Research Notes____________________________________________________________
Short communication of practical oriented research or relevant information in agriculture or seed technology are presented in this section.

Removal of Common Bunt Spores from Wheat Seed Lots by Brush Cleaning
by
Anders Borgen ¹

Abstract
A brush air cleaner can be used to remove spores of common bunt from wheat seed lots. It is demonstrated that a combined use of conventional cleaning followed by brush cleaning removes 99.8% of the spores in a seed lot. The efficacy of the treatment is comparable with the best chemical treatments available on the market to prevent seed-borne transmission.

Introduction
Common bunt caused by Tilletia carries or T. foetida is the most commonly prevalent seed-borne disease of wheat worldwide. The pathogen infects wheat seedlings just after sowing before the plant emerges from the soil. The wheat seed per se could be healthy at the time of sowing, but could be infected from spores resting on the seed surface or in the soil. Seed contamination, however, is found to be by far the most significant source of infection (Borgen, 2000).

The common bunt in infected seed lots can be controlled by killing the spores with chemicals or heat treatment, by preventing infection using different agronomic practices (use of resistant varieties, adjusting sowing time) or by removing the spores from the seed lot through cleaning (Borgen, 2004).

In another study, Bechel et al (1998) reported that only a small fraction of the spores of the closely related bunt species (T. contraversa) end up in the flour, while the majority are removed when cleaning the seed before or during milling process. However, there is little information available about the fate of the spores during seed cleaning for sowing purposes. This article reports the results of an experiment dealing with cleaning of a seed lot contaminated with common bunt spores.

Materials and Methods
A field containing one common bunt (T. tritici) infected plant 1m^-2 was harvested with a combine harvester. After harvest the seed lot was cleaned using three treatments: (i) air screen cleaner, (ii) brush cleaner (ø=400mm) (Anonymous, 2005), and (iii) combined air screen cleaner and brush cleaner. After air screen cleaning the seed lot still contained weed seeds and inert matter which could be improved by cleaning with a second air screen cleaner or gravity table.

The air stream in the brush cleaner was modified during the experiment compared with the standard operation and the data presented shows the optimal adjustment. The contamination of bunt spores was estimated by counting spore in a haemocytometer as described by Keitrieber (1984). The effect on seed vigor was estimated by the emergence of 200 seeds, germinated in a sand test planted at 10°C. The emergence was assessed on the 13th day after sowing.

Results and Discussion
After harvest, the contamination of bunt spores in the seed lot was 230,000 spores g^-1. The cleaning of the seed lot with the air-screen cleaner alone reduced the number of spores by 69.4% whereas in comparison the brush cleaner alone reduced the number of spores by 83.9%. However, if the seed lot was first cleaned by air screen cleaner, and then cleaned by the brush cleaner the effect was significantly improved. .

Figures 1 and 2 show the results of an experiment, where the seed was treated in a batch and the treatment duration was controlled precisely. Figure 1 shows that the longer the seed is treated, the higher the effect of the treatment on reducing the spore contamination (15 vs 60 seconds). However, it shows that the larger the quantity of seed, the lower the efficacy in removing the spore contamination (1 versus 4 kg seed).

Figure 1. The effect of brush cleaning on bunt spore contamination in a batch treatment

Figure 2: Effect of brush cleaning on seed vigor

Figure 3. The effect of brush cleaning on bunt spore contamination in a continuous flow treatment