Date of Award:

5-1959

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Soil Science

Committee Chair(s)

R. L. Smith

Committee

R. L. Smith

Committee

Herman Weibe

Committee

Raymond Miller

Abstract

Line-induced chlorosis is a nutritional disease affecting many fruit trees, berries, ornamental shrubs, and flowers in Utah and the western United States. In fact, this disease is of wide distribution on calcareous soils throughout the world. Lime-induced chlorosis has contributed to untold economic loss and has challenged the technical ingenuity of plant and soil scientists throughout the world. As yet the exact cause of chlorosis has not been determined; consequently, no permanent cures have been found.

The first symptoms of this disease are characterized by an interveinal yellowing of younger leaves, with the veins remaining green. In more severe cases the entire leaf becomes yellow or white and then may burn or die. Mild chlorosis induces marked reductions in crop yields, and severe cases are associated with die-back of terminal growth and ultimate death of the plant. Frequently only a branch of a tree is affected, or perhaps only a few scattered trees in an orchard may be affected. In some areas it is impossible to keep young peach trees alive longer than two years. Some fruit areas have gone completely out of fruit production because of lime-induced chlorosis.

The symptoms of chlorosis are identical to the iron deficiency symptoms of plants grown in nutrient solutions lacking iron. This led to the theory that this disease was caused by a lack of iron. When iron salts were injected into the trunks of trees, normal green color was restored to the leaves for several months. However, this form of iron deficiency is unique in that soil and plant analysis usually reveal ample quantities of iron in the soil and plant. These observations have led to the conclusion that lime-induced chlorosis is caused from some factor in the soil inhibiting the uptake of iron or the inactivation of iron within the plant.

Although no single factor has given an adequate explanation for this physiological disease, experiments have indicated increased chlorosis under conditions of high soil moisture with a subsequent increased carbon dioxide solubility and increased bicarbonate concentration in the soil solution. Increased chlorosis has also been noted under conditions of high phosphorus concentration and conditions of high pH. The pH and phosphorus effects appear to involve reduced iron solubility, while the exact effects of the bicarbonate ion on chlorosis have not yet been established. It is not known whether the bicarbonate ion affects the iron-plant relationship in a direct or indirect manner. A direct influence might be decreased respiration and decreased iron uptake. Indirect influences might be where another ion, such as phosphorus, is made more soluble and then interacts with iron and decreases its solubility or availability for plant use. Since the solubility of ions in solution are affected by the pH, the influence of bicarbonate ion on internal pH may be such that iron is precipitated within the plant, primarily in the translocating system.

The purpose of this research was to investigate these indirect effects of bicarbonate ion on the translocation of iron within the plant. It was also thought important to know whether plants that are known to be susceptible or resistant to chlorosis behave in the same manner to external concentrations of ions and pH. If chlorosis-susceptible and chlorosis-resistant plants react differently with these variables, it might shed some light on where the mechanism lies that makes some plants sensitive to lime-induced chlorosis.

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