Effect of simulated acid rain on quantity of epiphytic microfungi on Scots pine (Pinus sylvestris L.) needles

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.  .

Genome sequencing of four Aureobasidium pullulans varieties: biotechnological potential, stress tolerance, and description of new species

BACKGROUND

Aureobasidium pullulans is a black-yeast-like fungus used for production of the polysaccharide pullulan and the antimycotic aureobasidin A, and as a biocontrol agent in agriculture. It can cause opportunistic human infections, and it inhabits various extreme environments. To promote the understanding of these traits, we performed de-novo genome sequencing of the four varieties of A. pullulans.

RESULTS

The 25.43-29.62 Mb genomes of these four varieties of A. pullulans encode between 10266 and 11866 predicted proteins. Their genomes encode most of the enzyme families involved in degradation of plant material and many sugar transporters, and they have genes possibly associated with degradation of plastic and aromatic compounds. Proteins believed to be involved in the synthesis of pullulan and siderophores, but not of aureobasidin A, are predicted. Putative stress-tolerance genes include several aquaporins and aquaglyceroporins, large numbers of alkali-metal cation transporters, genes for the synthesis of compatible solutes and melanin, all of the components of the high-osmolarity glycerol pathway, and bacteriorhodopsin-like proteins. All of these genomes contain a homothallic mating-type locus.

CONCLUSIONS

The differences between these four varieties of A. pullulans are large enough to justify their redefinition as separate species: A. pullulans, A. melanogenum, A. subglaciale and A. namibiae. The redundancy observed in several gene families can be linked to the nutritional versatility of these species and their particular stress tolerance. The availability of the genome sequences of the four Aureobasidium species should improve their biotechnological exploitation and promote our understanding of their stress-tolerance mechanisms, diverse lifestyles, and pathogenic potential.

Decline in diversity and abundance of endophytic fungi in twigs of Fagus sylvatica L. after experimental long-term exposure to sodium dodecylbenzene sulphonate (SDBS) aerosol

Sodium dodecylbenzene sulphonate (SDBS) is an anionic synthetic detergent found in polluted sea aerosol and is known for its harmful effects on leaf surface ultrastructure on conifers and broadleaved trees. Four-year-old saplings of European beech were sprayed weekly for three consecutive growing seasons with either a 50 mg l(-1) solution of SDBS in deionized water or with pure deionized water (control). Two- to three- year-old twigs were collected from SDBS-treated and control plants during the growing season one year after the last treatment to isolate endophytic fungi. The frequency of colonization by endophytic fungi was significantly lower on SDBS-treated plants (63.8%) than on control plants (85.4%). Multiple colonization of twigs occurred more frequently and diversity of endophyte species was higher in control plants than in SDBS-treated plants. Thirty-six fungal species were isolated from 360 twigs. Cladosporium cladosporioides, Coryneum compactum, Phialocephala dimorphospora, and a species each of Mycosphaerella and Phomopsis were the most abundant endophytes with frequencies of colonization of more than 5%. The abundance of the Phomopsis species proved to be significantly reduced by the SDBS treatment. Within the limits of the indoor experimental conditions, the obtained results suggest that long-term exposure of aerial parts of beech to SDBS can affect the amount and composition of endophytic fungal communities of lignified twigs. Degradation of the leaf epicuticular wax layer and changes of the assimilation capacity and leaf water content (transpiration) of the crowns are presumed to be responsible for the reduction of endophytic fungi detected in twigs of SDBS-treated plants.

The host-pathogen system of Gremmeniella abietina (Lagerb.) Morelet and Scots pine; effects of non-pathogenic phyllosphere fungi, acid rain and environmental factors

Scots pine seedlings (1-yr-old) were inoculated either once, or three times, with the conidia of two saprophytic Honmmema species. After these inoculations, the seedlings were inoculated later with conidia of the pathogenic fungus Gremmeniella abietina (Lagerb.) Morelet. Seedlings received irrigation with simulated acid rain at pH 3, with water of pH 6. or no irrigation, during and after the inoculation treatments, The severity of the symptoms caused by G. abietina, and rhe isolation frequency of endophytic (symptomless) G. abietina and the saprophytes, were measured 11 months after G. abietina inoculation. The isolation frequencies of the two Hormunema species increased significantly in the seedlings inoculated three times with saprophyte conidia. Irrigation treatments did not affect the saprophytes. The disease symptoms caused by G, abietina were positively correlated with tree density. Symptomless G, abietina was isolated most often from the seedlings that had received irrigation at pH b. The isolation frequency was lowest in seedlings with acidic irrigation. The seedlings inoculated three times with conidia of Hormonema sp. 1 had a lower frequency of G. abietina isolations than other seedlings, but the difference was not statistically significant.

Conidiogenesis, nutritional physiology and taxonomy of Aureobasidium and Hormonema

Diagnostic criteria for the distinction of the slightly osmophilic species, Aureobasidium pullulans, and the opportunistic pathogen on conifers, Hormonema dematiodies, are provided. Reliable identification requires a combination of characters of conidiogenesis, expansion growth and assimilative abilities. Relationships with species of Kabatiella, and with the teleomorph genera Pringsheimia, Dothidea and Dothiora, all having Dothiora, all having Hormonemia-like cultural states, are discussed. An identification key is provided.

Effects of larval age and prolonged simulated acid rain on the susceptibility of European pine sawfly to virus infection

We studied the effect of simulated acid rain treatment of host trees on the susceptibility of the European pine sawfly larvae to virus, and possible differences when larvae of two different ages were infected. Older larvae were less susceptible to virus. Most larvae treated with virus 2 days after they started feeding on experimental foliage (group A) died rapidly within 10 days after the virus treatment, and survival to the end of the larval period was only 8-25%. Larvae treated with virus 1 week later (group B) were less affected by the virus and 36-49% survived. In group A the larval survival in the pH 3 treatment was higher than in other treatments; at the end of the larval period the difference was twofold. In group B there were no clear effects of acid rain on the susceptibility of larvae to virus. The study yielded the following new information: (1) the effect of prolonged acid rain treatment on reducing the efficacy of virus on young larvae was more distinct than in a previous study with shorter exposure to acid rain, and the difference was maintained to the end of larval period; (2) the susceptibility of older larvae to virus was not affected by acid rain treatments; (3) pH inside the needles did not explain the larval mortality caused by virus.