Testing clubroot-resistance of turnips in the netherlands and the physiologic specialization of plasmodiophora brassicae

Abstract

• 1. Clubroot is the main disease of fodder turnips in the Netherlands. Growing resistant varieties is the only practical means of control.

• 2. Sowing seeds in the first half of July is more efficient for selection for clubroot resistance than sowing in the normal period, early in August.

• 3. Artificial infestation of a field soil may have advantages over a naturally infested field in selecting for resistance. “Furrow infestation” i.e. putting soil from heavily diseased farm fields into the furrows before sowing the turnips, seems a practicable method.

• 4. Ten strains of Plasmodiophora brassicae were distinguished in the Netherlands and Belgium on the basis of the infection spectrum in a large set of differential hosts. Seven of them originate from farm fields where turnips are frequently grown. Each strain represents a group of clubroot isolates with similar infection spectra.

• 5. Turnip varieties included in the 39 th Dutch Descriptive List of Varieties of Field Crops (1964) can be divided into three main groups based on their reaction to clubroot strains: 1) the V-group, comprising varieties which are very susceptible on nearly all diseased fields, 2) the M-group, varieties which are fairly resistant on most infested fields, and 3) the E-group, varieties which are fairly to very resistant on nearly all infested fields in the Netherlands; however, they are just as susceptible as the V-and M-group on a number of fields in Belgium. In addition a fourth group may be distinguished, viz. the L-group, comprising some varieties not mentioned in the “List”. These are moderately resistant on all clubroot fields in the Netherlands.

• 6. Races of the fungus which are aggressive to the M-group apparently have been prevalent in certain clubroot fields for many years. In other fields these races gradually increase during some years when varieties of the M-group are grown. A mixture of different races is likely to occur in every infested field. Each of the above mentioned strains also has to be regarded as a mixture of races.

• 7. Turnip varieties found resistant abroad usually turn out to be susceptible in the Netherlands. Only some Belgian varieties proved to be very resistant in our country. A few varieties which are susceptible in the Netherlands were found to be very resistant in some other countries. Clubroot races occurring in turnip fields in foreign countries, therefore, generally appear to be different from those found in the Netherlands.