Archives - Allelopathy Journal

We investigated the soil toxicity in passion fruit plantations, the effects of old soils on the growth of the replanted passion and changes in photosynthetic parameters, physiological and biochemical parameters in the passion fruit leaves. In laboratory bioassays, we found that older soils of 1-, 2- and 3-year plantations significantly inhibited the root length of lettuce and passion fruit. The growth parameters (stem girth and perimeter, vine length, leaf area and shoot dry weight of passion fruit seedlings were significantly decreased when cultured in the older soils, compared with the virgin soils. Photosynthesis in the replanted seedling leaves cultured in the older soils were significantly lower than that cultured in the unplanted soils. The activity of antioxidant enzymes [superoxide dismutase (SOD), Peroxidase (POD) and catalase (CAT)] were significantly decreased in the replanted seedling leaves, along with decrease in insoluble carbohydrate and soluble protein. In replanted seedling leaves, the level of malondialdehyde (MDA) and abscisic acid (ABA) significantly increased, but the levels of indole-3-acetic acid (IAA) and cytokinins (ZR) of significantly decreased. Thus the older soils of passion fruit plantations have negative effects on the replanted passion fruit seedlings, suggesting the presence of soil autotoxicity in passion fruit plantations.

To screen for mycoherbicides, we isolated 33 fungi from the rhizosphere soil of allelopathic rice variety PI312777, using the plate dilution method. One fungal culture with strong weed suppression potential and no adverse effects on the growth of rice, was identified as Penicillium decumbens strain ZQ001. The optimal culture conditions for this fungal strain were determined. In pot culture with soil, the fungal culture broth added at 100 µL /g soil concentration, reduced the barnyard grass growth significantly. HPLC analysis of the culture broth showed that it contained protocatechuic, p-hydroxybenzoic acid, vanillic acid, salicylic acid and cinnamic acid. Our results suggest that P decumbens strain ZQ001 inhibited the barnyard grass through the production of phenolics) and thus could be a potential mycoherbicide.

In petri plate, laboratory bioassays we studied the herbicidal potential of aqueous leachates of petals of Gliricidia sepium (Jacq.) Kunth ex Walp against the weed Alternanthera tenella. Colla. The petal leachates at all concentrations completely inhibited the seed germination of A. tenella Colla at 24 h. The reduction in root length and shoot length was concentration dependent. Seed germination and seedling growth of A. tenella was inhibited due to presence of phenolic compounds (Gallic acid, catechol and tannic acid) in the G. sepium petals. As compared to standard phenolic compounds, the petal leachates caused adverse effect on seed germination, root length and shoot length of A. tenella Colla in both petriplate and soil bioassays. In 20 % petal leachate, appreciable amount of total phenolics (24.12 mg per 100 ml) and phytochemicals Hydrocoumarin, 3-(2- Hydroxyphenyl) propionic acid, Diphenyl ether and Hydroxybiphenyl were detected and identified by GC-MS. The RP-HPLC technique quantified the final content of 28.91 mg/100ml for 3-(2-Hydroxyphenyl) propionic acid and 43.82 mg/100ml for Hydrocoumarin. Both 3-(2-Hydroxyphenyl) propionic acid and Hydrocoumarin at low concentrations (5, 10 and 15 ppm) adversely affected the seed germination and seedling growth of A. tenella Colla. However, except 10 ppm 3-(2-Hydroxyphenyl) propionic acid in soil bioassay slightly increased the root length and shoot length.

The water soluble polyphenols extracts from the Eucalyptus grandis litter and leaves inhibited the germination of beans but the soil extract was not inhibitory. Germination of beans inside the Eucalyptus trees plantations under natural conditions was 90 %, 92 % and 86 % in 1.5, 3 and 6 years old trees, respectively. Bean production under 1.5 years old trees canopy significantly differed from both 3 and 6 years old canopies. The amount of water soluble polyphenols in the soil under Eucalyptus increased with tree age but was less than that present in litter or leaves. Soil water repellency increased with age of Eucalyptus tree and was strong during the dry spells and decreased with soil depth in the soil profile. The contents of water soluble polyphenols and moisture in the soil were the key factors influencing the soil water repellency under Eucalyptus grandis trees. Mixing of the soils with litter during crop cultivation under Eucalyptus trees reduced the soil water repellency.

We determined the chemical composition of Eucalyptus camaldulensis leaf extract and studied its allelopathic effects on germination, seedling growth and physiological parameters [(chlorophyll content, net photosynthetic activity, transpiration, stomatal conductance, malondialdehyde, membrane integrity and proline content)] of Triticum turgidum subsp. durum (Desf.) Husn.,Vicia faba subsp. paucijuga (Alef.) Murat., Phaseolus vulgare var. vulgaris L., Sinapis arvensis L., Eruca vesicaria (syn. Brassica vesicaria L.) and Scorpiurus muricatus L. Fifteen phenolics compounds were isolated from the leaves of E.camaldulensis. Dose-response studies were conducted under field and laboratory conditions. Germination, seedling growth and net photosynthetic rates were decreased by E. camaldulensis aqueous extract. The greatest reduction in net photosynthetic activity was observed at the highest concentration over the control. The trend for transpiration in response to E. camaldulensis leaf extract was similar to net photosynthetic rate, except that the effects were greater in magnitude than on leaf photosynthesis. Stomatal conductance followed patterns similar to those observed for transpiration and leaf photosynthesis. Besides, E. camaldulensis leaf extract induced electrolyte leakage indicating membrane damage and loss of integrity, while the higher level of proline suggested the induction of oxidative stress. The test plants responded differently to eucalypt leaf extract exhibiting a differential species-specificity. Indeed, the weeds were affected more strongly than the crops. The E. camaldulensis leaf extracts inhibited the growth and many physiological processes of test species, showed strong phytotoxicity and weed-suppression potential. Therefore, its active components could be exploited for developing bioherbicides

We studied the performance of Impatiens balsamina in soil incorporated with the leaf litter of Cinnamomum japonicum. The application of 40 or 80 g litter in 8 kg soil, significantly inhibited the vegetative growth and photosynthetic rate of I. balsamina. These treatments also changed the normal blooming pattern of the receptor plant. Though the fruit and seed yield per plant of I. balsamina was not influenced by C. japonicum leaf litter, but the seed yield per fruit was increased at the highest dose. Incorporation of boiled leaf litter to soil did not affect the growth of I. balsamina, which indicated that the allelochemicals of C. japonicum were neutralized by boiling i.e. high emperature. Eight compounds (terpenoids, aldehyde and esters, which are Dihydrocoumarin, 1,8-Cineole, Cinnamaldehyde, trans-Caryophyllene, alpha-Terpineol, (+)-Spathulenol, Caryophyllene oxide and Borneol L.), were found in C. japonicum leaf litter. These may be potential allelochemical candidates. In conclusion, C. japonicum leaf litter during its decomposition was allelopathic to I. balsamina. The allelopathic effects inhibited the carbon-fixation ability, thereby reduced the vegetative growth and flower production of I. balsamina.

We studied the sensitivity of 21-accessions, from 6-botanical families (Asteraceae, Brassicaceae, Fabaceae, Lamiaceae, Pedaliaceae, Poaceae) of different seed mass, to essential oil of Baccharis psiadioides (Less.) Joch. Mull during its germination. The essential oil was obtained from fresh leaves by distillation and was used as allelochemical. Seeds were submitted to a dose-response experiments to determine the sensitivity of each accession. Germination inhibition was calculated with the effective dose (ED50). We found a positive correlation between the seed size and ED50. Smaller seeds required less quantity of essential oil to inhibit their germination than larger seeds. Effects reported herein may be a pattern for action of other essential oils, however, others studies may be conducted relating to other seed attributes as seed reserve or embryo size.

To evaluate the impacts of two alien mangrove species Laguncularia racemosa and Sonneratia apetala on the native mangrove plants on Hainan Island, we chose a native mangrove species, Sonneratia caseolaris, because it has similar ecological requirements to the two alien species and they are usually planted close to it. The effects of aqueous leachates from the two alien species on S. caseolaris were analysed by measuring the germination rate of seeds and antioxidative activity of seedlings. The activities of SOD, POD and APX in the seedlings of S. caseolaris were inhibited by 0.2 and 0.4 g/mL concentration of leachates from the two exotic mangrove species, but the CAT activity increased, when the concentration of leachates increased. The leachates from S. apetala, increased the activities of SOD, POD, APX and CAT. However, the activities of SOD and CAT increased, while POD and APX were inhibited < 0.1g/mL concentration of the leachates from L. racemosa. The changes in the antioxidative activity may be an adaptive regulatory strategy in S. caseolaris seedlings in response to the allelochemicals of L. racemosa and S. apetala. Furthermore, the chemical components in aqueous leachates from mixed fresh branches, leaves and fruits of L. racemosa and S. apetala were characterized by GC-MS. Octadecanoic acid, 3-[(1-oxododecyl)oxy]-1,2-propanediyl ester was found at relatively high contents in every leachate of both of the exotic species, which may play an important allelopathic role in the leachates.

This study aimed to assess the genetic diversity among the 46-allelopathic rice accessions from Bangladesh Rice Research Institute (BRRI) and Malaysian Agricultural Research and Development Institute (MARDI) and Africa using 20 minisatellite or inter simple sequence repeat (ISSR) markers. Out of 20 ISSR markers, 10-markers generated 188 polymorphic loci. The highest polymorphic loci (41) were found in accession BRRI dhan47, whereas, the lowest was in BR11 (22). Mean Shannon’s information index and polymorphic information content were 0.37 and 0.19, respectively, in ten markers. The mean effective number of alleles in the 10-ISSR markers varied from 1.24 to 1.56. The number of polymorphic loci was highest (29) in WITA3 and lowest (24) in WITA12 accessions of African population. The cluster analysis revealed 10-main groups, including several subgroups at 0.31 similarity coefficient. The principal component analysis elucidated 36.94% complete variations in all accessions in this study. There was considerable genetic diversity in rice accessions in this study. The information about genetic diversity and relationship obtained from the study may be used to develop the allelopathic rice in future breeding programmes.

Rhizosphere soils from Tieguanyin tea plantations of 0, 3, 9 and 25 years old wereextracted and eluted through 5 resins of different polarity. Tea seedlings were then grown withthe 5 eluents and their effects were determined on the photosynthetic indices and leaf quality.Among the 5 resins, soil eluents through ADS-7 resin most strongly inhibited the root length andheight of the receptor lettuce, photosynthetic indices and leaf quality of new tea plants. And theinhibitory effects increased with soil age, especially, the ADS-7 resin eluents from 25-year-oldsoil showed the strongest inhibitory effect. The GC-MS analysis of ADS-7 resin eluents showedthe presence of amides, esters, acids and other types, which changed significantly as the tea plantsoil age increased, and the content of all acids increased significantly, while the phenolic ketonecontent of all soil samples remained unchanged.