Abstract

Media summary

Key Words

Introduction

Weeds impose an important biological constraint to wheat production worldwide. In China, lambsquarters (Chenopodium album L.) and redroot amaranth (Amaranthus retroflexus L.) are widespread weeds in wheat field and substantially reduce wheat yield. Their control has been characterized by hand and high dose of herbicides. It is desirable to have alternative weed control method in wheat fields. Application of allelopathy to control weeds can avoid environmental contamination and improve crop yield. Allelopathic control refers to the eco-friendly method that exploits allelochemicals from volatile, leachate, exudates or residues of certain plant to control weeds (Weston 1996).

In recent years, it has been found that some wheat varieties have allelopathic traits and can suppress weed growth through the allelochemicals synthesized and released from wheat varieties themselves. Alleopathic wheat varieties have been evaluated from different wheat germplasm collections (Blum et al. 1992; Oueslati 2003; Weston 1996; Wu et al. 2001; Wu et al. 2002). Wu et al. (1998) showed that radical elongation of ryegrass was inhibited over a range from 19.2% to 98.7% and for seed germination from 4.2% to 73.2% among thirty-eight wheat (Triticum aestivum L.) and one durum wheat (Triticum durum Desf.) cultivars. This indicates that allelopathic potential of wheat varieties was correlated with their heredity and allelochemicals released into the environment under natural conditions (Kong et al. 2002; Wu et al. 2003). Thus, wheat allelopathy has a potential to improve weed management in wheat production.

The objective of this study is to evaluate allelopathic potential of 27 wheat varieties from a Chinese germplasm collection with different origins and agronomic traits against C. album and A. retroflexus.

Methods

Plant material

Seeds of 27 Chinese wheat varieties with different origins and agronomic traits were provided by the Crop Breeding Institute, Academy of Agricultural Sciences in Liaoning (LNAA), Jilin (JLAAS) and Heilongjiang (HLJAAS) provinces, Academy of Agricultural Sciences in Jinzhou (JZAAS), Baicheng (BCAAS) and Tieling (TLAAS) cities, Northeast Normal University (NNU) and Shenyang Agricultural University (SYAU). The origin of 27 wheat varieties is described in Table 1. Seeds of lambsquarters (C. album L.) and redroot amaranth (A. retroflexus L.) were collected at the Shenyang Experimental Station of Ecology (41°31' N, 123°22' E), Chinese Academy of Sciences.

Table 1. The origin of wheat varieties

No.	Variety	Origin	No.	Variety	Origin	No.	Variety	Origin
1	Liaochun 10	LNAA	10	Jin 2003	JZAAS	19	Fengqiang 5	JLAAS
2	Liaochun 11	LNAA	11	Liaochun 9	LNAA	20	Fengqiang 7	JLAAS
3	Longfu 970227	HLJAAS	12	Liaochun 13	LNAA	21	Fengqiang 9	JLAAS
4	Longfu 9	HLJAAS	13	Tiechun 1	TLAAS	22	Fengqiang 10	JLAAS
5	Longfu10	HLJAAS	14	Tiechun 3	TLAAS	23	Jichun 9806	JLAAS
6	Longfu12	HLJAAS	15	Shenmian 85	SYAU	24	White spring 5	BCAAS
7	Longfu13	HLJAAS	16	Jin 2004	JZAAS	25	Fengqiang 6	JLAAS
8	Jin 2001	JZAAS	17	Fengqiang 3	JLAAS	26	Fengqiang 8	JLAAS

Pot culture

The pot culture experiment was conducted in a greenhouse. Soil used for pot culture was obtained from Shenyang Experimental Station of Ecology. Soil characteristics are: pH 6.46, total organic carbon 1.03 %, alkali N 97.70 mg/kg, and total N 0.07 %. The experiment design was a complete randomized design with four replications. The 27 wheat varieties tested were divided into three groups. The soil was sieved with 5mm mesh screen and thoroughly mixed. A plastic pot (18 cm diameter, 14 cm high) was filled with 2.5 kg soil. Seeds of C. album and A. retroflexus were soaked with 1 mol/l KNO₃ for 45 min to break dormancy, and then rinsed several times with distilled water. The seeds of test weeds and wheat were pre-germinated in Petri dishes covered with filter papers. After germination, the 0.045-0.05 g seeds (about 100 seeds) of C. album and A. retroflexus were sown in the center of each pot and 20 seeds of wheat were sown around weeds, and then covered with soil. Seedlings were thinned to 12 plants per pot after emergence. During the growth period, the plants were irrigated with tap water regularly, and urea fertilizer was applied before jointing stage. At wheat heading stage, the root length of test weeds was measured. The growth of test weeds alone without wheat was selected as control. Every group had its own control.

ECAM (Equal-compartment-agar method)

The ECAM described by Wu et al. (Wu et al. 2000) was slightly modified. All seeds were stirred with a magnetic stirrer with 2.5% (v/v) sodium hypochlorite solution for 10 min to surface sterilize, then washed with sterilized water for three times (3 min per time). The surface-sterilized seeds of test weeds were soaked in sterilized water for 12h then incubated in Petri dish covered with filter paper. A quantity of 1.5% agar and Petri dishes (15 cm diameter) were autoclaved. Each Petri dish was filled with 200 ml of 1.5% agar. Each Petri dish was irrigated with 10 ml sterilised water every day. The root length of weeds was measured after 8 days of growth of wheat and test weeds in the same dish.

Data analysis

All experiment data were subjected to statistical analysis of variance (ANOVA) in the SPSS statistical package. The inhibitory activities of all wheat varieties were evaluated using the following Response Index (RI) (Williamson and Richardson 1988). RI= 1-C/T (T≥C) or =T/C-1 (T<C). C (Control) is the root length of C. album or A. retroflexus growing alone without wheat. T (Treatment) is the root length of C. album or A. retroflexus growing with different wheat varieties.

Results

The inhibitory effects of wheat varieties on root length of C. album and A. retroflexus

In the first group, the inhibitory effects of wheat varieties (from No. 1 to 10) on the root length of C. album and A. retroflexus are shown in Figure 1A. Root length of C. album and A. retroflexus differed significantly among 10 wheat varieties in pot culture and laboratory condition. It also showed that there was a larger variation in root length of C. album in pot culture than in laboratory condition. Root length of test weeds ranged from 2.53cm to 6.66cm in pot culture, and in ECAM from 0.88 cm to 1.59 cm. Among these test wheat varieties, No. 2, 3 and 9 exhibited stronger inhibitory effect than other wheat varieties. Compared with other varieties, inhibitory effects of these three varieties had significant differences (P < 0.01). According to the results, these wheat varieties could be screened as candidates with allelopathic traits.

The results of the second group (Figure1B) indicated that there are differences among varieties (from No. 11 to 18). Root length of C. album and A. retroflexus varied from 0.96 cm to 2.34 cm in laboratory and from 5.53 cm to 8.02 cm in pot culture. Significant differences were observed in root length of C. album in pot culture (P < 0.05) and A. retroflexus with ECAM (P < 0.01). Wheat varieties of No. 16, 17 and 18 had a greater inhibitory effect than others.

A	B	C

Figure 1. The inhibitory effect of wheat varieties on root length of C. album and A. retroflexus ( A-the first group; B- the second group; C- the third group).

RE-Root length of A. retroflexus with ECAM；RP- Root length of A. retroflexus in pot culture；LE- Root length of C. album with ECAM；LP- Root length of C. album in pot culture; 0-control.

The results of the third group (Figure1C.) suggested that root length of C. album and A. retroflexus differed significantly among different wheat varieties. Larger variation existed in root length of C. album and A. retroflexus cultured in pot culture experiment. The root length of C. album and A. retroflexus varied from 0.8cm to 1.98cm in laboratory and from 0.45 cm to 5.48 cm in pot culture. In these test wheat varieties, No. 20, 21 and 23 exhibited strong allelopathic traits and were selected as candidates with allelopathic traits, No. 19 and 25 had the least inhibitory activity among the third group of wheat varieties.

Table 2. Response Index (RI) of different wheat varieties on the growth of C. album and A. retroflexus

	ECAM				Pot culture				Average RI
NO.	C. album		A. retroflexus		C. album		A. retroflexus
1	-0.21	bcdefg	-0.10	bcdefgh	-0.69	gh	-0.73	i	-0.43	cde
2	-0.37	efg	-0.21	cdefghi	-0.78	gh	-0.75	i	-0.53	e
3	-0.41	fg	-0.25	defghi	-0.66	gh	-0.72	i	-0.51	de
4	-0.40	fg	-0.15	bcdefgh	-0.70	gh	-0.65	ghi	-0.48	cde
5	-0.04	abc	-0.20	cdefghi	-0.59	g	-0.69	hi	-0.38	bcde
6	-0.22	bcdefg	-0.05	bcdef	-0.61	gh	-0.59	defghi	-0.37	bcde
7	-0.11	bcde	-0.03	bcdef	-0.76	gh	-0.62	efghi	-0.38	bcde
8	-0.15	bcdef	-0.06	bcdefg	-0.69	gh	-0.75	i	-0.41	bcde
9	-0.30	cdefg	-0.15	cdefgh	-0.82	h	-0.75	i	-0.51	de
10	-0.34	defg	-0.29	efghi	-0.63	gh	-0.66	ghi	-0.48	de
11	0.01	cdefg	0.21	b	-0.28	f	-0.50	cdefg	-0.14	abcd
12	0.23	a	0.59	a	-0.12	def	-0.45	bcde	0.06	a
13	-0.10	bcde	0.13	bc	-0.18	def	-0.54	cdefgh	-0.17	abcde
14	-0.21	bcdefg	0.11	bcd	-0.18	def	-0.44	bcd	-0.18	abcde
15	-0.32	cdefg	0.08	bcd	-0.05	cde	-0.45	bcde	-0.19	abcde
16	-0.23	cdefg	-0.46	hi	-0.12	def	-0.46	bcde	-0.32	abcde
17	-0.30	cdefg	-0.36	fghi	-0.05	bcde	-0.41	bc	-0.28	abcde
18	-0.34	defg	-0.39	fghi	-0.04	bcd	-0.46	bcdef	-0.31	abcde
19	0.06	ab	-0.05	bcdef	-0.29	f	-0.09	a	-0.09	abc
20	-0.15	bcdef	-0.41	ghi	-0.31	f	-0.63	fghi	-0.38	bcde
21	-0.08	bcd	-0.52	i	0.12	abc	-0.32	b	-0.20	abcde
22	-0.33	defg	-0.07	bcdefg	-0.66	gh	-0.15	a	-0.30	abcde
23	-0.20	bcdefg	-0.13	bcdefgh	-0.23	def	-0.32	b	-0.22	abcde
24	-0.31	cdefg	-0.20	cdefghi	-0.27	ef	-0.07	a	-0.21	abcde
25	-0.22	bcdefg	0.58	a	0.19	a	-0.45	bcd	0.03	a
26	-0.45	g	0.06	bcde	0.30	a	-0.02	a	-0.03	ab
27	-0.16	bcdef	-0.37	fghi	0.17	ab	-0.14	a	-0.13	abcd

All values in a row not followed by the same letter are significantly different. Small letter represent significant level at 5%.

Through the RI calculation, 27 different varieties could be compared under a uniform criterion (Table 2). Positive values indicate stimulation and negative values inhibition. The absolute value of RI varied directly with the strength of the effect. From the Table 2, we observed that the RI of all seedlings ranged from –0.78 to 0.58. Significant differences (P < 0.01) were found in inhibitory effects among wheat varieties tested in these studies. Through the analysis of the average value of RI, we selected several strongly allelopathic wheat varieties that included No.2, 3, 4, 9, 10, and 20 and their average RI values were between–0.53 and–0.38, and the average RI values of wheat No.12, 19, 25, 26 and 27 were between–0.13 and 0.06. They showed no allelopathic potential and should be considered as non-allelopathic varieties. These results were similar with that of Fig.1.

Conclusion

Several allelopathic wheat varieties were screened using ECAM and pot culture methods. Root length was the most reliable response parameter because it had high sensitivity to allelochemicals and easy to measure (Belz and Hurle 2004). Therefore, root length may be a key parameter to verify allelopathic strength of different wheat varieties. The results suggested that several wheat varieties, such as No. 2, 3, 9, 16, 17 and 18, are allelopathic to lambsquarters and redroot amaranth. The use of these allelopathic wheat varieties is likely to reduce high dose herbicide application to control weeds in wheat fields. Further research is necessary　to confirm these allelopathic wheat varieties using chemical finger-printing and to evaluate their weed-suppressive effect under natural conditions.

Acknowledgements

This work was financially supported by Hundreds-Talent Program of Chinese Academy of Sciences (BR0401) and the Natural Science Foundation of Liaoning Provice (20042008).

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