Chloroplast-DNA variation in cultivated and wild olive (Olea europaea L.)

Polymorphism in the lengths of restriction fragments of;he whole cpDNA mole cule was studied in cultivated olive and in oleaster (wild olive) over the whole Mediterranean Basin. Seventy two olive cultivars, 89 very old trees c ultivated locally, and 101 oleasters were scored for ten endonucleases. Mor eover, maternal inheritance of cpDNA in olive was shown by analysing the pr ogeny of a controlled cross between two parents which differed in their cpD NA haplotypes. In the whole species, three site- and three length-mutations were observed, corresponding to five distinct chlorotypes. The same chloro type (I) was predominant in both oleasters and cultivated olive trees, conf irming that these are closely related maternally. Three other chlorotypes ( II, III and IV) were observed exclusively in oleaster material and were res tricted either to isolated forest populations or to a few individuals growi ng in mixture with olive trees possessing the majority chlorotype. An addit ional chlorotype (V) was characterised by three mutations located in distin ct parts the cpDNA molecule but which were never observed to occur separate ly. This chlorotype, more widely distributed than the other three, in both cultivated and wild olive, and occurring even in distant populations, was o bserved exclusively in male-sterile trees showing the same specific pollen anomaly. However, in the present study, no evidence was provided for a dire ct relationship between the occurrence of the cpDNA mutations and male ster ility. It is suggested that the large geographic distribution of chlorotype V may be related to the high fruit production usually observed on male-ste rile trees. These may be very attractive for birds which are fond of olive fruit and spread the stones efficiently. Probably for the same reason, peop le preserved male-sterile oleasters for long periods and, in several places , used male-sterile cultivars over large areas.