Benefits of Glucosinolates in Broccoli
» Broccoli plant tissues contain glucosinolate compounds that may have beneficial properties for plants and humans.
» Glucosinolates break down into isothiocyanates, which may contribute to the suppression of plant pests and pathogens.
» Other factors associated with broccoli soil amendments may have additional effects to those of glucosinolates in the development of disease suppressive soils.
Growers have relied on broccoli and other Brassica crops in
crop rotations to help manage soil health and reduce
disease pressure. These crops contain compounds called
glucosinolates that may play a role in disease suppression.
WHAT ARE GLUCOSINOLATES?
Glucosinolates are sulfur-containing compounds found
naturally in Brassica species, such as broccoli and cabbage.1
When broken down by the enzyme myrosinase, also present
in Brassica plants, glucosinolates are converted into other
compounds including isothiocyanates (ITCs). ITCs have been
found to protect plants against some diseases and pests
and to be useful in biofumigation when Brassica plants are
incorporated into the soil as green manures.
Over 130 different glucosinolate compounds have been
characterized. Different compounds are produced by
different Brassica species, and various glucosinolates can be
found in different tissues (roots vs. leaves) in the same
plant.2 Glucosinolate compounds commonly found in
broccoli include sinigrin, glucoraphanin, and gluconapin, with
the highest levels typically found in broccoli leaves, flower
buds, seeds, and sprouts. The level of glucosinolates
produced in broccoli tissue is affected by soil and weather
conditions, as well as levels of fertilization, methods of
cultivation, and the cropping season (spring vs. fall).2
Glucosinolates and their ITC derivatives have become a
focus of research because of their role in plant defense,
their effects on soil health, and the potential health benefits
for people who consume Brassica vegetables such as
broccoli. A study on the effects of glucosinolates produced
by several Brassica crops on two bacterial pathogens and
two fungal pathogens found that glucosinolate derivatives
inhibited the growth of the pathogens in culture and that
the level of inhibition depended on the amount of the
compound tested. This study also showed that the different
pathogens responded differently to the specific compounds,
showing that the ability of a plant to suppress a pathogen
depends on the compounds present in the plant and the
particular strains of the pathogen involved.3
In addition to being a factor in the disease resistance
properties of a plant, glucosinolates and ITCs may be useful
for pest management by affecting pathogens and pests in
the soil. Biofumigation is the process in which the residue of
certain Brassica species, such as broccoli, are incorporated
into the soil for purposes of suppressing bacteria, fungi,
nematodes, and weeds.4,5 This suppression is thought to be
due, in part, to the release of ITCs from the macerated and
Laboratory studies have consistently shown the toxic effects
of ITCs on plant pathogens growing in culture3, but
extrapolating from lab studies to determining the effectiveness
in the field can be challenging. The amount of ITCs released
depends on more than just the level of glucosinolates present
in the plant residue. The conversion of glucosinolates to ITCs
depends on the amount of myrosinase present in the plant
tissue and environmental factors, such as soil temperature,
moisture, and other soil conditions. Therefore, the effectiveness
of biofumigation with Brassica species, such as broccoli, to
suppress soilborne pathogens can be greatly influenced by
methods of crop destruction and incorporation and various
soil environmental factors.12
A field study published in 1999 found that incorporating
broccoli residue into the soil effectively suppressed the
levels of Verticillium wilt in following broccoli and cauliflower
plantings (Figure 1).4 A follow-up study found that rotating
winter broccoli crops with summer strawberry crops in
California reduced the level of the pathogen Verticillium
dahliae in the soil, lowered the severity of Verticillium wilt on
strawberry, and increased growth of the strawberry plants
and fruit yield, when compared with rotations not including
Other studies have shown that soil amendments with
Brassica crop residues can inhibit a range of plant pests
including bacterial pathogens such as Ralstonia
solanacearum, Pseudomonas marginalis, and Streptomyces
scabies, nematodes including root-knot nematodes and potato
cyst nematodes, and fungal and fungal-like pathogens such
as Sclerotinia minor, Sclerotinia sclerotiorum, Verticillium
dahliae, Rhizoctonia solani, Aphanomyces euteiches, and
Applications of mustard crops residues as mulch were
shown to reduce disease levels of lettuce drop, caused by
the fungus Sclerotinia minor, and to increase lettuce yields.
Lettuce plants also produced larger heads in plots treated
with the mustard variety ‘Ida Gold’, which produces high
levels of glucosinolates.10 Other studies looking at the effects
of cover crops and green manures on lettuce drop have
found little to no disease suppression associated with
Brassica treatments.11 The effects of Brassica biofumigation
and the role of glucosinolates in the suppression of
soilborne diseases are still unclear and topics of continuing
Compounds other than glucosinolates found in broccoli and
other Brassica crops also appear to be involved in pathogen
suppression. The addition of broccoli residue to soil was
found to stimulate the naturally occurring community of
biocontrol organisms in the soil, and the activity of these
antagonists also suppressed soilborne pathogens.7 Other
Brassica crops, including canola, rapeseed, radish, turnip, yellow
mustard, and Indian mustard have been studied for their
effects on soil disease suppression.9,13 The advantage of
using broccoli as a green manure is that it is also a valuable
horticultural crop that provides farm revenue, and broccoli
fits well in rotation schedules with other vegetable crops.
BROCCOLI AND HUMAN HEALTH
The consumption of broccoli, cabbage, and other Brassica
vegetables has long been considered to contribute to a
healthy diet, and studies have found that some of those
benefits may result from glucosinolates and isothiocyanates.
The results from a group of studies looking at the health
benefits of eating Brassica vegetables showed an association
of eating more Brassica vegetables with reductions in risks
of several types of cancer and a reduced risk of myocardial
infarction (heart attack).5,14
Broccoli varieties with enhanced levels of glucosinolates
have been developed, primarily for their potential human
health benefits*.15 These varieties may also be useful in
managing soilborne plant pathogens and the diseases they
1 James, D., Devaraj, S., Bellur, P., Lakkanna, S., Vicini, J., and Boddupalli, S. 2012. Novel concepts of broccoli sulforaphanes and disease: Induction of phase II antioxidant and detoxification enzymes by enhanced-glucoraphanin broccoli. Nutrition Reviews 70 :654–665.
2 Motisi, N., Montfort, F., Doré, T., Romillac, N., and Lucas, P. 2009. Duration of control of two soilborne pathogens following incorporation of above- and below-ground residues of Brassica juncea into soil. Plant Pathology 58:470–478.
3 Sotelo, T., Lema, M., Soengas, P., Cartea, M., and Velasco, P. 2015. In vitro activity of glucosinolates and their degradation products against Brassica-pathogenic bacteria and fungi. Appl Environ Microbiol 81:432– 440.
4 Subbarao, K., Hubbard, J., and Koike, S. 1999. Evaluation of broccoli residue incorporation into field soil for Verticillium wilt control in cauliflower. Plant Dis. 83:124-129.
5 Traka, M. and Mithen, R. 2009. Glucosinolates, isothiocyanates and human health. Phytochem Rev 8: 269-282.
6 Subbarao, K., Kabir, Z., Martin, F., and Koike, S. 2007. Management of soilborne diseases in strawberry using vegetable rotations. Plant Dis. 91:964-972.
7 Shetty, K., Subbarao, K., Huisman, O., and Hubbard, J. 2000. Mechanism of broccoli-mediated Verticillium wilt reduction in cauliflower. Phytopathology 90:305-310.
8 Larkin, R. 2015. Soil health paradigms and implications for disease management. Annual Review of Phytopathology 53:199–221.
9 Larkin, R. and Griffin, T. 2007. Control of soilborne potato diseases using Brassica green manures. Crop Protection 26:1067–1077.
10 Daugovish, O., Downer, J., and Mochizuki, M. 2007. Mustard-derived biofumigation for lettuce in coastal California. Hortscience 42:953-953.
11 Bensen, T., Smith, R., Subbarao, K., Koike, S., Fennimore, S., and Shem-Tov, S. 2009. Mustard and other cover crop effects vary on lettuce drop caused by Sclerotinia minor and on weeds. Plant Dis. 93:1019-1027.
12 Matthiessen, J. and Kirkegaard, J. 2006. Biofumigation and enhanced biodegradation: opportunity and challenge in soilborne pest and disease management. Critical Reviews in Plant Sciences 25: 235-265.
13 Debode, J., Clewes, E., De Backer, G., and Hofte, M. 2005. Lignin is involved in the reduction of Verticillium dahliae var. longisporum inoculum in soil by crop residue incorporation. Soil Biol. Biochem. 37:301-309.
14 Johnson, I. 2002. Glucosinolates in the human diet. Bioavailability and implications for health. Phytochemistry Reviews 1: 183–188.
15 Sarikamis, G., Marquez, J., MacCormack, R., Bennett, R., Roberts, J., and Mithen, R. 2006. High glucosinolate broccoli: a delivery system for sulforaphane. Molecular Breeding 18:219-228.
* Please note that any consumer product labels that bear broccoli-related health or nutrient content claims would need to be in compliance with FDA regulations applicable to such claims.
For additional agronomic information, please contact your local seed representative. Developed in partnership with Technology Development & Agronomy by Monsanto.
Individual results may vary, and performance may vary from location to location and from year to year. The information provided in this communication may not be an indicator of results you may obtain as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible. The recommendations in this article are based upon information obtained from the cited sources and should be used as a quick reference for information about the association of glucosinolates with suppression of plant pathogens and pests. The content of this article should not be substituted for the professional opinion of a producer, grower, agronomist, plant pathologist, or similar professionals dealing with this topic. SEMINIS DOES NOT WARRANT THE ACCURACY OF ANY INFORMATION OR TECHNICAL ADVICE PROVIDED HEREIN AND DISCLAIMS ALL LIABILITY FOR ANY CLAIM INVOLVING SUCH INFORMATION OR ADVICE. 170928070900 010818DME
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