TURNIP MOSAIC DISEASE

Press, Volume XCV, Issue 28252, 13 April 1957, Page 9

TURNIP MOSAIC DISEASE

RESISTANCE TO THE VIRUS

“NO SATISFACTORY VARIETY”

Investigation has proved that there is no satisfactory commercial turnip variety either in New Zealand or the United Kingdom with resistance to Mosaic. The Crop Research Division, however, will continue the search for resistance in other varieties in their collection from many different countries.

In making this statement to the writer this week, Dr. Harvey C. Smith, mycologist, Crop Research Division, Lincoln, explained that 24 lines of turnips, representing 17 varieties, were obtained from Gartons’, Suttons’, Webbs’, Sharpes’, and Bells’ of England and these, together with 13 lines of New Zealand and one of American seed were sown in a Department of Agriculture trial at Timaru. All varieties made excellent growth until they were affected by the aphis and the Mosaic virus disease. Since then they all became 100 per cent, infected and completely rotted away. Several swede varieties, however, were resistant and produced fine healthy crops. They were Wilhelmsburger, Calder and Sensation.

Regarding the implication that increased disease has been due to New Zealand-grown seed, all the research work carried out to date has shown that New Zealand does produce the cleanest seed in the world. New ZdHand-grown pea seed, for example, was found by an English Research station to be free from fungus disease while their own lines had up to 20 per cent, infection. Similarly with brassica seeds; a recent investigaon at Lincoln has shown that chou moellier seed imported from

the United Kingdom had over 1 per cent, with dry-rot disease, which is the most serious disease attacking swedes in Otago and Southland today. All the New Zealand lines of turnip, swede, Kale, choumoellier and rape seed were free from infection.

The Mosaic disease in turnips in New Zealand is undoubtedly an importation from England. Its history shows that it was serious in England in 1950 in turnip and cauliflowers. In New Zealand it was first described in 1952 and since then has been causing damage, each year, to turnip crops near Rangiora and Waimate. It is important that New Zealand be protected against the possible introduction of further new diseases so that eventually when we do have the present diseases under control we may be able to grow healthy crops, as were grown in the early days, before these diseases were . introduced.

Restrictions on seed importation are a necessity if we are to keep disease out of New Zealand. However, because New Zealand seed is equal to the world’s best we are at a decided advantage compared to other countries. Small importations of overseas varieties are introduced at intervals to compare the New Zealand selections with, and in all comparisons, the New Zealand seed has been equal to, or superior to, the introduced varieties.