Sorghum allelopathy under field conditions may be caused by a combination of allelochemicals

Figures & data

Table 1. Some of the weeds found in southern Africa, reported to be suppressed by sorghum allelopathy.

Weed species	Common name	Category	Family name	Reference
Abutilon theophrasti Medik.	Velvetleaf	Broadleaf	Malvaceae	Roth et al., 2000
Aeschynomene indica l.	Indian jointvetch	Broadleaf	Fabaceae	Uddin et al., 2013
Amaranthus retroflexus L.	Redroot pigweed	Broadleaf	Amaranthaceae	Uddin et al., 2014
Amaranthus hybridus L.	Smooth pigweed	Broadleaf	Amaranthaceae	Mandumbu et al., 2016
Amaranthus palmeri S. Wats.	Palmer amaranth	Broadleaf	Amaranthaceae	Forney et al., 1985
Anagallis arvensis L.	Scarlet pimpernel	Broadleaf	Primulaceae	Ashraf & Akhlaq, 2007
Avena fatua L.	Wild oat	Grass	Poaceae	Khan et al., 2018
Bidens pilosa L.	Blackjack	Broadleaf	Asteraceae	Tibugari et al. 2020c
Chenopodium album L.	Fat hen	Broadleaf	Chenopodiaceae	Naeem et al., 2018
Convolvulus arvensis L.	Field bindweed	Broadleaf	Convolvulaceae	Cheema, 1988
Cynodon dactylon (L.) Pers.	Couch grass	Grass	Poaceae	Cheema et al., 2002
Cyperus rotundus L.	Purple nutsedge	Sedge	Cyperaceae	Kandhro et al., 2014
Cyperus iria L.	Rice flatsedge	Sedge	Cyperaceae	Forney et al., 1985
Dactyloctenium aegyptium (L.) Willd.	Crowfoot grass	Grass	Poaceae	Mubeen et al., 2012
Datura stramonium L.	Jimsonweed	Broadleaf	Solanaceae	Einhellig & Souza, 1992
Digitaria sanguinalis (L.) Scop.	Hairy crabgrass	Grass	Poaceae	Uddin et al., 2014
Digitaria ischaemum Schr. Muhl.	Smooth crabgrass	Grass	Poacea	Putnam & DeFrank, 1983
Echinochloa colona (L.) Link	Junglerice	Grass	Poaceae	Yar et al., 2020
Echinochloa crus-galli (L.) P. Beauv.	Barnyard grass	Grass	Poaceae	Panasiuk et al., 1986
Eclipta prostrata (L.) L.	False daisy	Broadleaf	Asteraceae	Uddin et al., 2010
Eleusine indica (L.) Gaertn.	Goose grass	Grass	Poaceae	Murimwa et al., 2019
Erigeron canadensis (L.) Cronquist	Canadian fleabane	Broadleaf	Asteraceae	Uddin et al., 2010
Euphorbia heterophylla L.	Wild poinsettia	Broadleaf	Euphorbiaceae	Ayeni & Kayode, 2013
Fumaria indica Hauskn.	Fumitory	Broadleaf	Fumariaceae	Ashraf & Akhlaq, 2007
Galium spurium L.	False cleavers	Broadleaf	Rubiaceae	Uddin et al., 2010
Ipomoea triloba L.	Three-lobe morning glory	Broadleaf	Convolvulaceae	Kim et al., 1993
Lemna minor L.	Common duckweed	Grass-like	Lemnaceae	Einhellig & Souza, 1992
Lolium rigidum Gaudin	Rigid ryegrass	Grass	Poaceae	Rashid et al., 2020
Lolium perenne (L.) ssp. multiflorum (Lam.) Husnot	Italian ryegrass	Grass	Poacea	Forney & Foy, 1985
Lolium temulentum L.	Darnel ryegrass	Grass	Poacea	Jassim et al., 2022
Medicago polymorhha L.	Bur clover	Broadleaf	Fabaceae	Ashraf & Akhlaq, 2007
Parthenium hysterophorus L.	Famine weed	Broadleaf	Asteraceae	Javaid et al., 2006
Phalaris minor Retz.	Littleseed canarygrass	Grass	Poaceae	Khan et al., 2018
Plantago asiatica L.	Chinese plantain	Broadleaf	Plantaginaceae	Uddin et al., 2014
Portulaca oleracea L.	Purslane	Broadleaf	Portulacaceae	Uddin et al., 2014
Rottboellia cochinchinensis Lour. W.D. Clayton	Itchgrass	Grass	Poaceae	Kim et al., 1993
Rumex acetosella L.	Sheep’s sorrel	Broadleaf	Polygonaceae	Panasiuk et al., 1986
Rumex crispus L.	Curly dock	Broadleaf	Polygonaceae	Forney & Foy, 1985
Rumex dentatus L.	Toothed dock	Broadleaf	Polygonaceae	Cheema, 1988
Rumex japonicus Houtt.	Japanese dock	Broadleaf	Polygonaceae	Uddin et al., 2010
Senebiera didyma L. Pers.	Lesser swinecress	Broadleaf	Brassicaceae	Cheema & Ahmed, 1992
Setaria viridis (L.) P. Beauv.	Green foxtail	Grass	Poaceae	Uddin et al., 2013
Trianthema portulacastrum L.	Horse purslane	Broadleaf	Aizoaceae	Khaliq et al., 2011
Xanthium strumarium L.	Common cocklebur	Broadleaf	Asteraceae	Alsaadawi et al., 2015

Figure 1. Fresh root processing and drying of solvent extract.

Table 2. Characteristics of sorghum accessions used in the field experiment.

Accession	Description	Origin	Sorgoleone content (µg/mg r.f.w)	Days to flowering post-rainy	Days to flowering rainy	100 seed weight (g)
Macia	OPV	Botswana, Mozambique, Tanzania, Zimbabwe	2.5	60	65	2.0
IS35583	Landrace	Namibia	104.3	73	85	3.72
IS13807	Landrace	South Africa	50.0	73	54	2.5
IS9409	Landrace	South Africa	152.3	84	67	2.67
IS9362	Landrace	South Africa	252.9	89	62	2.3
IS14002	Landrace	South Africa	381.2	82	62	3.35
IS14003	Landrace	South Africa	472.7	84	58	2.96
IS9456	Landrace	South Africa	584.7	69	56	3.2
IS19462	Landrace	Botswana	302.8	70	55	3.82
IS23342	Landrace	Zambia	207.1	98	133	2.13
IBS718	Sweet	Zimbabwe	20.1	*	*	*

* Details omitted since this accession is not cultivated for grain.

Table 3. Sorgoleone content of the eleven sorghum accessions evaluated for allelopathic effects on summer and winter weeds at Panmure Experiment Station, Zimbabwe.

Accession	Description	Origin	Sorgoleone content (µg/mg r.f.w)
Macia	Commercial (OPV)	Botswana, Mozambique, Tanzania, Zimbabwe	2.5
IBS718	Sweet stem	Zimbabwe	20.1
IS13807	Landrace	South Africa	50.0
IS35583	Landrace	Namibia	104.3
IS9409	Landrace	South Africa	152.3
IS23342	Landrace	Zambia	207.1
IS9362	Landrace	South Africa	252.9
IS19462	Landrace	Botswana	302.8
IS14002	Landrace	South Africa	381.2
IS14003	Landrace	South Africa	472.7
IS9456	Landrace	South Africa	584.7

Source: Tibugari et al., 2019b.

Figure 2. Rainfall received and irrigation applied in summer and winter months of the trial. Source: Panmure Experiment Station Weather Station, Shamva, Zimbabwe. Temperatures ranged from 5 °C to about 20 °C (Figure 3).

Figure 3. Average maximum and minimum monthly temperatures for the summer (A) and winter (B) seasons. Source: Panmure Experiment Station Weather Station, Shamva, Zimbabwe.

Figure 4. Stacked bar charts for summer (A) and winter (B).

Table 4. Effect of sorghum accession and weeding regime on sorghum growth and yield in summer (January to June 2018).

Sorghum accession	% emergence	Final crop stand	Height (cm)	Head weight (g)	Grain weight (g)	Stover biomass (g plant^−1)
IBS718	76.4ab	85.0ab	154.3ab	535abc	241ab	138.1
IS13807	48.6ab	72.7a	190.5ab	407ab	181a	100.7
IS14002	38.9a	73.3ab	131.2a	218a	192a	153.5
IS14003	83.3ab	91.0ab	234.2bc	444ab	189a	156.7
IS19462	75.0ab	83.7ab	196.2abc	1126cd	681bc	110.4
IS23342	84.7b	88.7ab	177.3ab	959bcd	578abc	151.1
IS35583	57.0ab	76.3ab	195.7abc	400ab	178a	144.1
IS9362	43.1ab	77.5ab	228.5bc	348ab	207a	150.8
IS9409	47.2ab	73.2ab	194.8abc	594abc	422abc	135.2
IS9456	52.8ab	75.7ab	275.0c	346ab	130a	139.3
Macia	75.0ab	91.7b	158.0ab	1281d	837c	140.4
p Value	p < 0.05	p < 0.05	p < 0.001	p < 0.001	p < 0.001	P > 0.05
s.e.d.	12.67	5.48	23.06	178.6	133.6	23.46
Weeding regime
Unweeded	59.6	79.8	190.2	499a	295	129.7
Weeded	64.4	81.7	198.1	712b	403	146.7
P value	P > 0.05	P > 0.05	P > 0.05	p < 0.05	P > 0.05	P > 0.05
s.e.d.	5.40	2.34	9.83	76.1	56.9	10.00
Sorghum accession × weeding regime interaction
P value	P > 0.05	P > 0.05	P > 0.05	p < 0.05	P > 0.05	P > 0.05
s.e.d.	17.92	7.76	32.61	252.5	188.9	33.18

Means within a column followed by the same letter are not significantly different at P > 0.05.

Figure 5. Sorghum accession × weeding regime interaction.

Table 5. Effect of sorghum accession and weeding regime on sorghum growth and yield in warm winter (July–December 2018).

Sorghum accession	% emergence	Final crop stand	Height (cm)	Head weight (g)	Grain weight (g)	Stover biomass (g plant^−1)
IBS718	84.72	88.0	166.8a	526a	274a	132.6
IS13807	83.32	86.5	179.8a	648ab	341ab	141.1
IS14002	90.28	92.7	158.0a	719ab	363ab	139.7
IS14003	84.70	87.8	203.7ab	678ab	378ab	140.7
IS19462	87.50	89.5	165.2a	622ab	381ab	118.1
IS23342	86.10	88.8	152.2a	556ab	252a	135.9
IS35583	86.12	90.2	156.7a	504a	267a	150.3
IS9362	84.72	88.3	207.8ab	556ab	244a	134.4
IS9409	80.57	84.8	170.7a	526a	248a	102.2
IS9456	83.35	88.8	248.5b	459a	185a	147.8
Macia	80.55	87.0	142.8a	1007b	570b	103.0
P value	P > 0.05	P > 0.05	p < 0.001	p < 0.05	p < 0.05	P > 0.05
s.e.d.	4.354	3.911	18.47	131.5	84.4	25.94
Weeding regime
Unweeded	83.83	87.7	178.0	605	309	131.8
Weeded	85.61	89.2	177.0	631	328	131.0
P value	P > 0.05	P > 0.05	P > 0.05	P > 0.05	P > 0.05	P > 0.05
s.e.d.	1.856	1.668	7.87	56.1	36.0	11.06
Sorghum accession ˟ weeding regime interaction
P value	P > 0.05	P > 0.05	P > 0.05	P > 0.05	P > 0.05	P > 0.05
s.e.d.	6.157	5.531	26.12	185.9	119.3	36.69

Means within a column followed by the same letter are not significantly different at P > 0.05.

Figure 6. Loadings plot correlations for summer (A) and winter (B).

Table 6. Weed species recorded in summer and winter.

Weed species	Family name	Common name(s)	Summer	Winter
Grasses
Digitaria sanguinalis	Poaceae	Crab finger grass	p (m)	a
Eleusine indica	Poaceae	Goosegrass	p (m)	a
Rottboellia cochinchinensis	Poaceae	Itchgrass/Shamva grass	p (m)	a
Hyparrhenia filipendula	Poaceae	Hyparrhenia	p (m)	a
Cynodon nlemfuensis	Poaceae	African Bermudagrass	p (m)	a
Broadleaf
Acanthospermum hispidum	Asteraceae	Upright starbur	p (m)	a
Ageratum conyzoides	Asteraceae	Billygoat weed	p (d)	p
Bidens pilosa	Asteraceae	Hairy beggarticks	p (m)	p
Richardia scabra	Rubiaceae	Mexican clover	p (d)	p
Sida alba	Malvaceae		p (m)	p
Commelina benghalensis	Commelinaceae	Wandering jew	p (m)	a
Amaranthus hybridus	Amaranthaceae	Slim amaranth	p (m)	p
Ipomoea involucrata	Convolvulaceae	Morning-glory	p (m)	a
Euphorbia heterophylla	Euphorbiaceae	Mexican fireplant	p (m)	a
Physalis angulata	Solanaceae	Wild gooseberry	p (m)	a
Sesbania sesban	Fabaceae	Egyptian riverhemp	p (m)	p (m)
Leucas martinicensis		Bobbin weed	p (m)	p (m)

Key: p = present; a = absent; (m) = minor weed; (d) = dominant weed.

Figure 7. Interaction between sorghum presence and weeding regime on A. conyzoides (A), R. scabra (B) and total weed density (C) in summer 65 DAS (Error is for comparison for no sorghum and sorghum presence).

Table 7. Effect of sorghum presence, sorghum accession and weeding regime on weed density (square root (x + 0.5) transformed weed number m⁻²) in summer 65 DAS.

	A. conyzoides	R. scabra	Minor weeds	Total
Sorghum presence
With sorghum	2.208a (4.61)^1	2.142a (4.35)	1.800a (2.82)	3.447 (11.78)
With no sorghum (control)	2.638b (6.67)	2.675b (7.00)	2.075b (3.83)	4.192 (17.5)
P value	P = 0.002	p < 0.001	p < 0.05	p < 0.001
s.e.d.	0.13	0.1402	0.1195	0.1608
Sorghum presence × Sorghum accession interaction
P value	P > 0.05	P > 0.05	P > 0.05	P > 0.05
s.e.d.	0.1784	0.1898	0.1619	0.2177
Sorghum presence ˟ Weeding regime interaction
P value	p < 0.001	p < 0.001	P > 0.05	p < 0.001
s.e.d.	0.0.1863	0.1982	0.1691	0.2274
Sorghum presence ˟ Weeding regime ˟ sorghum accession interaction
P value	P > 0.05	P > 0.05	P > 0.05	P > 0.05
s.e.d.	0.2522	0.2684	0.2289	0.3079

•Means (square root (x + 0.5) transformed weed numbers m⁻²) within a column followed by the same letter are not significantly different at p < 0.05.

•¹Data in brackets are back-transformed actual weed numbers per m⁻².

Figure 8. Interaction between sorghum presence and sorghum accession on S. alba density in winter at 65 DAS.

Figure 9. Effect of sorghum presence and weeding regime on A. conyzoides (A), A. hybridus (B), B. pilosa (C) and total weed density (D) in winter 65 DAS (Error is for comparison for no sorghum and sorghum presence).

Figure 10. Interaction between sorghum presence and sorghum accession on A. conyzoides (A) and total weed biomass (B) in summer at 65 DAS.

Table 8. Effect of sorghum presence, sorghum accession and weeding regime on weed density in winter 65 DAS.

	A. conyzoides	A. hybridus	B. pilosa	R. scabra	S. alba	Total
Sorghum presence
With sorghum	2.147a (4.36)^1	1.951a (3.62)	2.044a (3.94)	1.729a (2.56)	1.709a (2.485)	4.112 (16.95)
With no sorghum (control)	2.901b (8.50)	2.700b (7.00)	2.578b (6.83)	1.985b (3.50)	1.985b (3.500)	5.374 (29.33)
P value	p < 0.001	p < 0.001	p < 0.001	p < 0.05	p < 0.05	p < 0.001
s.e.d.	0.0938	0.1461	0.1082	0.1102	0.1004	0.1105
Sorghum presence ˟ Sorghum accession interaction
P value	P > 0.05	P > 0.05	P > 0.05	P > 0.05	P = 0.021	P > 0.05
s.e.d.	0.1270	0.1978	0.1465	0.1492	0.1360	0.1497
Sorghum presence ˟ Weeding regime interaction
P value	p < 0.001	p < 0.001	p < 0.001	P > 0.05	P > 0.05	p < 0.001
s.e.d.	0.1327	0.2066	0.1530	1.559	0.1420	0.1563
Sorghum presence ˟ Weeding regime ˟ Sorghum accession interaction
P value	P > 0.05	P > 0.05	P > 0.05	P > 0.05	P > 0.05	P > 0.05
s.e.d.	0.1797	0.2798	0.2072	0.2110	0.1923	0.2117

•Means (square root (x + 0.5) transformed weed numbers m⁻²) within a column followed by the same letter are not significantly different at p < 0.05.

•¹Data in brackets are back-transformed actual weed numbers per m⁻².

Figure 11. Effect of sorghum presence and weeding regime on biomass of minor weeds (A) and total weed biomass (B) in summer at 65 DAS.

Table 9. Effect of sorghum presence, accession and weeding regime on weed biomass (g m⁻²) in summer 65 DAS.

	A. conyzoides	R. scabra	Minor weeds	Total
Sorghum presence
With sorghum	6.53	3.59a	11.25a	21.37b
With no sorghum (control)	5.65	5.12b	20.42b	31.18a
P value	P > 0.05	P = 0.028	p < 0.001	p < 0.001
s.e.d.	0.586	0.674	1.175	1.615
Sorghum presence × Sorghum accession interaction
P value	P = 0.003	P > 0.05	P > 0.05	P = 0.041
s.e.d.	0.793	0.913	1.591	2.187
Sorghum presence × Weeding regime interaction
P value	P > 0.05	P > 0.05	p < 0.001	p < 0.001
s.e.d.	0.829	0.953	1.662	2.284
Sorghum presence × Weeding regime × Sorghum accession interaction
P value	P > 0.05	P > 0.05	P > 0.05	P > 0.05
s.e.d.	1.122	1.291	2.251	2.324

• Means within a column followed by the same letter are not significantly different at p < 0.05.

Figure 12. Interaction between sorghum presence and sorghum accession on B. pilosa (A) and R. scabra biomass (B) in winter at 65 DAS.

Table 10. Effect of sorghum presence, sorghum accession and weeding regime on weed biomass (g m⁻²) in winter 65 DAS.

	A. conyzoides	A. hybridus	B. pilosa	R. scabra	S. alba	Total
Sorghum presence
With sorghum	5.60	5.41	5.38	5.52	5.41	27.32
With no sorghum (control)	4.65	4.50	5.53	4.82	4.13	23.63
P value	P > 0.05	P > 0.05	P > 0.05	P > 0.05	P > 0.05	P > 0.05
s.e.d.	0.781	0.819	0.416	0.686	0.651	1.985
Sorghum presence ˟ Sorghum accession interaction
P value	P > 0.05	P > 0.05	p < 0.001	P = 0.008	P > 0.05	P > 0.05
s.e.d.	1.057	1.109	0.563	0.929	0.881	2.687
Sorghum presence ˟ Weeding regime interaction
P value	P > 0.05	P > 0.05	P > 0.05	P > 0.05	P > 0.05	P > 0.05
s.e.d.	1.104	1.158	0.588	0.970	0.920	2.807
Sorghum presence ˟ Weeding regime ˟ Sorghum accession interaction
P value	P > 0.05	P > 0.05	P > 0.05	P > 0.05	P > 0.05	P > 0.05
s.e.d.	1.495	1.568	0.796	1.314	1.246	3.800

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Data availability statement

Data will be made available upon request.