Shift from morphological to recent advanced molecular approaches for the identification of nematodes.

Nematodes are the most diverse but most minor studied microorganisms found in soil, water, animals, or plants. Either beneficial or pathogenic, they significantly affect human and animal health, plant production and ultimately affect the environmental equilibrium. Knowledge of their taxonomy and biology are the main issues to answer the different challenges associated with these microorganisms. The classical morphology-based nematode taxonomy and biodiversity studies have proved insufficient to identify closely related taxa and have challenged most biologists. Several molecular approaches have been used to supplement morphological methods and solve these problems with markable success. The molecular techniques range from enzyme analysis, protein-based information to DNA sequence analysis. For several decades, efforts have been made to integrate molecular approaches with digital 3D image-capturing technology to improve the identification accuracy of such a taxonomically challenging group and communicate morphological data. This review presents various molecular techniques and provides examples of recent advances in these methods to identify free-living and plant-parasitic nematodes.

Year-Long Assessment of Soil Nematode Diversity and Root Inhibition-Indicator Nematode Genera in Rice Fields.

Soil nematodes contribute to nutrient cycling. This year-long study aimed to investigate the changes in the diversity of soil nematodes during the spring, summer, and winter seasons in rice fields at 24 sites and to determine the indicator nematode genera that inhibit the roots of rice plants. A total of 216 soil samples were collected during three seasons, and the collection of 72 root samples was carried out during rice cropping. Forty-four soil nematode genera were identified. They exhibited significant changers in their abundance, which were dependent on the seasons and on soil characteristics. In particular, the abundance of plant-parasitic nematodes (PPNs) and free-living soil nematodes was 49% and 15% higher during the summer than during the spring and winter seasons, respectively. Soil characteristics, such as soil nitrogen (N) contents, carbon (C) contents, and soil moisture were significantly higher during the summer than in the spring and winter seasons, but soil pH was significantly lower during the summer than in the spring and winter seasons. Moreover, Hirschmanniella,Meloidogyne, and Heterodera emerged as good indicators for rice root inhibition, corroborating the frequency, density, and prominence value of PPNs of the sampled soil and rice roots. This study also indicated that free-living nematode genera, such as Rhabdolaimus, Diplogaster, and Rhabditis, might function as ecological indicators for soil health.

Influence of ecological and edaphic factors on biodiversity of soil nematodes.

Nematodes are the most diverse and highly significant group of soil-inhabiting microorganisms that play a vital role in organic material decomposition and nutrient recycling. Diverse geographical locations and environmental gradients show a significant impact on the diversity of nematodes. Present study aims to assess the effects of ecological (altitude, temperature, moisture) and edaphic (soil pH, nutrients, soil patches) factors on the soil nematode diversity and structure at five different landscape patches (forests, apple orchards, rice fields, pastures, and alpine zone) from ten different sites of Kashmir valley (India). Differences in the altitudinal gradients results in the shift of generic nematode population. Among the soil patches, highest nematode diversity was observed in forest soil and least in alpine soil; however, bacteriovorous nematodes dominated all the soil patches. The temperature and moisture have a significant effect on nematode diversity, the highest nematode trophic levels were observed above 21°C temperature, and 30% moisture. Nematode abundance decreased from alkaline to acidic pH of the soil. Soil nutrients such as, nitrogen (N) and phosphorus (P) have shown a detrimental effect in nematode richness at each site, where nematode diversity and richness of genera were higher at abundant soil N and P but decreased at low soil nutrients. Ecological indices like diversity index (DI), Shannon-Wiener Index (H'), enrichment index (EI), and maturity Index (MI) values demonstrated forest soil more favourable for nematodes and high soil health status than other soil patches. This study suggested that these indices may be helpful as soil monitoring tools and assessing ecosystem sustainability and biodiversity.