We investigated variation in concentration of the secondary metabolite, camptothecin (CPT), in relation to leaf, branch and tree age, season, and leaf drying method in Camptotheca acuminata Decaisne saplings. Younger leaves contained higher CPT concentrations than older leaves. Within a branch, there was a linear decline in CPT concentration from leaves at the apex of the branch down to Leaf 7. Comparing leaves of similar age, those from younger trees had higher CPT concentrations than those from older trees. Over the course of the growing season, there was a steady decline of 11% per month in leaf CPT concentration. Branches showed a similar seasonal decline in CPT concentration to leaves; however, the rate of decline was threefold greater in leaves than in branches. Freeze-dried tissues had a 27% higher CPT concentration than oven- or air-dried tissues, suggesting that oven- and air-drying caused degradation of CPT. The decline in CPT concentration with tissue aging may reflect a genetically determined mechanism whereby, in young trees, chemicals serve as a first line of defense against attacks by herbivores and pathogenic microorganisms until other mechanisms are developed and deployed. We hypothesize that chemical defense mechanisms are programmed for early ontogenic stages, whereas they are induced by biotic and abiotic factors during later ontogenic stages.

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A survey of the nutrient status of the citrus groves of Louisiana was conducted to determine the extent of possible deficient or toxic areas of the region and to help determine the accuracy of critical values developed in the major citrusgrowing regions of the world and their relevance to a region where critical values had not been developed. The nutrient status of 29 orchards of Washington navel orange (Citrus sinensis) and satsuma mandarin (Citrus unshiu) trees on P. trifoliate rootstock representing 90% of the citrus region in Louisiana were determined using critical values from the literature. Twenty percent of survey samples ranked excessively high in chloride indicating possible toxicity from recent salt-water intrusion. Chloride contents were higher in groves closer to the Gulf of Mexico. More than 60% of the leaf 1 Approved for publication by the Director of the Louisiana Agricultural Experiment Station as manuscript no. 95-09-9243. 733 734 BELL, VAUGHN, AND BOURGEOIS samples analyzed were diagnosed as having very low concentrations of zinc (Zn) and manganese (Mn). Soil tests of surface soils to a 15-cm depth did not prove useful in predicting Zn and Mn nutrition of trees, as all soil samples had medium or high levels of DTPA-extractable Zn and Mn. Phosphorus (P) and potassium (K) were low in more than 20% of the leaf samples and high in less than 5% of the samples. Calcium (Ca) in the young leaves was low or very low in 95% of the samples, but no samples from older leaves were low or very low in Ca. These results indicate possible transient effects, errors in the critical values used, or environmental conditions that inhibit Ca uptake.

No abstract

Additional index words. citrus, cultivar development, satsuma mandarin, Citrus unshiu 'LA Early' (Fig. 1), a new early maturing satsuma mandarin cultivar (Citrus unshiu Marcovitch), is a product of the Louisiana State Univ. (LSU) AgCenter citrus research program. The objective of the program is to develop fresh market lines of citrus fruits (navels, satsumas, and other cultivars) with improved quality, fruit characteristics, and production (