Role of VA-mycorrhiza in growth and mineral nutrition of apple (Malus pumila var.domestica) rootstock cuttings |
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Authors: | M A Gnekow H Marschner |
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Institution: | (1) Institute of Plant Nutrition, University Hohenheim, Box 70 05 62, D-7000 Stuttgart 70, FRG |
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Abstract: | One-year-old apple cuttings (Malus pumila var.domestica cv. M26) were grown for 6 months in pot culture with and without inoculum of the VA-mycorrhizal fungus (VAMF)Glomus macrocarpum in soil from a long-term fertilizer field experiment with different P availability (20, 210, and 280 mg CAL-extractable P
kg−1). The indigenous VAMF propagule density was reduced by 0.5 Mrad X-irradiation. At harvest, non-inoculated and inoculated
plants had similar proportions of root length bearing vesicles. Net dry weight of tree cuttings was significantly increased
by inoculation only at 20 mg P kg−1 (+62%). Increasing P availability from 210 to 280 mg P kg−1 led to a 4-week depression of shoot elongation rate only in the inoculated plants. Uptake of P was significantly enhanced
by inoculation at 20 and 210 mg P kg−1 (+64 and +12%, respectively). On average, inoculated plants had significantly higher concentrations of Zn in leaves and in
roots (+16 and +14%, respectively) and of copper in stems and in roots (+13 and +126%, respectively). Proportion of vesicle
bearing root length was significantly correlated with root caloric content. A lipid content of 0.9–4.5% in the root dry matter
was attributed to the presence of vesicles corresponding to 1.6–8.2% of total root caloric content.
As the control plants were also infected, the beneficial effect of VA-mycorrhiza on nutrient uptake and growth of apple cuttings
was underestimated at all P levels. Furthermore, VAM-potential at the lowest P level was not fully exploited as onset of infection
was most certainly delayed because of a decreased photosynthetic rate due to P deficiency. Energy drain by VAMF-infection
was most probably underestimated considerably, due to, among others, loss of infected root cortex during root growth, sampling
and staining.
It is concluded that apple cuttings rely on VA-mycorrhizal P-uptake at least in low P soils. In high P soils, apple cuttings
may profit predominantly from the uptake of Zn and Cu by the fungal symbionts. |
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Keywords: | apple Malus pumila phosphorus nutrition shoot growth rate VA-mycorrhiza zinc and copper uptake |
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