Detecting BSR-infected Oil Palm Seedlings using Thermal Imaging Technique

Basal Stem Rot (BSR) is the most destructive disease instigated by a white wood rotting fungus called Ganoderma boninense, which cause great economic setback in oil palm productivity. It attacks the basal stem of oil palm trees, causing them to slowly rot. It also affects the xylem tissues that eventually interrupt water transportation to the upper part of the oil palm, turning the leaves at the frond become yellow. This problem should be prevented during nursery stage by separating between healthy and BSR-infected seedling. Therefore, this study focuses on the potential use of thermal imaging for detecting BSR in oil palm at seedling. Thermal images of oil palm seedling from healthy and BSR-infected were captured and processed to extract several thermal properties of the seedling, i.e., maximum, minimum, mean, and standard deviation of pixel intensity value. These values were then undergone statistical analysis to identify its significant different in differentiating healthy and BSR-infected seedling. Several classification models were tested including Linear Discriminant Analysis (LDA), Quadratic Discriminant Analysis (QDA), Support Vector Machine (SVM) and k-Nearest Neighbour (kNN). Principal Component Analysis (PCA) was used to reduce the dimensionality of the dataset. The results demonstrated that the highest accuracy achieved at 80.0 % using SVM (fine gaussian) classification model with PC1 and PC3 as the input parameter. This summarizes the potential of thermal imaging in detecting BSR-infected oil palm trees at seedling stage.

Detection of Two Peronospora spp., Responsible for Downy Mildew, in Opium Poppy Seed

Downy mildew is a serious threat to opium poppy production globally. In recent years, two pathogen species, Peronospora somniferi and Peronospora meconopsidis, which induce distinct symptoms, have been confirmed in Australia. In order to manage the spread of these pathogens, identifying the sources of inoculum is essential. In this study, we assessed pathogen presence associated with poppy seed. We developed PCR and qPCR assays targeting the coxI and coxII gene regions, for the detection, differentiation, and quantification of P. somniferi and P. meconopsidis in poppy seed. These results were complemented and compared with direct seed histological examination and a seed washing combined with viability staining for oospore detection. The majority of seed lots from all harvest years contained detectable P. meconopsidis, the earliest (1987) predating the first official record of the disease in Tasmania (1996). In contrast, only seed lots harvested in 2012 or later contained P. somniferi, evidence of its more recent introduction. P. meconopsidis contamination was estimated to be as high as 33.04 pg DNA/g of seed and P. somniferi as high as 35.17 pg DNA/g of seed. Incidence of pathogen contamination of seeds, estimated via a group testing protocol, ranged from 0 to 9% (P. meconopsidis) or 0 to 11% (P. somniferi). Mycelia were predominately found external to the seed coat. Seed washing and viability staining demonstrated that putatively viable oospores were present in the majority of seed lots. Transmission testing confirmed both pathogens can be successfully transmitted from infested seed to infected seedling. PCR and qPCR pathogen assays were found to be reliable and offer a routine test for determining pathogen inoculum in poppy seeds.

Seasonal Pattern of Tomato Mosaic Tobamovirus Infection and Concentration in Red Spruce Seedlings

ABSTRACT Tomato mosaic tobamovirus (ToMV) infects red spruce (Picea rubens) and causes significant changes in its growth and physiology. The mechanism of infection and the pattern of virus concentration in seedling roots and needles were investigated. One-year-old red spruce seedlings were obtained from the nursery in April and June 1995 and August 1996 and tested for ToMV using enzyme-linked immunosorbent assay (ELISA). Virus-free seedlings were divided into three treatments: control, root inoculated, and needle inoculated. Two control, five root-inoculated, and five needle-inoculated seedlings were sampled destructively at biweekly intervals for 3 months and then tested for ToMV by ELISA. ToMV was transmitted to seedlings by root but not by needle inoculation. The virus was detected in 67 to 100% of roots but in less than 7% of needles of root-inoculated seedlings. The percent infection of root-inoculated seedlings differed significantly between the April and June and between the April and August inoculation periods. Virus concentration in infected seedling roots increased initially, peaked within 4 weeks postinoculation, and steadily declined thereafter. Significant differences in ToMV concentrations in roots also were detected among inoculation periods and sampling dates. Early spring may represent the optimal time for infection of seedlings, as well as for assaying roots for ToMV.