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Allelopathy in China

Chuihua Kong

Chinese Allelopathy Society, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China.
E-mail: kongch@mail.edu.cn

Abstract

Allelopathic phenomena had been recorded in ancient Chinese literature. Since 1990s allelopathy involved in natural and managed ecosystems has been widely investigated in China and substantial progress has been achieved. In recent years, allelopathy research in China has focused on staple food crops of rice and wheat. The allelopathic rice and wheat accessions were evaluated and screened from Chinese germplasm collections. A new method to assess allelopathic crop accessions and individual plants in a non-destructive manner has been developed using chemical fingerprinting. The 1st Chinese Allelopathy Conference was held in 2004 and the Chinese Allelopathy Society (CAS) was established in the same year.

Media summary

Allelopathy involved in natural and managed ecosystems has been widely investigated in China and substantial progress has been achieved in recent years. The Chinese Allelopathy Society was established in 2004.

Key Words

Aquatic ecosystem, allelopathy, crop, forestry, weed

Introduction

China is a large and old country with over 5000-years of history with agriculture being the biggest industry. Rotations and mixed/intercropping systems have been practiced since long time. Allelopathic phenomena had been repeatedly recorded in ancient Chinese literature. For instance, a soil sickness case was cited in the famous ancient Agricultural Book Qi-Min-Yao-Shu that was written more than 1500 years ago. Allelopathy in China has been widely investigated since 1990’s with the support of the National Natural Science Foundation of China (NSFC).Research revealed the occurrence of allelopathy in both terrestrial and aquatic ecosystems, natural or managed, and various plant species involved. In more recent years, allelopathic research has focused on the staple food crops of rice and wheat. Allelopathic rice and wheat accessions were evaluated and screened from Chinese germplasm collections (Kong et al. 2002; Zuo et al. 2005). A new method to assess allelopathic crop accessions and individual plants in a non-destructive manner has been developed using chemical fingerprinting (Kong et al. 2002). Many allelochemicals have been isolated and identified, and a few have been modified and synthesized. Most of this research is published in Chinese with the monograph “Allelopathy and Its Application”(Kong and Hu, 2001), being the first publication introducing the word allelopathy in the Chinese literature. Nevertheless, an ever increasing number of papers have been published in several international journals in recent years.

Currently, more than one hundred Chinese groups are doing research on allelopathy. The 1st Chinese Allelopathy Conference was held in May 18-20, 2004, during which the Chinese Allelopathy Society was established. Selected papers and abstracts from the Proceedings of this Conference were published in a Special Issue of Allelopathy Journal, in January 2005 (Volume 15, Issue 1). Here is an outlook of the current status and progress in allelopathy research in China.

Crop allelopathy

Although crop allelopathy had been observed and recorded long ago in China, allelopathic research is only at an early stage in the country. Nevertheless, substantial progress has been achieved in recent years. Allelopathy of rice, wheat, soybean and peanut (Arachis hypogaea) has been studied since 1990’s. Generally, peanut and soybean inter-plant or rotate with other crops. Peanut rotated with rice can increase rice yield by 20%-25%. Root exudates from A. hypogaea at early growth stages, before the formation of root nodules, promoted growth of rice, maize, radish and rye grass. This seems to be due to triacontanol, found in root exudates of A. hypogaea at 1-3 leaf growth stage, which has positive effects on plant growth (Hu and Kong, 2002).

In China, it was found that planting wheat or mulching with wheat straw can effectively control Imperata cylindrica in fields and orchards. To understand the mechanism, a series of experiments were conducted to determine whether this phenomenon was due to allelopathic effects, and if so, what parts of wheat produced allelochemicals, and which were the allelochemicals that played the key role in this process (1997). Water extracts of wheat roots, stems and hulls significantly inhibited not only growth of I. cylindrica, but also of Amaranthus retroflexus and Stellaria media. Allelopathic effects of extracts of wheat straws varied depending on the extraction method, the growth stage, and the accession. The alkaline extracts of wheat caused greater weed inhibition than the acidic and water extracts. The content of allelochemicals in root exudates was maximal at the jointing stage. Ferulic, vanillic, p-hydroxybenzoic and cinnamic acids were isolated. Field experiments demonstrated that growing alleopathic wheat varieties significantly decreased weed infestation in the wheat field; also, their stubble greatly reduced the weed biomass in the following corn crops (Ma et al. 1996; Li et al. 2005). Mulching of wheat straw effectively controlled the weeds in corn fields and is it is now becoming a common practice for weed management in the crop fields of North China.

Allelopathy of wheat genotypes was also studied. The results indicated that all genotypes, excluding Secale cereale L., had allelopathic effects; inhibition caused by the wheat genotypes increased as their genome changed from 2n to 4n to 6n (Zuo et al. 2005). Triticum boeoticum L., French, Secale cereale L., Aegilops.tauschii Cosson Syn, Triticum dicoccoides K., Tritium aestivum L. Var. Shaan 160 and T. aestivum Var. No.1 Ningdong had a weak effect, Triticum monococcum L., Aegilops.speltoides L. and Triticum dicoccum S. had an intermediate effect, whereas T. aestivum Var. common wheat had a strong effect.

Rice allelopathy has also been studied in China. Around 5000 rice accessions from Chinese germplasm collections were evaluated and screened in a non-destructive manner giving about 30 allelopathic rice accessions(Kong et al. 2002). Chemical fingerprinting by means of HPLC is the method used to evaluate the allelopathic potential of rice varieties and of individual plants. Secondary metabolites of the allelopathic accessions were systematically isolated and identified, and the activity of 123 compounds was examined. It was found that flavones, cyclohexenone, momilactones and hydroxamic acids playe a key role in rice allelopathy. Phenolic acids, regarded as allelochemicals in rice root exudates, were not among the primary allelochemicals.Presence of E. crus-galli, ultraviolet irradiation, herbicide stress, jasmonic acid application and heavy metal damage had a positive effect on the production of allelochemicals(Kong et al. 2004a; Zhao et al. 2005).

A population of 134 recombinant inbred lines (RILs) derived from a cross between indica rice variety Zhong 156 Gumei 2 were employed to map the genes responsible for the allelopathic effect on barnyardgrass (Xu et al. 2003). Available DNA markers and the bioassay of the relay seeding technique were used, the latter with slight modification. One main QTL (quantitative trait loci) on 7 chromosome was detected, explaining 32.3% of the phenotypic variation. Proteomic analysis demonstrated that four proteins, 3-hydroxy-3-methyglutary-CoA reductase 3, phenyalanine ammonia-lyase (PAL), thioredoxin M-type and peroxidase 2 precursor, which are related to the pathway of the secondary metabolites, were associated with allelopathic effects of rice plants against barnyard grass. Random amplified polymorphic DNA (RAPD) markers were used to estimate genetic diversity among 57 allelopathic rice accessions. There were 59 polymorphic bands in the 85 RAPD loci within the tested accessions, and the percentage of polymorphic bands (PPB) was 69.4%. Breeding for allelopathic rice cultivars has been done in China since 2001. Several advanced lines with allelopathic potential have been bred.

Weed allelopathy and utilization

Allelopathy of various weeds, especially exotic weeds, has been investigated in China; Ageratum conyzoides L. has been studied in detail (Kong et al. 2004b). Its allelopathic potential varied with growth stage and environmental conditions. A. conyzoides could release more volatile allelochemicals (ageratochromene and its derivatives, monoterpenes, sesquiterpenes and flavones) under adverse conditions. These allelochemicals not only inhibited the germination and growth of associated plants, but also adversely affected microbes and insects.

Intercropping of A. conyzoides in citrus orchards effectively suppressed the weeds and controlled other insect pests. Weeds and soil pathogenic fungi were effectively suppressed through ageratochromene and other allelochemicals released into the soil by A. conyzoides (Kong et al. 2004c). Reversible transformations to and from ageratochromene and its two dimers were detected; this may be an important mechanism maintaining allelochemicals at effective concentrations in the soil. A. conyzoides also produced and released volatile allelochemicals. These volatiles were found to control the populations of predatory mites (Amblyseius spp.), which are effective natural enemies of the pest mite Panonychus citri. Consequently, the population of P. citri was maintained at non-harmful levels. Because of its multfunction in the field, A. conyzoides is intercropped in citrus orchards in >150,000 ha in South China. This resulted into substantial ecological and economic benefits and provides an excellent example of applied aspects of allelopathy in agro-ecosystems.

Allelopathy in forestry

Casuarina equisetifolia was introduced in 1950’s into South China seashores to offer shelter from strong winds and high tides. About 15 to 20 years ago, the species gave clear signs of severe sickness. Research showed that C. equisetifolia produced and released allelochemicals that significantly inhibited root growth of C. equisetifolia seedlings (Deng et al. 1996). Five allelochemicals were isolated and identified from its leachates: kaempferol-3-α-rhmanoside, quercetin-3-α-araboside, luteoli-3’,4‘-dimethoxy -7-β- rhamnoside, keampferol-3-β-dirhamnoside, and quercetin-3-β-glucoside.

Eucalyptus exserta and E. urophylla are dominant species in man-made forest communities in South China. Due to their fast growing, they are very important for the paper industry of the country. However, because of allelopathic interactions, there are problems in the communities formed. To face them, it has been suggested to intercrop tolerant species, such as Leucaena leucocephala and Acaia mangnigum.

Cunninghamia lanceolata is an endemic fir with rapid growth and high timber yields. It usually grown as monoculture, a declination always occurs in north subtropical areas of South China. Various factors that could be responsible for this decline have been considered and examined, among which allelopathic interactions. Several allelochemicals were isolated and identified from C. lanceolata litter and soil in C. lanceolata woods; they significantly inhibited the growth of C. lanceolata seedlings and substantially affected the regeneration process (Chen et al. 2005).

Allelopathy in aquatic ecosystem

Given the harmful algae and aquatic weeds boom in various freshwater bodies, allelopathy in aquatic ecosystems has been seriously studied in China. It was found that macrophytes and algae were antagonistic to each other in several aquatic ecosystems (Xian et al. 2005). Phragmites communis could effectively inhibit the growth of Microcystis aeruginosa. The different parts of P. communis had different activity with the foliage showing the strongest inhibitory activity. Aqueous extracts of three submerged macrophytes (Ceratophyllum demersum, Vallisneria spiralis and Hydrilla verticillata) and their ethyl acetate fractions showed even stronger growth inhibition of M. aeruginosa.

Eupatorium adenoporum, originated from Mexico, has become a vicious weed all over the watershed of Langcang River in China. The causes of the problem and its impact on the biodiversity of the watershed are major concerns. It is possible that this is due to the allelopathic potential of E. adenoporum as compounds with strong inhibitory activity, such as 9-Oxo-ageraphorone has been isolated from the extracts of E. adenoporum. The major allelochemicals isolated were of low polarity and could be absorbed by soil and the litter. Acorus tatarinowii is widely distributed in freshwater ecosystems in South China. Allelopathy and competition between A. tatarinowii and algae were investigated under different environmental conditions (Ye et al. 1999). Algae grown with A. tatarinowii were inhibited, even at high nutrients, indicating mineral nutrients were not responsible for the low growth. When algae cells were treated with water from A. tatarinowii culture, chlorophyll a of algae was destroyed, the photosynthetic rate of algae markedly declined and the ability of cells to reduce TTC decreased.

Mangrove is a very important natural community in seashore. Bruguiera gymnorrhiza and Kandelia candel are the most important mangrove species in South China. B. gymnorrhiza regeneration is almost impossible in natural conditions, along the Guangxi seashore. Aqueous extracts of all parts of B. gymnorrhiza strongly inhibited the hypocotyls of B. gymnorrhiza seedlings, but the mixture of aqueous extract from B. gymnorrhiza and K. candel branches promoted them (Mo and Fan, 2001). It has been found that the mixture of allelochemicals from both species had antagonistic effects on the growth of B. gymnorrhiza. Actually, communities of B. gymnorrhiza along the Guangxi seashore always associate with K. candel. Clarification of the allelopathic mechanism may contribute into developing sustainable mangrove community along the seashore.

Chinese Allelopathy Society

Since 1990’s, allelopathy in China has attracted the attention of both the scientists and the government. More and more scientists from various fields have been joining this exciting research field. In parallel, proposals for allelopathy research have been funded by the National Natural Science Foundation of China (NSFC) and other funding agencies. An ever increasing number of publications of Chinese scientists have been delivered in Chinese and English. The 1st Chinese Allelopathy Conference was held in May 18-20, 2004 in Shenyang, Northeast China.

The Chinese Allelopathy Society was established during the above mentioned conference with Professor Chuihua Kong, research fellow of Hundreds-Talent Programme of Chinese Academy of Sciences, being its founder president. The Society aims at developing academic exchanges and cooperations with all scientists and organizations from other countries that work on allelopathy. The Chinese Allelopathy Society is located at the Institute of Applied Ecology, Chinese Academy of Sciences, P. O. Box 417, Shenyang 110016, China. Tel:+86-24-83970452, Fax: +86-24-83970300. www.allelopathy.org.cn

References

Chen LC, Wang SL and Yu XJ (2005). Effect of Phenolics on seedling growth and 15N nitrate absorption of Cunninghamia lanceolata. Allelopathy Journal 15, 57-66.

Deng LG, Kong CH and Luo SM (1996). Isolation and identification of extract from Casuarina equisetifolia branchlet and its allelopathy on seedling growth. Chinese Journal of Applied. Ecology 7,145-149. (In Chinese)

Hu F and Kong CH (2002). Allelopathic potentials of Arachis hypogaea on crops. Journal of South China Agricultural University 23,9-12(In Chinese)

Kong CH and Hu F (2001). ‘Allelopathy and Its Application’ China Agricultural Press, Beijing.

Kong CH, Xu XH, Hu F, Chen XH, Ling B and Tan ZW (2002). Using specific secondary metabolites as markers to evaluate allelopathic potentials of rice varieties and individual plants. Chinese Science Bulletin 47, 839-843.

Kong CH, Xu XH, Zhou B, Hu F, Zhang CX and Zhang MX (2004a). Two compounds from allelopathic rice accession and their inhibitory effects on weeds and fungal pathogens. Phytochemistry 65,1123-1128.

Kong CH, Hu F, Xu XH, Liang WJ, Zhang CX (2004b). Allelopathic plants. XV: Ageratum conyzoides L. Allelopathy Journal 14, 1-12.

Kong CH, Liang WJ, Hu F, Xu XH,Wang P, Jiang Y. (2004c). Allelochemicals and their transformations in the Ageratum conyzoides intercropped the citrus orchard soil. Plant and Soil, 264, 149-157.

Li SL, You ZG, Liang DX and Li SR (1997). Extraction and isolation of allelochemicals in wheat and their herbicidal efficacy on Imperata cylinderica. Acta Phytophylacica Sinica 24, 81-83. (In Chinese)

Li XJ, Wang GQ, Li BH and Blackshaw RE (2005). Allelopathic effects of winter wheat residues on germination and growth of crabgrass (Digitaria ciliaris) and corn yield. Allelopathy Journal 15, 41-48.

Ma RX, Liu XF, Yuan GL, Sun SE (1996). Study on allelochemicals in the process of decomposition of wheat straw by microorganisms and their bioactivity. Acta Ecologica Sinca 16, 632-639. (In Chinese)

Mo ZC and Fan HQ (2001). Allelopathy of Bruguiera gymnorrhiza and Kandelia candel. Guangxi Sciences 8,61-62. (In Chinese)

Xian QM, Chen HD, Qu LJ, Zou HX and Yin DQ (2005). Allelopathic potential of aqueous extracts of submerged macrophytes against algal growth. Allelopathy Journal 15, 95-104.

Xu ZH, He Y, Cui SR, Zhao M, Zhang X and Li D (2003). Genes mapping on rice allelopoathy against barnyardgrass. Chinese Journal of Applied Ecology 14, 2258-2260. (In Chinese)

Ye JX, He CQ and Chen SF (1999). Allelopathic effect of Acorus tatartinowii on algae growth. Acta Phytoecologica Sinica 23,379-384.(In Chinese)

Zhao H, Li HB, Kong CH, Xu XH and Liang WJ (2005). Chemical response of allelopathic rice seedling under varying environmental conditions. Allelopathy Journal 15,105-110.

Zuo SP, Ma YQ, Deng XP and Li XW (2005). Allelopathy in wheat genotypes during the germination and seedling stages. Allelopathy Journal 15,21-30.

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