Molecular diversity in pineapple assessed by RFLP markers

Pineapple, Ananas comosus (L.) Merr, is the third most important tropical F ruit cultivated in all tropical and subtropical countries. Pineapple germpl asm includes all seven species of the genus Ananas and the unique species o f the related genus Pseudananas. A knowledge of its diversity structure is needed to develop new breeding programs. Restriction fragment length polymo rphism (RFLP was used to study molecular diversity in a set of 301 accessio ns, most of which were recently collected. This sample was analysed using 1 8 homologous genomic probes. Dissimilarities were calculated by a Dice inde x and submitted to Factorial Analysis. The same data were represented as a diversity tree constructed with the score method. Pseudananas sagenarius di splayed a high polymorphism and shares 58.7% of its bands with Ananas. With in Ananas, variation appears continuous and was found mostly at the intrasp ecific level, particularly in the wild species Ananas ananassoides and Anan as parguazensis. As for the cultivated species, Ananas comosus appears rela tively homogeneous despite its wide morphological variation and Ananas brac teatus, which is grown as a fence and for fruit, appears still much less va riable. By contrast Ananas lucidus, cultivated by the Amerindians for fiber , displays a high polymorphism. This tree displayed a loose assemblage of n umerous clusters separated by short distances. Most species were scattered in various clusters, a few of these being monospecific. Some accessions whi ch had not been classified, as they shared morphological traits typical of different species, re-group with one or the other, and sometimes with both species in mixed clusters. No re-productive barrier exists in this germplas m and these data indicate the existence of gene flow, enhancing the role of effective sexual reproduction in a species with largely predominant vegeta tive multiplication.