The incidence and  severity  of leaf blight disease of Hevea  brasiliensis  Muell. Arg. caused  by Periconia heveae Stevenson & Imle were studied  over a period of four consecutive years from 1990 in three locations (two in Assam and one in Meghalaya).  High incidence and severity of the disease was noticed in January-February which decreased abruptly thereafter in all the three locations.  Temperature  ranging 15-25°C, cool nights, dew and relative humidity around 90 percent  favoured  development  of the disease.  The optimum  temperature  for the growth of the fungal pathogen  was 25°C and  the pathogen  exhibited very little growth  at 10°C and 30°C.  In vitro studies  revealed carbendazim  (0.1% ai) to be superior  to mancozeb (0.2% ai) in checking the growth of the pathogen.   These fungicides proved to be effective under field conditions also.

A model  for  predicting seasonal yield  of  rubber  (Hevea  brasiliensis )  tree  was  evolved  using meteorological  data, crop   phenology  and  production  of  trees  of  clone  RRIM  600  at Jose Bonifacio county, Sao Paulo state, Brazil  close to 21"00'S, 49°42'W and  470 m above  sea  level. To  quantify monthly and  ten day  basis  yield  response  the  model  was  adjusted considering the ratio of actual to potential  yield as a productory of  penalization by moisture  and  thermal factors.   The monthly and decendial  potential  yield were  estimated as a senoidal  curve, which fits  well  to  the seasonal   periodicity of  latex  production.   The  best  performance for  the  ten day basis  model  was  found  considering  100  mm  of  storage  soil  water  and  moisture  factor expressed   by  the  ratio  of  actual to  potential   evapo-transpiration,  resulting  in  R_² =0.73 and d-index  = 0.90.

Xylem vessel  dimensions  in  terms of lumen  diameter  and  element  length  and  their  distribution  pattern  along with certain qualitative  traits were compared  in three clones (RRIC 52, RRII 105 and PR 261) of H. brasiliensis grown  under  two agroclimates.  Mean vessel diameter from transections showed significant clonal differences.  The mean vessel diameter  for RRIC  52 was significantly more (0.1640 mm) than that of RRII 105 (0.1448 mm) and  PR 261 (0.1325 mm).  There was no location-wise variation for these traits.  The mean length of vessel element was higher for RRIC 52 (0.6197 mm) followed by RRII 105 (0.5913 mm) and PR 261 (0.5855 mm).     A significant reduction in vessel element  length  was observed  in the  cIones grown in Dapchari.  Significant clonal differences for vessel dimensions were observed, which appeared to influence  the conduit  anatomy of different  clones.  Vessel shape was found  to be diagnostic of the  clones  to a certain  extent.

Rate of dark respiration was measured in the soft bark tissue of ten clones of Hevea and related to the biochemical composition of the tissue and  the dry  rubber  yield and  biomass  of the trees.  The rate of respiration showed a positive correlation with total proteins, soluble sugars and starch contents  in the laticiferous tissue.   Tapping  increased  the rate of respiration  in the bark.  There was a positive correlation between the rate of respiration  and the latex yield on a given day, indicating that a high respiratory activity was required  to sustain high yield. Tapping led to substantial loss of biomass in all the clones and this was positively associated with  dry  rubber  yield.   There was more than proportionate loss of biomass as  the annual mean dry rubber yield increased among the clones. This unaccountable loss of biomass could possibly be due  to an increase in the maintenance respiration  in the bark tissue of the high yielding  clones which  may  be metabolically more active  to sustain  a high  yield.   Thus, it appears  that  the high yielding clones in general have poor efficiency in converting  biomass into  rubber.

A multiobjective land use planning model for one hectare farm was developed  using the compromise  programming approach.   Maximization of gross margin and family labour employment as well as minimization of hired labour and capital borrowing were the objectives used and the activities (crops) included were banana, tapioca, yam, colocasia, turmeric, ginger and cowpea.  The compromise set of farm plans showed gross margins ranging from Rs.15691 to Rs. 21250 per  ha  where  different  weights  were assigned  to the four  objectives.

The morphology, physico-chemical properties  and  exchange characteristics  of  five representative pedons of soils under rubber (Hevea brasiliensis), at different altitudes, in Mizoram were studied  and classified as per soil taxonomy.  The soils in general were deep, well drained with rapid permeability and have mixed clay mineralogy. The texture of lower altitude soils at 150 and  280m above mean sea level (msl) ranged  from silty clay loam at the surface  to clay in the lower solum  whereas  soils at 400 and  500m above msl were sandy clay loam to clay loam. The soils showed considerable homogeneity and exhibited  A-Bw-C to A-Bt C profiles.  They were strongly acidic to very strongly acidic and high in organic carbon which showed a decreasing trend with depth.   Exceptionally high acidity had resulted in low cation exchange  capacity and  poor  base status  of the soils.   The soils of pedon  at altitudes  150, 280 and 750m above msl were classified as Typic Hapludults  whereas soils at 400 and 550m above  msl were Umbric Dystrochrepts.