ABSTRACT

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.

摘要

1911 年和 1917 年，在东南亚的印度尼西亚和马来西亚进行了非洲油棕（Elaeis guineensis Jacq.）的第一次商业种植。在不到 15 年的时间里，马来西亚报道了基部茎腐病 (BSR)。又花了将近七年的时间才将 BSR 的主要病原体确定为真菌Ganoderma boninense。从那时起，研究工作集中在了解G. boninense疾病的流行病学、生物学和病因学上，但在表征病原体遗传多样性、空间结构、致病性和毒力方面取得的进展有限。本研究描述了G. boninense 的病原体变异性、基因流、种群分化和遗传结构在砂拉越（马来西亚）、马来西亚半岛和苏门答腊（印度尼西亚）通过 16 个高度多态性的 cDNA-SSR（简单序列重复）标记推断。标记推断的基因型多样性表明种群内和不同种群之间的个体之间存在高度的病原体变异性。这种遗传变异显然是担子孢子异交产生重组基因型的结果。虽然我们的结果表明种群之间的基因流动很高，但在区域尺度上，G. boninense种群之间没有显着的遗传分化。这表明G. boninense 的基因组成在广泛的地区是相似的。此外，我们的结果揭示了G. boninense的三个混合遗传簇的存在与在整个砂拉越、马来西亚半岛和苏门答腊采样的 BSR 病油棕榈有关。我们假设种群结构可能反映了G. boninense种群的高遗传变异性。反过来，这可以通过来自东南亚的G. boninense担子孢子与从世界不同地区引入的遗传来源之间非常成功的异交以及各种病原体基因型对不同棕榈宿主的区域适应性进行解释。病原体变异性和种群结构可用于推断G. boninense的流行病学，以及人工林栽培实践对不同地区 BSR 病害控制的影响。