Abstract

Media summary

Key Words

Introduction

Allelopathy is a phenomenon of chemical regulating and controlling in natural ecological system and is a mechanism of organisms accommodating environment (Peng et al. 2004). Resent years, a lot of work has been conducted in the allelopathy of plants worldwide (Li et al. 2002). But the study of the allelopathy of microorganisms has been very limited. The action of microorganisms on allelopathy is very important. Such as many plants’ diseases are caused by the toxin which produced by pathogenic microorganisms (Rice 1984). Some metabolites of microorganisms have stimulatory effects on plants growth and have inhibitory effects on weeds’ growth (Sturz 1998; Wang 2004). The fairy ring in nature is a typical example of microorganisms inhibited weeds’ growth. In 1845, the fairy ring of Marasminus oreades was reported in English Gard. Chron (Montrose 1845), Yang (1986).and Mao (1992) found the fairy ring phenomenon also. We found there is special fairy ring at the surroundings of Lactarius hatsudake in nature when we collected mushroom from Xinan County, Guilin, Guangxi Province. L.s hatsudake always grow with Lmperata cylindvica, Heteropogon contortus and Cynodon dactylou. But there are few dicotyledons and other monocotyledons’ plants at the surrounding of L. hatsudake (Mo 2004). In order to look into the causes of this phenomenon, we have studied the allelopathy of aqueous extracts of L. hatsudake on Orytza sativa, Radish, Rape and Barnyardgrass in this paper.

Methods

Experimental Material

L. hatsudake fruit bodies were collected in the Mountain of Xinan County, Guilin, Guangxi Province. Seeds of Rice, Radish, Rape and Barnyardgrass were procured from the Agronomy Department of South China Agricultural University in Guangzhou, P. R. China during August-September.

Extraction of allelochemicals of L. hatsudake fruit bodies

Allelochemicals of L. hatsudake were extracted by the method of water-bath-oscillator extraction under temperature 45°C. Vibration frequency is 120 r/min. The extraction solvent is water. The powder of L. hatsudake fruit bodies: water =1: 6. After extracted, the extraction was condensed with a rotary evaporator. Then, the extracts were made up at different concentrations with sterilised water.

Bioassay of aqueous extracts of L. hatsudake fruit bodies

The bioassay method is according Zeng (1999). The bottom of 10-cm-diam Petri dishes were covered with Whatman No. 40 filter paper. The paper was moistened with different concentration extracts and water (as controls). Twenty seeds [radicle lengths about 1 mm, programmed according to the rules of the International Seed Testing Association (1976) of each acceptor plant species were placed on a Petri dish (four dishes each treatment). The uncovered Petri dishes were placed in an environmentally controlled chamber (2m³), in which there was a source of aqueous extracts of L. hatsudake fruit body. Ordinary air in the chamber served as the control. Acceptor plants were grown for 8 days under a cycle of 13L: 11D photoperiod (236μE/sec/m²) at 28° and 23°, respectively. The shoot height and root length of each seedling of four dishes were measured. The response index (RI) was calculated according Williamson and Richardson (Willamson 1988). All experiments were conducted under the same conditions and were repeated four times, with each time representing one replicate in the statistical analysis. RI=1-C/T (when T ≥C), RI=T/C-1 (when T <C). T is the treatment response and C is the control response. RI values range from +1 to -1, RI>0 means stimulation, RI<0 means inhibition. Absolute values of RI varied directly according to allelopathic effects.

Results

Allelopathy of Aqueous extracts of L. hatsudake on seedling growth of barnyardgrass

The allelopathic effects of aqueous extracts of L. hatsudake on seedling growth of barnyardgrass are listed in Table 1. The data showed that the seedling growth of barnyardgrass was inhibited by aqueous extracts of L. hatsudake significantly. Extract treatments resulted in the formation of yellow leaves, smaller the root lengths and shoot heights, and some seed mortality. Six days after the treatment with 4.5mg.ml^-1 aqueous extracts of L. hatsudake, the RIs of roots and shoots were –0.91, -0.84. The RIs of 2.5 mg.ml^-1and 5.5 mg.ml^-1 treatments were not significant different from those of the 4.5 mg.ml^-1 treatments at an alpha level of 0.05.

Table 1. Influence of aqueous extracts of Lactarius hatsudake on seedling growth of barnyardgrass

Concentration (mg. ml-1)	Root length and Shoot height RI
	Root length			Shoot height
	6day	7day	8day	6day	7day	8day
4.50	-0.91a	-0.74a	-0.67a	-0.84a	-0.73a	-0.67a
5.50	-0.63a	-0.66ab	-0.63ab	-0.69ab	-0.71ab	-0.64a
2.50	-0.84a	-0.72a	-0.63ab	-0.82a	-0.59abc	-0.52ab
.50	-0.74a	-0.53ab	-0.45ab	-0.63abc	-0.46 c	-0.39 b
1.50	-0.62a	-0.55ab	-0.44ab	-0.51 bc	-0.53 bc	-0.44 b
3.50	-0.19 b	-0.44 b	-0.38 b	-0.43 c	-0.58abc	-0.51ab

Numbers with different letters within a column refer to significant difference at 0.05 level according to Duncan’s new multiple-range test.

Allelopathy of aqueous extracts of L. hatsudake on seedling growth of Radish

The inhibitory effect was stronger at higher concentration from 0.50 mg.ml^-1 to 5.50 mg.ml^-1 on radish (Table 2). Six days after the treatment with 5.50mg.ml^-1 aqueous extracts of L. hatsudake, the shoots of radish did not develop, the RIs of roots and shoots were –0.86, -1.00, respectively. The RIs of 4.50 mg.ml^-1 treatment were not significant different from those of 5.50mg.ml^-1 treatment at an alpha level of 0.05.

Allelopathy of aqueous extracts of L. hatsudake on seedling growth of Rape

Table 3 showed that the growth of rape seedlings was significantly inhibited by the aqueous extracts of L. hatsudake and the inhibitory effect was stronger at higher concentrations. Although some seeds germinated, they stopped continuous growth immediately after germination. Six days after the treatment with 5.50 mg.ml^-1 aqueous extracts of L. hatsudake, the RIs of roots and shoots were –0.98, -1.00, respectively.

Table 2. Influence of aqueous extracts of Lactarius hatsudake on seedling growth of radish

Concentration ( mg. ml-1)	Root length and Shoot height RI
	Root length			Shoot height
	6day	7day	8day	6day	7day	8day
5.50	-0.86a	-0.90a	-0.89a	-1a	-0.98a	-0.95a
4.50	-0.81a	-0.78a	-0.71a	-0.96a	-0.92a	-0.87a
3.50	-0.66a	-0.61a	-0.58b	-0.86b	-0.76b	-0.70b
2.50	-0.68c	-0.64bc	-0.55c	-0.32b	-0.28c	-0.32c
1.50	-0.55d	-0.54cd	-0.46cd	-0.32b	-0.23cd	-0.25c
0.50	-0.46e	-0.42 d	-0.36d	-0.11b	0a	-0.07d

Numbers with different letters within a column refer to significant difference at 0.05 level according to Duncan’s new multiple-range test.

Table 3. Influence of aqueous extracts of Lactarius hatsudake on seedling growth of rape

Concentration (mg. ml-1)	Root length and Shoot height RI
	Root length			Shoot height
	6day	7day	8day	6day	7day	8day
5.50	-0.98a	-0.94a	-0.91a	-1.00a	-1.00a	-0.95a
4.50	-0.90a	-0.89a	-0.85a	-1.00a	-0.88a	-0.76b
3.50	-0.80b	-0.59b	-0.76b	-0.64b	-0.57b	-0.53b
2.50	-0.47c	-0.21cd	-0.06d	-0.52c	-0.47bc	-0.39c
1.50	-0.56c	-0.26c	-0.38c	-0.51c	-0.42c	-0.36c
0.50	0.08d	0.04 d	0.007d	-0.29d	-0.29 d	-0.34d

Numbers with different letters within a column refer to significant difference at 0.05 level according to Duncan’s new multiple-range test.

Allelopathy of aqueous extracts of L. hatsudake on seedling growth of Rice

The allelopathic effects of aqueous extracts of L. hatsudake on seedling growth of rice are listed in Table 4. However, concentration effects were evident for rice. For concentrations >4.50 mg.ml^-1, the allelopathic effects on rice root were inhibitory and for concentrations <4.50 mg.ml^-1, the allelopathic effects on rice root were stimulation. For concentrations from 0.50 to 5.50 mg.ml^-1, the allelopathic effects on rice shoot were stimulatory. Six days and eight days after the treatment with 5.5 mg.ml^-1 aqueous extracts of L. hatsudake, the RIs on the roots of rice were -0.26, -0.23 and on the shoots were 0.45, 0.36, respectively. Six days after the treatment with 3.5 mg.ml^-1 aqueous extract of L. hatsudake, the RIs of rice root and rice shoots were 0.26 and 0.24, respectively.

Table 4. Influence of aqueous extract of Lactarius hatsudake on seedling growth of rice

Concentration (mg. ml-1)	Root length and Shoot height RI
	Root length			Shoot height
	6day	7day	8day	6day	7day	8day
.50	0.11 c	0.35 c	0.25 cd	0.05a	0.04a	0.02a
1.50	0.26 d	0.40 c	0.30 d	0.14ab	0.19ab	0.15ab
2.50	0.28 d	0.08 b	0.04 bc	0.31abc	0.19ab	0.15ab
3.50	0.26 d	0.41 c	0.31 d	0.24abc	0.22ab	0.20ab
4.50	-0.59 a	-0.52 a	-0.38 a	0.39 bc	0.34ab	0.31ab
5.50	-0.26 b	-0.58 b	-0.23 b	0.45 c	0.39 c	0.36 c

Numbers with different letters within a column refer to significant difference at 0.05 level according to Duncan’s new multiple-range test.

Conclusion

These results indicated that the seedling growth of barnyardgrass, radish and rape were significantly inhibited by aqueous extracts of L. hatsudake. However, concentration effects were evident for rice. The extracts stimulated rice growth at low concentrations (<4.50 mg.ml^-1) and inhibited rice root at high concentrations (>4.50 mg.ml^-1). But concentrations from 0.50 to 5.50 mg.ml^-1, the extracts stimulated rice shoot elongation. This demonstrated that the aqueous extracts of L. hatsudake has inhibitory effect on barnyardgrass, but has stimulatory effect on rice. It meant that the extracts of L. hatsudake have the potential to be a useful herbicide for integrated weed management.

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