Impact of Brassica Juncae L. Biofumigation on Annual Weed Ecology and Population Dynamic in Organic Soil PDF Download

Author: Maxime Lefebvre
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Languages : en
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Book Description
"Critical processes, including seed bank persistence, seedling establishment, and interspecific interference govern agricultural annual weed population dynamics. Agronomic practices alter weed populations and limit the weed pressure via those key processes. Among them, biofumigation is an innovative technique to control soilborne pests and weeds. Biofumigation is a mass release of volatile chemicals following Brassicaceae tissue disruption when myrosinase enzymes hydrolyze glucosinolates (GSLs). The most common volatile produced following this reaction are isothiocyanates (ITCs). The project focused on assessment of weed species susceptibility, surviving weed responses, and key population dynamic process changes in response to allelochemicals generated during biofumigation. First, a laboratory experiment examined relationships amongst seed dormancy, seed morphology, and weed seed susceptibility to biofumigation. A novel Petri dish biofumigation methodology exposed seeds of eight different weed species to allelochemicals released by increasing rates of Indian mustard (Brassica juncea L.) biomass. The first experiment demonstrated that the dormancy state was an important factor related to seed germination, seed mortality and changes in seed dormancy. Weed species expressed specific dose responses, estimated ED50, LD50, and maximal mortality. Among species in the experiment, hairy galinsoga (Galinsoga quadriradiata Cav.) and wild carrot (Daucus carota L.) were the most affected by biofumigation, where maximal mortality reached 97 and 95%, ED50 values for germination were 2.30 and 3.23 mg cm-2, and LD50 were 3.99 and 4.44 mg cm-2 of mustard tissue, respectively. Second, laboratory and greenhouse experiments assessed the impact of biofumigation on common ragweed (Ambrosia artemisiifolia L.) and velvetleaf (Abutilon theophrasti Medik.) fitness components of surviving plants. Potential alterations of fitness components of the second and third generations were also examined. The second project research outlined that biofumigation modifies weed fitness components by reducing seed germination and survival, promoting seedling mortality, deferring emergence and flowering, and in some cases, decreasing number of seeds produced. However, following generations of surviving weeds may improve their tolerance to biofumigation by an increased number of dormant seeds, greater survival of seedlings, possible increased seed production, and increased relative weight of the embryo, and testa thickness. Finally, a three-year field experiment assessed seasonal variation and impact of biofumigation on weed community and population dynamics. Indian mustard cover crops sown in the spring and fall, once or twice a year were compared to an oat (Avena sativa L.) cover crop and weedy check plots. At full flowering of mustard, all cover crops were finely chopped and incorporated into the soil. Weed emergence, establishment and weed community data were recorded during the cover crop growth and after biomass incorporation. Indian mustard cover crop impacts on weeds were associated to biofumigant potential. As the amount of ITC detected increased in 2015 and 2016, Indian mustard reduced weed establishment within the cover crop growth, and post incorporation weed spring emergence. Allelopathic interference of Indian mustard increased above the corresponding GSL level in tissues generating more than 600 μg of allyl-ITC g-1. Biofumigation technique realized in good conditions may lead in lower weed species richness and diversity and contribute to altering community structure, according to biofumigant potential of mustard, weed community and sites. This project exposes the potential of biofumigation for weed control, allows a better recognition of allelopathy as a defining factor of population dynamics Overall, the project provides a comprehensive understanding of mechanisms of weed population and community responses to Indian mustard biofumigation. " --