Of the multitudes of bacteria species that feed on dead plant tissue only a few can enter the corn leaves. Most bacterial require a moist environment to duplicate and to avoid desiccation. Leave epidermis and its waxy cuticle covering inhibits most bacterial from entering the leaf.
Stomata, while open during daylight, are vulnerable to invasion by bacteria but relatively few bacteria species become established through them. Stomata are a low percentage of the surface of a leaf, decreasing the probability of stomata being exposed to potential bacterial invaders. Bacterial species capable of entering stomata tend to be those with swimming structures such as in the Xanthomonas and Pseudomonas genera, although only a few species of these genera appear to enter the corn leaf. There is evidence in other plant species of some stomata temporarily closing when exposed to bacteria. In these cases, the stomata would be closed for a few hours, only to open later. There is also evidence that some variants of the bacteria produce chemicals to inhibit their detection, effectively negating this defense system.
Bacterial stripe, caused by Pseudomonas andropogonis and chocolate spot caused by a variant of Pseudomonas syringae are examples of diseases caused by bacteria entering through stomata. Another example is bacterial leaf streak caused by Pseudomonas campestris pv zeae, a more recent disease in the USA but known in South Africa since 1949.
Two corn diseases caused mainly by bacteria entering injured tissue are Stewarts disease and Goss’s bacterial wilt and blight. Pantoea stewartii enters through injury and commonly is vectored by the corn flea beetle as if feeds on corn leaves, inserting the bacteria into the leaf mesocotyl. Goss bacteria (Clavibacter michiganensis subsp. nebraskensis) mostly are associated with hail leaf injury in which infected debris from a previous crop are exposed to inner leaf tissue.
After entrance in the leaf tissue, the bacteria utilize intercellular nutrients and moisture to multiply, killing cells as well. Eventually the host plant’s resistance system limits the destruction. Resistance genetics varies among inbreds and hybrids, with relatively few incapable of stopping these bacterial from causing significant damage.
It is a dynamic battle between potential pathogens and corn plants.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.