Tuesday, August 18, 2015

Featured Diagnosis: Crown Gall (Agrobacterium tumefaciens)

Image of a large bacterial gall on a tree trunk
 Tree trunk infection by Agrobacterium tumefaciens. Resultant gall
nearly 2 feet across. (Photo N. Goldberg NMSU - PDC)
Crown gall, caused by the soilborne bacterium Agrobacterium tumefaciens, has a wide host range among woody and herbaceous plants. More than 600 plant species in over 90 plant families are susceptible. Some of the most common species affected in New Mexico include: apple, cottonwood, elm, grapes, juniper, pear, poplar, pecan, purple-leaf plum, pyracantha, roses, stone fruits, and willows. The bacterium stimulates host cells to divide and enlarge, causing tumor-like galls to develop. Galls on woody plants usually occur on roots and/or trunks at or just below ground level (the root crown) and at graft unions. The bacterium may become systemic in some host plants and cause galls on trunks, stems, branches and leaves above the root crown. Galls may also develop above the crown by pruning with infested cutting shears. On herbaceous plants, galls form on the roots and stems and, occasionally on leaves. Initially, galls are whitish, soft, and spongy. Later, the gall develops an irregular, rough, corky surface and a hard or woody interior. It eventually turns brown or black and may slough off the plant. Galls increase in size as the plant grows and may be less than an inch in diameter to several feet in diameter. The galls impede water and nutrient movement in the plant. Reduced transport of water and nutrients causes chlorosis, stunting, slow growth, and a general decline in plant health.

Large gall occurring at the graft union on a rose plant
Crown gall infection at the graft union on rose.
(Photo N. Goldberg NMSU-PDC)

Very large gall at the root flare of a large tree
Root flare infection by crown gall. (Photo: N. Goldberg NMSU-PDC)

Golf ball to baseball sized galls occurring all over the trunk of a tree
Severe crown gall infection on the trunk and
branches of a lime tree.
 (Photo: N. Goldberg NMSU -PDC)

Quarter sized galls on the roots of a peach tree
Large galls on peach tree roots caused by
Agrobacterium tumefaciens
(Photo: J. FrenchNMSU - PDC)

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