Mildew Races Review Advocated

Press, Volume CVI, Issue 31125, 30 July 1966, Page 10

Mildew Races Review Advocated

TN the view of Dr. I. D. Blair, reader in microbiology at Lincoln College, there is an urgent need for a reexamination of the strains of powdery mildew fungus infecting wheat crops. He said this last week speaking at a farm seminar in Southland. Dr. Blair said that mildew reduced yield to the extent that the parasitism destroyed leaf, tissue or impaired physiological activity. Experiments at Lincoln had shown that yield could be reduced by up to a third of the potential. The severity of the disease Was related to the time infection became established —if this was early in the growth cycle, as in Southland, the yield loss would be severe. In Canterbury infection often developed late—not until ears were well formed—and in this event yield losses were much lower.

The infection, he said, came from a spore form surviving on litter or residues of previously infected wheat straw.

Dr. Blair said that four distinct physiological races or strains of the fungus were known. It was 17 years since Dr. H. C. Smith had shown that races 3 and 4 were commonly occurring on Canterbury wheat, but he had no samples for testing south of Taieri. There was an urgent need for re-examination of

this position for it was conceivable, indeed quite probable, that any of the other races of the fungus, numbers 1 and 2, had since become established in Southland and as a consequence had contributed to the severity and prevalence of the disease. Dr. Blair said that both Hilgendorf (1961) and Cross 7 (1961) had originally been produced with a high measure of resistance to mildew. In 1964 it had been reported that both these new releases had developed significant field infection. Hybrid 650.01, similar to Aotea agrpnomically, had shown mildew resistance in Canterbury but not in South Otago. These latter

points suggested very strongly that the form and distribution of races of the casual organism were different in Southland and that there was there a form or organism that was widespread and severe. In plant breeding resistance had to be obtained for the specific race or races in an area..