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In 1911 and 1917, the first commercial plantings of African oil palm (Elaeis guineensis Jacq.) were made in Indonesia and Malaysia in Southeast Asia. In less than 15 years, basal stem rot (BSR) was reported in Malaysia. It took nearly another seven decades to identify the main causal agent of BSR as the fungus, Ganoderma boninense. Since then, research efforts have focused on understanding G. boninense disease epidemiology, biology, and etiology, but limited progress was made to characterize pathogen genetic diversity, spatial structure, pathogenicity, and virulence. This study describes pathogen variability, gene flow, population differentiation, and genetic structure of G. boninense in Sarawak (Malaysia), Peninsular Malaysia, and Sumatra (Indonesia) inferred by 16 highly polymorphic cDNA-SSR (simple sequence repeat) markers. Marker-inferred genotypic diversity indicated a high level of pathogen variability among individuals within a population and among different populations. This genetic variability is clearly the result of outcrossing between basidiospores to produce recombinant genotypes. Although our results indicated high gene flow among the populations, there was no significant genetic differentiation among G. boninense populations on a regional scale. It suggested that G. boninense genetic makeup is similar across a wide region. Furthermore, our results revealed the existence of three admixed genetic clusters of G. boninense associated with BSR-diseased oil palms sampled throughout Sarawak, Peninsular Malaysia, and Sumatra. We postulate that the population structure is likely a reflection of the high genetic variability of G. boninense populations. This, in turn, could be explained by highly successful outcrossing between basidiospores of G. boninense from Southeast Asia and introduced genetic sources from various regions of the world, as well as regional adaptation of various pathogen genotypes to different palm hosts. Pathogen variability and population structure could be employed to deduce the epidemiology of G. boninense, as well as the implications of plantation cultural practices on BSR disease control in different regions.

Ganoderma boninense, the causal agent of basal stem rot (BSR) disease, has been recognized as a major economic threat to commercial plantings of oil palm (Elaeis guineensis Jacq.) in Southeast Asia, which supplies 86% of the world’s palm oil. High genetic diversity and gene flow among regional populations of 417 G. boninense isolates collected from Sabah, Sarawak, and Peninsular Malaysia (Malaysia) and Sumatra (Indonesia) were demonstrated using 16 microsatellite loci. Three genetic clusters and different admixed populations of G. boninense across regions were detected, and they appeared to follow the spread of the fungus from the oldest (Peninsular Malaysia and Sumatra) to younger generations of oil palm plantings (Sabah and Sarawak). Low spatial genetic differentiation of G. boninense (FST = 0.05) among the sampling regions revealed geographically nonrestricted gene dispersal, but isolation by distance was still evident. Analysis of molecular variance (AMOVA) confirmed the little to no genetic differentiation among the pathogen populations and the three genetic clusters defined by STRUCTURE and minimum spanning network. Despite G. boninense being highly outcrossing and spread by sexual spores, linkage disequilibrium was detected in 7 of the 14 populations. Linkage disequilibrium indicated that the reproduction of the fungus was not entirely by random mating and genetic drift could be an important structuring factor. Furthermore, evidence of population bottleneck was indicated in the oldest oil palm plantations as detected in genetic clusters 2 and 3, which consisted mainly of Peninsular Malaysia and Sumatra isolates. The population bottleneck or founding event could have arisen from either new planting or replanting after the removal of large number of palm hosts. The present study also demonstrated that migration and nonrandom mating of G. boninense could be important for survival and adaptation to new palm hosts.

In 1911 and 1917, the first commercial plantings of African oil palm (

White root disease caused by the pathogenic Rigidoporus microporus (Sw.) Overeem, in rubber trees (Hevea brasiliensis Muell. Arg.) could limit latex production by reducing the number of productive rubber trees. Fungicolous ascomycetous Cladobotryum semicirculare G.R.W. Arnold, R. Kirschner & Chee J. Chen, was assessed for its capability of suppressing Rigidoporus microporus mycelia growth in vitro and its efficacy in reducing white root disease of rubber seedlings. Mycelia growth of Rigidoporus microporus was inhibited by Cladobotryum semicirculare mycelia (direct antagonism) with 79% inhibition at nine days-after-inoculation through a dual — culture assay and heat stable antifungal Cladobotryum semicirculare filtrates (exudates sterilised through either filter-sterilisation or autoclaving — antibiosis) followed by the poison agar test. Cladobotryum semicirculare was also found to reduce the regeneration of Rigidoporus microporus mycelia. Area under the disease progress curve, calculated using disease severity of white root disease, were reduced by 47 to 50% through application of Cladobotryum semicirculare inoculant on two separate scion-rootstocks (PB 350 — RRIM 2025 and PB 347 — RRIM 2025) combinations of rubber clones, respectively. There was no scion-rootstock interaction observed.

Determination of chlorophyll contents often requires destructives analysis and involves lengthy procedures while measurement on photosynthetic rate requires specialized equipment that often limits extensive in-field application. SPAD chlorophyll meter gives indirect measurement of leaf chlorophyll contents in a rapid, non-destructive and convenient manner. The use of SPAD meter for each individual plant species require calibration curve for each individual plant species, as the accuracy of the estimation are highly affected by the leaf anatomical characteristics. This study reports the result of correlating SPAD-502 chlorophyll index readings to the actual extracted chlorophyll content and photosynthetic rate of oil palm leaf as well as the leaf nitrogen and potassium concentration. Concentration of oil palm leaf nitrogen and chlorophyll pigment as well as photosynthetic rate were highly correlated to SPAD-502 chlorophyll index with R of above 0.80. With good calibration equation, the SPAD-502 chlorophyll meter are extremely versatile for rapid determination of oil palm leaf nitrogen and chlorophyll concentration as well as photosynthetic rate.