Variation in Allyl Isothiocyanate Production Within Brassica Species and Correlation with Fungicidal Activity

Brassica nigra (black mustard) and B. juncea (Indian mustard) genotypes were tested for pathogen suppression and release of allyl isothiocyanate (AITC), a fungitoxic volatile produced in mustard tissue after enzymatic hydrolysis of allyl glucosinolate (sinigrin). In bioassays, 28 genotypes of B. nigra and 35 genotypes of B. juncea were screened for inhibition of the potato pathogens Helminthosporium solani and Verticillium dahliae by volatiles released from macerated leaf tissue. Release of AITC from plant tissue was quantified by gas chromatography; isothiocyanate profiles were determined by headspace analysis. All mustard genotypes produced compounds that suppressed radial growth of both fungi. Growth suppression and AITC release differed significantly (P < 0.001) among genotypes of B. nigra and B. juncea. Mustard treatments releasing >1.2 mg AITC/g plant tissue were fungicidal to both pathogens. Headspace analysis confirmed that allyl glucosinolate was the major glucosinolate in all genotypes of B. nigra tested; most genotypes also produced 2-phenylethyl-isothiocyanate (ITC). Brassica juncea genotypes produced variable amounts of AITC and other volatiles with antimicrobial activity, including 2-phenylethyl-ITC, benzyl-ITC, and 3-butenyl-ITC. Evaluating mustards from geographically diverse locations allowed selection of mustard genotypes that may be useful in breeding programs designed to develop disease-suppressing green manure cultivars.     

Glucosinolate preservation in stored Brassicaceae seed meals

Limited profitability restricts expanded U.S. production of Brassicaceae oilseed crops despite their positive rotational benefits and capacity to provide biodiesel feedstocks. Improved profitability is possible if the seed meals remaining after oil removal are commercialized as biopesticides. Our objective was to determine storage stability of the precursor pesticidal compounds called glucosinolates within Brassica napus, Brassica juncea, and Sinapis alba seed meals. The seed meals were stored at temperatures of −20, 4, and 25 °C in paper bags, polyethylene containers, or under vacuum for 30 months after purging in a N₂ atmosphere. Glucosinolate concentrations measured every 6 months using HPLC-MS decreased only in meal samples stored at 4 °C, and to the greatest extent in samples stored within paper bags. Relative humidity averaged 80% at this temperature, thus promoting visually obvious fungal growth. Glucosinolate preservation within stored seed meals is possible for 30 months and possibly much longer providing the seed meals are protected from exposure to moisture conditions that promote microbial growth.     

Changes in the dry matter,sugar, plant fibre and lignin contents of swede,rape and kale roots in response to turnip root fly (Delia floralis) larval damage

Plants from two genotypes of swede (Brassica napus var napobrassica), kale (B oleracea var. acephala) and rape (B napus var napus) were each inoculated at the three to four true leaf stage with 10 eggs of the turnip root fly, Delia floralis. After 8 weeks the damage caused by the resultant larvae significantly reduced the weight of leaves, stems and roots compared with uninoculated plants, with the greatest reduction (26–46%) being found in the roots. Dry matter content, which did not differ between either crop type or cultivar, was unaffected by larval damage. Ethanol-soluble sugar content was reduced in all cases by larval damage, but only significantly in one rape and one swede cultivar. The effect of D floralis damage on the concentrations of individual sugars (glucose, fructose and sucrose) was crop type and cultivar dependent. The neutral detergent fibre and lignin contents of the undamaged swede roots were significantly lower than in either the undamaged kale or rape cultivars studied. In all crop types the neutral detergent fibre and lignin content significantly increased following D floralis damage. The six Brassica genotypes studied fell into two groups on the basis of host status for D floralis. The two kale cultivars and the forage rape Hobson were considered poor hosts for D floralis, with low percent age pupation (38–41%) and low pupae weight (12.5–14.4 mg). The two swedes and the oilseed rape Ariana were considered good host for D floralis, with both higher percentage pupation (51–59%) and pupae weights (19.8–20.0 mg). The possible relationships between the root composition of undamaged and attacked roots, and D floralis resistance are discussed.     

Allelochemicals Isolated from Tissues of the Invasive Weed Garlic Mustard (Alliaria petiolata)

Garlic mustard (Alliaria petiolata) is a naturalized Eurasian species that has invaded woodlands and degraded habitats in the eastern United States and Canada. Several phytotoxic hydrolysis products of glucosinolates, principally allyl isothiocyanate (AITC) and benzyl isothiocyanate (BzITC), were isolated from dichloromethane extracts of garlic mustard tissues. AITC and BzITC were much more phytotoxic to wheat (Triticum aestivum) than their respective parent glucosinolates sinigrin and glucotropaeolin. However, garden cress (Lepidium sativum) growth was inhibited to a greater degree by glucotropaeolin than BzITC, possibly due to conversion to BzITC by endogenous myrosinase. Sinigrin and glucotropaeolin were not detected in leaf/stem tissues harvested at the initiation of flowering, but were present in leaves and stems harvested in the autumn. Sinigrin levels in roots were similar for both sampling dates, but autumn-harvested roots contained glucotropaeolin at levels over three times higher than spring-harvested roots. The dominance of garlic mustard in forest ecosystems may be attributable in part to release of these phytotoxins, especially from root tissues.