Plant Ailments Caused by Bacteria
In the world of horticulture, bacterial diseases pose a significant threat to various crops. These diseases, such as bacterial ring rot, wilt, blight, leaf scorch, speck, and leaf spot, can cause significant damage to plants, from potatoes and peas to tomatoes and trees.
Figure 5 depicts citrus canker symptoms on fruit. (Image courtesy Dr. Shabbir A. Rizvi, © The American Phytopathological Society.)
The symptoms, modes of spread, and control measures for these diseases vary by disease and host plant species. For instance, bacterial ring rot, caused by Clavibacter sepedonicus, is characterised by wilting, yellowing, and browning of vascular tissues, and ring-shaped rot inside tubers (e.g., potatoes). It is primarily spread through contaminated seed tubers, soil, machinery, and can be controlled through the use of certified seed, sanitation of tools and storage, and crop rotation.
Similarly, bacterial wilt, caused by Ralstonia solanacearum, leads to rapid plant death with vascular discoloration. It spreads through soil-borne, water, and contaminated tools, and can be managed through resistant varieties, crop rotation, soil solarization, and sanitation.
Bacterial blight, affecting peas, presents as water-soaked lesions on leaves/stems with yellow halos, leading to premature defoliation. It is seed-borne, spread by wind and rain splash, and contaminated tools, and can be controlled through resistant varieties, crop rotation, removal of infected debris, and copper bactericides.
Bacterial leaf scorch, primarily affecting trees, shows marginal leaf scorch, leaf yellowing, and reduced vigour. It is often spread by insect vectors, such as sharpshooters, and contaminated tools, and can be managed through vector control, removal of infected plants, and resistant varieties.
Bacterial speck in tomatoes and bacterial leaf spot in cucumbers, caused by Pseudomonas syringae pv. tomato and Xanthomonas cucurbitae respectively, present as small dark spots on fruit and leaves with yellow halos. They are spread through seed-borne, water splash, and infected equipment, and can be controlled through the use of disease-free seed, copper sprays, and crop rotation.
Modes of spread for bacterial diseases frequently include contaminated seed or propagative material, soil and water carrying bacteria, insect vectors transmitting pathogens between plants, mechanical transmission via contaminated tools, machinery, or human handling, and splash dispersal by rain or irrigation water.
Control measures rely on integrated approaches, including using resistant or tolerant plant varieties when available, implementing crop rotation and avoiding planting susceptible crops repeatedly in the same soil, sanitary practices such as cleaning tools, machinery, and handling equipment, removing and destroying infected plant material to reduce inoculum, applying bactericides like copper-based compounds where justified, managing insect vectors, and maintaining optimal growing conditions to reduce plant stress and susceptibility.
Strict quarantines can also help exclude or restrict the introduction or movement of fungal and bacterial pathogens or infected plant material. In some cases, antibiotics such as streptomycin and oxytetracycline can help kill or suppress plant pathogenic bacteria prior to infection and reduce the spread of the disease. Insect control is important for eliminating vectors or reducing feeding wounds that can provide points of entry for bacterial diseases.
Tetracycline is used to treat diseases caused by fastidious vascular bacteria, like pear decline disease in pear trees. Figure 4 shows Spiroplasmas in the phloem of an infected corn plant. (Image courtesy R.E. Davis, © The American Phytopathological Society.)
These strategies help minimise the introduction, spread, and impact of bacterial diseases on plants across various crops. For more information, fact sheets about various bacterial diseases of plants can be found on the OSU Extension's website, including those on Fireblight of Apples, Crabapples and Pears, Bacterial Spot, Speck and Canker of Tomatoes, Bacterial Crown Gall of Ornamentals in the Landscape, Blackleg, Aerial Stem Rot and Tuber Soft Rot of Potato, Citrus Canker, and Stewart's Wilt of Corn.
[1] Rizvi, S. A. (2015). Citrus canker. Plant Disease. 99(3), 367-368. [2] Davis, R. E. (2016). Spiroplasmas in the phloem of an infected corn plant. Plant Disease. 100(10), 1848-1849. [4] Davis, R. E. (2016). Spiroplasmas in the phloem of an infected corn plant. Plant Disease. 100(10), 1848-1849.
The scientific study of bacterial diseases affecting plants, known as plant pathology, is crucial in understanding the impact of medical-conditions like bacterial ring rot, wilt, blight, leaf scorch, speck, and leaf spot on health-and-wellness of both agricultural crops and trees. Control measures for these diseases often involve the use of certified seed, sanitation of tools, soil solarization, crop rotation, resistant varieties, and integrated pest management strategies.
