Evaluation of pear seedlings P.betulifolia for tolerance to lime-induced chlorosis

The aim of this research is to introduce the superior characteristics of P.betulifolia pear rootstock in comparison to the commercial Pyrodwarf (control) in terms of leaf parameters {leaf-N, -K, -Mg, Ca, -Fe, -Zn and leaf-B content; leaf area; chlorophyll (SPAD-Value); Chlorophyll fluorescence parameters (F0:minimum fluorescence; FM: maximum; fluorescence and value of photochemical capacity of photosystem 2 (FV/FM)}, growth traits (shoot length, diameter of shoot) under active lime tolerance in heavy-textured to clayey soils.

 The experiment was conducted in a factorial design within the construction of a completely randomized blocks design, using pots. The factors included: 1- Soils with lime in the range of 15% (texture: clay-loam), 20% (texture: clay), 25% (texture: loam), and 45% (texture: sandy loam). 2- Rootstocks P.betulifolia, Pirrodwarf (as a control). In total, the experiment was carried out on 120 units (5 different levels of soil lime * 2 non-grafted rootstocks * 3 replications * 4 trunk of each studied rootstock/). Data analysis was performed using SPSS and SAS software, involving mean comparisons using Duncan’s method and determining regression relationships.The preparation of pots was carried out as follows: initially, drainage holes were created at the bottom of plastic pots and covered with gravel. Then, a layer of sand and gravel was added to the depth of the pots, followed by the application of animal manure. At this stage, the soils under study, representing different combinations of texture and lime treatments, were added to the 3-kilogram pots. Each pot’s soil composition consisted of 1/3 sand and gravel, 1/3 animal manure, and the remaining being the specified soil samples. Prior to commencing the experiment, the soil samples underwent chemical analysis to determine their general characteristics, including total neutralizing value (TNV), saturation pH, electrical conductivity, soil texture, and organic matter content. In this research, the “Chlorosis Power Index” (CPI) was employed using the formula: CPI = 10000 * (active lime) / (Fe, ppm) ² to estimate the intensity of chlorosis resulting from soil liming for the studied rootstocks. The iron content, extracted as active iron (Fe, ppm) ² using ammonium oxalate, was reported in milligrams per liter, while CPI was reported in milligrams per kilogram.

P.betulifolia rootstock, compared to the control rootstock Pyrodwarf, showed lower sensitivity to the soil’s “Chlorosis Power Index.” Negative and significant regression relationships between the increase in the soil’s “Chlorosis Power Index” and the investigated traits were not observed in the P.betulifolia rootstock.

Notably, P.betulifolia demonstrated superior features, including active lime soil tolerance up to 45% lime (sandy loam texture and alkaline pH), in terms of leaf uptake of nutrients such as potassium, boron, total iron, and active iron, chlorophyll content, and growth traits like leaf length, leaf width, height, and trunk diameter.