Microscopic observations of leaf midrib cross-sections: The damage to the phloem observed in cross sections of midrib tissue show the phloem cell wall thickening, collapsed cambium, and phloem cell plugging in Las infected leaves with normal and high B fertilization rates. Only a single leaf sample from the boron deficient plants was both infected with Las and not suspected to have a recent change in fertilization. There is little of note of the Las infected boron deficient leaves. However, noninfected boron deficient leaves showed similar microscopic symptoms to HLB infection. Boron deficiency also results in phloem cell wall thickening, cambium collapse, and starch accumulation. Although less frequent, some phloem plugging can also be observed. Unlike the leaf midribs with HLB damage under normal fertilization in this experiment, there has been substantial phloem multiplication leading to a thickened phloem layer in the B deficient noninfected leaves. However, phloem multiplication is a common symptom of HLB in leaf midribs. In most cases the B deficiency symptoms resemble the damage observed in the early stages of HLB symptom development (personal observations). However, this damage would be uniform throughout the tree in B deficiency compared to the noncontinuous symptoms observed in HLB affected trees. It has previously been subjected that Las in damaged phloem tissue is mostly dead (Folimonova et al., 2010). This damage caused by B deficiency is most likely responsible for the loss of detection of Las in B deficient trees. The poor rate of infection could also be due to phloem damage limiting the spread of Las from the infected budwood. This would fit with the hypothesis that the active Las population exists in presymptomatic leaves. After symptoms develop and phloem damage occurs the bacteria appear to become trapped and die. At present there is little evidence of a significant effect of B fertilization on HLB with a lack of effect on leaf chlorophyll content, trunk caliper, or leaf nutrient status. However, Las population data suggest that phloem degeneration could be reduced at high B fertilization rates although this is not readily observed in leaf midrib cross sections. The most conclusive results will come from analysis of a B fertilization and HLB interaction of biomass measures taken at the end of the experiment. However, microscopy analysis does show similarities in phloem damage occurring from HLB and B deficiency. Although increased B fertilization does not appear to alleviate phloem damage, this does suggest that the damage is caused by similar mechanisms. B deficiency is known to inhibit proper cell wall formation resulting in physiological responses due to plant cell sensing of weakened cell wall structure. It is possible that as Las inhabits and grows in phloem tissue it causes damage to cell wall integrity, through an unknown mechanism and triggers a similar physiological response to that of B deficiency. Please refer to the final comprehensive report for final biomass analyses, with no page limitations and including figures and tables which better illustrate the microscopy results.