Paul Holford

Western Sydney University · School of Science

Viroids occur in plants as swarms of sequence variants clustered around a dominant variant, leading to adoption of the term ‘quasispecies’ to describe the viroid population in an individual host. The composition of the quasispecies can potentially change according to the age of the infection, the position of the leaf or branch in the canopy, and th...

The brown marmorated stink bug ( Halyomorpha halys ), a native of Asia, has become an invasive pest in North America and Europe. Given the severity of H. halys and the need for better and environmentally-friendly control methods for this pest, we evaluated the virulence four entomopathogenic nematode species ( Heterorhabditis indica , Oscheius myri...

The natural pollinator of the major species of commercially-grown vanilla, Vanilla planifolia, is unknown, and the crop requires hand pollination to achieve significant levels of fruit set; however, the traditional technique (using a toothpick) is costly, as it requires skilled personnel. To overcome this problem, two native Australian bees, Tetrag...

The presence of Telenomus remus Nixon, a scelionid egg parasitoid of noctuids, including the fall army worm (Spodoptera frugiperda (J.E. Smith)) in Việt Nam and Lao PDR is reported. Records suggest that T. remus originated in Malesia, a region encompassing Malaysia, Indonesia, the Philippines, and northern Australasia. It subsequently spread more w...

Infection with pathogens can increase the fecundity and other fitness-related traits of insect vectors for their own advantage. Our previous research has reported the pivotal role of DcKr-h1 in the fecundity improvement of Diaphorina citri induced by the bacterium, “Candidatus Liberibacter asiaticus” (CLas), and the fungus, Cordyceps fumosorosea (C...

The assessment of hull-less barley germplasm for salt tolerance is crucial for future barley breeding programs, as it allows them to be classified for their adaptability to salt stress. Here, the salt tolerance of 224 hull-less barley genotypes was assessed under different NaCl concentrations during the seedling stage. Three hydroponic experiments...

Arsenic (As) contamination of agricultural soils poses a serious threat to crop productivity and food safety. Zinc oxide nanoparticles (ZnONPs) have emerged as a potential amendment for mitigating the adverse effects of As stress in plants. Soybean crop is mostly grown on marginalized land and is known for high accumulation of As in roots than othe...

Diaphorina citri serves as the primary vector for ‘ Candidatus Liberibacter asiaticus ( C Las),’ the bacterium associated with the severe Asian form of huanglongbing. C Las-positive D. citri are more fecund than their C Las-negative counterparts and require extra energy expenditure. Therefore, understanding the molecular mechanisms linking metaboli...

Diaphorina citri serves as the primary vector for ‘ Candidatus Liberibacter asiaticus’ ( C Las), the bacterium associated with the severe Asian form of huanglongbing. C Las-positive D. citri are more fecund than their C Las-negative counterparts and require extra energy expenditure. Therefore, understanding the molecular mechanisms linking metaboli...

The phloem-limited bacterium, 'Candidatus Liberibacter asiaticus' (CLas), is the putative causal pathogen of the severe Asiatic form of huanglongbing (citrus greening) and is most commonly transmitted by the Asiatic citrus psyllid (ACP), Diaphorina citri. CLas severely affects many Citrus species and hybrids and has been recorded in the Citrus rela...

Molecular confirmation of the presence of the tomato leafminer, Phthorimaea (Tuta) absoluta Meyrick, 1917 (Lepidoptera: Gelechiidae), in the Paksong region of the Bolaven Plateau in Champasak province in south-western Lao PDR is reported. The moth, which is native to South America, has invaded many countries in Europe, Africa, and Asia since 2006,...

Diaphorina citri is the primary vector of the bacterium, ‘ Candidatus Liberibacter asiaticus’ ( C Las) associated with the severe Asian form of huanglongbing. C Las-positive D. citri are more fecund than their C Las-negative counterparts and require extra energy expenditure. Therefore, understanding the molecular mechanisms linking metabolism and r...

Diaphorina citri is the primary vector of the bacterium, ‘ Candidatus Liberibacter asiaticus’ ( C Las) associated with the severe Asian form of huanglongbing. C Las-positive D. citri are more fecund than their C Las-negative counterparts and require extra energy expenditure. Therefore, understanding the molecular mechanisms linking metabolism and r...

Ultraviolet radiation (UVR) has positive and negative impacts on organisms and affects entire ecosystems. It is currently receiving attention because of the interactions of UVR with changes in climate that are likely to affect agriculture and food security. A review is provided on the effects of different types of UVR on the survival, development a...

Drought is one of the main environmental factors affecting crop growth, and breeding drought-tolerant cultivars is one of the most economic and effective ways of increasing yields and ensuring sustainable agricultural production under drought stress. To facilitate the breeding of drought-tolerant wheat, this study was conducted to evaluate genotypi...

Aluminum-activated malate transporters (ALMTs) and slow anion channels (SLACs) are important in various physiological processes in plants, including stomatal regulation, nutrient uptake, and in response to abiotic stress such as aluminum toxicity. To understand their evolutionary history and functional divergence, we conducted phylogenetic and expr...

The evolution of insect vector‐pathogen relationships has long been of interest in the field of molecular ecology. One system of special relevance, due to its economic impacts, is that between Diaphorina citri and ‘ Candidatus Liberibacter asiaticus’ ( C Las), the cause of the severe Asian form of huanglongbing. C Las‐positive D. citri are more fec...

Diaphorina citri is the primary vector of the bacterium, Candidatus Liberibacter asiaticus (C Las) associated with the severe Asian form of huanglongbing. C Las-positive D. citri are more fecund than their C Las-negative counterparts and require extra energy expenditure. Therefore, understanding the molecular mechanisms linking metabolism and repro...

Citrus Vein Phloem Degeneration (CVPD), caused by the bacterium Liberibacter asiaticus with Diaphorina citri Kuwayama as the pest vector, decreases citrus yield. This study looked at the effectiveness of Cymbopogon nardus extract in repelling D. citri populations in various formulations and concentrations. The major goal of the reaserch was to iden...

The Diaspididae (Hemiptera: Coccomorpha), also known as armoured scale insects, is a diverse family of obligate, phytophagous parasites that include major economic pests of terrestrial plants. There are over 2,700 diaspidid species, about 116 of which have been recorded worldwide feeding on species and hybrids of citrus. Citrus is widely cultivated...

Apple stem grooving virus, the causal agent of citrus tatterleaf disease, was detected for the first time in the Lao People’s Democratic Republic. Samples were collected from citrus trees across the southern provinces for testing in Australia. RNA was extracted and tested using conventional and real-time reverse transcription polymerase chain react...

Guar (Cyamopsis tetragonoloba L.) is a summer legume that is becoming a crucial industrial crop because of its high gum and protein content. Thus far, the combined effects of arbuscular mycorrhizal fungi (AMF) and Bradyrhizobium on the yield and chemical composition of guar plants are not well studied. Therefore, the current investigation was desig...

Populations of Diaphorina citri decline with elevation and, in a study in Bhutan, were rarely found above 1200 m ASL. The impact of ultraviolet (UV) radiation, particularly UV-B, on immature stages of the psyllid was proposed as limiting factor. As no studies have been undertaken on the influences of UV radiation on the development of D. citri, we...

Detection of new viruses or new virus hosts is essential for the protection of economically important agroecosystems and human health. Increasingly, metatranscriptomic data are being used to facilitate this process. Such data were obtained from adult Asian citrus psyllids (ACP) (Diaphorina citri Kuwayama) that fed solely on mandarin (Citrus ×aurant...

Chromium (Cr) contamination of agricultural soils is a major threat to human and plant health worldwide and causes reductions in plant growth and crop yields. 24-epibrassinolide (EBL) and nitric oxide (NO) have been shown to ameliorate the reductions in growth caused by the stresses induced by heavy metals; however, the interactions between EBL and...

Rice (Oryza sativa L.) has inherently low concentrations of nitrogen (N) and zinc (Zn), and those concentrations are falling as the atmospheric concentration of carbon dioxide ([CO2]) increases, threatening the quality of human diets. We investigated the effect of two levels of Zn supply (marginal and luxury), on Zn and N concentrations in whole gr...

Citrus exocortis viroid (CEVd), the causal agent of exocortis, is a pathogen that is thought to infect all citrus varieties, although it is asymptomatic in most. Symptoms of exocortis develop on susceptible rootstocks, resulting in stunting and yield reduction. To aid the detection and management of CEVd, a rapid near-field assay was developed usin...

The mechanisms underlie increased stress tolerance in plants of salinity stress in plants by arbuscular mycorrhizal fungi (AMF) are poorly understood, particularly the role of polyamine metabolism. The current study was conducted to investigate how inoculation with the AMF, Funneliformis constrictum, affects maize plant tolerance to salt stress. To...

Citrus fruit are important crops in many regions of the world and are valuable sources of carbohydrates, fibre and health-promoting compounds. Like other crops, production of these fruits is affected by a range of pests and pathogens that can affect the sustainable development of citriculture. The most devastating of these is huanglongbing (HLB), a...

Citrus vein phloem degeneration (CVPD) is the Indonesian name for the Asian form of the devastating and incurable citrus disease known internationally as huánglóngbìng. It is associated with a phloem-limited pathogen, ‘Candidatus Liberibacter asiaticus’ (CLas) and transmitted by the Asiatic citrus psyllid (ACP), Diaphorina citri. ACP originated in...

Rice (Oryza sativa), a staple crop for a substantial part of the world’s population, is highly sensitive to soil salinity; however, some wild Oryza relatives can survive in highly saline environments. Sodium/hydrogen antiporter (NHX) family members contribute to Na+ homeostasis in plants and play a major role in conferring salinity tolerance. In th...

Gene editing using clustered regularly interspaced short palindromic repeat/CRISPR-associated proteins (CRISPR/Cas) has revolutionized biotechnology and provides genetic tools for medicine and life sciences. However, the application of this technology to miRNAs, with the function as negative gene regulators, has not been extensively reviewed in pla...

Photosynthesis in wheat (Triticum aestivum L.) pericarps may contribute appreciably to wheat grain yield. Consequently, we investigated the temporal variation of traits related to photosynthesis and sucrose metabolism in the pericarps and flag leaves of three wheat genotypes, Huandoy, Amurskaja 75 and Greece 25, which are reported to differ in expr...

Keeping the significance of potassium nutrition in focus, this study explores the genotypic responses of two wild Tibetan barley genotypes (drought tolerant XZ5 and drought sensitive XZ54) and one drought tolerant barley cv. Tadmor, under the exposure of polyethylene glycol-induced drought stress. The results revealed that drought and K deprivation...

Species of wild rice ( Oryza spp.) possess a wide range of stress tolerance traits that can be potentially utilized in breeding climate-resilient cultivated rice cultivars ( Oryza sativa ) thereby aiding global food security. In this study, we conducted a greenhouse trial to evaluate the salinity tolerance of six wild rice species, one cultivated r...

An apscaviroid, tentatively named citrus viroid VII (CVd-VII), was recently discovered in citrus in Australia. A diagnostic assay using real-time reverse transcription polymerase chain reaction was developed and validated to detect the viroid in citrus plants. The assay showed a high level of sensitivity, reliably detecting 2,000 plasmid copies per...

Citrus tristeza virus was detected for the first time in the Lao People’s Democratic Republic. Samples were collected from citrus trees across the southern provinces for testing in Australia. RNA was extracted and tested using conventional and real-time reverse transcription polymerase chain reactions with the virus detected in 12 of 59 samples tes...

The black curry leaf psyllid, Diaphorina communis, is a host of the citrus pathogen, ‘Candidatus Liberibacter asiaticus’ (‘CLas’). However, there is a paucity of information on its biology; hence, this study was conducted to evaluate survival and development on citrus, in this instance mandarin (Citrus reticulata) and curry leaf (Bergera koenigii),...

Heat stress is a major environmental threat affecting crop growth and productivity. However, the molecular mechanisms associated with plant responses to heat stress are poorly understood. Here, we identified a heat stress‐sensitive mutant, hts1, in rice. HTS1 encodes a thylakoid membrane‐localized β‐ketoacyl carrier protein reductase (KAR) involved...

Metalloids such as boron and silicon are key elements for plant growth and crop productivity. However, toxic metalloids such as arsenic are increasing in the environment due to inputs from natural sources and human activities. These hazardous metalloids can cause serious health risks to humans and animals if they enter the food chain. Plants have d...

The use of zinc oxide nanoparticles (ZnO NPs) is expected to increase soil fertility, crop productivity, and food quality. However, the potential effects of ZnO NP utilization should be deeply understood. This review highlights the behavior of ZnO NPs in soil and their interactions with the soil components. The review discusses the potential effect...

The Asian citrus psyllid, Diaphorina citri, is a major threat to citrus production worldwide, as it transmits ‘Candidatus Liberibacter asiaticus’, the pathogen associated with the devastating Asian form of huanglongbing. The psyllid has spread widely from its native South Asia during the past 300 years, most recently to Africa. We report the first...

Wild rice Oryza rufipogon, a progenitor of cultivated rice Oryza sativa L., possesses superior salinity tolerance and is a potential donor for breeding salinity tolerance traits in rice. However, a mechanistic basis of salinity tolerance in this donor species has not been established. Here, we examined salinity tolerance from the early vegetative s...

Citrus in Bhutan is cultivated on steep hillsides up to ~ 1550 m above sea level (ASL). Since 2000, the Asiatic form of huanglongbing caused by ‘Candidatus Liberibacter asiaticus’ (CLas) has led to dramatic losses of trees below 1200 m ASL. Surveys prior to this study indicated a low incidence of the disease and the psyllid Diaphorina citri (the pr...

‘Candidatus Liberibacter asiaticus’ (CLas) is an insect-transmitted, phloem-restricted α-proteobacterium associated with huanglongbing (HLB). Here, we provide the whole genome sequence of CLas strain, ReuSP1, from its insect vector Diaphorina citri (Hemiptera: Liviidae) collected in La Réunion. The genome is composed of 1,230,064 bp and has a 36.5%...

Citrus exocortis viroid, citrus bent leaf viroid, hop stunt viroid and citrus dwarfing viroid were detected for the first time in Lao PDR. Samples were collected from citrus trees across southern Lao PDR for laboratory testing in Australia. RNA was extracted and amplified using quantitative reverse transcription polymerase chain reaction (qRT-PCR);...

The draft genome sequence of a novel "Candidatus Liberibacter" species detected in an unidentified species of Zanthoxylum (Rutaceae) collected in Bhutan is reported. The total length is 1,408,989 bp with 1,169 coding sequences in 96 contigs, a GC content of 37.3%, and 76 to 77% average nucleotide identity with several other "Ca Liberibacter" specie...

Background: Several plant-pathogenic bacteria are transmitted by insect vector species that often also act as hosts. In this interface, these bacteria encounter plant endophytic, insect endosymbiotic and other microbes. Here, we used high throughput sequencing to examine the bacterial communities of five different psyllids associated with citrus a...

Salinity stress affects global food producing areas by limiting both crop growth and yield. Attempts to develop salinity-tolerant rice varieties have had limited success due to the complexity of the salinity tolerance trait, high variation in the stress response and a lack of available donors for candidate genes for cultivated rice. As a result, fi...

The false coconut scale, Aspidiotus rigidus Reyne (Hemiptera: Diaspididae), is a serious pest of coconut in the Indonesian and Philippine archipelagos. Field surveys in Viêt Nam in 2015–2018 discovered A. rigidus (a new country record). Also found were three of its primary hymenopteran parasitoids: an unidentified ectoparasitic Aphytis species (Aph...

A greenhouse hydroponic experiment was performed using salt-tolerant (cv. Suntop) and -sensitive (Sunmate) wheat cultivars and a salt-tolerant barley cv. CM72 to evaluate how cultivar and species differ in response to salinity stress. Results showed that wheat cv. Suntop performed high tolerance to salinity, being similar tolerance to salinity with...

Background: Orange jasmine has a complex nomenclatural history and is now known as Murraya paniculata (L.) Jack. Our interest in this common ornamental stemmed from the need to resolve its identity and the identities of closely related taxa as hosts of the pathogen 'Candidatus Liberibacter asiaticus' and its vector Diaphorina citri. Understanding...

Stomata are unique plant structures responsible for photosynthesis, transpiration and innate immunity to pathogens, and guard cells are one of the most studied cell types with respect to plant cell functioning, signalling, and stress responses. The ability to easily purify large quantities of high purity guard cell protoplasts (GCPs) would facilita...

Aims: Cadmium (Cd) is a toxic metal in soils and its accumulation in plants poses severe problems to agricultural production and human health. Most of research has focused on the Cd toxicity to plants, but reports on Cd co-transport and regulation by the major counter ion Chloride (Cl) is limited. This study aims to understand the mechanisms of the...

Soil microorganisms are essential to the functioning of soil ecosystems, and this study aimed to examine the effects of additions of carbon and nitrogen (N) to the soil on soil microflora, and whether these amendments could be used to both increase and reduce plant N concentrations in an orchard crop, thereby facilitating studies on the multitrophi...

Melaleuca deanei F.Muell. is a rare, serotinous shrub with a naturally restricted distribution centred over the sandstone ridges around Sydney. Sexual reproduction and seedling recruitment occur rarely, and plants appear to spread and persist largely by clonal root suckering. A potentially outcrossing breeding system, combined with extensive clonal...

Inductively coupled plasma-mass spectroscopic (ICP-MS) analysis of leaves from 22 cabbage crops in the Sa Pả and Bắc Hà districts of Láo Cai Province, North-Western Việt Nam, revealed unexpectedly high concentrations of chromium (Cr) and nickel (Ni). The concentrations were strongly linearly related (r² = 0.94), indicating sample contamination duri...

Elevated concentrations of carbon dioxide (e[CO2]) affect plant growth and physiological characteristics, including metal accumulation, and the activity of anti-oxidant enzymes. These effects were investigated in cadmium (Cd) tolerant wheat (Triticum aestivum L.) and sorghum (Sorghum bicolor (L.) Moench.) cultivars. Plants were grown at the ambient...

Aluminum (Al) toxicity and drought are two major constraints on plant growth in acidic soils, negatively affecting crop performance and yield. Genotypic differences in the effects of Al/low pH and polyethyleneglycol (PEG) induced drought stress, applied either individually or in combination, were studied in Tibetan wild (XZ5, drought-tolerant; XZ29...

Cadmium (Cd) in the soil solution is in dynamic equilibrium with the reservoir of bioavailable Cd attached to the solid phase, i.e. the labile pool (CdE). Traditionally, CdE is estimated using the radioisotope ¹⁰⁹Cd, which has severely restricted access to estimates of CdE. Using stable isotope dilution and isotope ratio measurement by inductive co...

The Australian sugarcane industry is facing a new threat of the currently undiagnosed Yellow Canopy Syndrome (YCS). Here, we investigated if YCS is linked to detrimental shifts in soil microbial function and/or altered physico-chemical soil properties. We examined changes in rhizosphere soil microbial assemblages, functional gene profiles and micro...

BACKGROUND Diaphorina citri is a vector of “Candidatus Liberibacter asiaticus” (CLas) associated with citrus Huanglongbing. In this study, the infection and titers of CLas in the psyllid, were monitored for life cycle stage, sex, host‐plant CLas titer, host‐plant genotype, and ambient temperature. RESULTS Acquisition efficiency of CLas by D. citri...