Interactions involving allelopathy in cropping systems

Allelopathic inhibition typically results from the combined action of a group of allelochemicals which, collectively, interfere with several physiological processes. The objectives of this paper are to summarize research that illustrates the joint action of allelochemicals, and to provide evidence that both the amount and detrimental action of these compounds depends an the extent of associated abiotic and biotic stresses. Allelopathy is strongly coupled with other stresses of the crop environment, including insects and disease, temperature extremes, nutrient and moisture variables, radiation, and herbicides. These stress conditions often enhance allelochemical production, thus increasing the potential for allelopathic interference. In the paradigm of interactions, the data indicate that crops are more sensitive to allelopathy when moisture, temperature, or nutrient conditions are less than optimal. For example, the inhibition threshold concentration for ferulic acid to affect seedling growth was reduced with even minor moisture stress (ψ = -0.15 MPa) or a growth temperature at the higher end of the normal range for a species. Under greenhouse conditions, additive inhibition resulted from the joint action of ferulic acid with low levels of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], atrazine [6-chloro-N-ethyl-N\u27-(1-methylethyl)-1,3,5-triazine-2,4-diamine], or trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine]. Interactions of multiple stresses in crop environments will determine the relative impact of allelopathy. Allelopathy-stress interactions also have implications for herbicide and residue management strategies, crop rotations, biological control measures, and tillage practices that can contribute to a more sustainable agriculture

The effects of ferulic acid on the mineral nutrition of grain sorghum

Two week old sorghum seedlings (Sorghum bicolor L. Moench) were treated with ferulic acid added to the nutrient solution. Effects on tissue concentration of P, K, Mg, Ca, Fe, and Zn were evaluated after 3 and 6 days. Treatemnts of 0.25 m M ferulic acid approximated the growth inhibition threshold, and after 6 days 0.5 m M treated plants weighed less than controls. Both treatments reduced the P content of the roots and shoots at the 3- and 6-day harvests in three replicate experiments. Roots of treated plants at both harvests had a lower concentration of K and Mg. These reductions in P, K, and Mg were most extensive from the 0.5 m M ferulic acid regime. In some cases at both harvests, shoot K was lower and Mg was higher than control tissue. Ferulic acid effects at the 3-day harvest included an elevation of Ca and depression of Fe in shoots. Changes in nutrient content preceded measurable differences in plant weight. These data indicate that one mechanism of growth inhibition by this allelochemical may be an alteration of nutrient balance

Synergistic inhibitory effects of p-coumaric and ferulic acids on germination and growth of grain sorghum

The data support the hypothesis that there is a synergistic phytotoxic effect when p-coumaric and ferulic acids are found together. Equimolar mixtures of both acids showed greater reduction in sorghum seed germination, shoot elongation, and total seedling growth than either phytotoxin caused when alone. Repeated experiments showed mixtures containing 5×10-3 M p-coumaric and 5×10-3 M ferulic acids reduced germination to 34% of controls after 24 hr and 59% by 48 hr. The same concentration of either phenol-treated seeds alone showed 69 and 92% germination at comparable times. The phytotoxic action of the combination approximated the inhibitory effect on germination of 10-2 M ferulic acid and was a greater reduction than caused by 10-2 M p-coumaric treatments. Sorghum seedling growth was more sensitive than germination, with an equimolar mixture of 2.5×10-4 M p-coumaric and 2.5×10-4 M ferulic acids reducing seedling dry weight significantly below weights of seedlings treated separately with 2.5×10-4 M p-coumaric or ferulic acids. Further dilutions showed a 1.25×10-4 M concentration of either phenol was stimulatory to seedling growth, whereas a mixture of these two produced inhibition

Allelochemic Effects of Leaf Extracts of Ambrosia trifida (Compositae)

Aqueous extracts from leaves of giant ragweed reduced growth in sorghum seedlings, and reduced germination in sorghum and radish. Five phenolic compounds from these extracts were isolated and characterized, but not identified. Germination bioassays using these compounds demonstrated that each of the five depressed germination, and the depression related to concentration. It is suggested that the water-soluble allelochemics from giant ragweed contribute to any interference effect this weed may have on growth of associated species

Effects of pilocarpine on Drosophila larval salivary gland cells

Pilocarpine fed to Drosophila larvae in concentrations of 1, 10, 100, or 1000 p.p.m. induced depletion of all synthesized material from the larval salivary gland cells, as shown by loss of cytoplasm granularity and changes in cell shape. Determination of the nuclear and nucleolar diameters of salivary gland cells from the several treatments showed a reduction in nuclear to nucleolar diameter ratio after 10 or 100 p.p.m. treatments

Potencial alelopático de 2-benzoxazolinona (boa) e sua interação com atrazine no crescimento de plantas

Two laboratoy experiments were carried out at the University of South Dakota, Vermillion, SD, USA, in 1990, to determine the effects of hydroxamic acid benzoxazolinone (BOA), the herbicide atrazine, and a mixture there of on duckweed growth and its chlorophyll content. BOA at 0.5 mM concentration was applied in combination with atrazine at 0.001 and 0.005 mM in a 2.5 ml cell tissue cluster dish containing three fronds of duckweed in nutrient solution. Single applications of BOA and atrazine inhibited duckweed frond number, frond dry weight, and its chlorophyll content. Atrazine showed stronger inbibition effect than BOA. The combination BOA and atrazine at 0.001 mM was antagonistic where the inhibition induced by the herbicide was counteracted. Unlike atrazine at 0.00I mM, BOA added to atrazine at 0,005 mM did not counteract the inhibitio caused by the herbicide

Effects of Scopoletin and Chlorogenic Acid on Stomatal Aperture in Tobacco and Sunflower

Both scopoletin and chlorogenic acid are natural growth inhibitors which have previously been shown to increase in plants under a variety of stress conditions. In order to determine if these inhibitors interfere with stomatal function, tobacco and sunflower seedlings were treated with scopoletin or chlorogenic acid in a nutrient culture. After treatment, daily measurements were made of stomatal apertures by making Duco cement prints from the lower epidermis. It was found that 10-3 M and 5 x 10-4 M treatments of both compounds caused stomatal closure in tobacco within one day after treatment. This closure persisted for several days, but eventually stomata returned to near normal. Stomata of sunflowers treated with 10-3 M and 5 x 10-4 M chlorogenic acid reacted similarly with less extreme effects in the latter group. Both tobacco and sunflower seedlings treated with scopoletin or chlorogenic acid of 10-4 M levels showed an enhancement of stomatal openings. Stomatal reductions induced by 10-3 M and 5 x 10-4 M scopoletin treatments correlate well with growth retardation and photosynthetic reductions previously established in these seedlings. It appears that one mechanism of growth inhibition induced by scopoletin and chlorogenic acid operates through stomatal closure