The GARDENA gardening expert
Dear Mr. K., when intact fruits burst open, this is generally a consequence of sudden, excessive water intake trying to enter tissue which has been kept very dry. You can frequently see the same effect on tomatoes, radishes, horse radish and kohlrabi. For this reason, I assume that your trees are subjected to dryness (whether from the soil or weather conditions). In the coming season, try to keep the plants evenly watered through irrigation as necessary. A sufficient supply of potash is also expedient for improving the cell strength and the water management. Try feeding both trees with a potash fertiliser or compound fertiliser.