Document Type : Research Paper - Biotic and Abiotic Stress
Authors
1 Associate prof., Member of scientific board , Horticultural Science Research Institute (HSRI), Kara j
2 Temperate Fruits Research Center Center, Horticultural Science Research Institute, Ag. Research Education Extension Org. Karaj, Iran.
3 Temperate Fruits Research CenterHorticultural Science Research Institute, Ag. Research Education Extension Org. Karaj, Iran.
4 Tarbiat Modars University, PhD student
Abstract
The calcareous nature of soils is considered one of the fundamental and limiting challenges in pear production. Overcoming these challenges requires the use of rootstocks that are more tolerant. The P.betulifolia pear rootstock shows relatively high tolerance to abiotic stresses such as drought and salinity. However, detailed and documented information on its tolerance to calcareous soils is lacking. In this study, the effects of soil substrates with lime content in the range of 15% (clay-loam texture), 20% (clay texture), 25% (loam texture), and 45% (sandy loam texture) on growth characteristics (length and width of leaves, diameter, height, and internode length) and leaf nutrient uptake (nitrogen, potassium, calcium, magnesium, boron, zinc, active iron, and total iron) were investigated. Additionally, the tolerance to iron chlorosis due to soil calcareousness was measured using the “Chlorosis Power Index” or CPI for both rootstocks. The experiment was conducted in a completely randomized design. Results indicated a significant positive correlation between the “Chlorosis Power Index” and the amount of soil calcium carbonate in a regression, while a negative and significant correlation was observed with soil iron content. P.betulifolia exhibited lower sensitivity to the “Chlorosis Power Index” compared to the Pyrodwarf rootstock (control). Negative and significant regression relationships between increasing “Chlorosis Power Index” and the studied traits were not observed in the P.betulifolia rootstock. Differences in phenological and leaf greenness traits during spring observations were significant between rootstocks, specifically in the parameter of minimum and maximum chlorophyll fluorescence. Soil lime factor alone resulted in significant differences in trunk diameter. In fall observations, differences in growth traits were statistically significant between rootstocks, soil treatments, and their interaction for internode length. Leaf width and trunk height were significant in the rootstock factor. Nutrient uptake results showed the lowest leaf uptake of total iron and active iron in both rootstocks fewer than 45% lime soil (sandy loam texture). However, in 45% lime soil and the P.betulifolia rootstock, leaf uptake of total iron and active iron was approximately 7% higher than the Pyrodwarf rootstock. Differences in leaf uptake of calcium and nitrogen did not show significance due to increased calcium carbonate in the soil for both rootstocks. In the P.betulifolia rootstock, leaf uptake of calcium, potassium, and zinc was approximately 12% more, and magnesium was nearly 40% more compared to the Pyrodwarf rootstock. However, leaf uptake of nitrogen and boron was 78% and 56% higher, respectively, in the Pyrodwarf rootstock. Regarding nutrient leaf uptake and their regression relationships with the soil CPI index in P.betulifolia and Pyrodwarf rootstocks, the results showed that the Pyrodwarf rootstock had a significant decrease in leaf uptake of total iron and active iron with an increase in the CPI index, while this decrease was not significant in the P.betulifolia rootstock. The regression slopes and intercepts for growth traits between the regression curves of P.betulifolia and Pyrodwarf were homogeneous. The regression slopes for the mentioned traits in both Pyrodwarf and P.betulifolia rootstocks were below zero, indicating that the “Chlorosis Power Index” was a suitable calibration for estimating the correlation level. The superior characteristics of the P.betulifolia rootstock, compared to the Pyrodwarf rootstock, in terms of tolerance to active soil lime up to 45%, including leaf nutrient uptake such as potassium, boron, total iron, and active iron, chlorophyll content, and growth traits such as length and width of leaves, height, and trunk diameter, favored this rootstock over the Pyrodwarf rootstock.
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