Role of arbuscular mycorrhizal fungi in alleviating the adverse effects of acidity and aluminium toxicity in zucchini squash

The aim of the current research was to assess whether arbuscular mycorrhizal (AM) inoculation would give an advantage to overcome acidity and aluminium (Al) toxicity problems and to study the changes induced by AM at agronomical and physiological level. A greenhouse experiment was carried out, to determine yield, growth, fruit quality, SPAD index, electrolyte leakage, and mineral composition of zucchini squash (Cucurbita pepo L.) inoculated (+AM) and noninoculated (−AM) with arbuscular mycorrhizal and cultured in pots filled with quartziferous sand. Plants were supplied with nutrient solutions having different pH and aluminium concentration (pH 6.0, pH 3.5 or pH 3.5 + Al). The low pH treatment had the same nutrient composition plus HCl, whereas the aluminium treatment (pH 3.5 + Al) was induced by adding 1.0 mM of AlCl3·6H2O. The AM root colonization was higher in the control treatment (pH 6.0; 48.5%), followed by pH 3.5 (23.4%), and finally in pH 3.5 + Al treatment (17.1%). Significant depression of yield, biomass, SPAD index, leaf area, N, P, Mg, Fe, and Zn concentration in leaf tissue was observed in response to low pH level with more detrimental effects with pH 3.5 + Al. The inoculated plants under acidity and Al conditions had higher total, marketable yield, and total biomass than noninoculated plants. Zucchini-fruit quality, in particular fruit dry matter, total soluble-solids content, P, and Fe concentration, was improved by mycorrhizal colonization. Mycorrhized zucchini plants grown under acidity and Al conditions had a higher macronutrient concentration in leaf tissue compared to noninoculated plants. The better crop performance in inoculated plants were related to the capacity of maintaining higher SPAD index, lower electrolyte leakage, and better nutritional status (high N, P, K, Ca, Mg, Fe, Zn, and B and low Al accumulation) in response to Al stress with respect to −AM plants.