Agrobacterium tumefaciens

Pest (common name): 
Crown gall
Pest type: 
Bacteria
Hosts:
Apple, Blueberry, Cherry, Grapevine, Kiwi, Olive, Pear
Biological characteristics: 
Taxonomic position: Domain: Bacteria; Phylum: Proteobacteria; Class: Alphaproteobacteria; Order: Rhizobiales; Family: Rhizobiaceae
Description: This pathogen can survive on the soil for many years as saprophyte; i.e. it feeds on rotting matter. It can penetrate host plants through recent injuries caused by agricultural tools, graftings, insects, nematodes, frost, or cracks at root emergence. Inside the host plant, the bacterium modifies the genetic material of the host, thus making it release a great number of hormones that form galls by stimulating cellular division and growth.
Symptoms according to crop: In grapevine crops, tumors or galls of different shapes and sizes appear. These may be found in the neck, root, stem and vine shoots. Either the adult trees are unaffected by this disease, or recently settled plants may die. In adult plants, the disease is chronic. The level of infection in plant nurseries can affect 90% of the population. Depending on the degree of proliferation and the location of galls, there may be a serious interruption in the absorption and translocation of water and nutrients. The affected plants develop poorly: smaller, chlorotic leaves and a higher vulnerability to other pathogens and unfavorable environmental conditions, specially low temperatures in winter.
At the beginning, the galls have the aspect of small, round, soft protuberances in roots and trunk, near the surface. They can be either spongy or woody and hard, depending on the amount of vascular tissue they hold. During the fall, some tumors may totally or partially rot from the outside to the center; the tumors resume their growth during the spring, and new tumor areas may appear.
Recently formed tumors are not protected by epidermis and are easily attacked by saprophytic insects and microorganisms. When the outer section of the gall decomposes, the bacterium is released on the soil, thus being propagated at great distances by irrigation water, floods and by clinging to tillage devices and plants.
In cherry crops, the bacterium also produces tumors in roots and neck. At the beginning, these tumors are small, soft, light-colored protuberances, and they may be mistaken for root primordia. The tumors grow rapidly and acquire a darker color and a woody consistency. The age of the plant at which the infection takes place is very important: if this process occurs in adult specimens, the depressive effect of the bacterium goes unnoticed. However, if it occurs in plant nurseries or during the first years of commercial plantations, the economic impact can be really significant.
In olive plants, the bacterium produces tumors in the neck of the plant and in primary roots. At the beginning of the infection, the tumors are small and round, with a smooth surface and of a light chestnut-whitish coloring. When the tumors grow bigger, the surface turns coarse and takes on a dark brown coloring. The tumors disintegrate in the fall, thus releasing bacteria. Tumor formation results in the disorganization of xylem vessels.
In blueberry, the bacterium produces tumors (galls) at the level of the neck and deformities in roots because of abnormal growth. At the beginning, the galls,which are greenish, soft and humid, raise the bark.
Plants with a great number of galls may bear chlorosis; they may weaken, stunt and even render unproductive. In Argentina, A. tumefaciens is a primary pest in blueberry crops in all productive areas.
Predisposing conditions: 

In grapevine, the galls are visible about two to four weeks after the infection, when temperatures range between 20 and 30 ºC. Symptoms appear later when temperatures are below 15 ºC; some infections may remain dormant until the second or third growth season. The infection is hindered with temperatures over 32 ºC. As the cells of the galls increase in number and size, they press on the normal tissues that surround them, thus deforming or even tearing them.

Bibliography:
Cucchi, Nello J. A.; Becerra, V. C. 2009. Manual de Tratamientos Fitosanitarios para Cultivos de clima templado bajo riego. Sección III: Vid - Tomo I. Instituto Nacional de Tecnología Agropecuaria; Centro Regional Mendoza - San Juan INTA; Estación Experimental Agropecuaria Mendoza; Centro de Estudios de Fitofarmacia. Page/s: 368. ISBN: 978-987-1623-14-3. URL: ab. Hosts: Apple; Grapevine; Pear - Reference: 342.
Gordó, M. 2008. Guía práctica para el cultivo de Arándanos en la zona norte de la provincia de Buenos Aires. Protección del cultivo. Instituto Nacional de Tecnología Agropecuaria (INTA); Estación Experimental Agoprecuaria - San Pedro. Page/s: 11. URL: http://www.inta.gov.ar/sanpedro/info/doc/2008/mg_0801.htm. Checked on: 30/09/2010. Host: Blueberry - Reference: 79.
Bado, S. 2007. Boletin Manejo Integrado de Plagas. Problemas fitopatológicos del cultivo de cerezo en la Región Patagonia Sur. Instituto Nacional de Tecnología Agropecuaria (INTA); Boletín MIP Nº 7; Estación Experimental Agropecuaria - Chubut; Área Fruticultura - Protección Vegetal. Page/s: 1. URL: http://www.inta.gov.ar/imyza/info/bol/mip/07/bol7/mip7.htm#3. Checked on: 7/1/2011. Host: Cherry - Reference: 417.
Dobra, A. C.; Rossini, M. N.; Barnes, N. E.; Sosa, M. C. 2007. Árboles Frutales. Ecofisiología, Cultivo y Aprovechamiento. Capítulo17: Manejo integrado de enfermedades de los frutales de pepita. Editorial Facultad de Agronomía _ Universidad de Buenos Aires; Editor: Sozzi, Gabriel O. Page/s: 805. ISBN: 950 - 29 - 0974 - 7. Checked on: 05/01/2011. Host: Pear - Reference: 181.
Villareal, P.; Ballivián, T.; Gutierrez, A.; Mendoza, A.; Pujó, J.; Raffo, D.; Romagnoli, S.; Santagni, A.; Segatori, A. 2006. Pautas tecnológicas: cerezo. Manejo y análisis económico financiero. Instituto Nacional de Tecnología Agropecuaria (INTA); Centro Regional Patagonia Norte; Estación Experimental Agoprecuaria - Alto Valle; Sección comunicaciones INTA Alto Valle. Page/s: 140. ISBN-10: 987-521-208-3 ISBN-13: 987-987-521-208-4. Host: Cherry - Reference: 47.
Seleme, F.; González Vera, C.; Di Barbaro, G.; Pernasetti, S.; Batallán, S. 2006. Agalla de corona en plantas de olivo (Olea europaea L.) causada por Agorbacterium tumefaciens (Smith Thownsend) Conn. en la Provincia de La Rioja. Universidad Nacional de Catamatca; Facultad de Ciencias Agrarias; Cátedra de Microbiología Agrícola; Cátedra de Fitopatología; Revista del CIZAS. 7 (1 Y 2).: 55-63. 2006. Page/s: 9. ISSN 1515-0453. URL: http://www.editorial.unca.edu.ar/Publicacione%20on%20line/CIZAS/imagenes/pdf/V1y2/6.%20Seleme.55-63.pdf. Checked on: 22/10/2010. Host: Olive - Reference: 220.
Covatta, F.; Borscak, J. D. . 1988. El kiwi: cultivo alternativo. Hemisferio Sur S.A. ISBN: 950-504-411. Host: Kiwi

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