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Abstract
The present investigation was carried out during the two successive seasons of 2014 and 2015 in order to study the influence of three citrus rootstocks seedlings and four different
growth regulator amendments to alleviate salinity problem on the growth, mineral and chemical composition of citrus plants grown under salinity conditions. One-year-old Macrophylla lemon (Citrus macrophylla Wester), Volkamer lemon (Citrus volkameriana Tan. and Pasq.) and sour orange (Citrus aurantium, L.) seedlings were used in this study.
Seedlings were singly planted in black polyethylene bags filled with about two kilograms of mixed sandy and clay loam soil (1:1). On the 1st of April 2014. the plants of each rootstock
were divided equally into three groups; each of 25 plants were received one of either salinity treatments: 0 (Tap water; control), 2500 and 4000 ppm NaCl. The seedlings of each group (25
plants) were again subdivided to 5 sub-groups, each consisted of 5 plants and received one of the following plant growth regulators: Tap water (W); control, 10 μM abscisic acid, 1000 ppm
salicylic acid, 100 ppm gibberellic acid and of 250 ppm Paclobutrazol. All of them were applied as foliar spray treatments. from April till the end of September in 2014 and 2015 The experimental plants were arranged in a Randomized Complete Block Design
(RCBD), with split spilt plot arrangement, with five replicates in each treatment. Thus, 75 plants from each rootstock were used in either year of study (3 salinity levels x 5 plant growth regulators treatments x 5 replicates = 75 plants for each rootstock in each experimental
season).
The effect of rootstocks and different plant growth regulator treatments as well as that of the NaCl salinity levels on the growth rate, leaf area, stem cross-sectional area, total dry
weight, top dry weight, leaf dry weight and root dry weight as well as top to root dry weight ratio were measured. In addition, the effect of the different treatments on leaf and root mineral
composition (N, P, K, Ca, Mg, Na and Cl) and total leaf chlorophyll were also determined.
Besides, the reducing, non-reducing sugars and total soluble sugars, starch and total carbohydrate were calculated. Over and above, leaf and root proline content and leaf catalase and peroxidase activity were determined.
The results of the present study, as an average of both experimental seasons, could be summarized as follows:
I. Growth Indices:
1. The results for the rootstocks effect of both growing seasons generally indicated that the sour orange rootstock had higher growth rate, stem cross-sectional area, leaf dry weight,
top to root dry weight than other rootstocks, whereas Macrophylla rootstock showed significantly higher values of leaf area, total, root and top dry weights.
2. Regarding the interaction effect between salinity levels in growth and
rootstocks, the results of both growing seasons, in general indicated that irrigating plants with saline water caused significant reduction in the growth rate, leaf area, trunk cross-sectional area, total, top and leaf dry weights, top to root dry weight and
root dry weight in comparison with tap water.