The effects of external potassium and magnesium concentrations on the magnesium and potassium inflow rates and growth of micropropagated cherry rootstocks, “F.12/1” (Prunus avium L.) and “Colt” (Prunus avium L.) × Prunus pseudocerasus L.)

The effects (and interaction) of two solution concentrations of Mg (50, 500, μM) and two of K (250, 4250 μM) on the growth of micropropagated plants of “F. 12/1” and “Colt” were investigated using a flowing solution culture system. Magnesium inflow and growth of “Colt” and “F. 12/1” were inhibited to a similar extent by an increased concentration of K in the nutrient solution. However, the consequences of this inhibition were different. Reduced inflow of Mg in “F. 12/1” caused Mg deficiency symptoms at high and low concentrations of K, whereas this only occurred with a combination of high K concentration and low Mg concentration in “Colt”. The distribution of dry matter within the plant was significant in determining susceptibility to Mg deficiency. Since “F. 12/1” has a smaller root:shoot ratio than Colt it is unable to sustain the same concentration of Mg in leaves as “Colt” irrespective of external K concentration. The molar ratio of K:Mg in soil solutions should remain <8.5:1 in order to ensure maximum growth of “F. 12/1” and “Colt”. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effects of external magnesium concentration on the growth and magnesium inflow rates of micropropagated cherry rootstocks 'F.12/1' (Prunus avium L.) and 'Colt' (Prunus avium L. × Prunus pseudocerasus L.)

The cherry rootstock 'F.12/1' is more susceptible to Mg deficiency than the cherry rootstock 'Colt'. The effects of different external concentrations (3000, 500, 50 and 10 µM) of Mg on the growth of micropropagated plants of 'F.12/1' and 'Colt' were investigated in a flowing solution culture system. The relative growth rates (RGR) and total dry weight of both cultivars decreased similarly with the reduction in the external concentrations of Mg. The decreases were caused by a lower net assimilation rate (unit leaf rate). 'F.12/1' had a greater RGR than 'Colt' at all external concentrations of Mg and this is ascribed to its greater leaf weight ratio (leafiness). 'Colt' partitions more dry matter to roots than 'F.12/1', resulting in a smaller shoot: root dry weight ratio. 'F.12/1' required a greater inflow rate of Mg than 'Colt' to maintain its maximum growth rate. When the external concentration of Mg fell below 500 µM the concentration of Mg in the leaves of 'F.12/1' fell well below the critical concentration whereas for 'Colt' this did not occur until the concentration fell below 50 µM.