Salinity is one of the major factors limiting avocado yield, primarily due to the high concentration of ions in irrigation water. An experiment was conducted on 2 year old avocado plants (Persea americana Mill.) cv. Hass, grafted onto Duke 7 clonal rootstock growing in pots, to determine the effect of salt stress on growth, as well as physiological and biochemical responses, and the effect of seaweed extract (Ascophyllum nodosum) on salinity stress. Treatments consisted of different types of irrigation water: distilled water, 9 mM NaCl water, distilled water + 2.25 mL of seaweed extract, 9 mM NaCl water + 2.25 mL of seaweed extract and, 9 mM NaCl water + 1.5 mL of seaweed extract. The irrigation treatment was applied every 15 days for 8 months. Treatments with salt reduced plant growth by approximately 50% of the fresh weight of all avocado plant tissues. Seaweed extract reduced the effects of abiotic stress only at an early stage, and increased potassium (K) and calcium (Ca) concentrations in leaves.

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BACKGROUNDThe mechanisms of calcium (Ca) absorption and transport in plants are still poorly understood. This study focused on assessing the absorption and distribution of Ca in different plant organs after root (soil), foliar, or fruit application to 6‐year‐old ‘Clemenules’ mandarin trees, grown in pots, using 45Ca as a tracer.RESULTSThe rate of 45Ca absorption and transportation in plant tissues varied according to the treatment method. The fruit and shoot Ca supply led to a rate of 97% to 98% 45Ca retention in such organs. In Ca‐treated fruits, 22% of the applied 45Ca moved to the pulp and 78% remained in the flavedo and albedo. The fruit peel was examined by scanning electron microscopy and transmission electron microscopy (SEM and TEM) and variations were observed during fruit development. Following 45Ca soil treatment, approximately 56% of 45Ca activity was measured in the soil, with 19.5% determined in the roots, 14.6% in the trunks (90% in bark and sapwood and only 10% in heartwood), 9.6% in shoots, and 0.3% in fruits.CONCLUSIONCalcium mobility in ‘Clemenules’ mandarin trees is limited and depends on the mode of Ca fertilizer application. The distribution of Ca to and within the fruits may be limited during development because of structural and functional constraints. © 2020 Society of Chemical Industry

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Searching for new strategies to mitigate the effects of low water availability for citrus production, a study was carried out on potted mandarin cv. W. Murcott, with the objective of evaluating the physiological and growth response of the plants to polyacrylamide gel application in the substrate in water restriction conditions. The following treatments were evaluated, T0 (control) with 100% ETc water replenishment, T1 with 50% ETc water replenishment, and T2 with 50% ETc water replenishment plus the application of polyacrylamide polymers to the substrate. Temperature and water volumetric content (ϴ: m3 m−3) were evaluated in the substrate. Plant water-status parameters such as stem water potential (SWP), stomatal conductance (gs), and chlorophyll fluorescence (Fv/Fm), as well as biomass, nutrients levels, and proline biosynthesis were measured in the plants in response to the treatments. The results showed that the substrate moisture for T2 was kept significantly higher than T0 and T1, despite receiving the same irrigation rate as T1 and a half of T0; however, this higher moisture availability in the substrate of T2 was not reflected in the plant’s water status or growth. On the contrary, the T2 plants showed responses such as lower total biomass, lower vegetative development, and lower root biomass, as well as a higher concentration of proline in the root. According to these results, it is concluded that polymers such as polyacrylamide sodium allow the retention of water in the substrate, but do not necessarily release that water for plants, probably because that moisture is kept in the hydrogel and not released to the substrate media or the roots, or if released, in this case, this occurs with an increase in the concentration of sodium available to the plants, which could lead the citrus crop to a worse situation of water and/or osmotic stress.