Investigations about the genetic resources of grapes with regard to resistance characteristics to powdery mildew (Oidium tuckeri)

During 1991 through 1993 a total of 475 cvs were rated for oidium infection of leaves and berries. It was established that there was no infection of the berries of 41 cvs and on the leaves of one cultivar. A comparison with the V. vinifera cvs Mueller-Thurgau and Silvaner clearly shows that all impressive number of genotypes have a substantially lower degree of infection. The wide genetic variation offers a good basis upon which new cvs with improved oidium resistance can be bred. Despite the significant correlation between oidium infection on leaves and berries, there was, in many cases, considerable variation in leaf infection within one level of berry infection, or in berry infection within one level of leaf infection. Therefore, a precise conclusion as to the resistance of berries can not be made on the basis of screening procedures in the greenhouse or in vitro to determine the degree of resistance on leaves.