Gummy Pitting - Gum Pocket - Wood Pitting

 

HISTORY, SYMPTOMATOLOGY, DISTRIBUTION AND IMPORTANCE

“Wood pitting” was described in Argentina as a disease characterized by gum-impregnated projections on the cambial face fitting into creases in the wood of the trifoliate orange (Poncirus trifoliata)rootstock. “Gum pocket” was described in South Africa as gum pockets and malformation of the trifoliate orange rootstock under sweet orange scions (Schwarz and McLean, 1969) and considered similar to wood pitting. “Gummy pitting” was described in Australia and characterized by the development of gum-impregnated pits in the surface of the wood of trifoliate orange rootstocks. The presence of severe pitting can be detected externally by uneven, flattened or depressed areas of bark (Fraser et al., 1976). Similar symptoms have been seen in Italy (Cartia et al., 1984), Turkey and Chile.

These diseases occurred in old budwood lines. Use of budwood derived from shoot tip grafting in vitro or nucellar embryony has overcome these problems.

 

 

NAME OF DISEASE AND SYNONYMS

Wood pitting refers to the symptoms described in Argentina.  Gum pocket refers to the gum pockets described in South Africa. Gummy pitting refers to the development of gum-impregnated pits in the surface of the wood. These symptoms are very similar and can be considered as a single alteration.

Abbreviation: GP for Gum pocket and Gummy pitting.

 

 

SYMPTOMATOLOGY

 

General aspect of affected field tree

Not described.

 

Symptoms on trunk (on rootstock and/or scion), limbs and shoots

Wood pitting characterized by gum-impregnated projections on the cambial face fitting into creases in the wood of the trifoliate orange (Poncirus trifoliata)rootstock. Usually associated with an indented ring at the bud-union, flattened and longitudinal fissures and laminate shelling of the bark (not exocortis) (Du Charme and Knorr, 1954; Fernandez-Valiela et al., 1965; Foguet and Oste, 1968).

Gum pocket: gum pockets and malformation of the trifoliate orange rootstock under sweet orange scions (Schwarz and McLean, 1969) and considered similar to wood pitting.

Gummy pitting: development of gum-impregnated pits in the surface of the wood of trifoliate orange rootstocks, associated with gumming in xylem and phloem and varying in degree from very few small pits with little gum to large heavily gummed pits occurring singly or in groups (GP. 01, 02, 03). Presence of severe pitting can be detected externally by uneven, flattened or depressed areas of bark (GP. 04) (Fraser et al., 1976).

 

Symptoms on leaves

Not described.

 

Symptoms on fruit

Not described.

 

Histological and cytological symptoms

Not described.

 

 

CAUSAL AGENT

Gummy pitting was initially found in dwarfing budlines associated with citrus viroids (Fraser et al., 1976), but later research showed gummy pitting present in trees of some clones (eg Barlow Ellendale tangor) free of viroids.

Gum pocket was associated with a viroid-like RNA with the electrophoretic mobility of CVd-III, but Koch’s postulates were not fulfilled (Marais et al., 1996).

Verniere et al. (2002) found gum deposits in all trifoliate orange stocks in field trials to determine the effects of different citrus viroids on Clementine trees on P. trifoliata, both viroid-infected treatments and uninoculated controls.

Duran-Vila et al. (2002) considered the possibility of gummy pitting being of physiological or stress origin enhanced by viroid infection.

 

 

HOST RANGE

Sweet orange, Marsh grapefruit, Eureka lemon, Clementine mandarin on P. trifoliata rootstocks.

 

 

TRANSMISSION

Graft inoculation from symptomatic trees eg to nucellar Eureka lemon on trifoliate orange rootstock and by direct propagation (Fraser et al., 1976).

 

 

EPIDEMIOLOGY

Not studied.

 

 

DIAGNOSIS

 

Diagnostic field symptoms

Gum impregnated pits in the surface of the wood of the trifoliate orange stock associated with gumming in xylem and phloem. Symptoms are most severe in the shoulder of the stock below the bud union. Presence of severe pitting can be detected externally by uneven, flattened or depressed areas of bark (Fraser et al., 1976).

 

COMPARISON WITH OTHER DISEASES

Similar symptoms to cachexia in Orlando tangelo, xyloporosis of Palestine sweet lime, gummy bark of sweet orange and Kassala disease of grapefruit, but probably differing aetiology.

 

 

SELECTED REFERENCES

Bové, J.M. 1995. Virus and virus like disease of citrus in the Near East region.
FAO eds. Rome. 518p.

Cartia, G., Rosa La Rosa, A. Catara (1984). A gummy pitting of trifoliate orange in Italy. p. 184-187. In: S.M. Garnsey, L.W. Timmer and J.A. Dodds (eds) Proc. 9th Conf. Int. Organization Citrus Virol., Univ. California: Riverside.

Du Charme, E.P., L.C. Knorr. (1954). Vascular pits and pegs associated with diseases in citrus. Plant Disease Reporter 38: 127-142.

Duran-Vila, N., L. Botella, C. Vernière (2002). Wood pitting – gum pocket – gummy pitting of trifoliate orange: considerations about their etiology. p. 384-386. In: N. Duran-Vila, R. G. Milne, J. V. da Graça (eds.). Proc. 15th Conf. Int. Organization Citrus Virol., Univ. California: Riverside.

Fernandez Valiela, M.V., C. Fortugno, F. Corizzi (1965). Incidence of bud-union crease in citrus trees grafted on trifoliate rootstock in the Delta del Parana and San Pedro areas of Argentina. p. 182-186. In: Price WC (ed.) Proc. 3rd Conf. Intern. Organization Citrus Virol., Univ. Florida Press, Gainesville.

Foguet, J.L., C.A. Oste (1968). Disorders of trifoliate orange rootstock in Tucumán, Argentina. p. 183-189. In: Price WC (ed.) Proc. 3rd Conf. Intern.Organization of Citrus Virol. Univ. Florida Press, Gainesville.

Fraser, L.R., P. Broadbent , J.E. Cox (1976). Gummy pitting of Poncirus trifoliata:its association with dwarfing of citrus in New South Wales. p. 147-151. In: E.C. Calavan (ed) Proc. 7th Conf. Intern. Organization  Citrus Virol. International Organization of Citrus Virologists, Univ. California: Riverside.

Marais, L.J., R.F. Lee, J.H.J. Bretenbach,B.Q. Manicom, S.P. van Vuuren. (1996). Association of a viroid with gum pocket disease of trifoliate orange. p. 236-244. In: J.V. da Graça, P. Moreno, R.K. Yokomi  (eds) Proc. 13th  Conf. Intern. Organization Citrus Virol., Univ. California, Riverside.

Schwarz, R.E. & A.P.D. McLean. (1969) Gum pocket, a new virus-like disease of Poncirus trifoliata.  Plant Disease Reporter 53: 336-339.

Vernière, C., L. Botella, A. Dubois, C. Chabrier & N. Duran-Vila. (2002). Properties of citrus viroids: symptom expression and dwarfing. p. 240- 248. In: N. Duran-Vila, R. G. Milne, J. V. da Graça (eds) Proc. 15th Conf. Int. Organization Citrus Virol. Univ. California: Riverside.

 

 

Prepared (2007) by Patricia (Broadbent) Barkley

Australian Citrus Growers’ Inc.,

Mildura

Australia