Differential Effects of Bentazon and Molinate on Anabaena cylindrica, an Autochthonous Cyanobacterium of Portuguese Rice Field Agro-ecosystems

Abstract

The effects of bentazon and molinate, two selective herbicides recommended for integrated weed management in rice, were studied in Anabaena cylindrica, an abundant cyanobacterium isolated from a Portuguese rice field agro-ecosystem. Comparative effects of both herbicides on A. cylindrica were estimated under laboratory conditions by measuring its dry weight yield, photopigments, and carbohydrate and protein contents in a time-and dose-dependent exposure throughout 72 h. Photosynthesis and respiration were also monitored. The results revealed that both herbicides exerted a pleiotropic effect on the cyanobacterium at the range of concentrations tested (0.75-2 mM). Growth, chlorophyll a, carotenoids and phycobiliproteins were more adversely affected by molinate than by bentazon.Cyanobacterial growth inhibitions of over 50% were observed after 48 h when 1.5-2 mM of molinate were applied. Bentazon concentrations ranging from 0.75 to 2 mM did not significantly modified chlorophyll a content with time, however, considerable reductions in chlorophyll a, carotenoids and specially phycobiliproteins were observed with molinate. Protein content increased with both herbicides although the effect was particularly noticeable with the highest concentration of molinate. Herbicide effects on carbohydrate content were contrasting: molinate increased this organic fraction whereas bentazon decrease it. Photosynthesis and respiration were inhibited by both herbicides and higher molinate concentrations (1.5-2 mM) completely ceased O 2 evolution after 48 h. Since A. cylindrica is abundant in Portuguese rice fields and could be used as an inoculum source in rice biofertilization programs, their protection from potential residual effects of herbicides is fundamental for a correct management of local soil fertility.

Morphological, biochemical and molecular characterization of Anabaena, Aphanizomenon and Nostoc strains (Cyanobacteria, Nostocales) isolated from Portuguese freshwater habitats

“…The study area details of sampled rice fields were similar to those described by Marques et al (2008), and Vela Lake biotic and abiotic characteristics were extensively monitored previously (de Figueiredo et al, 2006). The samples from rice fields and Vela Lake were collected in situ according to the methodologies described in Galhano et al (2009) andde Figueiredo et al (2006), respectively. Cyanobacterial strains were isolated by capillarity, agar plate spreading and serial dilution techniques (Andersen & Kawachi, 2005).…”

“…The native strains frequently found in European rice fields mainly belong to the heterocystous genera Anabena and Nostoc, but also Calothrix and Tolypothrix (Whitton, 2000;Ariosa et al, 2006;Galhano et al, 2009). On the other hand, the diversity, ecology and genetic heterogeneity among planktonic Anabaenalike and Aphanizomenon-like morphospecies require a deeper characterization, since there is neither a clear phylogenetic nor a morphological separation (Hindák, 2000;Rajaniemi et al, 2005;Stüken et al, 2009).…”

Impact of Herbicides on Non-Target Organisms in Sustainable Irrigated Rice Production Systems: State of Knowledge and Future Prospects

“…In one of those studies, the effects of the two selective herbicides recommended for IWM on rice were laboratory-assessed in Anabaena cylindrica during a short-term experiment of 72 h (Galhano et al, 2009). The results obtained in this work revealed that both herbicides had a pleiotropic effect on the cyanobacterium at the range of concentrations tested (0.75-2 mM).…”

“…Photosynthesis (P m Chl ) and dark respiration (R d Chl ) normalized to Chla were inhibited by both herbicide formulations in a time-and dose-response manner within the experiment time, and higher Ordram concentrations full stopped O 2 evolution after 48 h. Pointing to safety environmental precautions, the findings obtained with our study suggest the reduction or even ban of molinate from the agro-ecosystem rice field because of its strong inhibitory action on soil autochthonous microflora, mainly on the important diazotrophic primary producers, the cyanobacteria. Together with pulse-amplitudemodulation (PAM) fluorimetric routine parameters, namely maximum photosystem II (PS II) quantum efficiency (Fv/Fm), effective quantum efficiency of PS II for a light-acclimated sample (Ф PSII ), and photochemical quenching (qP; proportion of light excitation energy converted to photochemical act by the active PS II reaction centres), part of the results published by Galhano et al (2009) were previously presented to the overall scientific community in the 15 th European Bioenergetics Conference held in Dublin, from 19 to 24 July 2008 (Galhano et al, 2008). Relevant findings related to Basagran and discussed in the meeting are displayed in Figure 1 carpet-plot.…”

Differential effects of pesticides on soil microflora in cultivated soil of Indian rice field agro-ecosystems

“…The effects of soil micro flora following use of pesticides have been a subject of present interest through difference in doses and methods of assessing their effect, make comparisons hard. Studies on the effects of Bentazon and Molinate on Anabaena cylindrica of Portuguese rice field agro-ecosystems have provide extensive research foundations (Galhano et al, 2009). Insect pest make a grave problem in the field of agriculture but indiscriminate use of pesticide in cultivated field, creates deleterious effect to the population of soil micro flora.…”