Citrus Seedling Growth and Susceptibility to Root Rot as Affected by Phosphite and Phosphate

ABSTRACT

The growth of ‘Ridge Pineapple’ sweet orange [Citrus sinensis (L.) Osbeck] seedlings and their susceptibility to Phytophthora root rot were studied under contrasting supplies of phosphate (Pi) or Phosphite (Phi). After 10 weeks of repeated applications of nutrient solutions, Phi concentrations were barely detectable in soil. Soil Pi was higher in Phi treatments than in pots that received Pi alone. Seedling growth was greatest when supplied with Pi or Phi separately, but when Pi and Phi were combined, growth was reduced to levels comparable to plants that received no P. Phi was found in both stems and leaves after it was applied to soil supporting the mobility of Phi within the plant. In addition, a small amount of Phi was found in roots after applications of Phi in foliar sprays. Different sources of soil-applied P did not affect the amount of Pi in roots, while the amounts of Pi in leaves were higher in plants that received Phi and Pi combined. Root resistance to Phytophthora root rot of citrus seedlings treated with Phi alone or in combination with Pi was greater than in plants treated with Pi alone, confirming the antifungal effect of Phi.

Keywords:

• Nutriphite®
• P nutrition
• phosphorous acid
• sweet orange

ACKNOWLEDGMENTS

This work was supported by the University of Florida, Institute of Food and Agricultural Sciences, Citrus Research and Education Center (UF/IFAS/ CREC), and funded in part by the Florida Citrus Production Research Advisory Committee (FCPRAC). Authors would like to acknowledge the technical assistance of Shannon Sloan and Jill Dunlop.

Notes

^z Means within a column followed by different letters differ significantly as tested with Duncan's multiple range test at P < 0.05.

^z Means within a column followed by different letters differ significantly as tested with Duncan's multiple range test at P < 0.05.

^z Means within a column followed by different letters differ significantly as tested with Duncan's multiple range test at P < 0.05.

^z ns = not significantly different.

^z Category 1 = no visible rot; category 2 = mostly healthy roots; category 3 = some healthy roots; category 4 = few healthy roots; and category 5 = very few or no healthy roots.

^y Means within a column followed by different letters differ significantly as tested with Duncan's multiple range test at P < 0.05.