|Owens, R. A. - USDA/ARS, BELTSVILLE|
|Thompson, S. M. - USDA/ARS, BELTSVILLE|
|Sieburth, P. J. - BUR. OF CITRUS BUDWOOD|
Submitted to: International Organization of Citrus Virologists Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: November 3, 2005
Publication Date: November 3, 2005
Citation: Owens, R., Thompson, S., Sieburth, P., Hilf, M.E. 2005. Viroid infection leads to reduced root growth in greenhouse-grown citrus. International Organization of Citrus Virologists Proceedings. Technical Abstract: Close planting of viroid-infected citrus growing on trifoliate orange or trifoliate hybrid rootstocks has been shown to increase fruit yield and lower production costs. We would like to adapt Citrus viroid III (CVd-III) for use with other rootstocks and, toward that end, have examined the ability of this viroid to dwarf citrus growing under greenhouse conditions. Groups of 3-7 young Carrizo or Rangpur lime seedlings were graft inoculated with either CVd-IIIa, CVd-IIIb, or blind buds from uninfected Etrog plants and maintained as single leader trees in the greenhouse in a mixture of Metro-Mix 510 and perlite (50:50, v/v) with fertigation as required. Although no obvious symptoms of viroid infection were visible in the foliage 21 months post inoculation, root systems of viroid-infected plants were significantly smaller than those of the uninfected controls. Average root volume (as measured by liquid displacement) and root dry weight were reduced by 9-32%, but analysis of variance among groups (ANOVA) did not support any interaction between viroid (CVd-IIIa or CVd-IIIb) and host (Carrizo or Rangpur lime) genotypes. Experiments are underway to i) determine the minimal incubation period necessary to observe these effects on root system development and ii) assess the effect of mutations within a putative 'loop E'' motif on CVd-III symptom expression. Sequence changes in the corresponding portion of Potato spindle tuber viroid result in a striking 'flat top' phenotype in which cell growth and shoot development in Rutgers tomato are markedly inhibited [Qi and Ding. 2003. Plant Cell 15, 1360-13274].