Waarnemingen omtrent de dwergziekte bij framboos en wilde braam II

Summary

To study further the effect of heat treatments on „stunt” disease (1), small pieces of roots bearing shoots, taken from stunt diseased raspberry plants, were treated in different ways with high temperatures in January 1952. They were afterwards planted in sand in the greenhouse, and were transplanted to the field when the plants had developed sufficiently. As typical symptoms of the disease are slow to appear, observations were made during the whole summer, and for the last time on 3 October 1952.

In the first series the diseased shoots were kept in petri dishes, covered inside with moist filter paper, in an incubator at 46°C for periods of 1, 1 1/4, 1 1/2, 1 3/4, 2, 2 1/4, 2 1/2, 2 3/4, 3 and 3 1/4 hours. The results are summarized in Table 1. It is evident that heat treatment for about 2 3/4 hours or less stimulated the growth of the shoots as compared with the control shoots. A longer treatment proved to be harmful. Shoots treated 1 3/4 hours or longer produced in most cases plants which were still healthy on 3 October 1952. Irregularities in the results are perhaps attributable to poor circulation of air in the dishes, with the result that the expected temperature was not reached or was reached for too short a time only.

In the second series the diseased shoots were immersed in water at 45°C for periods of 1, 1 1/4, 1 1/2, 1 3/4, 2, 2 1/4, 2 1/2, 2 3/4 and 3 hours (Table 2). Growth of these shoots was less than the growth of those in the first series treated for 2 3/4 hours or less, but all plants which survived still appeared healthy on 3 October 1952.

Shoots which had been immersed for periods of 5 to 60 minutes in water at 50°C showed similar results (Table 3). All surviving shoots produced plants that were still free from symptoms on 3 October 1952.

From our experience that heat treatment of raspberry shoots leads to a curing of the disease (1), it may be concluded that the symptomless plants developed from shoots treated in these experiments are really healthy.