title: Broad-leaved weed competition with Saudi wheat Triticum aestivum cv. Yecora Rojo and barley Hordeum vulgare cv. Jasto
Creators: name: Aytah, Ameera Ameen
Publisher: name: University of Glasgow
Year: 2008
Subjects: subject: Plant pathology, agronomy, wheat, barley, weeds, Saudi Arabia.

description: The present study investigated competitive interactions between two broad leaved weeds, Chenopodium album and Amaranthus retroflexus, and two Saudi Arabian cereal crops, wheat (Triticum aestivum cv. Yecora Rojo) and barley (Hordeum vulgare cv. Jasto), by looking at the effects on growth parameters such as plant height, whole-plant dry weight, shoot dry weight and root dry weight. The separation technique of roots and/or shoots was used allowing three types of interactions to be studied, root, shoot and root &amp; shoot interactions, respectively occurring below-ground, above-ground, and at whole plant level. The interference of weeds caused morphological changes in both crops, such as plant height, spike size, leaf chlorosis and root system. Chenopodium generally reduced all growth parameters of wheat under root interaction, and barley under all interactions, except for plant height. Amaranthus reduced dry matter accumulation in the shoots and roots of wheat plants under all three interactions. In the case of barley, Amaranthus reduced whole-plant dry weight under shoot interactions and root &amp; shoot interaction. The effects of wheat on Chenopodium plants were very limited and were only slightly significant when roots of both species interacted. Wheat also reduced all growth parameters of Amaranthus under root interaction, and plant height and whole-plant dry weight under shoot interaction. In contrast, barley was found to affect all growth parameters of Amaranthus regardless of the kind of interaction. In the case of Chenopodium, barley decreased all growth parameters related to dry matter accumulation. Aggressivity indices were used to determine the competitive ability of each of the weeds and the crops. Chenopodium was aggressive towards wheat when only the roots of both species interacted and when both roots and shoots interacted. In the case of barley, Chenopodium aggressivity was due to root interaction and both root &amp; shoot interaction. This suggests that Chenopodium aggressivity was mostly due to its roots' competitive ability. Under root interaction and based on all plant growth parameters, aggressivity was higher in Amaranthus towards wheat. Based on whole-plant or root dry weight, aggressively of Amaranthus against barley was null and barley was slightly more aggressive towards Amaranthus. This suggests dominance of barley over Amaranthus.Allelopathy was also investigated by looking at the effects of different extract concentrations from the weed plant Heliotropium europaeum on the wheat and barley seed germination and root length. The extracts significantly reduced root growth and strongly inhibited the germination percentage of seeds in both crop plants. Allelopathy caused also some morphological changes in both crop seeds such as browning and deformation of roots and deformation of the plumule in the germinating seeds of wheat. These results are discussed in the context of existing literature on the mechanisms of competition between crops and weeds.