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Abstract
Bearing ‘Valencia’ orange trees growing in a commercial orchard adjacent to a known source of fluoride air pollution were sprayed periodically over a 3-year period with Ca(OH)2 and CaCl2 sprays. These materials in spray and dust forms have been used successfully in the Pacific Northwest to protect gladiolus and peaches from the harmful effects of fluoride-containing atmospheres. It has been postulated that calcium reacts with fluoride gases to produce insoluble and therefore nontoxic CaF2.
Results of these studies indicated that under conditions of high fluoride air pollution, application of lime sprays may improve citrus fruit production, but the mechanism of protection or improvement was not as simple as previously postulated. Immediately adjacent to the source where fluoride air pollution was at a maximum, applications of both Ca(OH)2 and CaCl2 were associated with increased internal fluoride accumulation by ‘Valencia’ orange foliage. With increased distance and therefore diminishing air pollution, an apparent reversal in effect was observed with the calcium sprays resulting in reduced internal accumulation of fluoride.
Although the effects of CaCl2 sprays on fluoride accumulation closely paralleled those obtained with Ca(OH)2, fruit production was not improved where CaCl2 sprays were applied, possibly as a result of induced chloride toxicity.
Twelve avocado (Persea americana Mill.) rootstock selections were tip-grafted with a commercial scion, cv. Hass, and evaluated for their field resistance to Phytophthora cinnamomi Rands. Percentage difference in trunk cross-sectional area of the inoculated compared to uninoculated rootstock, the overall growth in trunk cross-sectional area, and visual rating of disease severity of the commercial scion were used to evaluate rootstock over 79 weeks. Avocado trees on the rootstock selections Thomas, Martin Grande (G75Sa, b, and c), Barr Duke, and D9 demonstrated the highest level of resistance to P. cinnamomi, whereas those on Topa Topa, Borchard, and G6 had the lowest levels. Trees on Duke 7, G1033, and Toro Canyon rootstock were intermediate in their levels of resistance. Among uninoculated rootstock, trees on Thomas and G6 exhibited the greatest growth in trunk cross-sectional area. whereas those on D9 showed the least.