Nematode community, trophic structure and population fluctuation in soybean fields

Abstract

Temporal (monthly in three fields for 12 months) and spatial (once in 23 fields during March-April) samplings were conducted in the major soybean (Glycine max)-growing region of the Brazilian Federal District. Fifty-three nematode genera were found in both samplings, but 13 were detected only by the temporal sampling, and one only by the spatial sampling. Fifty-three percent were plantparasites, 35% were bacterivores, and about 12% were fungivores, predators and omnivores constituted the community that was dominated by the genera Helicotylenchus (40% of total abundance), Acrobeles (15%), Cephalobus (7.6%), Meloidogyne (5.6%) and Pratylenchus (4.9%). Heterodera glycines was not found in this study. There were no differences in ten ecological measurements [Ds, H', Es, T, FF/BF, (FF+BF)/PP, MI, PPI, mMI, and Dorylaimida (%)] between the two sampling types, but differences in indexes d and J´. Plant parasite populations dropped at the end of the crop cycle, remained at low levels during the dry season and the seedling period, then increased again in the crop-growing season. Fungivores maintained their low populations throughout the year, increasing only in June and July, the post-harvest period, when soil fungi decomposed root tissue. The population of bacterivores slightly declined during the dry season and the initial rainy season, but peaked in the middle of the rainy season, apparently associated with soil humidity. In the five most abundant nematodes, those of Acrobeles and Pratylenchus were more populous in wet soils, Cephalobus and Meloidogyne adapted well in dry soils, but Helicotylenchus survived abundantly in a wide range of soil moisture.Additional keywords: Glycine max, population dynamics, nematode ecology, temporal and spatial samplings, and functional groups. RESUMO Comunidade de nematóides, estrutura trófica e flutuação populacional em plantações de sojaAmostragens temporal (mensalmente em três campos por 12 meses) e espacial (uma vez, em 23 campos, de março a abril) foram feitas na principal região sojícola do Distrito Federal. Nos dois tipos de amostragem foram encontrados 53 gêneros de nematóides, sendo 13 deles detectados apenas pela temporal e um somente pela espacial. Do total, 53% foram fitoparasitos, 35% bacteriófagos e cerca de 12% micófagos, predadores e onívoros. Esses constituíram a comunidade de nematóides, dominada por Helicotylenchus (40% da abundância total), Acrobeles (15%), Cephalobus (7,6%), Meloidogyne (5,6%) e Pratylenchus (4,9%). Heterodera glycines não foi encontrado neste estudo. Não houve diferença quanto aos índices Ds, H', Es, T, FF/BF, (FF+BF)/PP, MI, PPI, mMI e Dorylaimida (%) entre as duas amostragens, mas houve diferença quanto aos índices d e J´. Os fitoparasitas tiveram populações reduzidas no final do ciclo da cultura, se mantiveram em nível baixo na estação seca e no período de desenvolvimento inicial das plantas, aumentando durante o crescimento das mesmas. Os micófagos se mantiveram em baixa população durante o ano, mas se elevaram em junho e julho, período de pós...

Seasonal fluctuations of the nematode communities in a hop garden soil

“…The larger proportion of BF at 20 cm soil depth would indicate that nematodes of this trophic group contribute to decomposition of cattle manure. This is confirmed by the prevalence of PP on BF in soil with cereals without organic amendment reported by Valocká et al (2001) and Renčo (2003Renčo ( , 2004, and also in soybean fields (Gomes et al, 2003). A similar situation was recorded in ecosystems of vineyards in Austria, in which PP nematodes prevailed, followed by BF, F, O, P and IN (Hoschitz, 2004).…”

Depth-stratified soil sampling for assessing nematode communities

“…Because omnivorous nematodes of the Dorylaimidae family can be restricted to certain soil depths (RODRIGUES et al, 2011) and populations are usually low, especially in agricultural areas (NEHER;CAMPBELL, 1994;GOULART;TOMAZINI et al, 2008), the sampling method can significantly affect the results obtained. Because they are associated with anthropogenic activity and ongoing farming practices (GOMES et al, 2003), they form important groups in differentiating between the ecological processes that occur in agroecosystems and native ecosystems.…”

Differential responses of nematode communities to soybean genotypes resistant and susceptible to Heterodera glycines race 3

“…This result hints that there was a defined amount of relative abundance for plant parasites and bacterial feeders to function in a defined system, with both functional groups acting in a compensatory manner, one increasing while the other decreased. Gomes et al (2003) reported that the population of fungal feeders increased at the final growing cycle of soybean because the root tissue was in decomposition. McSorley & Frederick (1996) also showed that the abundance of plant parasites was slightly higher in the old soybean plants.…”