The effect of two boron compounds on growth and chemical composition of two fruit rootstocks

Abstract

The aim of this work was to determine the effects of boron (B) application on the physiological and anatomical characteristics of MM106 (Malus × domestica Borkh.) and sour orange (Citrus aurantium L.) plants. The experiment was carried out under semi-field conditions and lasted 165 days. The experimental design included seven B treatments with five replications for each treatment. The plants were grown in pots filled with a substrate of sand: perlite (1:1) and fertigated initially with a Hoagland nutrient solution. Afterwards, they were treated with boric acid (BA) (0, 7.5, 30 and 60 mg kg(‑1)) and borax (SB) (7.5, 30, and 60 mg kg‑1). Boron treatments were applied in two doses with a month interval. At the end of the experiment, in general, sour orange B use efficiency (BUE) presented a negative correlation with added B. On the other hand, BA treatments (30 and 60 mg kg(‑1)) led to decreased B use efficiency in MM106 plants. The BA and SB treatments (60 mg kg(‑1)) led to increased leaf and stem B concentrations of MM106 plants. Furthermore, the SB treatments (30 and 60 mg kg(‑1)) and BA treatment (60 mg kg(‑1)) showed the highest B concentration in all parts of sour orange plants. However, high B doses caused B toxicity symptoms in leaves. SB treatments increased leaf K concentration in both genotypes. Fresh matter weight of MM106 plants was negatively correlated with the applied B amount, while in sour orange no effect was observed. No other growth parameters (plant height, stem diameter, shoot length, lamella length and the number of leaves and nodes) of MM106 plants were affected by B application. Chlorophyll concentration was slightly increased in leaves of B-treated plants, especially in MM106. Additionally, SB (7.5 mg kg(‑1)) was the only treatment which significantly increased the photosynthetic rate of MM106 plants, without being associated with plant growth. Overall, the use of lower B doses than those used in this experiment was recommended, in order to prevent plants from B toxic effects.