Prospects of breeding for blast disease resistance in the oil palm (Elaeis guineensisJacq.)
SummaryBreeding for nursery blast resistance in the oil palm can reduce blast from around 50% to 1–6% loss, when a parent is carrier of dominant resistant gene(s). At such low blast levels, most of the costly agronomic methods to reduce blast incidence, need not be used.Plant material originating from the arid regions in Nigeria is more blast susceptible than that from the rain forest areas.
Co-infection by a species of Pythium and Rhizoctonia lamellifera small in blast disease of Oil-Palm seedlings
The leaf and root symptoms of blast disease are described. Isolations from roots in an advanced state of decay yielded Rhizoctonia lamellifera whereas isolations from primary infections yielded a Pythium species. Inoculation experiments are reported which demonstrate that typical blast symptoms develop only when a mixed inoculum of R. lamellifera and Pythium sp. is employed. A laboratory experiment showed that R. lamellifera is capable of parasitizing the Pythium species. Blast disease appears to result from co-infection of oil-palm seedling roots by a Pythium sp. and R. lamellifera .
Investigations on the rôle of organic matter in plant nutrition
1. As the result of decomposition of green manure in a swamp soil, the coarse fractions (including coarse and fine sand) of the surface layer (first 3 inches) decreased by 11·2 per cent. while the fine ones (silt+clay) increased by 9·8 per cent. in the course of 43 days. The effect was less pronounced in the manured soil maintained at 60 per cent. saturation, while no alteration was to be noticed in the case of the unmanured specimens. 2. Treatment with dilute hydrochloric acid prior to dispersion had no appreciable effect on the estimates of mechanical composition obtained in the different cases. Loss in solution was also comparatively small. 3. The silica-sesquioxide ratio increased slightly as the result of decomposition of green manure in swamp soil. The composition of the fine fractions was also altered, the total percentages of the oxides of iron, aluminium and silicon increasing from 90·5 to 99·3 in the course of 71 days. 4. The practical significance of the above and related observations has been discussed.