Evaluation of Calcium Bicarbonate Effects on Physiological Reaction and Growth Indices of Almond Cultivars Grafted on GN15 Rootstock

Iron chlorosilicon caused by calcium carbonate can be controlled widely with iron chelate in nutrition management of gardens, but it has high costs and potential environmental hazards. Such constraints have led to alternative strategies for managing iron nutrition in relation to soil and plant parameters. Almond rootstocks and almond x peach hybrids (GF 677) are widely used as the rootstock for almonds, peaches and nectarines in the Mediterranean basin, moreover, in addition to its drought resistance, has a high tolerance to iron chlorosis. Different references of almond tree have introduced this fruit tree as a chlorosis resistant, but it shows different ranges of chlorosis when grafted on almond x peach hybrids such as GF677 and GN15. Therefore, this study carried out to evaluate the effect of calcium bicarbonate on some physiological characteristics of selected almond cultivars on the GN15 rootstock.

This research was conducted during 2015 and 2016 to evaluate the resistance to bicarbonate and the amount of chlorosis produced in selected almond cultivars on the hybrid rootstock (peach and almond) as a factorial experiment with completely randomized design with three replications in greenhouse conditions. The first factor consisted of different concentrations of calcium bicarbonate (0, 20, 10, 30 and 40 mmol L-1) and the second factor included nine selected almond cultivars grafted to the GN15 rootstock and a GN15 (non-grafted) rootstock. Almond cultivars included 9 cultivars including Supernova, 25-1, 40-13, Mamaei, 16-1, Kaghazi, Sahand, 200A, 7-9, and GN15 rootstock. Each plot included a pot, where the rootstock planted. In the spring, the cultivars and GN15 rootstock planted in plastic pots with soil compositions including perlite (50%) and cocopeat (50%). After sufficient growth of these rootstocks in the pots, almond cultivars were grafted onto them and immediately after the transplantation, the calcium bicarbonate treatments began after proper growth of the scions. In order to apply bicarbonate treatment, 1.62, 3.23, 4.86 and 6.48 g L-1 calcium bicarbonate (Ca (HCo3) 2) were added to the pots. In addition, 10% of calcium bicarbonate added also to the pots because of the deficiency of 10% chemical purity. After applying the treatments, chlorophyll, chlorophyll a and b, carotenoids, chlorophyll fluorescence were measured in two stages at intervals of 30 and 90 days. After the end of the growth period, the length and diameter of the current season branches and the leaf length and width of each almond cultivar were measured and recorded in different treatments. Two-way ANOVA of the data was carried out using SAS software (v. 8.02, SAS Institute, Cary, NC) and the means were compared based on Duncan’s multiple range test.

Based on the ANOVA results, it was determined that the effects of calcium bicarbonate, cultivar and their interactions on the content of chlorophyll a and b were statistically significant (p≤0.01). The lowest decrease levels of chlorophyll a and b were found in the leaflets of Kaghazi, Mamaei, saplings, 25-1, and 40-13 cultivars, but the highest decrease was observed in Supernova cultivar, 7-9, and GN15. The reasons for decreasing the chlorophyll content of the leaf with the increase of bicarbonate levels can be related to iron deficiency and its deactivation and the role of iron in the synthesis of chlorophyll. Nevertheless, the difference for chlorophyll depletion at different levels of bicarbonate in different cultivars can be due to the capacity of these cultivars to tolerate higher levels of bicarbonate and the possibility of the synthesis of chloroplastic proteins in leaf cells even with a relative lack of iron. In all cultivars, as well as the GN15 rootstock, the level of carotenoids decreased with increasing concentrations of calcium bicarbonate. However, the response of the cultivars was different. Under bicarbonate conditions, reducing leaf iron concentration reduces chlorophyll and carotenoids. The results of the mean comparison showed that bicarbonate induced height growth reduction and branch diameter in the current season, while the reaction of the studied rootstocks were also different. So that the highest decrease in growth rate was observed in Supernova, 7-9 cultivars and GN15 rootstock and the lowest decrease of growth rate were found in the cultivars of Kaghazi, 1.25-1 and -40-13. High concentrations of bicarbonate, by disabling and decreasing iron absorption, indirectly reduces DNA synthesis, cell division, and thus decreases cell growth and plant biomass. The results of this study are in agreement with Ghasemi et al. (2010) in different responses of the rootstock to bicarbonate concentration on the height and diameter decreasing of current season branch. Mean comparison of data showed that the length and width of leaf area in all studied cultivars decreased with increasing concentration of calcium bicarbonate in irrigation water. Also, leaf length and width decrease in rootstock grafted cultivars had a significant difference, so that the lowest reduction in leaf length and width was in pepper, midwifery and 25-1, and the highest leaf area decrease in Supernova cultivars, 7-9 and GN15 base was observed. Leaf growth decreases in calcareous soils due to a decrease for iron in the symplast. The specific effects of high bicarbonate on leaf growth in almond cultivars and the different reaction of almond rootstocks in this study are in agreement with Tedaion et al. (2004) results in orange, as well as Wahom et al. (2001) in olive and peach.

Totally, the results of this study indicate that cultivar and rootstock cause the amount of chlorosis tolerance induced by calcium bicarbonate. In general, in terms of morphological and physiological traits studied in this research, Kaghazi and 25-1 cultivars are the most tolerant, while 7-9 and supernova are the most sensitive cultivars to bicarbonate.