RESISTANCE OF SUNFLOWER INBRED LINES TO VARIOUS FORMS OF ATTACK BY SCLEROTINIA-SCLEROTIORUM AND RELATIONS WITH SOME MORPHOLOGICAL CHARACTERS

Twenty sunflower inbred lines were studied for their reactions to 7 Sc lerotinia sclerotiorum tests on different plant parts. A principal com ponent analysis (P.C.A.) and t-tests on the means of resistant and sus ceptible groups indicated that reactions of inbred lines to infection of capitula by ascospores are independent from those to ascospore infe ctions of terminal buds. They are even more contrasted with the result s of any test measuring mycelial extension. However, for the last, the re is a close association between the reactions of roots, leaves and c apitula. Of the inbred lines, some showed good levels of resistance to most forms of attack, others were generally susceptible and there wer e some with good resistance to one particular form of attack. A P.C.A. of 18 morphological and field characters showed no general associatio n between these characters and Sclerotinia sclerotiorum test results, although it was found that lines resistant to mycelial extension on ca pitula were generally earlier than those that were more susceptible. I t is proposed that breeding programmes for general resistance to Scler otinia sclerotiorum should include a combination of two or three tests .