It appears that insects can contaminate cruciferous plants with the bacterium Xanthomonas campestris pv. campestris (Xcc) when they pollinate the flowers. Insects such as blowflies, bumble bees and honeybees are frequently used in the Netherlands for pollinating cruciferous plants. As a result, even isolated parcels can become contaminated with Xanthomonas.
Xcc, also known as black rot disease, is the most important seed-transmitted disease in crucifers. Research conducted by Plant Research International, part of Wageningen UR, has shown that blow flies can contaminate flowers of crucifers with Xcc. According to Jan van der Wolf of Plant Research International, contamination of the flowers leads relatively often to contamination of the seed. It was previously assumed that Xcc contamination of crucifers was primarily caused by water splashing from an adjacent parcel or by contaminated crop residues in the soil.
During a two-year study funded by the Ministry of Agriculture, Nature and Food Quality, cauliflower plants were pollinated by blow flies that were contaminated with the Xcc bacterium. Following completion of the study, it turned out that 30% of the seed was contaminated with Xcc, both before and after warm water treatment of the seed. The contamination was also transmitted to the seedlings.
It can be concluded isolated parcels on which cruciferous plants are grown for seed production can become contaminated with Xcc if they lie within the flying distance of insects that are infected with the bacterium.
The researchers from Plant Research International also studied whether the Xcc bacterium could survive in the flies. For this purpose, the flies were fed with Xcc bacteria grown on agar. Large numbers bacteria were initially found. However, these numbers declined rapidly, and after five days no Xcc bacteria could be found in the flies.