Abnormal leaf fall disease was observed to cause 9 to 16 per cent yield loss in susceptible clones of Hevea brasiliensis, of 10 to 25 years age, when prophylactic spraying was  skipped for one season.    The disease adversely affected growth and bark renewal of the trees. The yield in the subsequent year was also affected adversely in unsprayed areas. The disease increased the plugging index and reduced the dry rubber content of the latex. Weed growth was more in the untreated plots.

Application of liquid natural rubber (LNR) as a reactive plasticiser in nitrile rubber (NBR) was studied  using compounds  containing different loadings of dibutyl phthalate (DBP) and LNR.   Cure characteristics, physical properties as well as ageing and ozone resistance were measured on compounds containing the plasticisers upto 15 phr.    Changes in rheological behaviour, imparted  by the plasticiser on NBR, were evaluated  using four compounds  containing 5, 10, 15 and 20 phr of plasticiser.    The study showed that LNR can be  used as a plasticiser in NBR without affecting its cure characteristics,  storage  life and  most  of  the physical properties except brittle point. Improvement was observed in properties like green strength, mill shrinkage and compression set. Rheological studies showed that LNR system at high temperatures and shear rates have lower viscosity  than  the  corresponding DBP systems which enables easier moulding. Die swell also  decreased  with  the  incorporation   of LNR.   The use of LNR as a reactive plasticiser was justified by the higher volume swell in oil indicative of its ability to compensate for the shrinkage resulting from leaching.

Profiles were exposed in the conventional rubber growing areas in Kanyakumari, Kottayam, Trichur and Calicut and  in the non-conventional  region in Dapchari,  Maharashtra.    Soil samples were collected horizon-wise from these profiles and analysed for mechanical composition, organic carbon, pH, total iron, total manganese and exchangeable manganese. Correlations were worked out between the two forms of manganese and physico-chemical properties of the soil.  It was observed that the total as well as the available manganese are high in Dapchari compared to other regions studied. The total manganese was found to be significantly correlated with the exchangeable manganese, fine sand, silt and total iron.    The high content of manganese (1373 ppm) in the soil of Dapchari may not cause any adverse effect on growth of rubber, as rubber is found   to  be growing satisfactorily  in  soils  having similar manganese status in other rubber growing countries.                                                    

Seedling progenies of three male sterile clones (GT 1, Ch 2, and RRII  35), along with pro­ genies of a fertile clone (Mil 3/2) as  standard, of Hevea brasiliensis were evaluated  in the nursery.   Seeds from the male sterile clones recorded early and higher percentage of germination.    The progenies of the male sterile clones were more vigorous compared to  the control.    Test tapping yield also indicated the superiority of the progenies of male sterile clones.   The male sterile clones recorded higher heritability along with higher genetic advance indicating additive gene action.    They also had higher general combining ability. Among the male sterile clones,  GT  1 showed  significant  superiority  over  the  others.

Fragments of internal  tegument from immature seeds of Hevea brasiliensis cultured  in vitro produced substantial quantities of hydrogen cyanide (HCN).  Release of HCN was considerable during  the initial  hours  and  probably  resulted  from  intracellular  decompartmentation caused by the slicing of the  tissues in culture  preparation. Cyanogenic potential depends on the age of seed and appears  to be variable from one clone to another.   When culture was carried out under confined atmosphere,  HCN  was present for the first 20 days. Cellulose caps enhanced gas exchanges and led to better callogenesis under the conditions of the experiment.

Four hundred and forty nine seedlings belonging to fourteen cross combinations were evaluated at an age of one year by an incision test method. A special knife was designed for this purpose.    Normal test tapping was adopted when the seedlings attained an age of two years. The yield at one year by test incision method showed a highly significant positive correlation (P  < 0.01) with the test tap yield.   Hence the comparatively  simpler and  rapid  incision test method is suggested as an alternative for the more elaborate and time consuming test tap methods.

Girth of one year old seedlings was positively correlated  with that at two years (r = 0.81**) and also with yield at the age of one year (r  = 0.76**)

Among the 14 families, the cross combinations  PB 242 x RRII  105, PB 242 x PB 86 and PB 5/51 x RRII 208 recorded higher girth and juvenile yield at one year as well as at two years. A similar trend was noticed for plant height at one year age.   The families RRII 105 x PR 107, RRIM  600 x G1 1 and RRIM  600 x RRII 203 recorded higher number of leaf flushes.   Test of significance for the different characters revealed no significant difference between families but there were significant differences within the families for girth, incision test yield and test tap  yield.