Understanding the Mechanisms of Weed Interference with Crops through Photosynthetic and Antioxidative Physiology

Background: Crop losses due to weed interference continue to be a serious impediment to global attempts to boost food and fibre supply. Despite the fact that weed interference with crops affects both biotic and abiotic components of the agroecosystem, most weed research concentrates on crop-weed competition for scarce resources. Crop-weed competition studies, understandably, focus on crop variables in order to generate weed management recommendations that minimise crop losses. As a result, they tend to focus on the competition for resources such as light, water, and nutrients between the crop and weed(s), attempting to provide insight into which resource becomes more limited during different growth stages of the crop in the presence of differing weed densities (s). However, in cotton and many other cropping systems in the United States and other industrialised countries, cultural practises such as appropriate crop densities, frequent irrigation, and recommended fertiliser application affect the competition for those resources. As a result, directly applying the knowledge gained from the aforementioned studies to these cropping methods is problematic. For example, under such cropping systems, the idea that weeds with similar growth habits and morphology to the crop impose more severe competition to the crop may not hold true. Simultaneous studies of major physiological processes such as carbon gain in both the weed(s) and the crop under controlled settings during interference, on the other hand, can reveal how the weed(s) may interfere with the crop in such cropping systems. The research reported here reveals how a weed species belonging to the same family as the crop and having a similar growth behaviour to the crop maintains a gas exchange strategy that differs from the crop, giving researchers a better understanding of the crop-weed interference process. It also tries to demonstrate how the crop-weed system would adapt to a mild, rather than severe, drought, and the recovery expected between irrigation times in a well-managed agricultural system, using potted experiments under controlled settings.

Using potted plants of two cotton species (Gossypium hirsutum L. cv. Delta Pine 5415 and Gossypium barbadense L. cv. Pima S-7) and spurred anoda (Anoda cristata L. Schlecht.) of the Malvaceae, the effect of plant intervention and a mild drought on gas exchange and oxidative stress was examined. Cotton and spurred anoda demonstrated identical net photosynthesis (Pnet) without intervention, but distinct pigment profiles. Spurred anoda had higher stomatal conductance (gs) and transpiration rate (E) than cotton. Spurred anoda interference lowered net photosynthesis and biomass in cotton more than intraspecific interference. Cotton’s xanthophyll cycle conversion state and a-tocopherol levels increased with interference, but spurred anoda remained same. Plant interference had no effect on catalase, ascorbate peroxidase (APX), or glutathione reductase (GR) activities. When compared to cotton, spurred anoda had reduced APX and equivalent catalase and GR activity without intervention. Drought boosted APX activity in cotton by more than 40%, and in spurred anoda by 26%. Drought-induced APX activity was still higher in cotton after recovery from drought, and GR activity was higher in previously drought-stressed cotton and spurred anoda plants than in well-watered plants. Cotton biomass is impacted more by stimulated anoda interference than intraspecific interference, owing to lower carbon gain in cotton.

Author(S) Details

H. Harish Ratnayaka
Department of Biological Sciences, Xavier University of Louisiana, 1 Drexel Drive, New Orleans, LA 70125, USA.

William T. Molin
Southern Weed Science Research Unit, PO Box 350, Experiment Station Road, Stoneville, MS 38776, USA.

Tracy M. Sterling
Department of Biological Sciences, Xavier University of Louisiana, 1 Drexel Drive, New Orleans, LA 70125, USA.

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