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Title: Bioassay-directed isolation and identification of phytotoxic and fungitoxic acetylenes from Conyza canadensis

Author
item QUEIROZ, SONIA - Embrapa
item Cantrell, Charles
item Duke, Stephen
item Wedge, David
item Nandula, Vijay
item MORAES, RITA - University Of Mississippi
item CERDEIRA, ANTONIO - Embrapa

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2012
Publication Date: 5/21/2012
Citation: Queiroz, S.C., Cantrell, C.L., Duke, S.O., Wedge, D.E., Nandula, V.K., Moraes, R.M., Cerdeira, A.L. 2012. Bioassay-directed isolation and identification of phytotoxic and fungitoxic acetylenes from Conyza canadensis. Journal of Agricultural and Food Chemistry. 60:5893-5898.

Interpretive Summary: Conyza Canadensis, also known as horseweed, is a plant species indigenous to America, now distributed globally. C. canadensis is a common weed found in more than 40 crops. C. canadensis infests orchards, roadsides, vineyards, field crops such as corn, soybean and cotton, hay crops, pastures and rangeland throughout North, Central, and South America. It is problematic because of the frequent occurrence of biotypes with evolved resistance to glyphosate and paraquat, and the weed’s ability to complete its life cycle as a winter or summer annual weed. This weed has caused economic losses to farmers due to the decrease in quality and quantity of crop production. To combat the herbicide-resistant weed biotypes there is a need for new herbicides with new modes of action. Several phytochemicals produced by certain types of plants can affect the germination and the development of other nearby competing species. no studies on the isolation and identification of the phytotoxic compounds from C. canadensis have been done using a bioassay-directed isolation of active compounds, a process likely to discover highly bioactive, novel compounds. The objective of this study was to identify the phytotoxic compounds of C. canadensis by systematically performing bioassay-directed isolation and subsequent identification of the bioactive constituents. The activity of the isolated compounds is also reported against various species of plant pathogenic fungi.

Technical Abstract: Conyza canadensis (L.) Cronquist syn. (horseweed), is a problematic and invasive weed with reported allelopathic properties. In order to identify the phytotoxic constituents of the aerial parts, a systematic bioactivity-guided fractionation of the dichloromethane extract was performed. Three active enyne derivatives, (2Z,8Z)-matricaria acid methyl ester, (4Z,8Z)-matricaria lactone and (4Z)-lachnophyllum lactone, were identified. The lactones inhibited growth of the monocot Agrostis stolonifera (bentgrass) and the dicot Lactuca sativa (lettuce) at 1 mg ppm-1, while the (2Z,8Z)-matricaria acid methyl ester was less active. In a dose-response screening of the lactones for growth inhibitory activity against Lemna paucicostata, (4Z)-lachnophyllum lactone was the most active with an IC50 of 104 Micro M, while the (4Z,8Z)-matricaria lactone was less active (IC50 of 220 Micro M). In a fungal direct bioautography assay, the two lactones at 10 and 100 Micro g/spot inhibited growth of the plant pathogenic fungi Colletotrichum acutatum, C. fragariae, and C. gloeosporioides. In a dose-response screening of the lactones against six different plant pathogenic fungi, (4Z,8Z)-matricaria lactone was more active than the commercial fungicide azoxystrobin on C. acutatum, C. fragariae, and C. gloeosporioides at 30 Micro M and about as active as the commercial fungicide captan against C. gloeosporioides, while (4Z)-lachnophyllum lactone was less active.