RIBOSOMAL DNA VARIATIONS IN WILD AND CULTIVATED RUBBER TREE (HEVEA-BRASILIENSIS)

Ribosomal DNA variations were surveyed to assess the genetic variabili ty among Hevea brasiliensis genetic resources. One hundred and sixty-e ight individuals, including 73 cultivated Wickham clones and 95 wild c lones from a prospection, were analyzed. Restriction mapping of rDNA u nits showed that RFLP variations are the result of both length and sit e (EcoRI) variations in the intergenic spacer (IGS). These variations can be revealed between as well as within individuals. A total of 12 s pacer length variants is scored in the whole population, as well as tw o different ribosomal units (refered as type I and type II), defined b y the presence or absence of an EcoRI site. Particular associations be tween spacer length variants and unit types can be revealed, leading t o complex RFLP patterns. Cultivated clones appear to be less variable than prospections but show, however, a relatively high level of variab ility despite their narrow genetic base. Furthermore, IGS variations a llowed a structuring within wild clones to be drawn, based mainly on t heir geographical origin. Some interesting discrepancies with previous work on isozyme variations are discussed and show the interest of sur veying different genetic markers for diversity studies.