METHODS OF DETERMINING THE REACTION OF SUNFLOWER GENOTYPES TO TERMINAL BUD ATTACK BY SCLEROTINIA-SCLEROTIORUM (LIB) DEBARY

Possible methods to test the reaction of sunflower genotypes to terminal bud attack by Sclerotinia sclerotiorum were studied. Percentage attack in the field under natural conditions was taken as a basis for comparison of the different test methods, since it has been shown that genotype ranking according to reaction to natural attack is stable. Two tests gave results significantly correlated with those of natural attack. A test measuring mycelium extension along the young stem from an explant placed on the terminal bud gave a correlation of r = 0.554 (n = 20). An infection by ascospores after wounding a young leaf with a soldering iron gave a correlation of r = 0.444 (n = 20). These tests can be used in breeding programmes. The results of other tests on leaves and stems were not correlated with terminal bud attack, confirming that reaction of sunflowers to S sclerotiorum depends on the plant part attacked.