Where do bacteria come from? Bacteria that serve as primary inoculum survive within the soil, or saprophytically on residual plant parts, or epiphytically on plant surfaces, within buds, flowers, fruits, roots and other tissues, or in seeds. Many are introduced within planting material (seeds, transplants, etc. Some survive within an insect vector. ** Images and lecture material were not entirely created by J. Bond. Some of this material was created by others.**

Where do bacteria come from? How do the bacteria cause disease? Bacteria are moved by rain or in irrigation water, by insects, by contact with other infected plant parts, and cultural practices. During rainfall, bacteria multiply on plant surfaces, enter through natural openings or wounds, cause the local destruction of tissue, and often move through the plants to infect the vascular system. Bacteria from wound surfaces also exude onto plant surfaces creating more inoculum for new infections.

Bacterial Diseases of Plants 1. Soft rots - Bacteria attack fleshy plant parts and produce a soft watery rot that usually stinks - may produce pectinase to break down middle lamella & “uncement" cells - may produce cellulase - may cause plasmolysis to allow cell contents to leak into intercellular spaces - may produce foul-smelling gases as byproducts of bacteria consuming plant material

Bacterial Diseases of Plants 2. Leaf spots - small lesion on leaf usually surrounded by yellow halo (chlorosis). Tissue in lesion may die and drop out, leaving "shot hole" in leaf. This is most common bacterial disease symptom. 3. Blight - similar to leaf spots, but necrosis advances rapidly and causes sudden, severe damage to flowers, stems, or leaves

Bacterial Diseases of Plants 6. Cankers - necrotic, often sunken lesion in stem or branch tissue. Incorporates vascular and parenchyma tissue. 7. Scabs - a roughened, crustlike or corky diseased area on plant organs, usually formed below ground

Bacterial Diseases of Plants 4. Wilts - bacteria grow in vascular elements and plug up xylem. Result is water deficit distal to plugged area, followed by wilting. 5. Galls - abnormal overgrowth of host cells due to hyperplasia (increased cell number) or hypertrophy (increased cell size). These are induced by bacterial products (including bacterial DNA)

Plant Pathology, G.N. Agrios

Plant Pathology, G.N. Agrios

Plant Pathology, G.N. Agrios

L - PHASE BACTERIA L-Phase bacteria are similar in all manners to normal bacteria except that they have a pleomorphic stage, i.e., no cell wall. Bacterium is bound only by cell membrane. Named after Joseph Lister - Back in 1865, Dr. Joseph Lister first demonstrated the use of an antiseptic in surgery.

L-Phase can be induced by : 1. Low light 2. Low doses of penicillin, to interfere with wall production during replication. 3. Inclusion of certain amino acids in growth medium. Generally, bacteria revert to normal phase after stimulus is removed. There are only two plant pathogenic bacteria that are known to have an L-Phase: a. Agrobacterium tumefaciens - crown gall b. Erwinia carotovora pv. atroseptica - black leg of potato Only in Agrobacterium tumefaciens is the ability to cause disease retained in the L-Phase