Mottaglighet och tolerans hos olika betsorter gentemot betcystnematoden Heterodera schachtii 2011

Conclusion

The beet cyst nematode (BCN) is a serious pathogen on sugar beet in many countries. The most important control measure is growing a tolerant variety (NT). The first tolerant varieties that were introduced on the market were able to maintain a high yield level despite the occurrence of nematodes in the soil. However, on soil without nematodes, the yield level was lower than for standard varieties. Tolerant varieties should therefore only be used on fields were nematodes have been confirmed. In contrast to resistant varieties, tolerant varieties will not decrease the number of nematodes in the soil. New tolerant varieties that are tested in 2011 (Cactus) show better yield also on soil without nematodes. In addition, the beet quality is improved compared to older NT varieties.
Among the standard varieties there are varieties that can maintain a normal yield level on soil with low densities of BCN. These semi-tolerant varieties are called nematode-escape varieties (NE). NE-varieties tested in this study were Nexus, Rosalinda and Sabrina. The standard variety used as control was Mixer.
The aim of this study was to investigate the relationship between population density and yield in five different varieties.
Two field trials were drilled in 2011, one in Sweden (Mixer, Nexus, Rosalinda, Julietta and Cactus) and one in Denmark (Mixer, Sabrina, Rosalinda, Julietta and Cactus).
Population dynamics
The standard variety Mixer had the largest increase in the number of BCN, 11 times the initial density in the Swedish trial and 12 in the Danish (mean 11.8).
The increase in BCN for the NE-varieties Nexus, Sabrina were 5.7 (Sweden) and 6.8 (Denmark) respectively, and for Rosalinda 3.1 (Sweden) and 8 (Denmark), mean 5.5.
The increase in BCN for the NT-variety Julietta was 7.6 in the Swedish trial and 2.3 in the Danish, mean 4.9.
The increase in BCN for the new NT-variety Cactus was 4.8 in the Swedish trial and 8.0 in the Danish, mean 6.4.
Tolerance
The tolerance to BCN for the variety Mixer was 0.7 in the danish trial, for Sabrina 0,4 and Rosalinda 0,3 (R2 = 60%). Previous studies have shown that the tolerance to BCN for a standard variety can be as low as < 0.5 (Å. Olsson, NBR; S. Andersson, Nematodlaboratoriet, SLU). Several factors influence the tolerance e. g weather conditions. Frequent rain reduces the damage on the sugar beet plants. Sugar yield There was a clear relationship between increasing Pi and decreasing sugar yield for Mixer and Sabrina in the Danish trial. There was also a relationship between increasing Pi and decreasing sugar yield for Rosalinda. The sugar yield for Julietta and Cactus was relatively constant with increasing Pi. Green house experiment Two seeds each of the varieties Mixer, Cactus and Rosalinda were sown in 13 replicate plastic bags. Juveniles were added to the plastic bags in the concentrations 100, 250, 500, 750 and 1000 juveniles per bag. After 20 weeks, the roots were washed and cysts counted. For the low concentrations of juveniles there were no differences between varieties in number of cysts per plant. In the higher concentrations there were more cysts on the roots of Mixer and Rosalinda compared to the NT varieties. The eggs and larvae in the cysts from the concentration with 750 juveniles were also counted. The average number of eggs and larvae in the cysts from Cactus was 76, Rosalinda 108 and Mixer 166.