Stripe rust reactions of Australasian wheats

Summary

Seedling and field reactions to four European races of stripe rust were determined for 254 wheat cultivars, mostly from Australia and New Zealand. Numerical analyses of the data employed a divisive classification procedure with termal reallocation to form 10 groups which were then further classified, ordinated and diagnosed by several procedures. The groups formed ranged from one comprising four wheats with low seedling reactions to all four rust strains and mean field rust of only 1.0%, to one comprising 105 wheats with high seedling reactions and mean field rust of 64.7%. Groups of cultivars with intermediate levels of rust resistance were classified both on relative level of overall rust and on differential reactions to rust strains. One group of 13 cultivars had moderately high seedling reactions but averaged only 1.5% rust in the field.

Seedling response to gibberellic acid (GA) was also measured and diagnosed as an external attribute, along with grain type and region of origin. Principal co-ordinate analysis revealed that greater resistance to stripe rust was associated with the insensitivity to GA typical of semidwarf wheats and with an origin in northern Australia, where semidwarf wheats have been most used in the breeding program. In terms of numerical analysis of disease data in plant breeding programs, the study highlighted the advantages of using divisive classification with terminal reallocation of group members.