Variability in phosphite sensitivity observed within and between seven Phytophthora species

Phosphite is used to control and manage many phytophthora diseases in horticultural systems worldwide and natural ecosystems in Australia, Africa, New Zealand and parts of Northern America and Europe. Phosphite does not kill Phytophthora species, but inhibits growth while also stimulating host defence responses. Phytophthora species differ in their underlying tolerance to phosphite and isolates have been shown to acquire tolerance after prolonged exposure. Intra- and inter-specific variability in phosphite sensitivity is of interest to determine the efficacy and sustainability of phosphite for the treatment of phytophthora diseases, which continue to spread globally. Seven Phytophthora species were tested for their sensitivity to phosphite in vitro in a mycelial growth experiment. Phytophthora agathidicida was the species most sensitive to phosphite, being inhibited by 98.7% on average at the lowest phosphite treatment (15 µg/mL phosphite), followed by P. aleatoria, P. cinnamomi, P. pluvialis, P. multivora, P. kernoviae and P. citricola. Huge intraspecific variability was observed with P. kernoviae, which raises the question of whether diseases caused by P. kernoviae such as phytophthora needle blight of Pinus radiata could be managed effectively with phosphite. Further work is required to determine the phosphite sensitivity of different introduced and native Phytophthora species growing in key hosts and whether tolerance observed in vitro is also expressed in vivo.

Weather Variables Associated with Spore Dispersal of Lecanosticta acicola Causing Pine Needle Blight in Northern Spain

In the last decade, the impact of needle blight fungal pathogens on the health status of forests in northern Spain has marked a turning point in forest production systems based on Pinus radiata species. Dothistroma needle blight caused by Dothistroma septosporum and D. pini, and brown spot needle blight caused by Lecanosticta acicola, coexist in these ecosystems. There is a clear dominance of L. acicola with respect to the other two pathogens and evidence of sexual reproduction in the area. Understanding L. acicola spore dispersal dynamics within climatic determinants is necessary to establish more efficient management strategies to increase the sustainability of forest ecosystems. In this study, spore counts of 15 spore traps placed in Pinus ecosystems were recorded in 2019 and spore abundance dependency on weather data was analysed using generalised additive models. During the collection period, the model that best fit the number of trapped spores included the daily maximum temperature and daily cumulative precipitation, which was associated to higher spore counts. The presence of conidia was detected from January and maximum peaks of spore dispersal were generally observed from September to November.

First Report of Diplodia mutila on Blue Pine (Pinus wallichiana) in Kashmir Valley, India

Blue pine (Pinus wallichiana) is prone to a number of diseases amongst which needle blight caused by Diplodia mutilaposes a serious threat to its regeneration in Kashmir valley. The disease initiated in the month of March as minute chlorotic spots on current year needles.

Molecular-Based Reappraisal of a Historical Record of Dothistroma Needle Blight in the Centre of the Mediterranean Region

In this work, we rechecked, using species-specific Loop mediated isothermal AMPlification (LAMP) diagnostic assays followed by sequencing of fungal isolates at the beta-2-tubulin (tub2) gene region, a historical and never confirmed report of Dothistroma needle blight (DNB) in the introduced Monterey pine (Pinus radiata D. Don) in the mountains in the extreme tip of southern Italy. The report dates back to the mid-1970s, and predates the molecular-based taxonomic revision of the genus Dothistroma that defined the species accepted today. In the fall of 2019, symptomatic needles of Monterey pine and Corsican pine (Pinus nigra subsp. laricio (Poir.) Palib. ex Maire) were sampled in the area of the first finding. The applied diagnostic methods revealed the presence of Dothistroma septosporum (Dorogin) M. Morelet on both pine species. In this way, we: (i) confirmed the presence of the disease; (ii) clarified the taxonomic identity of the causal agent now occurring at that site; (iii) validated the species-specific LAMP diagnostic protocol we recently developed for Dothistroma for use on a portable field instrument, and (iv) showed that the pathogen now also attacks the native P. nigra subsp. laricio, a species particularly susceptible to the disease, indigenous to the mountains of Calabria, which is one of the very few areas where the species’ genetic resources are conserved. Comparative genetic analysis of the rare populations of D. septosporum found in the central Mediterranean region and in the native range of P. nigra subsp. laricio could help to clarify the history of the spread of the pathogen in southern Europe and better evaluate the risk it poses to the conservation of native pine species.

First report of Mycosphaerella dearnessii Rostrup, teleomorph of Lecanosticta acicola (Thüm.) Syd., in Europe

Conifers severely affected by brown needle blight disease caused by the ascomycete Lecanosticta acicola (Thüm.) Syd. show defoliation, reduced growth and death. Although L. acicola is known in Europe since 1942, its teleomorph, Mycosphaerella dearnessii Rostrup, has not yet been found. In this brief, we address the occurrence of Mycosphaerella dearnessii in Pinus radiata D. Don cast dead needles collected in the north of Spain (Basque country). To our knowledge, this is the first report of Mycosphaerella dearnessii Rostrup, teleomorph of Lecanosticta acicola (Thüm.) Syd., in Europe.

First Report of Brown Spot Needle Blight on Pinus thunbergii Parl. Caused by Aureobasidium pullulans in China

Pinus thunbergii Parl., known as black pine, is widely distributed all over China. This pine variety can prevent soil desertification and promote soil conservation and is excellent for constructing fast-growing forests and shelter belts. The timber of this species can be used for infrastructure construction and furniture production. In August 2020, needle blight symptoms were found on several trees of black pine in Sichuan Province, China. Further surveys showed that these symptoms are common while the disease incidence is less than 30% which indicated the severity of the disease is mild. The tips of old needles first turn grayish green and developed into brown bands ranging from 1 to 2 mm. To determine the pathogen, 20 needle samples with typical symptoms were disinfected with 75% alcohol, and sections of the tissue were cut from joints of diseased and healthy tissues (visually healthy) with a sterilized scalpel, surface sterilized for 45 seconds in 75% alcohol, soaked for 90 seconds in 1.5% NaCIO, rinsed in sterilized water and dried. Small cut tissues were placed on potato dextrose agar (PDA) at 25℃ for 10 days. Pure cultures were obtained by monosporic isolation. The colonies initially appeared white to cream, yeast-like, and later turned to pink and remained at least 10 days. Conidia were hyaline, smooth-walled, single-celled, and ellipsoidal with variable shape and size, 7.5 to 16 × 3.5 to 7 µm (Zalar et al. 2008). DNA was extracted from the mycelium of the isolate by the cetyltriethylammonium bromide (CTAB) method and amplified through polymerase chain reaction (PCR) with the internal transcribed spacer (ITS) region of rDNA and partial β-tubulin genes of a representative isolate (SC05) were amplified using the ITS1/ITS4 and Bt2a/Bt2b primer pairs, respectively(Wu et al. 2017). The sequences submitted to GenBank (Accession Nos. MW228368 for ITS and MW256762 for β-tubulin) showed high similarity with BLAST sequences of Aureobasidium pullulans (ITS, KR704881 [100%]; β-tubulin, MT671934 [99.49%]). For the pathogenicity test, a conidial suspension was prepared with a concentration of 2.0 × 107 conidia/ml. The suspension was sprayed onto 3 annual seedlings’ needles, and the control was sprayed with sterile water. Inoculated and non-inoculated plants were kept in humid chambers in a glasshouse. After 10 days, typical symptoms appeared on inoculated needles, whereas control needles remained symptomless. The fungus, A. pullulans, was reisolated from those lesions, confirming Koch's postulates. No symptoms were observed on control plants. Aureobasidium pullulans, a ubiquitous saprophytic fungus on many fruits and very rarely reported to cause disease on pine needles. Only reported invasion of Ozone‐injured needles in P. strobus (Costonis and Sinclair 1972) and needles damaged by acid rain in P. sylvestris (Ranta 1990). To our knowledge, this is the first report of brown spot needle blight on P. thunbergii caused by A. pullulans in China. The disease represents a threat to pine manufactures and more research on the pathogenesis and management is needed.

Mycosphaerella gibsonii (needle blight of pine).

Mycosphaerella gibsonii is a fungal pathogen causing needle blight, primarily in Pinus species. It causes lesions on needles, first affecting lower needles and then spreading to the upper crown. The disease eventually causes needle necrosis and needle cast, leading to defoliation, stunted growth and host plant death; it is a major obstacle to the production of pine seedlings. M. gibsonii occurs in the tropics and subtropics of South and Central America, the Caribbean, sub-saharan Africa, India, South East Asia and East Asia; the native range is uncertain. Although natural dispersal by wind and water occur locally, international spread is largely due to movement of infected nursery stock. Phytosanitary control measures such as avoiding the planting of infected plants, removal and destruction of all infected pines in nurseries and cleaning between annual production cycles in nurseries can help to reduce the spread of the pathogen. It is listed as an A1 quarantine pest in the EPPO region, and is considered of quarantine significance in South America.

Mycosphaerella gibsonii (needle blight of pine).

Mycosphaerella gibsonii is a fungal pathogen causing needle blight, primarily in Pinus species. It causes lesions on needles, first affecting lower needles and then spreading to the upper crown. The disease eventually causes needle necrosis and needle cast, leading to defoliation, stunted growth and host plant death; it is a major obstacle to the production of pine seedlings. M. gibsonii occurs in the tropics and subtropics of South and Central America, the Caribbean, sub-saharan Africa, India, South East Asia and East Asia; the native range is uncertain. Although natural dispersal by wind and water occur locally, international spread is largely due to movement of infected nursery stock. Phytosanitary control measures such as avoiding the planting of infected plants, removal and destruction of all infected pines in nurseries and cleaning between annual production cycles in nurseries can help to reduce the spread of the pathogen. It is listed as an A1 quarantine pest in the EPPO region, and is considered of quarantine significance in South America.