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Specific Chloride Injury in Persea americana¹

ABSTRACT

The mode of chloride injury in avocado plants (Persea americana) was studied at variable Cl levels. The experiment revealed that when leaf burn occurred, it was associated with abnormally high content in total and leachable salt in the leaves. The substantial leachable fraction presumably represents high concentrations of extracellular salt, which accumulates in tips and margins of the leaves after termination of a vigorous growth. In avocado trees, the salt that builds up at the higher substrate Cl levels is associated with what appears to be a mass flow salt movement into conductive tissues causing, possibly, greater salt transport to the leaves than can ultimately be absorbed by leaf cells. The extracellular salt concentrations break down the gradients of osmotic pressure that are necessary to maintain turgor pressure, leading to characteristic tip and marginal necrosis associated with excessive accumulations of Cl. Growth reduction is probably due to energy spent in excessive salt accumulation and loss of photosynthetic area.

¹ Contribution of the Dept. of Soils and Plant Nutrition, Univ. of California, Riverside, Calif. Part of a dissertation presented by the senior author in partial fulfillment of the requirements for the Ph.D. degree. Presented before Div. S-4, Soil Sci. Soc. Amer., Nov. 10–15, 1968, at New Orleans, La.

² Former Graduate Student and Professors of Soil Science, respectively. Present address of senior author: Assistant Professor of Soils, Texas A&M University, McGregor Research Center, McGregor, Texas, 76657.

Received for publication December 29, 1969. Accepted for publication April 21, 1970.