Yu Hao
1984, 5(1): 93-104.
The nutrient diagnoses carried out on coffee trees affected by die-back in varying degrees indicated that potassium and carbohydrate in the bearing shoots reduced with the severity of the disease, and that, with bearing shoots as the biggest nutrient consumers, the nearer the adjacent branches stood to the bearing shoots, the more drastically would the amount of the above nutrients in the adjacent branches reduce, and the severer the disease would become. So it may be preliminarily concluded that the main cause of die-back lies in the tree's hunger for carbohydrate arising from the depletion of this nutrient due to over-bearing.
The root systems of the seriously affected plants also displayed acute nutrient deficiency. Lower total nitrogen (1%) and total carbohydrate(5%) in the root system would retard bud shooting in the coming year, thus to cause death of the tree. The cause of die-back also lies in the coffee tree's biological features:
1. Coffee relies on self-pollination with a high fruiting rate which leads to overbearing.2. Its reproductive growth preceding its vegetative growth in early spring, the bearing branches take a step earlier in getting nutrients, thus curbing the outgrowth of new shoots and foliage and favouring the occurrence of die-back.3. Its low capacity of photosynthesis and high sensitivity to variation in nutrient supplies weaken the physiological activity in the leaves or even give rise to defoliation.
4. Coffee root system often fails to supply enough water, nutrients and hormones to the above-ground parts due to weak absorbing ability and sensitivity to changes in soil conditions as well as high nutrient consumption by sumptuous fruit-setting, with the result that the biological activity of the root system is inevitably diminished, thereby causing the disease.
