Sinigrin, the predominant glucosinolate in the oriental mustard Brassica juncea, is mainly degraded upon the enzymatic action of myrosinase under normal conditions to give allyl isothiocyanate (AITC) in an aqueous media. Because AITC is considered to be the principal nematicidal ingredient in B. juncea, its stability in aqueous media is an important issue in achieving efficient nematode control. Pure sinigrin and AITC were found to be relatively stable in buffered water in the pH range of 5.00-7.00 but less stable at pH 9.00. Both sinigrin and AITC were more stable in soil water (supernatant of a 1:1 water/air-dried soil mixture) than in buffered water at the same pH range of 5.00-9.00. Sinigrin dissolved from the mustard bran or ground seed into water very quickly and was degraded by codissolved myrosinase to AITC. The AITC that formed from the degradation of sinigrin was found to be more stable in the soil water than in the buffered water. Buffer capacity was considered to be one of the factors that contributed to the stabilization of AITC in the soil water, but other unknown factors from both bran or seed and soil may also have contributed to the stabilization.

A reversed-phase HPLC method for the simultaneous determination of the glucosinolate sinigrin and its major degradation product allyl isothiocyanate (AITC) was developed and used for direct analysis of aqueous extracts from Oriental mustard (Brassica juncea L.) related materials (ground and cracked seeds, powders, and bran) and from soil samples. The lowest detection limit was 0.1 microg/mL for both sinigrin and AITC). The developed method was used to trace the degradation of sinigrin to AITC in aqueous extracts. One of the major advantages of this method is the complete estimation of sinigrin content. The simultaneous analysis of both sinigrin and AITC in a single run avoided the underestimation caused by separate analyses.

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The root‐lesion nematode (Pratylenchus penetrans Cobb) is a significant pest of many crops in Ontario. For example, more than 25 000 ha of land cropped to flue‐cured tobacco (Nicotiana tabacum L.) is fumigated annually at a mean cost for the fumigant materials alone of $484 ha−1. The objectives of these trials were to develop and evaluate a marigold (Tagetes sp.) rotation cropping system for the biological control of root‐lesion nematodes. In 1995 (site A) and 1996 (site B), field plots of Tagetes patula L. cv. Creole and Tagetes erecta L. cv. CrackerJack were established as rotation crops in comparison with the traditional rye rotation crop plus chemical fumigation prior to transplanting flue‐cured tobacco. Within 75 d of seeding marigold, P. penetrans population densities were reduced to less than 100 kg−1 soil, below the economic threshold of 500 P. penetrans kg−1 soil for tobacco. A marigold plant density of about 20 plants m−2 reduced P. penetrans population densities to levels below the economic threshold for the rotation crop year and the two following years. Tobacco yield was increased by a mean of 197 kg ha−1 by marigold rotation crops compared with rye plus chemical fumigation. The seed cost for a marigold crop at 20 plants m−2 varied from $221 ha−1 for T. patula to $294 ha−1 for T. erecta This new cropping system for the biological control of root‐lesion nematodes is a functional alternative to chemical fumigation for Ontario flue‐cured tobacco growers.

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