Varieties with Strong Allelopathic Potential

During cultivation, weed and pest resistance characteristics were ignored, and therefore the selection of high-yielding varieties caused the loss of allelopathic traits (Singh et al. 2001). For example, one of the ancestors of wheat, Triticum speltoides, contained significantly higher quantities of the allelochemical 2,4-dihydroxy-7-methoxy-1, 4-benzoxazin-3-one (DIMBOA) than Triticum aestivum (Niemeyer 1988). Another example is wild species Maximilian sunflower Helianthus maximiliani Schrad.

that produces phytotoxic 8b-sarracinoyloxycumambranolide (Gershenzon and Mabry 1984). The commercial sunflower (Helianthus annuus L.) produce the compound also but in dependence upon the variety (Macias et al. 1993). Therefore, the transfer of allelopathic traits from wild types is one of the possibilities for breeding strong allelopathic varieties.

Early seedling emergence, seedling vigor, fast growth, greater plant height, greater root volume, and longer growth duration increase the ability of varieties to compete with weeds (Kim and Shin 2003). However, it is not known if these traits are related to the production and release of allelochemicals.

The initial step in breeding for genetic improvement of allelopathic traits is to select crop varieties with the strongest allelopathic potential. Varieties with strong allelopathic potentials have been carried out in several field crops (Table 14.4), and crop varieties differ in their ability to inhibit the growth of certain weeds. The growing of crop varieties with elevated allelopathic activity could be a great chance for organic farming.

Allelopathic activity was identified as a quantitative trait in rice and wheat (Dilday et al. 1998; Wu et al. 2000; Jensen et al. 2001); therefore allelopathy is affected by both genetic effects and environmental conditions (Dilday et al. 1998). Little available knowledge is about changes of allelopathy at different growth stages and under different environmental conditions (He et al. 2004). For example, selection for allelopathic activity in rice should be performed during the three leaf phase. Allelopathic effects of wheat exhibited the highest heritability in the tillering stage (Zuo et al. 2007).

Jensen et al. (2001) described three quantitative trait loci (QTL) localized on chromosomes 2 and 3, explaining about 30% of allelochemical production in rice. Kong (2005) reported that one main QTL on chromosome 7 was detected, explaining 32.3% of the phenotypic variation was associated with allelopathic effects of rice. Wu et al. (2003) identified two major QTLs on chromosome 2B conferring wheat allelopathic activity. However, it is not known what kinds of gene are responsible for the allelopathic effect, but it is assumed that allelopathic potential might be polygenically controlled because of variation in the germplasm (Courtois and Olofsdotter 1998). It confirmed a sequence analysis of cucumber, when 43 unique genes that shared significant similarities to known plant genes potentially implicated in the autotoxic response were described. These genes are associated with detoxification, reactive oxygen scavengers, signaling components, and transcriptional regulators (Mao et al. 2007). According to Xiong et al. (2007), a "favorable" gene with positive effects might become "unfavorable" following transfer into a new variety due to the large negative additive effects in the new genetic background. Therefore, more emphasis on identifying the best multi-locus allelic combinations instead of pyramiding individual favorable QTL alleles should be done.

The three approaches to create more allelopathic crops are: the traditional breeding; the incorporation of allelopathic properties to hybrid crop; and genetic engineering. The results indicated that the heterotic effect on allelopathy was positively significant, so hybridization could be a promising method. At present, no commercial

Table 14.4 Summary of some strong allelopathic cultivars

Crops The inhibited species Strong allelopathic varieties Reference

Table 14.4 Summary of some strong allelopathic cultivars

Crops The inhibited species Strong allelopathic varieties Reference

Cucumber (Cucumis

Panicum mili ace wn L.,

PI 169391

Putnam

sativus L.)

Sinapis alba L.

and Duke 1974

Pearl millet (Pennisetum

Trianthema portulacastrum L.

HHB-67, 88004A 833-2

Khanh et al. 2005

glaucum (L.) R. Br.)

and Amaranthus spp.

Oat (Avena sativa L.)

-

PI-266281 the strongest - high content of scopoletin

Fay and Duke 1977

Alfalfa (M. sativa L.)

Inhibition of total weed

Rasen. Yuba

Khanh et al. 2005

biomass

Wheat (Triticum aestivum L.)

Annual ryegrass (Lolium

2 Distinct groups - condor-derivatives more allelopathic than

Wu et al. 2000

rigidum Gand.)

Pavon-derivatives

Tasman, Khapli. Wattines, AUS# 12627. TriUer. SST 6. AUS#

Wu et al. 2003

18060. Tunis 2. AUS# 18056. Meeting

No 6 Lankao', "No 22 Xiaoyan"

Zuo et al. 2007

Triticum speltoides Fla Kslo.

Wild oat (Avena spp.).

Ts8, TslO. Ts22, Ts25 - higher amounts of DIMBOA

Quader et al. 2001

Rice (Oryza sativa L.)

Neighboring plants

PI312777. Huagan-1

Kong et al. 2006

Ducksalad (Heteranthera

PI 338046. Katy

Dilday et al. 1998

limosa (Sw.) Willd.)

PI312777

Dilday et al. 1994

PI294400. PI 277414

Mattice et al. 1998

Barnyard grass (E. crus-galli

Inhibition (%) followed the order : landrace (50). improved

Lee et al. 2004;

(L.) P. Beauv.)

varieties (49) greater than or equal to Japonica (48) > weedy

Jensen et al. 2001

rice (44) > Indica rice (39)

Asian varieties "PI 312777." "Guichao," "Teqing"

Gealy et al. 2002

Iguape Cateto. PI312777. Azucena. Taichung Native 1. IAC25

He et al. 2004

RP 2269-424. LD 183-3. LDS 183-7. IET 1444. Dular, CI

Hassan et al. 1998

selection-63, UPR 82-1-7. GZ 1368-5-2. OR 131-58

Cyperus diffonnis L.

RP 2271-433-231. IET 11754. Dular. OR 131-5-8

Hassan et al. 1998

varieties with allelopathic properties are available. If allelochemicals or genes responsible for allelopathic effects will be identified, allelopathic traits could be easily incorporated into cultivars (Kim and Shin 2003). Detailed information about allelopathic breeding is given in Kim and Shin (2003).

Organic Gardeners Composting

Organic Gardeners Composting

Have you always wanted to grow your own vegetables but didn't know what to do? Here are the best tips on how to become a true and envied organic gardner.

Get My Free Ebook


Post a comment