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The selection of adequate substrate for soilless culture is based on technical and economic considerations. Therefore, the search for alternatives by the valorization of natural by-products is gaining importance. The main objective of this study was to compare the effects of local farm resources, date-palm waste, as culture substrate, to coconut fiber (CF) (commonly used in soilless culture) on melon (Cucumis melo L.) plant growth, water relations, photosynthesis, chlorophyll fluorescence as well as phytochemical analysis under hydroponics culture system. Two growing substrates were tested: the compost of date palm waste added to animal manure (7:3 w w−1) (DPAM) and the date palm trunk compost (DPT). Coconut fiber and soil were used as positive and negative controls, respectively, in randomized blocks. Results showed that the vegetative growth was improved under DPT and CF substrates while CF substrate enhanced fruit yield and phytochemical properties: Total soluble solids TSS (% Brix), total dissolved solutes (TDS); Titratable acidity (as citric acid); Sugar content and juice pH of melon fruit. Date-palm waste-based substrates enhanced the vegetative growth and the fruit yield of melon as compared to soil-based culture. It seems that date palm waste-based substrates, especially trunk compost, could be promising and cheaper alternatives compared to coconut fiber substrates commonly used in Tunisia in soilless cultures.

The effects of mannitol-mediated osmotic stress on water relations, plant growth and symbiotic N 2 -fixation in four common bean (Phaseolus vulgaris) lines (Coco Blanc, BAT 477, BRB 77 and Flamingo) were studied. After germination, seedlings were inoculated with a reference strain (Rhizobium tropici CIAT 899) and aerohydroponically grown in a glasshouse. Osmotic stress was applied by 50 mM mannitol. Plants were harvested 4 weeks after osmotic stress application. Measured parameters were plant water relations, growth, nodule development, and symbiotic N 2 -fixation (SNF) as well as leghemoglobin contents. Osmotic stress induced significant changes in water relations, growth and symbiotic N 2 -fixation in stressed plants compared to control ones in all lines studied. A noticeable different behaviour was observed in the end of the treatment: Flamingo was the most tolerant line, whereas Coco blanc was the most sensitive, the two other lines exhibited an intermediate behaviour. The four bean lines displayed significant differences in their responses to osmotic stress. This study indicated that the relative tolerance of Flamingo line seems to be due to its ability to maintain higher leaf water potential, adequate leaf area and abundant and efficient nodular system, which in turn determines an important rate of SNF.

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Few studies has been conducted on interaction between P. juliflora leaf extract sand crop germination under water deficit in arid regions. We conducted laboratory trials in order to evaluate crop species germination and recovery potentials under the combined effects of osmotic stress (0.4, 0.8 and 1 MPa) and allelopathic action of P. juliflora leaf extracts (0, 2.5%, 5% and 10%). Four crop species were assessed: Wheat (Triticum durum), barley (Hordeum vulgare), lettuce (Lactuca sativa) and tomato (Solanum lycopersicum). Statistical analyses highlighted a selective negative action of allelopathy on monocots compared to dicots. Combination of osmotic and allelopathic stresses exacerbated the negative effects on seed germination of all four species. Osmotic stress was the dominant factor, whereas allelopathy was the secondary factor when the two stresses were combined. While all treatments reduced germination, even at low stress levels, partial and total recovery levels were reported. Tomato, the least stress tolerant species, showed the highest recovery. In short, leaf extracts of P. juliflora exacerbated the effect of osmotic stress on seed germination of barley and wheat. In addition, the crops displayed differential adaptive strategies when exposed to the combined stresses.

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