Causes of leaf-tip scorch in the cultivated Protea hybrid 'Sylvia'
Soil and leaf samples were analysed in an attempt to identify the causes of leaf-tip scorch commonly observed in cultivated Protea sussannae and Protea eximia hybrid 'Sylvia'. Leaf-tip scorch was hypothesised to be caused by nutritional problems. Soil and leaf mineral contents were measured and compared between healthy plants and those suffering from leaf-tip scorch. Leaf-tip scorch was found to be associated with increase electrical conductivity, total cation concentration and the concentrations of Na, K, Ca, Mg, Mn and B in the soil. It was concluded that failed attempts of growers to remedy the problem by foliar spraying of micronutrients might have artificially increased the levels of Mn and B. Leaf-tip scorch was associated with decreased foliar concentrations of Fe and increased concentrations of Na and Mn. No association between leaf-tip scorch and either ∂13C or ∂15N was found. It was concluded that changes in water relations and N acquisition were not associated with the symptoms. The significant decrease in the Ca concentration in the tips of leaves showing advanced leaf-tip necrosis indicated that a deficiency of Ca in the leaf tips may have been the proximal cause of the pathology. Ca deficiency in the leaf tips may in turn be caused by high soil EC. © 2004 Elsevier B.V. All rights reserved.