Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 23, 1995
Publication Date: N/A
Interpretive Summary: Chlorosis is a major disease problem in citrus. Mineral deficiency or herbicidal sprays may cause it. We found that chlorosis is associated with changes in compounds stored in oil glands. Oil glands are numerous in citrus and are involved in disease resistance. We found a close correlation between chemical composition and oil gland number. The disease/oil gland relationship until now has been overlooked as a factor in understanding how chlorosis diseases effect tree health and ultimately fruit quality.
Technical Abstract: Oil gland densities in healthy and zinc deficient leaves of Citrus sinensis L. cv. Washington' (navel orange), and in healthy, iron deficient, and glyphosate damaged leaves of Citrus paradisi Macf. cv. Rio Red' (grapefruit) were distinctly different. Flavonoid levels were related to the leaf oil gland densities. Zinc chlorotic navel orange leaves had more oil glands than healthy leaves. The adaxial/abaxial sides of zinc chlorotic and healthy navel orange leaves of approximately 1100 mm**2 blade area had 276 +/- 28/198 +/- 14 and 176 +/- 17/29 +/- 5 oil glands/cm**2, respectively. An increase in flavonoid levels occurred in zinc deficient leaves compared to that in healthy leaves. Iron deficient grapefruit leaves had fewer oil glands compared to healthy leaves. The adaxial/abaxial sides of iron chlorotic and healthy grapefruit leaves of 5500 mm**2 blade area had 65 +/- 7/24 +/- 4 and 72 +/- 9/43 +/- 16 oil glands/cm**2, respectively. Flavonoid levels were less in iron deficient leaves compared to healthy leaves. Grapefruit glyphosate damaged leaves oil glands were concentrated at the midrib vein region instead of uniformly distributed over the blade as in healthy and chlorotic leaves. Adaxial/abaxial sides of glyphosate damaged leaves with an approximate 800 mm**2 blade area had 15 +/- 5/19 +/- 4 oil glands/cm**2. Correspondingly, glyphosate leaves produced the lowest flavonoid levels of all grapefruit treatments examined.