HLB has developed the variety selection test especially for the control of virulent potato cyst nematodes. There are major differences between nematode populations, so varieties that have an equivalent potato cyst resistance on paper can also differ greatly from each other in field populations. In the variety selection test, resistant varieties are therefore matched in a patch test with the nematode populations present in a plot.
In this way, it is better to estimate in advance what the resistance effects of the tested potato varieties are on the potato cyst contamination present and the best choice of variety can be made.
In a variety selection test, varieties are tested against a susceptible standard. In order to test as many varieties as possible in a variety selection test for which resistance can be expected, it is necessary to know which type of potato cyst population is involved. Nowadays, this is usually immediately included in the research into potato cyst nematodes contamination, but otherwise the species (G. pallida or G. rostochiensis or mixed contamination) can first be accurately determined with the help of a PCR test (DNA). Then, in consultation with the grower, it is determined which varieties will be tested. In the lab test it can be checked on which breeds this field population forms more or fewer cysts.
The variety selection test is therefore a real practice-oriented test, aimed at controlling PCN at plot level.
The potato variety test shows how a specific population reacts to different varieties. If sufficient larvae are available, the test is started with 8 varieties in 8 repetitions. The Desiree variety is used as an 8th and standard variety. For the test, cysts with living contents are collected from a large soil sample (2-3 litres) from problem spots after potatoes have been grown. The test are activated from February to the end of May in small pots with sterile soil and mini tubers. Each pot is then contaminated to the same extent with live larvae from the soil sample. After eight to ten weeks, the transparent jars are assessed on the outside and the number of cysts on the roots is counted. This gives a good idea of the susceptibility of a variety to the potato cyst nematodes population on the plot in question.
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