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Abstract

Abstract-A methanol extract of the pod surfaces of Cajanus cajan, a feeding stimulant for fifth-instar Helicoverpa armigera, was shown to contain four main phenolic compounds. Three of these were identified as isoquercitrin, quercetin, and quercetin-3-methyl ether, by comparing UV spectra and HPLC retention times with authentic standards. The fourth compound was isolated by semipreparative HPLC and determined to be 3-hydroxy-4-prenyl-5-methoxystilbene-2-carboxylic acid (stilbene) by NMR spectroscopy and mass spectrometry. Quercetin, isoquercitrin, and quercetin-3-methyl did not affect the selection-behavior of fifth-instar H. armigera. However, larvae were deterred from feeding on glass-fiber disks impregnated with the stilbene. Furthermore, larvae exposed to quercetin-3-methyl ether consumed significant amounts of both disks. In a binary-choice bioassay, a combination of quercetin-3-methyl ether and the stilbene on one disk and pure quercetin-3-methyl ether on the other disk resulted in increased consumption of both glass-fiber disks by larvae. In contrast, consumption was reduced if the combination was presented to larvae on one disk with purified stilbene on the other disk. Cajanus cajan cultivars that varied in their susceptibility to H. armigera were surveyed for the presence of the four phenolic compounds. An absence of quercetin and higher concentrations of isoquercitrin than the cultivated variety characterized pod surface extracts of pod-borer-resistant cultivars. In addition, the ratio of the stilbene to quercetin-3-methyl ether was greater in the pod-borer-resistant cultivars. These findings * To whom correspondence should be addressed. E-mail. p.stevenson@kew.org

Conventional and Molecular Approaches towards Genetic Improvement in Pigeonpea for Insects Resistance

“…The high density of type A (a characteristic feature present on the pods of cultivated types) increases the vulnerability of the host plant to pod borer to feed on the pods [32,37]. Dense non-glandular trichomes (type C) on pods of wild pigeonpea possibly act as a physical barrier to feeding by the young larvae of pod borer [27], while the glandular trichomes (type A) in C. cajan act as attractants [40] or phagostimulants for H. armigera [41]. There is an indication that the exudates from type A trichome contain a feeding stimulant for the larvae [41].…”

“…Dense non-glandular trichomes (type C) on pods of wild pigeonpea possibly act as a physical barrier to feeding by the young larvae of pod borer [27], while the glandular trichomes (type A) in C. cajan act as attractants [40] or phagostimulants for H. armigera [41]. There is an indication that the exudates from type A trichome contain a feeding stimulant for the larvae [41]. The type B trichome appears to give no protection against this insect.…”

Two New Stilbenoids from Cajanus cajan

“…Its molecular formula was determined as C 20 5.00 (1H, t, J = 6.5 Hz), 1.59 ppm (6H, s)], a methoxy [δ H = 3.76 ppm (3H, s)] and a carbonyl group (δ C = 198.1 ppm), which were very similar to those of longistylin C (compound 8) [8], except for the absence of two trans olefinic protons and the appearance of a carbonyl carbon resonance at δ C = 198.1 ppm and aliphatic signals at δ H = 4.21 ppm (2H, s) and δ C = 42.8 ppm, suggesting that the carbonyl and the aliphatic carbons are linked to the two benzene rings. This assumption was further evidenced by HMBC spectra (Fig.…”

“…], which belongs to the Cajanus genus, one of the most valuable perennial or annual leguminous food crops in Asia, Africa and some parts of tropical and subtropical areas of the world, has been reported to contain stilbenoids, flavonoids, coumarin, and other kinds of constituents [2 -7], yet the number of reported compounds is quite small. Our interest in the bioactivities of stilbenoids and the attempt to enrich the chemical constituents in pigeon pea led to the isolation of two new stilbenoids, cajanotone (1) and cajanamide A (2), six known ones (3)(4)(5)(6)(7)(8) and four known dihydroflavones (9)(10)(11)(12) (Fig. 1).…”

New Prenylated Stilbenes and Antioxidant Activities of <i>Cajanus cajan</i> (L.) Millsp. (Pigeon pea)

“…1 H-NMR data were obtained on compound 1 has similarities with the data cajanin acid stilbene found on pods of Cajanus cajan (L.) Millsp. from India [15].…”