The effects of boron and effluent (treated sewage water) on vegetative growth, fruit yield, and boron uptake of grafted and nongrafted melons (Cucumis melo L. cv. Arava) were studied. Nongrafted melon plants and melon plants grafted onto the commercial Cucurbita maxima Duchesne × Cucurbita moschata Duchesne rootstock ‘TZ-148’ were grown in pots filled with perlite in a heated greenhouse and were irrigated with fresh water or effluent. The two irrigation waters contained boron in five concentrations ranging from 0.1 to 10.4 mg·L−1. The boron concentration in the plants increased linearly with that in the irrigation water. The highest boron concentrations were found in old leaves, the lowest in the fruit, and intermediate concentrations were noted in the roots. The boron concentrations were, in general, significantly lower in grafted than nongrafted plants, possibly because the root system of the former had higher selectivity and lower boron absorption than that of the latter. Fruit yield and dry weight accumulation in shoots and roots decreased linearly as the boron concentration in the irrigation water increased, the nongrafted plants were more sensitive than grafted ones to the boron level, and both were more sensitive under fresh water irrigation than under effluent irrigation. It is suggested that the higher boron sensitivity of the root systems of the nongrafted plants probably decreased their capability to absorb water and nutrients, which in turn sharply reduced their fruit yields.
Excess of boron and salinity in soil and irrigation water can limit the production of melons (Cucumis melo). A greenhouse study was conducted in order to compare the responses of grafted and non-grafted melon plants to combinations of high levels of boron and salinity. Boron levels were 0.25, 0.8, 2.5, 5.0, 10.0 mg·L-1 and salinity levels were 1.8 and 4.6 dS·m-1. Foliar injury caused by boron was more severe in the non-grafted than in the grafted plants. Likewise, boron accumulation in leaf tissue from non-grafted plants was higher than in grafted plants. High salinity led to decreased boron accumulation in the leaves. Fruit yield was decreased only at a boron concentration of 10 mg·L-1, and the decrease in grafted plants was smaller than that in non-grafted plants. A negative correlation was found between boron accumulation in leaves and fruit yield. The results showed that melon plants grafted on Cucurbita rootstock are more tolerant than non-grafted ones to high boron concentrations, and this can probably be explained by the decrease in boron accumulation caused by the rootstock.
Tomato ‘Abigail’ (Solanum lycopersicum L.) and basil ‘Perry’ (Ocimum basilicum L.) were selected as model plants for selenium (Se) supplementation to evaluate a) effects of Se concentration in nutrient solution on Se content in different organs under fertigation, b) Se phytotoxicity threshold values, and c) mechanisms. Plants grown in a glasshouse were irrigated with 0, 1, 2, 5, and 10 mg Se/L in the first experiment, while with 0, 0.25, 0.5, 0.75, 1.0, and 1.5 mg Se/L in the second. Tomato plants accumulated Se linearly with rising Se concentrations, whereas accumulation in basil followed a saturation curve. Plants supplemented with 1.5 mg Se/L in the irrigation water accumulated 0.23 and 0.88 mg Se/g dry weight (DW) in tomato fruits and basil shoots, respectively. However, tomato roots, shoots and fruits DW were 56%, 36%, and 66% lower than in controls, respectively, and basil roots and shoots DW were 92% and 88% lower than in control, respectively. Calculated toxicity-threshold values were 1.27 mg Se/L for tomato and 0.44 mg Se/L for basil. Tomato crops were more tolerant than basil crops, although data suggested yield reduction at lower Se concentrations than those effecting biomass reductions. The results indicate that Se supplementation through drip irrigation may efficiently fortify tomato and basil. However, Se concentrations should be lower than 0.75 and 0.25 mg·L−1 for tomato and basil, respectively, to avoid yield reduction and possible Se phytotoxicity.