Archives - Allelopathy Journal

Using the qPCR, we studied the effects of intercropping of watermelon (Citrullus lanatus (Thunb.) Matsum & Nakai) with wheat (Triticum aestivum L. Poaceae family) on the abundances of total bacteria, beneficial microbes (Pseudomonas, Bacillus, Streptomyces, Actinomycetes and Trichoderma spp.) communities, total fungi, pathogenic microbes [(Fusarium oxysporum, Fusarium oxysporum f.sp. niveum (FON)] and allelochemicals 2,4-diacetylphloroglucinol (DAPG), phenazine-1-carboxylic acid (PCA) and pyrrolnitrin (PRN) producers in watermelon rhizosphere. The intercropping decreased the abundances of Pseudomonas and Actinomycetes spp., DAPG, PCA and PRN producers at 20 d, and later increased the PCA and PRN producers at 30 d and 40 d. The intercropping with wheat increased the abundances of total bacteria, Pseudomonas spp., Streptomyces, Actinomycetes and Trichoderma spp., and reduced those of total fungi, Bacillus spp., Fusarium oxysporum and FON at 40 d. These results indicated that intercropping of wheat + watermelon affected the microbial communities and increased the abundances of allelochemicals producing genes in watermelon rhizosphere.

We studied the allelopathic stress of C. ambrosioides volatile oil using the epidermal strip bioassay, microscopy and histochemical techniques on stomatal movement in leaves from broad beans (Vicia faba L.), peanuts (Arachis hypogaea L.) and peas (Pisum sativum L.). We also studied the changes in vacuoles, microfilaments and signalling molecules ROS, NO and Ca2+ in guard cells. The stomatal aperture of 3-test legume species decreased significantly (P < 0.05) in volatile oil concentration-dependent manner. Compared with control, the applied volatile oil increased the numbers of vacuoles but decreased their volume in guard cells of all 3-test crops. Aggregation of microfilament skeletons, increased the in ROS, NO and Ca2+ concentrations. These effects could be alleviated, when related inhibitors (Cytochalasin B, AS, LaCl3 and L-NAME) were used with volatile oil. It is speculated that the dynamic changes in guard cell microfilaments caused by volatile oil of C. ambrosioides could lead to increased ROS and NO levels by activating the related enzymes, which increased the cytoplasmic free Ca2+ levels in guard cells. Thereby the ion channels in plasma membrane and vacuolar membrane were affected. The bigger vacuoles in guard cells were divided into smaller ones, turgor pressure was decreased and stomata were closed. The stomatal movement of broad bean was most sensitive to volatile oil of C. ambrosioides, which showed strong allelopathy.

Soil sickness is a serious problem to establish new fruit orchards at the old orchard site. It is a complex soil sickness syndrome that reduces the plant growth, survival and yield of replanted trees. Various factors are responsible for soil sickness viz., (i) biotic factors i.e. rhizospheric microflora (bacteria, fungi, actinomycetes, nematodes and their interactions) and (ii) abiotic factors (phytotoxins, nutrient imbalance, low or high pH, soil structure and lack of excess soil moisture). In many cases, autotoxins may enhance soil-borne diseases by predisposing the roots to infection by soil-borne pathogens through direct biochemical and physiological effects. It is not easy to prevent the soil sickness problem because of its exact etiology and complex nature of problem and different biotic and abiotic factors are associated with it. The nature and intensity of incidence are variable from region to region and country to country and there is a lack of quick diagnostic methods. It cannot be controlled with one method and require integrated management practices. This review outlines the current knowledge on methods to reduce the negative effects of soil sickness in fruit orchards, which may be a promising strategy to improve the growth and yield of fruit trees in sick soils.