Soil augmentation test indicates potential ‘general’ suppressive soil characteristics of Blenheim soil for the control of Basal Stem rot disease in oil palm

This study explored the nature of a naturally occurring disease-suppressive soil, Blenheim soil (DS-BhS), to determine whether it functions as a ‘general’ or ‘specific’ suppressive soil and to establish its feasibility for controlling Basal Stem Rot (BSR) disease of oil palm. Non-sterilized DS-BhS was mixed with sterilized DS-BhS at ratios of 0:100, 30:70, 50:50, 70:30, and 100:0 (w/w). These soil mixtures were used to plant 2-month-old oil palm seedlings, which were challenged with Ganoderma boninense . Disease incidence (DI), disease severity index (DSI), disease progression (AUDPC), bole lesion development, leaf chlorophyll content, and plant growth parameters were recorded over a 20-week period. At 20 weeks post-inoculation (WPI), soil samples were collected to quantify G. boninense using qPCR. Disease suppression increased with a higher proportion of non-sterilized DS-BhS, becoming evident when the soil mixture contained 70% non-sterilized DS-BhS. At this soil mixture ratio, DI (67%), DSI (59.7%), AUDPC (418), bole lesion (62.7%), and G. boninense gDNA levels (0.17 ng/g of soil) were comparable to those observed in the 100% non-sterilized DS-BhS (100:0). In the latter, DI was 73%, DSI was 56.1%, AUDPC was 424, bole lesion was 62.9%, and G. boninense gDNA was 0.0792 ng/g soil. This study revealed that the disease suppressiveness of DS-BhS can be transferred when a larger proportion of non-sterilized DS-BhS (ratio of 70:30 or 100:0) is used. This suggested that DS-BhS, the only reported suppressive soil for BSR disease to date, may represent a potential general suppressive soil.