Conservation and storage of a haploid cucumber (Cucumis sativus L.) collection under in vitro conditions.

Over 3 consecutive years (1992-1994), a collection of cucumber haploids was obtained from three different lines and one hybrid. Attempts were made to maintain and store a subcollection of these haploids for 3 years. Cucumber haploids appeared to be stable when cultured in vitro. There were no instances of spontaneous doubling and only one morphologically changed plant. During the first year of storage, between 30% and 80% the clones were lost, due to disturbances in plant development, increased levels of endogenous bacteria, and physiological changes resulting in continuous flowering. After 2 years of storage haploids showed reduced vigour. Therefore, plants were regenerated directly from primordial leaf microexplants. Haploid plants were obtained from nearly all of the previous haploid plants. The rejuvenated haploids possessed the same ploidy level and morphological traits as the old collection. The only new characteristic was faster vegetative growth.