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Notes: The objective of this paper is to review the possibilities for using allelopathy to improve overall crop competitive ability against weeds, using rice, Oryza sativa, as an example. Laboratory, greenhouse and field screenings for allelopathy and overall weed suppression in rice have been made and allelopathic rice germplasm has been identified in laboratory and greenhouse screening. Field experiments revealed that allelopathy accounted for 34% of overall competitive ability in rice. For strongly allelopathic cultivars, allelopathy was the dominant factor determining competitive ability. Based on the results of the screenings, recombinant inbred line populations were developed for identification of quantitative trait loci (QTL) controlling allelopathy. Populations of recombinant inbred lines (RILs) were derived through single-seed descent from crosses between varieties with contrasting behaviour and QTL controlling allelopathy were identified. For rice and most probably also for other cereal crops, the findings presented can explain the limited success in previous breeding programmes for weed competition, as allelopathy has never before been acknowledged as an important factor. The findings in allelopathy indicate that it is possible to improve allelopathy in rice using marker-assisted selection. Optimizing allelopathy in combination with breeding for competitive plant types could result in crop cultivars with superior weed-suppressive ability.

Notes: The inhibitory activity of water extracts from the shoots and roots of three rice cultivars, Taichung native 1 (TN1) and IAC165 (both allelopathic rice) and AUS196 (non-allelopathic rice), grown in hydroponics was evaluated. The release of germination inhibitors by allelopathic rice plants into hydroponic solution was also determined with freshly collected solution and XAD-4 resin desorbate. The degree of the inhibition was quantified in terms of root growth in Echinochloa colona, Echinochloa crus-galli, Echinochloa crus-galli var. oryzicola, Triantema portulacastrum and Lactuca sativa. The allelopathic activity of rice was species specific, and depended on source and concentration. Root length of all test species was inhibited by the different concentrations of shoot extract of allelopathic and non-allelopathic rice. However, of the three cultivars, TN1 showed higher inhibition than IAC165 and AUS196 in all test species. Water extracts of shoots and roots significantly inhibited root growth in E. crus-galli but the shoot extract gave a greater inhibitory effect on E. crus-galli than the root extract. Root exudate of TN1 inhibited root elongation of E. crus-galli from 2 weeks after transplanting (WAT) and the inhibition continued for 4 WAT. The results confirmed the previous finding of a laboratory bioassay that the TN1 had allelopathic activity and produced allelochemicals that inhibit growth of some weed species.

Notes: Dose-response curves were established for the herbicides chlorsulfuron, metsulfuron-methyl, ethametsulfuron-methyl, imazamethabenz and glyphosate. The plant species were Daucus carota L. and Triticum aestivum L. in cell culture assays, and D. carota L., T. aestivum L., Stellariamedia L., Chenopodium album L. and Avena sativa L., in whole plant assays. Potency ranking of herbicides were similar in the two assays. Low doses of herbicide stimulated growth in both assays, but stimulation was greater in cell cultures. Image processing measured growth in cell cultures and was more sensitive to small differences in responses than manual counts of cell colonies. Dose-response curves had the same shape in both assays, but cell cultures were more sensitive than were whole plants. Comparaison d'essais biologiques d'herbicides effectués sur cultures de cellules et sur plantes entiéres Des courbes dose-effet ont étéétablies pour les herbicides metsulfuron-methyl, ethametsulfuron-methyl, imazamethabenz et glyphosate. Les espèces végétales étaient Daucus carota L. et Triticum aestivum L. en cultures de cellules, et D. carota L., T. aestivum L., Stellaria media L., Chenopodium album L. et Avena sativa L. dans les essais sur plantes entières. Le classement d'efficacité des herbicides était le meme dans les deux types d'essais. Les faibles doses d'herbicides stimulaient la croissance dans les deux essais mais la stimulation était plus importante en cultures de cellules. La mesure par analyse d'image de la croissance des cultures de cellules était plus sensible à de faibles différences que le comptage manuel des colonies. Les courbes dose-effet avaient la meme forme dans les deux essais mais les cultures de cellules étaient plus sensibles que les plantes entières. Vergleich von Herbizid-Biotests mit Zellkulturen und ganzen Pflanzen Fur die Herbizide Chlorsulfuron, Metsulfuronmethyl, Ethametsulfuron-methyl, Imazamethabenz und Glyphosat wurden Dosis/Wirkungs-Kurven erstellt. Die in den Zellkulturen verwendeten Pflanzenarten waren Daucus carota L. und Triticum aestivum L., und bei den Tests mit ganzen Pflanzen D. carota L., T. aestivum L., Stellaria media L., Chenopodium album L. und Avena sativa L. Die Reihenfolge der Herbizide hinsichtlich ihrer Wirksankeit war in beiden Tests ahnlich. Niedrige Herbiziddosen steigerten in beiden Tests das Wachstum, in den Zellkulturen jedoch deutlicher. Bei den Zellkulturen war die Bildanalyse-Messung fur das Erkennen geringer Unterschiede empfindlicher als das Auszahlen der Zellkolonien. Die Dosis/Wirkungs-Kurven hatten fur beide Testmethoden den gleichen Verlauf, aber auch hier erwiesen sich die Zellkulturen empfindlicher als die ganzen Pflanzen.