UC RiversideInternational Organization of Citrus Virologists Conference Proceedings (1957-2010)

TitleA Microbudding Technique for Biological Indexing and Ultra-High Density Planting of Citrus

Permalinkhttps://escholarship.org/uc/item/7b02p1rm

JournalInternational Organization of Citrus Virologists Conference Proceedings (1957-2010), 14(14)

ISSN2313-5123

AuthorSkaria, M.

Publication Date2000

DOI10.5070/C57b02p1rm Peer reviewed

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Fourteenth IOCV Conference, 2000—Short Communications

A Microbudding Technique for Biological Indexing and Ultra-High Density

Planting of Citrus

M. Skaria

ABSTRACT. A microbudding technique was developed to produce budded citrus trees fasterand cheaper. More than 900 trees were planted in the field, between June and December 1997.The trees grew well in field conditions. Results show that the microbudding technique is useful forcommercial production. In addition, preliminary results from virus indexing studies show thatmicrobudding may be useful in biological indexing for citrus tatter leaf virus.

Biological indexing is still thepreferred technique used to confirmthe presence of most graft-transmis-sible pathogens in fruit trees includ-ing citrus. This indexing processinvolves budding or grafting a fastgrowing rootstock or an indicatorseedling with the tissue from thetest plant (2). If a rootstock is usedinstead of an indicator plant, a budfrom a pathogen-free indicator plantis placed above the tissue from thetest plant. Normally, it takesapproximately 6 to 9 mo to grow therootstocks or indicator plants forbiological indexing. The foliar symp-toms are expressed from wk to a fewmo after budding, depending on thepathogen, the indicator plant, andthe growing temperature. Biologicalindexing requires advanced plan-ning to prepare the plants, as wellas considerable greenhouse orgrowth chamber space. A reliabletechnique that allows the buddingprocess and symptom expressionquicker with a lower space require-ment would be highly desirable.

Preliminary studies done in mylaboratory have shown that amicrobudding procedure was usefulin developing small budded treesefficiently (3). This procedure wasbased on budding rootstocks thatwere approximately 4-mo-old, usingsmall scion buds, but with no tapingto keep the bud in place. Instead,the buds were capped with a plasticpipette tip (Fig. 1). Moreover, this

technique enabled the production ofbudded plants faster and at a lowercost compared to conventionallybudded trees and required consider-ably less space. The procedure wassuccessful with several scion-root-stock combinations that weremicrobudded throughout the year ina greenhouse. Scion buds sliced forthis technique were kept refriger-ated for a week without significantloss in bud take. This technique isdifferent from previously describedmicrobudding from South Africa (1).

Biological indexing was per-formed for the identification of citrustristeza virus, psorosis virus, citrusexocortis viroid (CEVd), and citrustatterleaf virus (CTLV). Indicatorplants of Mexican lime, pineapplesweet orange, Etrog citron, andTroyer citrange were microbudded

Fig. 1. Microbudding steps: micro-budding and capping with a pipet tip,followed by cap removal after callusing.The arrow indicates new scion growth.

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Fourteenth IOCV Conference, 2000—Short Communications

with buds containing the above men-tioned viruses, respectively. Aftercallusing and at least four wk pastmicrobudding, the bud growth wascut off to force new growth of theindicator plant. Early signs of tatter-leaf symptoms associated with chlo-rosis were visible 3 wk after theemergence of new growth in Troyercitrange plants inoculated withCTLV. The initial chlorotic symptomswere clearly visible under a stereo-scope. So far, the microbudding sys-tem was found more useful for theindexing of CTLV (Fig. 2) comparedto other pathogens. Experimentswith CEVd showed early symptomsof leaf epinasty in Etrog citron, how-ever, the results were not consistent.Results indicate that the microbud-ding procedure can be modified toapply for indexing other graft-trans-missible pathogens of citrus. Sincesmaller plants are used, this systemis ideal and less cumbersome forgrowing the indicator plants in smallgrowth chambers at an optimumtemperature for symptom expres-sion. Apart from the biological index-ing, we were also able to successfully

microbud several genetically modi-fied Rio Red grapefruit explants onto rootstocks (5). This enabled genet-ically engineered explants to grow asplants quicker, and it saved time andeffort from a tedious and often lesssuccessful attempt to induce roots inthese explants.

Production of less expensive treesthrough microbudding opened up anopportunity to plant an ultra-highdensity block at a substantially lowercost. In Texas, severe freezes,drought, urbanization and a higherland value, and unpredictable fruitprices in the past several years havebeen major limiting factors faced bycitrus growers. These factorsprompted an investigation of the pos-sibilities of a microbudded, ultra-high density planting that wouldallow a rapid and better economicreturn for the growers, especially inthe early years of an orchard. Morethan 900 microbudded trees, mainlyMarrs orange and Rio Red grape-fruit, were planted at a close spacingof 3

×

6 ft. The objective was to studythe field performance of microbuddedtrees planted at a very young stage.So far, the microbudded trees havegrown well in field conditions (Fig. 3)and some orange, grapefruit, andlemon trees produced fruit in lessthan 2 yr after microbudding (4).

Fig. 2. CTLV induced tattering andchlorosis produced in Troyer citrange, 3wk after the emergence of new growth.

Fig. 3. Microbudded trees in the fieldgrew very well and out performed com-parable trees grown conventionally. Thetree in the pot was grown and buddedusing conventional procedures and root-stock seed were prepared at the sametime.

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LITERATURE CITED

1, Holtzhausen, L. G., P. J. Muller, and A. P. Vincent1974. Mikro-okulering: ’n Belowende kwekerypraktyk. Citrus Sub-Trop. Fruit J. 488: 5-8.

2. Roistacher, C. N.1991.

Graft-Transmissible Diseases of Citrus. Handbook for Detection and Diagnosis

.FAO, Rome. 286 pp.

3. Skaria, M.1997. Micro-budded plants: A new concept in citrus production and economics. TAMUKCitrus Center Newsletter 15 (4): 1-2.

4. Skaria, M. and Z. Tao2000. 2-year wonder: Microbudded citrus trees in Texas produce fruit within two years.Citrus Ind. 81(3): 28-19.

5. Yang, Z. N., I. L. Ingelbrecht, E. Louzada, M. Skaria, and T. E. Mirkov2000.

Agrobacterium

-mediated transformation of the commercially important grape-fruit cultivar ‘Rio Red’ (

Citrus paradisi

Macf.). Plant Cell Repts. 19: 1203-1211.