Effects of Pecan Bacterial Leaf Scorch on Growth and Yield Components of Cultivar Cape Fear.

Pecan bacterial leaf scorch (PBLS) recently was recognized to be caused by the bacterium Xylella fastidiosa. The objective of this work was to compare certain tree growth and yield components of trees with and without PBLS. The evaluations were made for 3 years (1999 to 2001) on the disease-sensitive cv. Cape Fear. At nut maturity (October) each year, the number of leaves and leaflets and the leaflet weight were significantly smaller on terminals from trees with leaf scorch than on terminals from trees not infected with X. fastidiosa. Similar amounts of defoliation occurred on bearing and nonbearing terminals. The symptomatic terminals averaged 58% fewer leaflets at the end of the growing season. The weight of terminals from diseased trees was significantly lower in 2 of the 3 years for nonbearing terminals compared with similar terminals from uninfected trees. Terminals of infected trees generally were not significantly shorter than terminals of uninfected trees. The weight of the nuts from terminals with leaf scorch was lower than the weight from uninfected trees each year. The primary effect was on kernel development, which averaged 16% lower weight. Phosphorus concentration was slightly but significantly lower in infected leaflets during October in three of six comparisons. There were no other consistent differences in the concentration of nine other elements in leaflets between diseased and uninfected terminals. PBLS is capable of causing economically significant yield reductions. Because the disease is chronic, the potential yield reduction over the life of a tree is large on disease-sensitive trees.