Phytophthora species were surveyed by collecting soil samples and placing bait leaves in selected streams during June-October in the years 2005, 2006 and 2010 at three sites in oak forests in Diqing Tibetan Autonomous Prefecture of NW Yunnan province, China. Seventy-three isolates of Phytophthora spp. were recovered from 135 baited leaf samples and 81 soil samples. Eight Phytophthora species were identified by observation of morphological features and ITS1-5.8S-ITS2 rDNA sequence analysis. The eight taxa included two well-known species P. gonapodyides and P. cryptogea, two recently described species P. gregata and P. plurivora, two named but as yet undescribed taxa, P. taxon PgChlamydo and P. taxon Salixsoil, and two previously unrecognized species, Phytophthora sp.1 and P. sp.2. The most numerous species, P. taxon PgChlamydo, and the second most abundant species, P. taxon Salixsoil, were recovered at all three sites. Phytophthora cryptogea was detected only once at site Nixi. Phytophthora gregata and P. sp.2 were isolated from a stream only at site Bitahai, while the other three species were each found at two sites. Phylogenetic analysis revealed that the isolates belonged to three ITS clades, one species including six isolates in clade 2, six species including 66 isolates in clade 6 and one species in clade 8. There was a relatively rich species and genetic diversity of Phytophthora detected in the investigated regions where the forest biotic and abiotic factors affecting the growth and evolution of Phytophthora populations were diverse.
The genetic variation and spatial distribution of the ectomycorrhizal fungus Tricholoma terreum was studied in an artificial Larix principis-rupprechtii stand in China. The 33 sporophores studied belonged to distinct genotypes, based on analysis of random amplified polymorphic DNA (RAPD) markers. The genets of T. terreum were small and no larger than 0.5 m. Two major phenetic groups, i.e. eight individuals in group 1 and 25 in group 2, were identified by principal component analysis and the unweighted pair group method with arithmetic means of simple matching coefficients, respectively. The genetic diversity as determined by the Shannon-Weaver diversity index was 4.52 for these 33 sporophores. Furthermore, there was a slightly lower diversity index in group 1 (4.28) than in group 2 (4.46). It is suggested that sexual spore propagation is very important in the life history of T. terreum in this larch forest.
Obolodiplosis robiniae is native to North America and is an important introduced insect pest that forms leaf margin roll galls on species of genus Robinia (Fabaceae) in China. It was first detected in China in 2004, but subsequently spread and provoked local outbreaks. An analysis of a 676-bp sequence of the mitochondrial DNA cytochrome oxidase subunit I was conducted in 560 individuals from 28 populations, in order to (1) assess population genetic structuring and (2) explore possible explanations for the rapid spread and invasion success of O. robiniae. Yet, only four haplotypes were identified and the nucleotide diversity was low (π = 0.00005) and among the 560 specimens studied, only ten showed haplotypic variation involving no more than three substitutions. The result showed a low degree of genetic diversity among populations of the successful invasive gall midge, which suggested that the pest experienced a severe genetic bottleneck and a loss of genetic diversity after its introduction. The successful establishment and spread of O. robiniae in China is attributed to the wide distribution of its host plant, thus allowing ample opportunities for gene flow in the pest species, and to the advantageous life history characteristics of O. robiniae.
Wild apple forests in the Tian Shan Mountains in north‐western China have been adversely affected by an unknown disease in recent years. Symptoms attributed to this disease that affects wild apple trees include xylem browning and dieback which are suggestive of infection by Fusarium species. Therefore, the research team conducted the first survey for Fusarium in the afflicted wild apple forests. Twig samples with symptoms of xylem browning and dieback were collected in the Xinyuan, Gongliu, Yining and Huocheng Counties of Xinjiang Uighur Autonomous Region in China. Based on phylogenetic analyses and morphological observation, sixty strains of Fusarium accounted for 48% of the total number of fungi isolated from samples were subsequently classified into six species including twenty‐four F. avenaceum, seventeen F. solani, ten F. tricinctum, five F. proliferatum, two F. sporotrichioides and two unfamiliar Fusarium sp. 1. The five previously known species of Fusarium were then tested for pathogenicity to leaves and twigs in vitro. The results indicated that all of the species, except for F. tricinctum, can cause obvious lesions on the leaves of host plants and on the twigs of Fuji and wild apple. This is the first report of Fusarium species pathogenicity in Xinjiang wild apple forests, confirming a new host for these pathogens in this study.
Phytophthora species are well-known destructive forest pathogens, especially in natural ecosystems. The wild apple (Malus sieversii (Ledeb.) Roem.) is the primary ancestor of M. domestica (Borkh.) and important germplasm resource for apple breeding and improvement. During the period from 2016 to 2018, a survey of Phytophthora diversity was performed at four wild apple forest plots (Xin Yuan (XY), Ba Lian (BL), Ku Erdening (KE), and Jin Qikesai (JQ)) on the northern slopes of Tianshan Mountain in Xinjiang, China. Phytophthora species were isolated from baiting leaves from stream, canopy drip, and soil samples and were identified based on morphological observations and the rDNA internal transcribed spacer (ITS) sequence analysis. This is the first comprehensive study from Xinjiang to examine the Phytophthora communities in wild apple forests The 621 resulting Phytophthora isolates were found to reside in 10 different Phytophthora species: eight known species (P. lacustris being the most frequent, followed by P. gonapodyides, P. plurivora, P. gregata, P. chlamydospora, P. inundata, P. virginiana, and P. cactorum) and two previously unrecognized species (P. sp. CYP74 and P. sp. forestsoil-like). The highest species richness of Phytophthora occurred at BL, followed by XY. P. lacustris was the dominant species at BL, XY, and JQ, while P. gonapodyides was the most common at KE. In the present paper, the possible reasons for their distribution, associated implications, and associated diseases are discussed.
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