Over-reaction to stripe rust

Press, 20 November 1981, Page 18

Over-reaction to stripe rust

By

H. J. BEZAR,

Crop

Research Division of the Department of Scentific and Industrial Research.

The director of the Crop Research Division of the Department of Scientific and Industrial Research, Dr H. C. (Harvey) Smith, feels there has been some over-reaction by growers and merchants to the current stripe rust problem. “The condition •of most crops at the moment is good,” said Dr Smith this week, “and I predict that in spite of stripe rust, wheat and barley yields in Canterbury will be above average this season.” Many observers of the wheat industry were full of doom and despondency about the future of wheat growing in Canterbury, said Dr Smith. However, they forgot that half of the wheat cultivars on the market were resistant to stripe rust, and that all the new breeding material in the pipeline at Crop Research Division had been tested for resistance to stripe rust both at Lincoln and in the Northern Hemisphere. Thus, he added, the immediate future was assured as adequate seed of all resis-

tant cultivars would be available for next season and the longer term future was guaranteed by the high yielding cultivars currently in the breeding programme, which showed good resistance to the disease. It was important, said Dr Smith, that all those involved in the industry appreciated the important varietal differences exhibited by the different cultivars. Oroua, Karamu; and Konini wheats were highly resistant to the disease and did not require spraying. However, some farmers might be concerned by the slight flecking which occurred on the leaf where spores had hit the leaf but failed to ‘take root.” Kopara and Arawa, which had adult plant resistance, might become infected at the seedling stage and might require an early spray. The economics of growing these varieties should still be con-

sidered good because in most seasons they would not need spraying at all. Rongotea. Aotea. Hilgendorf. Takahe and Tiritea were all susceptible cultivars. Striped necrotic areas were found on the leaves and small circles of bright yel-low-orange spores (less than the size of a pin-head) would be observed on both sides of the leaves. The accompanying photograph showed the resistant cultivars. Oroua and Kopara. with two levels of flecking, compared with the susceptible cultivars, Rongotea and Takahe, which had , many hundreds of spore pustules growing on the surface of the leaf. These cultivars also had a much larger area of necrotic tissue when infected. The Crop Research Division had been aware for some years now that stripe rust was likely to reach New Zealand and had been screening .material in Europe, where many races of stripe rust were present. Dr Smith said that he based his prediction of an above average 1981/82 crop on the fact that about 30 per cent of the national crop was resistant cultivars, which would be unaffected; most remaining crops had been sprayed and thus damage had been minimal; and he also felt that there were low levels of other diseases such as mildew, take-all and speckled leaf blotch. The low spring temperatures, and above average moisture, had been ideal for stripe rust, he said, but poor for other diseases. It should also be stressed that it was these conditions which had been ideal for crop growth. The D.5.1.R., Ministry of Agriculture and Fisheries and the Agricultural Merchants’ Federation took part in a field day yesterday so that field officers could inspect rust-infected crops at Lincoln. This was an effort to improve communications between sectors of the wheat industry. Some alarm was caused by the discovery of stripe .rust on some barley crops last week. Although scientists were surprised by this, they said it was restricted to one cultivar, Magnum. This was known to be very susceptible to the disease in Europe.