ISHS Acta Horticulturae 732: VIII International Symposium on Canopy, Rootstocks and Environmental Physiology in Orchard Systems
THE METHOD OF STUDYING THE EFFICIENCY OF APPLE ROOTSTOCKS TO ABSORB ZINC |
| Authors: | D. Swietlik, M. Wisniewski |
| Keywords: | chelate, chelator-buffered nutrient solution, DTPA, GEOCHEM-PC, hydroponics, Malus domestica, Zn deficiency |
| Abstract:
Zinc deficiencies have been associated with poor apple tree performance in many areas of the world. Although corrective treatments such as foliar or dormant sprays with Zn are available, they have serious limitations, and when repeated over many years may potentially lead to environmental contamination. Using genetic means to increase apple rootstocks’ efficiency to acquire Zn from the root environment creates the possibility to eliminate the need for applying Zn fertilizers. Such an approach, however, necessitates the development of an effective and precise method of assessing the efficiency of apple germplasm to acquire Zn from the rhizosphere. The method presented herein relies on the use of chelator-buffered nutrient solutions in which the level of Zn activity is precisely controlled and buffered with a strong chelator such as diethylenetriamnine pentaacetate (DTPA). This system proved quite effective in inducing varying degrees of Zn deficiency in ‘Red Delicious’ apple seedlings in both stationary and re-circulating nutrient solution systems. The deficiency was confirmed by tissue chemical analyses. In the re-circulating system, however, microbial build-up and apparent adsorption of chemicals were observed on tubing walls through which the nutrient solution was circulated. The data suggest that these two factors may lead to the removal of DTPA from the nutrient solution. Therefore, effective methods of preventing these phenomena must first be devised before the re-circulating system can be recommended for screening plant germplasm. These difficulties, however, posed no problem in the stationary system. Using a computerized chemical equilibrium model (GEOCHEM-PC) and the data obtained from the stationary nutrient solution system, we calculated that 10-9.95 М is the critical Zn+2 activity level needed to produce normally growing apple plants containing optimal levels of Zn in their tissues. It is therefore concluded that all future assays for Zn acquisition by apple plants should employ Zn activities in the rhizosphere that are lower than this critical level to identify germplasm of varying degree of resistance to Zn stress. | |
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