Vertical distribution of plant nematodes in an aquic brown soil under different land uses

The vertical distribution of the dominant genera of plant nematodes at the depth of 0–150 cm of an aquic brown soil were studied for four land use patterns, i.e., paddy field, maize field, fallow field and woodland in the Shenyang Experimental Station of Ecology, Chi- nese Academy of Sciences in November of 2003. The results showed that the numbers of some dominant genera under different land uses decreased with the increase of soil depth. Helicotylenchus was most dominant genus under each land use type. Genera of Filenchus, Psilen- chus and Tylenchus in paddy field occurred at the depth of 0–20 cm; while Paratylenchus in fallow field and woodland, as well as Praty- lenchus in maize field presented in the deeper soil layers (0–80 cm). Significant correlations between the numbers of dominant genera of plant nematodes and soil chemical properties were found in this study. The number of Helicotylenchus under different land uses was posi- tively correlated with C/N ratio, total C, total N, total P, alkai-N, and Olsen-P. The numbers of Filenchus and Paratylenchus in paddy field, Pratylenchus in maize field and Paratylenchus in fallow field were negatively correlated with soil pH, and positively correlated with total C, total N and alkai-N. This study results showed that it is essential to sample at a certain depth according to the vertical distribution informa- tion of different genera of plant nematodes in adequately assessing the population size of plant nematodes.

Viral pathogens and plant parasitic nematode

This special focus is dedicated to three parts：i）One of the most ubiquitous viral pathogens of stone fruit tree,Plum pox virus（PPV）;ii）a re-emerging pathogen,Wheat streak mosaic virus（WSMV）of cereal crops in Central Europe;and iii）a less studied plant parasitic,cyst-forming nematode in cereal crops Heterodera avenae.

The Use of RNA Interference in Enhancing Plant Resistance against Nematodes

Plant-parasitic nematodes caused severe yield loss in major crops all over the world.The most wild-used strategies to combat the nematodes is the chamical nematicides,but the overuse of synthetic nematicides threaten sustainable agriculture development.Other strategies,like resistance cultivars and crop rotation,have limited efficiency.Thus,the utilization of molecular biotechnology like RNA interference(RNAi)would be one of the alternative ways to enhance plant resistance against nematodes.RNAi has already used as a tool for gene functional analysis in a wide range of species,especially in the non-parasitic nematode,Caenorhabtidis elegans.In plant-parasitic nematodes,RNAi is induced by soaking nematodes with double strand RNA(dsRNA)solution mixed with neurostimulants,which is called in vitro RNAi delivery method.In another way around,in planta RNAi method,which is Host-mediated RNAi approach also showed a great success in conferring the resistance against root-knock nematodes.Two main advantages of RNAi-based transgenics are RNAi technology do not produce any functional foreign proteins and it target organisms in a sequence-specific way.Even though the development of RNAi-based transgenics against plant-parasitic nematodes is still in the initial phase,it offers the prospect into a novel nematode control strategy in the future.

Mechanistic insights toward identification and interaction of plant parasitic nematodes:A review

Nematode identification serves as an important param-eter to study their behaviour,importance and pathogenic-ity.Application of classical morphometric based identifica-tion methods prove to be lacking due to insufficient knowledge on morphological variations among closely related taxa.Molecular approaches such as DNA and protein-based information,microarray,probing,sequence-based methods and others have been used to supplement morphology-based methods for nematode identification.Ascarosides and certain protein-based nematode-associated molecular patterns(NAMPs),can be perceived by the host plants,and can initiate a signalling cascade.This review primarily emphasizes on an updated account of different classical and modern tools used for the identification of nematodes.Besides we also summa-rize the mechanism of some important signalling pathways which are involved in the different plant nematode interactions.Nematodes constitute most diverse and least studied group of soil inhabiting invertebrates.They are ecologically and physiologically important,however,wide range of nematodes show harmful impact on the individuals that live within their vicinity.Plant parasitic nematodes(PPNs)are transparent,pseudocoelomate,free living or parasitic microorganisms.PPNs lack morphometric identification methods due to insufficient knowl-edge on morphological variations among closely related taxa.As such,molecular approaches such as DNA and protein-based information,microarray,probing,sequence-based methods and others have been used to supplement morphology-based methods for their identification.To invade the defense response of different plant species,parasitic nematodes have evolved different molecular strategies.Ascarosides and certain protein-based nematode-associated molecular patterns(NAMPs),can be perceived by the host plants,and can initiate a signaling cascade.To overcome the host confrontation and develop certain nematode feeding sites,some members can inject effectors into the cells of susceptible hosts to reprogram the basal resistance signaling.This review primarily emphasizes on an updated account of different classical and modem tools used for the identification of PPNs.Besides we also summarize the mechanism of some important signaling pathways which are involved in the different plant nematode interactions.