Biodiversity And Population Dynamics Of Plant Parasitic Nematodes Associated With Pinaceae Plants

The tree species in family Pinaceae are important sources for Chinese forest ecosystem and dominant in the forestry produce. Pinus species plays important role in timber industry, landscape, environmental protection and soil persistence. Cedrus deodara is a special ornamental tree and regarded as the city tree of Nanjing, China. Plant parasitic nematodes (PPN) as a whole causes losses up to US 80$ billion every year. Among them,Bursaphelenchus xylophilus is regarded as one of the most damaging nematode and has become a serious threat for pine forestation. In 1982, it was first reported from Purple mountain of Nanjing. Thus a systematic research was carried out to identify the possible nematode biodiversity, population dynamics and their relationships with soil properties on three Pinus species and C. deodara.The rhizospheric soil samples of Pinus trees and C. deodara from Purple Mountain area in Nanjing were collected. The nematodes were extracted using Baermann funnel technique and the species were identified by the morphological and molecular characterization. The nematode species intercepted from Pinus wood materials imported at Ningbo Port were also studied. Twenty two nematode species from seven families were identified, including six species from family Hoplolaimidae, Helicotylenchus dihystera,Scutellonema brachyurus, Rotylenchulus reniformis and three unknown species of Rotylenchus; five species from family Criconematidae, Hemicriconemoides californianus,H. chitwoodi, H. kanayaensis, Xenocriconemella macrodora and one unknown Criconema sp.; two species from family Tylenchulidae, Paratylenchus nanjingensis and P.shenzhenensis; five species from family Aphelenchoididae, Bursaphelenchus parantoniae n. sp., B. saudi n. sp., B. hylobianum, B. parapinasteri and one unknown Aphelenchoides sp.; two unknown Xiphinema spp. from family Longidoridae; one unknown Ditylenchus sp.from family Anguinidae and one unknown Deladenus sp. from Family Neotylenchidae.The molecular characterization of 22 nematodes species yielded 21 sequences for 28S D2-D3 region of rDNA, 10 and 11 sequences for 18S and ITS 1/2 regions respectively. The phylogenetic trees based on 28S D2-D3, 18S and ITS sequences were constructed using Neighbor-joining method with the sequences amplified during present study and the related sequences obtained from GenBank. All the identified species clusters with the known species or the related species in a distinct clade, which also strongly support our morphological identification.The nematode population dynamics during March 2015 to Feburary 2016 were studied on Pinus and Cedrus tree species located at Purple Mountain area. Helicolenchus,Scutellonema, Paratylenchus, Xenocriconemella and Xiphinema were common genera associated with P. massoniana, P. taeda, P. thunbergii and C. deodara. During the year two population peaks were observed,one in spring and another in late autumn whereas in winter season a stable population trend was noticed. The results also showed that higher number of nematodes were associated with P. thunbergii while lower with C. deodara. This concluded that nematode population densities were regulated by seasonal fluctuations and above ground vegetation cover.The composite results of nematode community indices from all the tree species revealed that Shanon index (H’) was higher in P. massoniana and lower in P. thunbergii,plant parasitic index (PPI) was higher in C. deodara and lower in P. massoniana, nematode channel ratio (NCR) was higher in C.deodara and lower in P.thunbergii,species evenness(J’) was more or less similar in all tree species but lower in P. thunbergii, trophic diversity(TD) was higher in P. massoniana and lower in P. thunbergii. In all four trees P.massoniana had healthier soil as indicated by high H’ and TD while C. deodara soil had good ability to conduct decomposition processes indicated by high NCR.A seasonal correlation between soil physiochemical properties and nematode trophic groups were studies. The results showed that in all four seasons, PPN, fungivores (Fu) and bacterivores (Ba) were negatively while predatory (Pr) and omnivores (Om) were positively correlated with soil pH and moisture contents. PPN and Fu were positively co-related with total nitrogen and organic matter. Low concentration of both minerals caused negative co-relation with Pr and Ba whereas higher concentration caused positive co-relation with Om nematodes. Total phosphorus was negatively co-related with PPN and Fu, while it was positively correlated with Pr, Om and Ba in all seasons.The available phosphorus was negatively co-related with PPN, Fu and Om and positively with Ba and Pr in all seasons. Total and available potassium were negatively co-related with PPN and Fu whereas positively co-related with Pr and Om in all seasons. Total potassium was negatively co-related with Ba in spring and summer while it was positively co-related in autumn and winter seasons. Available potassium was positively co-related with Ba in all seasons. This suggested that soil physiochemical properties have sound effect on the trophic groups of nematodes in the natural conditions.