SCREENING PROCEDURES FOR POWDERY MILDEW RESISTANCE IN THE CUCUMBER

Nick E. Fanourakis
Screening and selection of cucumber ( Cucumis sativus L.), for resistance to powdery mildew (Sphaerotheca fuliginea ex Fr.) is usually applied by dusting leaf blades of young plants in the greenhouse with powdery mildew inoculum. Eventhough the fungus is easily growing on the surface of the inoculated leaf blades, a highly heterogeneous response is sometimes obtained even wilthin a homozygous population, due to several uncontrolled factors of the environment.

To overcome the above difficulties a new screening procedure for selection of resistant cucumber plants was developed, based on the inoculation of leaf discs of individual plants at the seedling stage. Cucumber seedlings at the one leaf stage are used for this screening procedure. Two leaf discs (two replications) are taken from each seedling when the first leaf is completely grown. A plastic container is filled up with a solution of gibberellic acid, to maintain the leaf tissues growing actively. A piece of foamy plastic is floating on the surface of the solution to support the leaf discs, with a hard plastic grid over it for the leaf disc identification. The upper surface of the discs is inoculated by dusting them with powdery mildew inoculun by the use of a painter's brush. Incubation and powdery mildew development is obtained by keeping the containers in a growth chamber for seven days. Powdery mildew resistance reaction is assessed by using a scale, according to the severity of the attack.

To compare the two screening procedures, leaf discs taken from young seedlings, as well as leaf blades of the same plants at a later stage, were inoculated with powdery mildew. Parallel and consistent results were obtained for the many varieties and lines used.

Leaf discs from leaves of completely developed plants in the greenhouse were also used for powdery mildew evaluation. The results were always comparable to those obtained either by the disc inoculation of seedlings or by dusting young plants in the greenhouse.

Fanourakis, Nick E. (1991). SCREENING PROCEDURES FOR POWDERY MILDEW RESISTANCE IN THE CUCUMBER. Acta Hortic. 287, 147-154
DOI: 10.17660/ActaHortic.1991.287.14
https://doi.org/10.17660/ActaHortic.1991.287.14

Acta Horticulturae