Dynamics of soil nematode communities in tomato crops from a productive region of Argentina

ACHINELLY , MARÍA F.; SALAS, A.

Congreso; Evento: 51 th ONTA Annual meeting.; 2018

ONTA

The objective of this work was to evaluate nematode communities through ecological indexes to determine those variables are the best indicators of changes in soils subjected to tomato crops under two different agricultural management systems, in La Plata, Buenos Aires province, the main tomato producing region of Argentina. A seasonal crop and an intensive conventional crop with use of agrochemicals were considered for the study. Site A, was characterized by tomato crops during spring and summer season and covered by weeds the rest of the year, using organic fertilizers as the only external income. Site B was represented by an intensive conventional culture with methyl bromide and Agrocelhone application as nematicide before the seedtime the first year and towards the end of the second year of sampling respectively. Soil samples were collected between September 2015 and October 2017. At each site, a single sample, totaling a minimum volume of 500 cm3, was collected; this comprised multiple soil cores (c. 20), taken to a depth of 20 cm using a steel auger (4 cm diameter). A total of nine samples were taken for each site. In lab the technique of centrifugation was performed for nematode isolation. The determination at the genus level and the count of nematodes was carried out to obtain the values of abundance per site. To identify changes in the structure of the nematode community, diversity and function indexes were analyzed and tested to search differences between sites. Following multivariate analysis were considered: ANOSIM to determine significant differences between sites, SIMPER to estimate the contribution of each taxon to average Bray Curtis dissimilarity and MDS to model the proximity (similarity) between the samples. The results showed significant differences between Richness (= N0), abundance, Margalef (d) and Σ MI, no differences being observed in MI, Shannon-Wiener, Pielou and other diversity indices analyzed. Significant differences were found between the sites using the ANOSIM test (global R= 0.5, p value=0.002). SIMPER analysis indicated that Helicotylenchus, Filenchus and the opportunistic enrichment nematode Rhabditis were mainly responsible for the dissimilarity between sites. The MDS indicated evident separation of samples taken after the application of methyl bromide and Agrocelhone. ∑MI showed changes in the community structure of soil nematodes. This could be related to the inclusion of plant-feeding nematodes in this index. Similar values for MI between sites could be related to the abundance of bacteriophage nematodes due to enrichment of the environment with organic fertilizers (Site A) and disturbance for fumigants (Site B). As results of this work, we present the most sensible variables in nematode communities, in soils under horticultural management in the city La Plata. The lack of studies in this region encourages to keep on this type of analysis to estimate changes in the diversity of nematofauna as measure of ecological quality for these agricultural soils.