DEVELOPMENT OF PEST, DISEASE RESISTANCE, AND STRESS TOLERANCE IN APPLE ROOTSTOCKS
Location: Plant Genetic Resources
Title: Soil pH, soil type and replant disease affect growth and nutrient absorption in apple rootstocks
Submitted to: New York State Fruit Quarterly
Publication Type: Trade Journal
Publication Acceptance Date: February 15, 2012
Publication Date: March 29, 2012
Citation: Fazio, G., Kviklys, D., Grusak, M.A., Robinson, T. 2012. Soil pH, soil type and replant disease affect growth and nutrient absorption in apple rootstocks. New York State Fruit Quarterly. 20(1):22-28.
Rootstocks are the foundation of a healthy and productive orchard. They are the interface between the scion and the soil, providing anchorage, water, nutrients, and disease protection that ultimately affect the productivity and sustainability of the orchard. Recent advances in the science of genetics/genomics of apple rootstocks show that at the molecular level different rootstocks have the ability to turn on/off or increase/decrease the production of proteins in the scion (trunk, leaves and even fruit). So, for example the tissues of a Gala scion grafted on M.9 will behave differently at the molecular level than the same tissues grafted on B.9. The mechanisms by which apple rootstock accomplish this feat are still not very well understood. We can hypothesize that a combination of signals transmitted by the rootstock machinery is detected and interpreted by the scion machinery to give visible effects on photosynthesis, growth, and productivity. Among these root signals we may find different levels of water, inorganic macro and micro-nutrients, plant hormones, and organic molecules such as sugars and micro-RNAs that may have capacity to improve productivity of apple trees. In order to better understand this relationship we decided to investigate just one possible set of signals that the rootstocks absorb from the soil and transmit to the scion: macro and micro nutrients such as molybdenum (Mo), calcium (Ca) and phosphorous (P), iron (Fe), manganese (Mn), nickel (Ni), potassium (K), copper (Cu), sodium (Na), zinc (Zn), magnesium (Mg) and sulfur (S). We designed two experiments to answer four questions: 1. How well do different rootstocks absorb and transmit macro and micronutrients? 2. Is this capacity influenced by soil type? 3. Is this capacity influenced by replant disease? And 4. Is this capacity influenced by soil pH levels? Our experiments with replant soils indicated that both the clay soil and the sandy soil showed differences in the final growth of the trees between pasteurized and unpasteurized treatments, indicating that there was a biological effect stunting tree growth. Leaf iron and molybdenum concentrations also showed a significant effect that patterned the tree growth, indicating that they were correlated to replant disease in some manner. Our experiments with different pH soils indicated that as a general trend, absorption of molybdenum (Mo), calcium (Ca) and phosphorous (P) increased with higher pH levels while absorption of iron (Fe), manganese (Mn) and nickel (Ni) decreased with increasing pH. Absorption of potassium (K), copper (Cu), sodium (Na), zinc (Zn), magnesium (Mg) and sulfur (S) did not seem to be greatly affected by soil pH. Over all the rootstocks, plant growth was affected adversely by low or high pH treatments and displayed optimum growth around pH 7.5. However when plant growth was examined in different rootstocks, each rootstock exhibited a different pattern of growth as influenced by soil pH. CG.3007, CG.5257 did not seem greatly affected by soil pH (almost flat curve), while rootstock CG.6589 had optimum growth at pH 5.5 and rootstocks G.41 and MM.111 had optimum growth at pH 7.5. In our experiments we learned that the absorption of soil nutrients once thought to follow similar trends in all apple rootstocks does not behave the same way in newer rootstocks. There is abundant genetic variation to be explored for breeding purposes. While this set of experiments has proven very useful to understand some of the dynamics of apple tree nutrition, it represents an exploration that needs to be greatly expanded to permit a better understanding of rootstock specific interactions with the parameters tested and permit a knowledge based recommendation of apple rootstocks tailored to specific growing sites.