High-yielding dwarf clones of Hevea brasiliensis are tolerant to wind damage and therefore useful for high-density planting. The identification of molecular markers for the dwarf character is very important for isolating true-to-type high-yielding dwarf hybrid lines in the early stage of plant breeding programs. We have identified a dwarf genome-specific random amplified polymorphic DNA (RAPD) marker in rubber tree. A total of 115 random oligonucleotide 10-mer primers were used to amplify genomic DNA by PCR, of which 19 primers produced clear and detectable bands. The primer OPB-12 generated a 1.4-kb DNA marker from both natural and controlled F(1) hybrid progenies (dwarf stature) derived from a cross between a dwarf parent and a normal cultivated clone as well as from the dwarf parent; it was absent in other parent (RRII 118). To validate this DNA marker, we analyzed 22 F(1) hybrids (13 with a dwarf stature and nine with a normal stature); the dwarf genome-specific 1.4-kb RAPD marker was present in all dwarf-stature hybrids and absent in all normal-stature hybrids. This DNA marker was cloned and characterized. DNA marker locus specificity was further confirmed by Southern blot hybridization. Our results indicate that Southern blot hybridization of RAPD using probes made from cloned DNA fragments allows a more accurate analysis of the RAPD pattern based on the presence/absence of specific DNA markers than dye-stained gels or Southern blot analysis of RAPD blots using probes made from purified PCR products. Detection of RAPD markers in the hybrid progenies indicates that RAPD is a powerful tool for identifying inherited genome segments following different hybridization methods in perennial tree crops.

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The Para rubber tree, Hevea brasiliensis Muell . Arg. belonging to the family Euphorbiaceae is the most important commercial source of natural rubber . The genus Hevea has nine species. Work on the cytogenetical aspects of the genus in general, and that of H. brasiliensis in particular, is rather meagre. Since the geneiic base of cultivated H. brasiliensis is limited, every effort has to be made to broaden the breeders' stock. An important method to cause genetic variability is the induc tion of polyploidy by artificial means and this technique has also been tried in Hevea (Shepherd 1969, Markose 1975, Zheng Xuequin et al. 1980. The Rubber Rese arch Institute of India has succeeded in inducing polyploidy in Hevea, by the appli cation of colchicine. This paper deals with the cytomorphological analysis of an induced polyploid in Hevea brasiliensis. Materials and methodsClone RRII 105, evolved by the Rubber Research Institute of India through hybridisation and selection with Tjir 1 and G1 1 as parents, was used for the present investigation. Plants raised in budwood multiplication nurseries were cut back and at the time of bud break they were swabbed with cotton. 0.75% aqueous colchicine was dropped on to these tender bud sprouts so that the cotton gets wet. The tre atment was continued daily for seven days. The shoot developing from the treated buds were regularly observed. The basal buds of those which showed morphologi cal variations were utilised for vegetative multiplication. Subsequent vegetative generations were also raised employing the basal buds of the respective shoots.Observations on morphological characters were recorded from one year old budgrafts of the VM 10* generation. Normal one year old budgrafts of RRII 105 were also observed for comparative purpose. Assessment of foliage characters was made from the middle leaflet of twenty selected leaves. Mitotic studies were made on tender leaf tips.Three year old budgrafts were ringbarked for early induction of flowering (Sa raswathy Amma 1975). For meiotic studies young male flowers at the appropriate stage of development were fixed in 1: 3 acetic alcohol mixture. Anther columns were dissected out and kept in 2% acetocarmine, overnight. Meiotic preparations * Vegetatively multiplicated 10th

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The present article surveys the possible reasons for early fruit drop in tree crops with special reference to rubber. They are environmental, physiological, embryological or pathogenic. Abortion of pistillate flowers and fruit occurs generally in three distinct periods: due to under developed flowers, failure of pollination and embryo abortion due to embryological and physiological factors. Fruit set can be increased by hand pollination, use of growth hormones or by the application of fertilizers. The failure of seed production results in the loss of numerous potentially good cross combinations thus limiting the progress of genetic improvement of the species. Moreover seeds are the rich sources of genetic variability.