Potato cultivar type affects the structure of ammonia oxidizer communities in field soil under potato beyond the rhizosphere

The effects of plants on the microbiota involved in the oxidation of ammonia in soils have been controversial. Here, we investigated the dynamics in the abundances and community structures of the bacterial and archaeal ammonia oxidizers (AOB and AOA, respectively) in two fields that were cropped with potato. Six different potato cultivars were used, including a genetically-modified one, in a fourfold replicated experimental set-up. On the basis of bulk and rhizosphere soil extracted microbial community DNA, AOB and AOA quantitative PCR as well as PCR-DGGE were performed. In addition, samples were used for the production and analysis of amoA gene fragment based clone libraries. Regardless of sample type (bulk versus rhizosphere soil) and across soils, the population sizes of AOA (of the order 10(4)-10(8) amoA gene copies g(-1) dry soil), were generally higher than those of AOB in the same samples (about 10(4)-10(5) g(-1) dry soil), resulting in ratio's of log-transformed values > 1.0. Whereas the AOB numbers were generally raised in the rhizosphere versus bulk soils in both soils, the opposite was true for the AOA numbers. Moreover, significant effects of cultivar type on both the AOB and AOA community structures were found in both soils, and these extended to beyond the rhizospheres. The effects were found across the whole growth season. Soil type did not significantly affect the community structures of AOA, but had a small effect on the community structure of AOB. Analysis of the structures of the AOB communities revealed a prevalence of AOB subgroups 2, 3a, 3b and 4 in one field soil and of 2 and 4 in the other one. With respect to the AOA, soil/sediment clusters (SS) I, II, III and IV were found to prevail

Potato cultivar type affects the structure of ammonia oxidizer communities in field soil under potato beyond the rhizosphere

The effects of plants on the microbiota involved in the oxidation of ammonia in soils have been controversial. Here, we investigated the dynamics in the abundances and community structures of the bacterial and archaeal ammonia oxidizers (AOB and AOA, respectively) in two fields that were cropped with potato. Six different potato cultivars were used, including a genetically-modified one, in a fourfold replicated experimental set-up. On the basis of bulk and rhizosphere soil extracted microbial community DNA, AOB and AOA quantitative PCR as well as PCR-DGGE were performed. In addition, samples were used for the production and analysis of amoA gene fragment based clone libraries. Regardless of sample type (bulk versus rhizosphere soil) and across soils, the population sizes of AOA (of the order 10(4)-10(8) amoA gene copies g(-1) dry soil), were generally higher than those of AOB in the same samples (about 10(4)-10(5) g(-1) dry soil), resulting in ratio's of log-transformed values > 1.0. Whereas the AOB numbers were generally raised in the rhizosphere versus bulk soils in both soils, the opposite was true for the AOA numbers. Moreover, significant effects of cultivar type on both the AOB and AOA community structures were found in both soils, and these extended to beyond the rhizospheres. The effects were found across the whole growth season. Soil type did not significantly affect the community structures of AOA, but had a small effect on the community structure of AOB. Analysis of the structures of the AOB communities revealed a prevalence of AOB subgroups 2, 3a, 3b and 4 in one field soil and of 2 and 4 in the other one. With respect to the AOA, soil/sediment clusters (SS) I, II, III and IV were found to prevail

Sulphur-oxidising and Sulphate-reducing Communities in Brazilian Mangrove Sediments

Mangrove soils are anaerobic environments rich in sulphate and organic matter. Although the sulphur cycle is one of the major actors in this ecosystem, little is known regarding the sulphur bacteria communities in mangrove soils. We investigated the abundance, composition and diversity of sulphur-oxidizing (SOB) and sulphate-reducing (SRB) bacteria in sediments from three Brazilian mangrove communities: two contaminated, one with oil (OilMgv) and one with urban waste and sludge (AntMgv), and one pristine (PrsMgv). The community structures were assessed using quantitative real-time polymerase chain reaction (qPCR), polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and clone libraries, using genes for the enzymes adenosine-5′-phosphosulphate reductase (aprA) and sulphite reductase (Dsr) (dsrB). The abundance for qPCR showed the ratio dsrB/aprA to be variable among mangroves and higher according to the gradient observed for oil contamination in the OilMgv. The PCR-DGGE patterns analysed by Nonmetric Multidimensional Scaling revealed differences among the structures of the three mangrove communities. The clone libraries showed that Betaproteobacteria, Gammaproteobacteria and Deltaproteobacteria were the most abundant groups associated with sulphur cycling in mangrove sediments. We conclude that the microbial SOB and SRB communities in mangrove soils are different in each mangrove forest and that such microbial communities could possibly be used as a proxy for contamination in mangrove forests.

Produtividade e principais problemas fitossanitários de cultivares de batata em Sergipe Yield and phytosanitary problems of potato cultivars in Sergipe, Brazil

Sete cultivares de batata (Solanum tuberosum L.) foram avaliadas durante três anos em Itabaiana-SE, com o objetivo de verificar a potencialidade de produção à altitude de 180 m e identificar os problemas fitossanitários que afetam a produtividade. Os experimentos foram conduzidos nos meses de junho a setembro, utilizando-se o delineamento experimental de blocos ao acaso, com cinco repetições. Após a colheita foram avaliadas a produção total, comercial (tubérculos sadios e com peso mínimo de 40 g) e perdas de produção decorrentes de sarna, podridão-mole, nematóide e insetos do solo. A análise conjunta das produções totais e comerciais de tubérculos revelou que as cultivares mais produtivas foram Baronesa (33,7 t/ha), Monalisa (32,7 t/ha) e Elvira (31,4 t/ha). A produção comercial variou de 3,4 t/ha a 22,5 t/ha, destacando-se as cvs. Elvira e Monalisa, com rendimentos de 22,5 t/ha e 20,5 t/ha respectivamente, com apenas três pulverizações com defensivos. Os problemas fitossanitários que mais afetaram a cv. Elvira foram sarna (13,1%) e nematóide das galhas (7,2%), enquanto a 'Monalisa' teve sua produção prejudicada mais pela incidência de insetos (15,1%), sarna (12,0%) e nematóide (9,7%). A cv. Monalisa apresentou tubérculos com melhores características para comercialização e está sendo cultivada a nível comercial em substituição às variedades Bintje e Baraka anteriormente cultivadas na região. Os resultados indicam a potencialidade da região de Itabaiana para a produção de batata.<br>The yield potential and main diseases affecting productivity of seven potato (Solanum tuberosum L.) cvs. were evaluated during a three years period in experiments carried out at low altitude conditions of Sergipe State, Brazil. The experimental plots were located at 180 m of sea level in a Red-Yellow Podzolic sandy-clay texture soil. The experimental design was of complete randomized blocks with five replications. Tubers were sown yearly in June and harvested in September. After harvest, total yield, commercial yield (healthy tubers with 40 g minimum weight) and losses caused by scab, soft-rot, nematodes, and soil insects were evaluated. The analysis of variance for total and commercial yield of tubers highlighted Baronesa (33.7 kg/ha), Monalisa (32.7 kg/ha), and Elvira (31.4 kg/ha) as the most productive cvs. The commercial yields varied from 3.4 t/ha to 22.a t/ha. The cvs. Elvira and Monalisa, yielded 22.5 kg/ha and 20.5 kg/ha, respectively. Only three insecticides applications were necessary. Scab (13.1%) and nematode (7.2%) were the main phytosanitary problems affecting Elvira cv. In relation to Monalisa, pin larvae soil insect (15.1%), scab (12.0%), and nematode (9.7%) were the main causes of yield loss. Because of its best commercial tuber characteristics Monalisa has been planted instead of Bintje and Baraka, both commonly used in the region. The results indicate the suitability of Itabaiana region for potato production