Intraspecific variation in susceptibility to dothistroma needle blight within native Scottish Pinus sylvestris

Dothistroma needle blight (DNB), caused by Dothistroma septosporum, is the most important disease currently affecting pine plantations in Britain. Intraspecific variation in susceptibility to DNB has been observed in several pine species, but it is not clear if similar variation occurs in Pinus sylvestris (Scots pine), Britain's only native pine. In three separate experiments 2‐ and 3‐year‐old Scots pine saplings from six native Scottish populations were artificially inoculated with D. septosporum conidial suspensions and incubated under conditions optimal for disease development. Conidial suspensions were produced using a single isolate from northeast Scotland. In one experiment, plants were also treated with various spore suspension concentrations to assess the impact of inoculum load on disease severity. There were no significant interactions between host population, plant height, and experiment/inoculum load (anova , P > 0·05), but population, height and inoculum load all significantly affected disease severity (anova , P < 0·05). Among the 2‐year‐old trees, those from Amat were less susceptible than those from Glen Loyne and Glen Cannich (anova , P < 0·05). Among the 3‐year‐old trees, those from Beinn Eighe were less susceptible than those from Abernethy. Plant height and DNB susceptibility had a slightly negative relationship. The use of a spore suspension with a concentration of 1·6 × 10⁶ spores mL^?1 was optimum for disease development. In an in vitro experiment, production of conidia was greater when cultures were incubated in darkness. This paper is the first to report intraspecific variation in DNB susceptibility within Scots pine.     

Between‐site and ‐year variation in the relative susceptibility of native Scottish Pinus sylvestris populations to dothistroma needle blight

Dothistroma needle blight (DNB), caused by Dothistroma septosporum, is currently the disease causing most concern in British pine plantations. Previous artificial inoculation (AI) experiments showed that native Scottish Scots pine (Pinus sylvestris) populations vary in susceptibility to DNB. However, it is unclear if the relative susceptibility of Scots pine populations observed in these experiments can be replicated under natural conditions. It is also unknown whether relative susceptibility of Scots pine populations varies between sites or years. To answer these two questions, young Scots pine plants from six native Scottish populations (Abernethy, Allt Broighleachan, Amat, Beinn Eighe, Glen Cannich and Glen Loyne) were exposed to natural D. septosporum inoculum at two Scottish sites (Culbin and Torrs Warren) between 2012 and 2014. DNB disease incidence and severity was assessed each October. Relative susceptibilities of the Scots pine populations varied between sites and across years. In two of the three years at Torrs Warren (2012 and 2014), the relative susceptibilities of the populations were strongly positively correlated with those observed in previous AI experiments. In these years, trees from Glen Loyne and Glen Cannich were the most susceptible. Conversely, there was no correlation between the relative susceptibilities seen in any year at Culbin with those observed in AI experiments. At Culbin, Beinn Eighe was the most susceptible population. Across both sites, there was a strong positive relationship between total summer precipitation and DNB severity (R = 0·93, t = 8·2, P = 0·001).     

SSR assessment of Phytophthora infestans populations on tomato and potato in British gardens demonstrates high diversity but no evidence for host specialization

Phytophthora infestans populations can differ in composition as a result of host specialization on tomato and potato hosts. In Great Britain many amateur gardeners grow outdoor tomatoes but there is little or no commercial tomato production outdoors. This study analysed isolates of P. infestans from British gardens with 12 multiplexed simple sequence repeat markers that are used to monitor the disease on commercial potato crops. Samples of P. infestans from tomato hosts were collected in 3 years and from potato in 1 year from across Great Britain. Seven previously unreported clonal lineages were detected in garden populations and higher frequencies of unique clonal lineages (28–40%) were present compared with populations from British commercial potato crops reported elsewhere. Garden populations had a lower proportion (11–48% less) of the most common lineages (13_A2 and 6_A1) that together made up at least 86% of the commercial potato populations during the sampling period. Host species accounted for only 2·0% of molecular variance detected between garden potato‐ and tomato‐hosted samples. No significant difference in clonal lineage composition was found between host species in Great Britain and this could be due to the whole P. infestans population overwintering on potato. British garden populations on both hosts were much more diverse than those on commercial potato crops; this finding may be influenced by less frequent fungicide use by gardeners and a higher diversity of unsprayed susceptible potato cultivars, enabling metalaxyl‐sensitive and less aggressive genotypes to survive in gardens.     

Susceptibility evaluation of Picea abies and Cupressus lusitanica to the pine wood nematode (Bursaphelenchus xylophilus)

Pine wilt disease (PWD), recently introduced into Europe, is caused by the pine wood nematode (PWN) Bursaphelenchus xylophilus and is a devastating illness that affects mainly pine trees. It is known that the PWN is capable of infecting other conifers; however, there is currently no information on which other plant species may be susceptible to PWD. In this study, the potential susceptibility of two common species of European forests, Picea abies and Cupressus lusitanica, to PWN was assessed through the monitoring of visual external symptoms, dimension and localization of the nematode population in stems, quantification of total chlorophyll, total soluble phenolics and lignin, at 7, 14, 21 and 28 days after inoculation. The degree of susceptibility was established through the comparison of symptoms with Pinus pinaster, a well‐known PWN host. Furthermore, the stem ultrastructure of P. abies, C. lusitanica and Pn. pinaster was analysed by scanning electron microscopy. The results suggest that P. abies and C. lusitanica are resistant to PWN, and that lignin biosynthesis in these species is affected at an early stage of the infestation. Nevertheless, P. abies seems to be a compatible host that could act as a repository for PWN.     

Annual and herbaceous perennial native Australian plant species are symptomless hosts of Phytophthora cinnamomi in the Eucalyptus marginata (jarrah) forest of Western Australia

Resistant annual and herbaceous perennial plant species were identified as key hosts which allow Phytophthora cinnamomi to persist on severely impacted black gravel sites within the Eucalyptus marginata (jarrah) forest of southwest Western Australia. Of the annual and herbaceous perennial plant species present on black gravel sites, 15 out of 19 species were found to be hosts of P. cinnamomi, and 10 of these were symptomless hosts. In particular, the native annual Trachymene pilosa and the two native herbaceous perennials Stylidium diuroides and Chamaescilla corymbosa were commonly found to be hosts of the pathogen. Species from 12 new genera including three from new families (Crassulaceae, Droseraceae and Primulaceae) are reported for the first time to be hosts of P. cinnamomi. The species from which P. cinnamomi was recovered were the native species: Chamaescilla corymbosa, Crassula closiana, Drosera erythrorhiza, Hydrocotyle callicarpa, Levenhookia pusilla, Paracaleana nigrita, Podotheca angustifolia, Pterochaeta paniculata, Rytidosperma caespitosum, Siloxerus multiflorus, Stylidium diuroides and Trachymene pilosa, and the introduced annual weeds Hypochaeris glabra, Lysimachia arvensis and Pentameris airoides.     

Screening of rice (Oryza sativa) cultivars for resistance to rice black streaked dwarf virus using quantitative PCR and visual disease assessment

Rice black streaked dwarf virus (RBSDV) causing rice black streaked dwarf disease is transmitted by the small brown planthopper (SBPH, Laodelphax striatellus) in a persistent propagative manner. The disease is considered among the most destructive in rice production in east and southeast Asia. For sustainable control of the disease, planting resistant cultivars is the most economical and efficient method. The virus content in different rice cultivars was quantified using a TaqMan RT‐qPCR assay under greenhouse conditions and the disease was visually assessed in these cultivars in both greenhouse and field conditions. Results revealed significant positive moderate correlation (r = 0.3787; P = 0.0009) between the virus content and visual disease assessment in the greenhouse under forced inoculation. Among 66 rice cultivars, there was no significant difference in RBSDV genome equivalent copies (GEC) in seven cultivars, namely Lian‐dao 9805 (200.2 ± 12), Liangyou 3399 (206.6 ± 28), Ningjing 4 (206.6 ± 28), DaLiang 207 (302.0 ± 61), X 008 (354.0 ± 30), Shengdao 301 (658.4 ± 69) and Liangyou 1129 (679.5 ± 98). These cultivars were also visually assessed as resistant under greenhouse and field conditions. These cultivars could be used in disease management to reduce the likelihood of epidemics.