Flora of Turkey and the East Aegean Islands.

Chlorophyll a Fluorescence – A Signature of Photosynthesis. Advances in Photosynthesis and Respiration, vol. 19, E. Papageorgiou, G.C. Govindjee (Eds.). Springer, Dordrecht, The Netherlands (2004), (820pp., price: Euro 270.00, GBP 187.00, USD 349.00), ISBN: 1-4020-3217-X

Weeds constitute the largest biotic threat affecting the yield of cultivated plants. While conventional agriculture relies principally on chemicals for weed control, alternative biological methods may be important tools to reduce weed pressure in agroecosystems. Furthermore, as the problem of excessive residue of plant protection agents in agroecosystems and the growing number of herbicide resistant weed biotypes continue to increase, new solutions that have smaller impacts on the environment are becoming increasingly desirable. One promising such method is the use of crops that exert a negative phytotoxic influence on weeds. This natural phenomenon describing the ability of certain plant species to produce compounds that affect the growth of other plants in their surroundings is called allelopathy. Managing weed infestations in cultivated fields by planting allelopathic crops is a sustainable, economic, and environmentally friendly approach that has been strongly articulated in the international arena. Among cultivated crops, sorghum ( Sorghum bicolor (L.) Moench) has been intensively studied because of demonstrated allelopathic potential. This report provides a comprehensive literature review of the applications of sorghum allelopathy in agriculture. A critical analysis of the allelopathic properties of sorghum identified the following areas contributing to its ability to reduce weed infestation in agroecosystems: 1. a large number of compounds produced by sorghum have allelopathic properties, 2. allelopathic compounds can be applied in the form of mixed plant extracts or in combination with herbicides, 3. sorghum extracts have a broad spectrum of activity, 4. sorghum may be used to produce bioherbicides.

Allelopathic Potential of Sorghum (Sorghum bicolor (L.) Moench) in Weed Control: A Comprehensive Review

Life on earth is sustained by oxygenic photosynthesis, a process that converts solar energy, carbon dioxide, and water into chemical energy and biomass. Sunlight is essential for growth and productivity of photosynthetic organisms. However, exposure to an excessive amount of light adversely affects fitness due to photooxidative damage to the photosynthetic machinery, primarily to the reaction center of the oxygen-evolving photosystem II (PSII). Photosynthetic organisms have evolved diverse photoprotective and adaptive strategies to avoid, alleviate, and repair PSII damage caused by high-irradiance or fluctuating light. Rapid and harmless dissipation of excess absorbed light within antenna as heat, which is measured by chlorophyll fluorescence as non-photochemical quenching (NPQ), constitutes one of the most efficient protective strategies. In parallel, an elaborate repair system represents another efficient strategy to maintain PSII reaction centers in active states. This article reviews both the reaction center-based strategy for robust repair of photodamaged PSII and the antenna-based strategy for swift control of PSII light-harvesting (NPQ). We discuss evolutionarily and mechanistically diverse strategies used by photosynthetic organisms to maintain PSII function for growth and productivity under static high-irradiance light or fluctuating light environments. Knowledge of mechanisms underlying PSII maintenance would facilitate bioengineering photosynthesis to enhance agricultural productivity and sustainability to feed a growing world population amidst climate change.

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A New Light on Photosystem II Maintenance in Oxygenic Photosynthesis.

Weeds and weed control.

Alfalfa is one of the most widely grown forage crops in Iran, especially in Shabestar county. Weeds play a significant role in reducing the feeding value of alfalfa. Weed survey was done in order to determine environmental factors on weed species distribution in alfalfa fields at Shabestar, Iran (2010–2011). The family dominance index (FDI) and relative dominance (RD) were used to find dominant families and species for infestation of Shabestar's alfalfa fields. Data were analyzed by principal component analysis (PCA) and canonical correspondence analysis (CCA). A total of 130 weed species belonging to 28 families were observed. The most dominant families, based on the FDI, were Asteraceae, Poaceae, and Brassicaceae with 66.3, 61.8, and 41.1 FDI, respectively. Alopecurus myosuroides and Convolvulus arvensis were the most dominant species according to the RD index, measuring 26.4 and 21.8, respectively. PCA showed that some weed species only infested specific areas, but a few species with broader environmen...

Weed flora survey in alfalfa (Medicago sativa L.) fields of Shabestar (northwest of Iran)

Weed flora survey in alfalfa (Medicago sativa L.) fields of Shabestar

The effect of seven herbicides (U-46 Combi Fluid, Cruz, MR, Basagran Bromicide, Lumax, and Gramoxone) on Xanthium strumarium plants was studied. Chlorophyll content and fluorescence, leaf temperature, and stomatal conductance were evaluated at 12 h, 36 h, 60 h, and 84 h after herbicides application. U46 Combi Fluid, Cruz, and MR did not have a significant effect on chlorophyll fluorescence induction curves as compared to the control treatment. However, Basagran, Bromicide, Lumax, and Gramoxone showed significant changes in the shape of polyphasic fluorescence transients (OJIP transients). Variations in chlorophyll content index, leaf temperature, and stomatal conductance parameters were dependent on the type of applied herbicide. Our study revealed that the specific impact of the applied herbicides on the photosynthetic efficiency of plants is related to their chemical groups and their mechanism of action.

https://www.mdpi.com/2223-7747/9/4/529/pdf

Early Identification of Herbicide Modes of Action by the Use of Chlorophyll Fluorescence Measurements.

Allelopathic effects of wheat seed extracts on seed and seedling growth of eight selected weed species.

In the present study, the effects of three allelopathic plant residues, namely Syrian bean-caper (Zygophyllum fabago L.), marigold (Calendula officinalis L.), and jimsonweed (Datura stramonium L.) on two cultivar of sweet basil (Ocimum basilicum L.) plants infested by dodder (Cuscuta campestris Yunck.) were examined using factorial experiment in randomized complete block design with three replications. Means comparison revealed that the degree of sensitivity to allelopathic plant residues and dodder infestation in Iranian cultivar (Mubarake) of the basil was more than that of the Italian cultivar. In the plants, infested by dodder, a significant increase in the content of total soluble sugars, peroxidase activity, catalase, superoxide dismutase, ascorbate peroxidase and the initial fluorescence (F0) was observed, while a noticeable decrease in their height, shoot dry weight, relative water content, pigment–protein content, the variable fluorescence (Fv) and the maximum quantum efficiency (Fv/Fm) of PSII was recorded. Depending on the allelopathic plants used in this study, the effect of the residues on dodder infestation and basil growth varied significantly. While the use of Z. fabago and D. stramonium residues positively correlated with the suppression of dodder emergence, D. stramonium residue use showed a negative impact on basils’ growth. In contrast, the usage of C. officinalis residues could not diminish dodder infestation, and in dodder-infested basils it decreased plant performance, RWC, pigment and protein content and the maximum quantum efficiency (Fv/Fm) of PSII. Meanwhile, the application of Z. fabago residues to dodder-infested basil plants decreased dodder emergence rate and increased basil plants’ height, dry weight of shoot, relative water content, pigment and protein content, and the maximum quantum efficiency (Fv/Fm) of PSII. Our findings suggest that as an environment-friendly treatment, Z. fabago residues could be used for controlling dodder infestation in basil plants.

Sirous Hassannejad

Papers

Weed flora survey in alfalfa (Medicago sativa L.) fields of Shabestar (northwest of Iran)

Weed flora survey in alfalfa (Medicago sativa L.) fields of Shabestar

Early Identification of Herbicide Modes of Action by the Use of Chlorophyll Fluorescence Measurements.

Allelopathic effects of wheat seed extracts on seed and seedling growth of eight selected weed species.

Physiological and biochemical responses of basil to some allelopathic plant residues and dodder infestation