CALIFORNIA DEPARTMENT OF FOOD AND AGRICULTURE APPROVES DISTRIBUTION OF TWO Tsn-RNAs FOR GROWTH MODIFICATION AND PERFORMANCE ENHANCEMENT IN CITRUS.

Citrus Clonal Protection Program Bulletin -November 21, 2000

Two Tsn-RNAs (Transmissible small nuclear ribonucleic acids) have been approved by the CDFA for distribution as CCPP plant materials. The Tsn-RNA IIIb has been shown to be effective in the reduction of tree size and increase in fruit size when Poncirus trifoliata, trifoliate orange is used as a rootstock. The other, Tsn-RNA IIa) has been shown to enhance fruit size in studies where trifoliate orange was used as the rootstock.

The Tsn-RNAs will be maintained by the CCPP as California Department of Food and Agriculture (CDFA) registered inoculum source trees in an isolated insect proof screenhouse. CCPP will release small amounts of the inoculum as budsticks to nurseries and growers so they may inoculate a 1-2 year old budded tree on any appropriate rootstock. The scion variety of this budded tree can be any variety that the nursery wishes to serve as a bud source mother tree for future production of Tsn-RNA modified field trees to be budded on trifoliate orange rootstock.

Nurseries receiving the inoculum and producing a mother tree for buds containing the desired Tsn-RNA will not release nor produce any Tsn-RNA modified trees until the inoculated mother tree is tested by CCPP to ensure the presence of the correct Tsn-RNA and the absence of Citrus tristeza virus (CTV). This testing can be done between six months and one year after inoculation of the mother tree. When testing is complete the mother tree will be registered with the CDFA Scion Source Registration Program as a source tree of the variety containing either Tsn-RNA IIIb or Tsn-RNA IIa. The registered tree must be tested each year for CTV and every three years for the appropriate Tsn-RNA.

Once registered, the Tsn-RNA inoculated mother tree may be used as a source of budwood for the direct budding of trifoliate orange rootstocks. Nursery increase of buds from the Tsn-RNA inoculated mother tree is not authorized by the CDFA permits.

Cost of the inoculum source budwood will be $10.00. The cost for the Tsn-RNA and CTV testing prior to registration will be $250.00. The normal Scion Source Registration Testing Program will cover the yearly retesting for CTV. Each retest for the Tsn-RNA will be $250.00. Distribution of the Tsn-RNA will begin with the June 2001 budwood cut.

It bears repetition that the effects on tree size and fruit production have been demonstrated for scions budded to trifoliate orange rootstocks. Experiments are currently in progress to determine if these beneficial effects on citrus performance can also be extended to other rootstock related to trifoliate.

More Information

Production of Tsn-RNA Trees.pdf