected from fields, where loose smut was observed in the growing season. The seed sample was cleaned by laboratory models of the standard equipment used by most commercial seed companies.
Results and Discussion
The experiment confirms that conventional seed cleaning affects the infection level of loose smut in a seed lot. When the seed lot was separated only by the seed size, only the largest seed fraction (>2.8mm) had significantly lower frequency of smut infection. As only 2% of the seeds in the seed lot fell into this category and more than 90% of the seeds fell into the category between 2.5-2.8mm, the potential of control by discarding the most infected categories is minimal. The fraction with the smallest seed cleaned by the Table Separator only represent only 15.7% of the seed lot, but by discarding this fraction, the infection level of the seed lot could be reduced significantly. The two fractions with the smallest seed cleaned by the Gravity Separator only represent only 17.3% and 8.7% respectively, and by discarding these fractions, the infection level of the seed lot could also be reduced significantly.
The result emphasises that the infection level of loose smut in a seed lot can be reduced by seed separation. Most effective is Table Separation and Gravity Separation, whereas seed size separation only has a limited potential, as the major part of the seed fall into fractions with a high infection level. The experiment also emphasises that it is of major importance whether seed samples taken from a seed lot for seed health analysis is taken before or after commercial seed cleaning.