Floral morphological studies on  the 1981 IRRDB wild  Hevea  germplasm collection maintained at the  Rubber Research Institute of India have revealed two genotypes which are different from  the rest.   These variants differ in  the  pattern of growth, colour of the  flower, presence of a disk  at the base  of the staminal column in the  male  flower and  morphology of the fruit.  The possibility of these being infraspecific variants or  interspecific hybrids is discussed.

The study  analysed the  comparative  commercial  yield performance and  related  aspects   of  19  Hevea clones during the  first ten  years of tapping based on  information on  467  fields, in  the estate sector,  with an  area of  6881.24 ha.   The analysis covered comparison of  yield  per   ha, yield per tree share of field    coagulum  (FC),    tappable stand,   tapping   intensity,   season-wise  yield composition  and  a  comparison  of   yield  rates of India  with  those  of  Malaysia. The clone RRII  105 was found to be  the  highest yielding and reported relatively lower FC, higher tappable stand and lower tappping intensity.  The RRIM clones other than RRIM  600 were low  yielding and recorded higher FC,  lower tappable stand  and higher tapping  intensity  The PB clones showed diverse trends but   among them PB  28/59,   PB 260  and PB 217 were found to be high yielding ones.  For the   eight clones compared, the  commercial yield in  Malaysia were found to be higher than those in India.

The  impact   of floral  attributes like  flowering, pollen  fertility,  stigma   receptivity and  ovule abortion  on  fruit  set  in  Hevea  brasiliensis was  investigated.  incomplete protandry  prompts differential  anthesis of  male  and  female  flowers  thereby   ensuring cross  pollination  and/or reduced  seed  set. A climatic  niche  (inclusive  of photoperiod and  moisture-temperature  stress) exerts  influence over  the emergence and  anthesis of flowers  which  turns  to be largely clone specific  with  RRIM 600 exhibiting endogenous rhythm.  The spectrum of pollen  fertility  status (from 50% in SCATC 88-13 to 98% in RRIM 600) is yet another aspect  that influences fruit  set. Receptivity  of stigma  lasts for less than  24 h, where  the early  appearance of staminate flowers and shortened stigma  receptivity stand  as a bottle neck in achieving required permutation gene combinations to represent factual  extent  of heterozygosity.  The Chinese  clones  (SCATC 88/13, SCATC 93/114 and Haiken  1) exhibited  relatively  low stigma  receptivity.  Histochemical studies indicated that ovule abortion occurs during 20-30 days after fertilization.  An obstinate tendency to continue generations through adventive embryony was detected in abortive ovules.   The non­ survival  of  nucellar   embryos  indicated  a  weak   genetic   control   over   their  induction  and continuance. The defoliation pattern of clones  presented a spectrum, where  clones  with  larger number of fruits ensured early senescence of leaves.   The attributes investigated deserve closer scrutiny to spell  out  the control  mechanisms.

A correlation study on ten Hevea brasiliensis clones showed that  the factors detrimental to girth increment on tapping  favours  the occurrence of tapping panel dryness.  Laticifer area index  was an  exception  which  has  positive association with  both.   The  number  of latex  vessel  rows, the number of intraxylary phloem  groups and  total volume  of latex produced  together contributed to 49 per cent variation in the occurrence of tapping panel  dryness of which  the two structural traits alone  governed 39 per cent variation.  The associations of characters indicated that  a very high number of latex vessel rows in high yielding  clones leads to high incidence of tapping panel dryness. Hence selection  based on high girth, good quantity of intraxylary phloem  and balanced number of latex  vessel  rows  is suggested for  sustainable  yield  by  reducing TPD.    The two structural traits  mentioned above  are  useful  parameters for early  prediction of clonal  susceptibility  to TPD at  least  to some  extent.    The  importance of laticifer  area  index  and  number of  intraxylary phloem  groups as selection  parameters is discussed.

Five  isolates of  Azotobacter collected  from   different  regions of  Kerala were  studied  for  their survival in  rubber (Hevea brasiliensis) plantation soil  and   for  their   nitrogen fixing  capacity   at different pH  levels.   Only two survived in soil at pH 4.8.  One  isolate showed more nitrogenase activity  from  pH 4.5 to 6 and  was  studied for its effects on growth of rubber seedlings when used in combination with  different levels  of the  recommended dose  of urea.   The  girth of seedlings  which  received 50 per  cent  of recommended dose of nitrogen with Azotobacter inoculation was comparable  to plants which received  100 per  cent  of the  recommended dose alone.  Azotobacter inoculation  augmented the  population of various  microorganisms in the  rhizosphere of rubber seedlings.

Different forms of natural rubber  were used for coating prilled  urea for developing a slow release fertilizer. The technique involved incorporation of prilled  urea at high loading into skim rubber, ISNR 5 and  reclaimed rubber  using  an internal mixer.   The highly  urea  filled  rubber  was  then extruded and  granulated. These  granules were  evaluated for volatilization loss, leaching and slow  release characteristics.  The results  indicated  that NR-encapsulated urea  has the characteristics of a slow  release  fertilizer.