Bioactive Diterpenes from the Brazilian Native Plant (Moquiniastrum pulchrum) and Their Application in Weed Control

Even today, weeds continue to be a considerable problem for agriculture. The application of synthetic herbicides produces serious environmental consequences, and crops suffer loss of their activity due to the appearance of new resistant weed biotypes. Our aim is to develop new effective natural herbicides that improve the problem of resistance and do not harm the environment. This work is focused on a bioassay-guided isolation and the characterization of natural products present in Moquiniastrum pulchrum leaves with phytotoxic activity and its preliminary application in weeds. Moquiniastrum pulchrum was selected for two reasons: it is an abundant species in the Cerrado region (the second most important ecosystem in Brazil, after the Amazon)-the explanation behind its being a dominant species is a major focus of interest-and it has traditional employment in folk medicine. Six major compounds were isolated in this plant: one flavone and five diterpenes, two of which are described for the first time in the literature. Four of the six compounds exhibited phytotoxic activity in the bioassays performed. The results confirmed the phytotoxic potential of this plant, which had not been investigated until now.This research was supported by CAPES-Coordination for the Improvement of Higher Education Personnel (Brazil) (Project 88881.119937/2016-01) and 'Ministerio de Economia, Industria y Competitividad' (MINEICO), Spain, Project AGL2017-88-083-R

Atividade fitotóxica de Serjania lethalis sobre a germinação e crescimento de Panicum maximum

Este artigo analisa a atividade fitotóxica de extratos aquosos de folhas jovens e maduras de Serjania lethalis A. St. -Hil. sobre a germinação e o crescimento de sementes de Panicum maximum Jacq. Foram preparados extratos aquosos nas concentrações de 2,5, 5,0, 7,5 e 10% a partir de folhas secas e água destilada. A porcentagem de germinação, velocidade de germinação e sincronia foram afetadas negativamente pelos dois extratos. Os extratos exibiram fitotoxicidade e reduziram o crescimento de plântulas, e esses efeitos são dependentes da concentração. As diferentes concentrações dos extratos provocaram mudanças significativas no processo de germinação e crescimento de plântulas de P. maximum, em alguns casos variando devido ao estágio de maturação foliar, porém, não diferindo entre si para maioria das variáveis analisadas

Fracionamento de extratos bioativos de Drimys brasiliensis Miers e identificação de compostos com atividade fitotóxica e inseticida

Along its evolutionary history, plants have developed biosynthetic routes to synthesize and accumulate a wide variety of secondary metabolites, which respond to the environment characteristics where they occur. The studies about these compounds effects on nearby organisms constitute the field of allelopathy. Allelopathy is an important phenomenon in plant chemical ecology that involves bioactive compounds, from which one can produce natural pesticides that would be more specific, less harmful to the environment and applied to a model of sustainable agriculture. Drimys brasiliensis Miers is found in the Atlantic Forest and in the Cerrado domain. It s chemically characterized by the presence of monoterpenes, sesquiterpenes and flavonoids, with great use potential in the pharmaceutical industry. There are few studies about the allelopathic potential of D.brasiliensis and its secondary metabolites to act as natural pesticides, specialy as herbicide or insecticide. Thus, in the first chapter we studied the phytotoxic potential of aqueous extracts of D.brasiliensis according to the seasonality and different plant organs. The phytotoxic effect of D.brasiliensis isinfluenced by the period of collection, with more evident activity in leaves collected in the dry season. Aqueous extracts from leaves, roots and stems of D.brasiliensis showed activity on crop plants, and all organs are a promising source in the search of phytotoxic compounds. In the second chapter, we investigated the phytotoxic potential of crude extract fractions from D. brasiliensis roots and leaves on weeds. The inhibitory effects of the root hexane fraction on seedling growth was similar to the herbicide, indicating that D. brasiliensis is a possible alternative form of control for the weed species examined. In chapter three, was carried a bioassay-guided isolation of bioactive compounds present in D.brasiliensis roots. Four drimanes sesquiterpenes were isolated from bioactive fractions of roots, determined as polygodial, polygodial 12 α- acetal, dendocarbin L and (+) fuegin. The polygodial caused phytotoxic effects on wheat coleoptile and on crop and weed species. In the last chapter, the effect of the hexane fraction and polygodial obtained from D.brasiliensis roots was evaluated on Toxoptera citricidus Kirkaldy (black citrus aphid), and both caused toxicity, with high mortality on nymphs and adults stages of this aphid. The polygodial, isolated for the first time in the roots of D. brasiliensis, may be the primarily responsible for the biological activities detected in this study. The herein presented data allow the indication of this compound as a potential biopesticide.Ao longo do seu processo evolutivo, as plantas desenvolveram rotas de biossíntese, através das quais sintetizam e acumulam uma ampla variedade de metabólitos secundários, que respondem às características do meio onde se encontram. Os estudos realizados sobre os efeitos desses compostos em organismos próximos constituem o campo da alelopatia. A alelopatia representa um importante fenômeno dentro da ecologia química de plantas e envolve a síntese de metabólitos secundários, a partir dos quais se pode produzir pesticidas naturais, mais específicos, menos prejudiciais ao ambiente e aplicáveis a um modelo de agricultura de base ecológica. A espécie Drimys brasiliensis Miers ocorre na Mata Atlântica e no domínio do bioma Cerrado. Fitoquimicamente é caracterizada pela presença de monoterpenos, sesquiterpenos e flavonóides com grande potencial de uso na indústria farmacológica. São poucos os trabalhos publicados que tratam de investigações do potencial de D. brasiliensis e de seus metabólitos secundários para atuarem como pesticidas naturais, principalmente no que concerne às ações herbicida e inseticida. Nesse sentido, no primeiro capítulo foram realizadas investigações sobre o potencial fitotóxico de extratos aquosos de D. brasiliensis em função da sazonalidade e de diferentes órgãos da planta. O efeito fitotóxico de D. brasiliensis foi influenciado pela época de coleta, com atividade mais evidente em folhas coletadas na estação seca. Extratos aquosos de folhas, raízes e cascas do caule de D. brasiliensis apresentaram atividade inibitória sobre plantas cultivadas, e todos os órgãos constituem uma fonte promissora para a busca de compostos fitotóxicos. No segundo capítulo, foi investigado o potencial fitotóxico de frações do extrato bruto de folhas e raízes de D. brasiliensis sobre as plantas infestantes Panicum maximum Jacq e Euphorbia heterophylla L. As inibições no crescimento inicial, decorrentes da aplicação da fração hexânica das raízes, foram similares ao efeito produzido pelo herbicida oxyfluorfen, indicando a eficiência de D. brasiliensis para o controle das espécies infestantes estudadas. No terceiro capítulo, foi realizado o isolamento biomonitorado de compostos presentes em raízes de D. brasiliensis. Foram isolados quatro drimanos sesquiterpenos das frações bioativas de raízes, determinados como poligodial, poligodial 12 α-acetal, dendocarbin L e (+) fuegin. O poligodial exerceu efeitos fitotóxicos sobre coleóptilos de trigo e sobre duas espécies infestantes e uma cultivada avaliadas. No último capítulo, o efeito da fração hexânica e do poligodial obtidos de raízes de D. brasiliensis foi avaliado sobre Toxoptera citricidus Kirkaldy (pulgão-preto dos citros), e ambos causaram toxicidade, provocando elevada mortalidade nas fases de ninfas e adultos deste afídeo. O poligodial, isolado pela primeira vez nas raízes de D. brasiliensis, pode ser o principal responsável pelas atividades biológicas registradas neste estudo. Os resultados obtidos permitem a indicação deste composto como um potencial biopesticida

Insecticidal action of Drimys brasiliensis Miers on black citrus aphid

ABSTRACT The aim of this study was to evaluate the insecticidal effects of a hexane fraction and polygodial compound obtained from Drimys brasiliensis roots on the mortality of adults and nymphs of Toxoptera citricida (black citrus aphid). For the hexane fraction, solutions of 0.12, 0.25, 0.50, 1.0, and 2.0 mg mL-1 were prepared, and for the compound, solutions of 62.5, 125, 250, and 500 µg mL-1 were prepared. A control with water and dimethylsulfoxide (5 µg mL-1) was also included. Two hexane-fraction-solution application methods were evaluated: spraying directly onto the insect, and submerging a young Citrus limonia shoots in the solution, which served as a refuge for the aphids. Nymph and adult mortality were assessed at 24 and 48 h after solution application. The hexane fraction caused high mortality amongst the T. citricida nymphs and adults. The lowest LC50 value (0.301 mg mL) was recorded in the nymphs when the solutions were applied directly onto the insects. The polygodial compound that was isolated from the hexane fraction significantly increased the mortality of adults and nymphs, with LC50 values of 293.8 and 176.77 µg mL-1, respectively. The insecticidal activity observed may have been caused by this compound