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. 2018 Oct 15;7(4):85. doi: 10.3390/plants7040085

Table 1.

Summary of the involvement of plant flavonoids in plant–nematode interactions. Rows in red indicate studies demonstrating the role of flavonoids in nematode defense responses, whereas rows in blue indicate studies demonstrating the role of flavonoids in nematode feeding sites and rows in purple indicate studies intersecting across both roles.

Name of Enzyme/Gene/Metabolite Flavonoid Accumulation Site Suggested Flavonoid Function Host Studied Nematode Studied Reference
Glyceollin Roots Glyceollin I and III accumulated more in the resistant cultivar compared with the susceptible cultivar. Soybean, Glycine max Soybean cyst nematode, Heterodera glycines [64]
Stele in roots Glyceollin was associated with the incompatible interaction between the resistant cultivar and M. incognita: accumulation was localised in the stele of resistant roots, high concentrations of glyceollin in resistant cultivar and glyceollin inhibited the motility of M. incognita. Soybean, Glycine max Root-knot nematodes, Meloidogyne incognita. and M. javanica [65]
Leaves Glyceollin accumulated at sufficiently high concentrations at infection sites to result in a localised hypersensitive response. It inhibited nematode motility and respiration as well as plant tissue death via inhibition of mitochondrial electron transport system. In vitro system Root-knot nematodes, Meloidogyne incognita, and M. javanica [66]
Phaseollin Hypocotyl and root Phaseollin found only in P. penetrans infected tissue. The survival of P. penetrans juveniles incubated for 16 h in 47 µg/mL of phaseollin solution was unaffected. Common bean, Phaseolus vulgaris Root-lesion nematode, Pratylenchus penetrans [67]
Sakuranetin Leaf Present only in resistant cultivars—suggested to be involved in defense Rice Stem nematode, Ditylenchus angustus [68]

  1. Formononetin and Formononetin-7-O-glu-coside-6”-O-malonate

  2. Medicarpin-3-O-gluco-side-6”-O-malonate

  3. Medicarpin

  4. Coumesterol glucosides

 Roots, meristems, leaves Isoflavonoid and pterocarpan (conjugate) accumulation correlated with nematode resistance.
Medicarpin inhibited P. penetrans in a concentration dependent manner.		 White clover, Trifolium repens Stem nematode, Ditylenchus dipsaci [47]
Lucerne, Medicago sativa Stem nematode, Ditylenchus dipsaci [52]
Lucerne, Medicago sativa Root-lesion nematode, Pratylenchus penetrans [69]

  1. O-methyl-apigenin-C-hexoside-O-deoxyhexoside

  2. Apigenin-C-hexoside-O-pentoside

  3. Luteolin-C-hexoside-O-pentoside

 Roots and shoots during P. neglectus and H. avenae infection Flavonoids possibly acted as broad defense compounds—induced in methyl jasmonate and nematode-treated plants. Plants treated with root extracts from methyl jasmonate-induced plants had reduced infection. Oats, Avena sativa Root lesion nematode, Pratylenchus neglectus, Cereal cyst nematode, Heterodera avenae, Stem nematode, Ditylenchus dipsaci [70]

  1. Coumesterol

  2. Psoralidin

 Roots Coumesterol and psoralidin accumulated in roots and were localised at lesion sites caused by nematodes only in lima bean. Coumesterol significantly inhibited nematode motility at 10–15 µg/mL concentrations. Lima bean, Phaseolus lunatus and snap bean, P. vulgaris Root-lesion nematode, Pratylenchus scribneri [71]

  1. Quercentagetin (hydroxy-flavone)

  2. Aurone

  3. Chalcone

 Adult female extracts The yellow coloration in G. rostochiensis and G. pallida is attributed to flavonoid quercetagetin, which was present in pathotypes with yellow color and absent in paler pathotypes. N/A Potato cyst nematodes, Globodera rostochiensis and G. pallida [48]

  1. Flavan-3,4-diols

  2. Condensed tannins

 Roots Flavan-3,4-diols and condensed tannins accumulated after nematode infection. Banana, Musa Burrowing nematode, Radopholus similis [72]

  1. Daidzein

  2. Genistein

  3. Other isoflavonoids

 Roots Daidzein and genistein increased in susceptible Sussex cultivar at two and four days post inoculation. Isoflavonoid production was enhanced in nematode infected plants in susceptible Sussex and resistant Hartwig cultivar at two and three days post inoculation. Soybean, Glycine max Soybean cyst nematode, Heterodera glycines [73]
Several compounds from the chalcone, flavone, flavanone, isoflavonoid and flavonol pathways. Purified compounds and plant extracts. Kaempferol, quercetin and myricetin repelled R. similis and M. incognita juveniles at 60–84 µg/mL. Luteolin, daidzein and genistein, repelled R. similis at 100–142 μg/mL. Kaempferol, quercetin, myricetin, rutin and quercitrin inhibited 13–41% of M. incognita juveniles after 48 h of incubation. Naringenin and hesperetin, apigenin, daidzein, and kaempferol reduced egg hatching in R. similis up to 21%. N/A Burrowing nematode, Radopholus similis, root-lesion nematode, Pratylenchus penetrans and root-knot nematode, Meloidogyne incognita [41]

  1. Patuletin

  2. Patulitrin

  3. Quercetin

  4. Rutin

 Purified compounds and marigold, Tagetes patula L. flower extracts Patuletin killed 100% of nematodes at various dilutions after 72 h, whereas patulitrin killed 10–50% and quercetin killed 70–80% of nematodes. Rutin at 0.5–1% killed all nematodes within 24 h. N/A Corn cyst nematode, Heterodera zeae [42]
(E)-chalcone Purified compound (E)-chalcone killed nematodes at 33 μM within 24 h and completely inhibited egg hatching at <10 μM within 15 days. N/A Potato cyst nematodes, Globodera rostochiensis and G. pallida [46]
Phenylalanine ammonia lyase (PAL) Roots Plants grown at 27 °C had optimal PAL activity, which enabled the plants to synthesise phenylpropanoids used in nematode defense, as opposed to 32 °C, which inhibited enzyme activity. Tomato, Lycopersi- cum esculentum Root-knot nematode, Meloidogyne incognita [74]

  1. Phenylalanine ammonia lyase

  2. Chalcone synthase

  3. Chalcone isomerase

  4. Isoflavone reductase

  5. Caffeic acid O-methyltransferase

  6. 4-coumarate-CoA ligase

  7. Cinnamoyl CoA reductase

  8. Dihydroflavonol 4-reductase

 Roots Gene expression levels generally induced by nematodes and higher in resistant plants. Alfalfa, Medicago sativa Root-lesion nematode, Pratylenchus penetrans [69]
Soybean, Glycine max Heterodera glycines and Meloidogyne incognita [75]
Cowpea. Vigna unguiculata L. Walp Meloidogyne incognita [76]
Soybean, Glycine max genotype PI 88788 Soybean cyst nematode, Heterodera glycines population NL1-RHg/HG-type 7 [77]
Flavonoid pathways:

  1. Arabidopsis: chalcone synthase, chalcone isomerase and flavonoid 3’ hydroxylase, dihydroflavonol 4-reductase

  2. Tobacco: Phenylalanine ammonia lyase, anthocyanidins

 Roots M. incognita reproduction was significantly higher in tobacco mutant with higher anthocyanidin content.
M. incognita reproduction in Arabidopsis tt mutants and wild-type plants were similar.		 Tobacco, Nicotiana tabacum and Arabidopsis thaliana Root-knot nematode, M. incognita [63]

  1. Quercetin 7-glucoside and other phenols

 Root extracts Root extracts inhibited nematode motility, reduced nematode egg hatching and reduced gall numbers. Lantana camara L. Root-knot nematode, Meloidogyne javanica [78]
Chalcone isomerase
Auxin-induced protein		 Roots Chalcone isomerase protein as well as an auxin-induced protein were increased at 4, 5, and 6 days post inoculation. Cowpea. Vigna unguiculata L. Walp Root-knot nematode, Meloidogyne incognita [79]

  1. Chalcone synthase

  2. Chalcone flavanone isomerase

  3. Isoflavone reductase (putative)

  4. Dihydroflavonol 4-reductase

  5. Quercetin 3-O-methyltransferase

  6. 4-coumarate-CoA ligase

  7. PIN 2

Root tissue Upregulation of flavonoid synthesis and PIN 2 genes in nematode infected roots. Soybean, Glycine max L. Merr. cv. Williams 82 Soybean cyst nematode, Heterodera glycines Ichinohe [80]

  1. Chalcone synthase genes, CHS1, CHS2, CHS3

  2. Auxin responsive gene, GH3

 Root tissue CHS1::gusA, CHS2::gusA and CHS3::gusA expressions overlapped with GH3::gusA expression at 48 h, 72 h and 120 h post inoculation. White clover, Trifolium repens cv. Haifa Root-knot nematode, Meloidogyne javanica [81]

  1. tt4 (chalcone synthase) mutant,

  2. tt5 (chalcone isomerase) mutant

  3. tt6 (flavonoid 3’ hydroxylase) mutant

 N/A Flavonoid deficiency in tt (transparent testa) mutant lines of single and double tt4, tt5, and tt6 did not reduce the number of adult females, with several lines producing more female nematodes. Arabidopsis thaliana Sugar beet nematode, Heterodera schachtii [62]
Chalcone synthase (silencing by RNA interference) Root tissue Flavonoid deficiency did not affect gall numbers. Flavonoid deficient roots had shorter galls and less pericycle cell division compared to roots with flavonoids. Barrel medic, Medicago truncatula Root-knot nematode, Meloidogyne javanica [82]