UPDATE: Bacterial Blight of Cotton

Characteristic symptoms of bacterial blight of cotton on bracts and bolls.

Over the past 7 days, numerous cotton fields have been determined to be infected with bacterial blight, caused by Xanthomonas axonopodis pv. malvacearum (formerly Xanthomonas campestris pv. malvacearum).  In addition to the growing number of acres in MS having been observed, the total number of acres infected is also increasing in AR (see: http://www.arkansas-crops.com/2011/07/20/alert-bacterial-blight-of-cotton-found-in-arkansas/ for additional information on the situation in AR).  Since the initial identification of the disease, widespread concern as well as important questions has been directed to consultants, producers, field personnel, extension specialists, the MS Plant Board, and company tech service reps.  

To update the situation and dispel any myths:

1. Bacterial blight has been identified on at least 3 varieties in MS to date.  One variety in particular has not only heavy infection at some locations but widespread infection in at least 4 counties (Bolivar, Coahoma, Monroe, Washington).

2. While insects are listed as a possible means of transmitting the disease they are NOT the only means of transmission or spread.  Equipment, wind, rain, splash from overhead irrigation, dew, people moving through the crop and transmitting the bacterium on their clothing, and even furrow irrigation moving dried and detached infected plant material that has dropped to the soil surface, can all move the causal organism on the farm.  However, the growing number of acres infected with bacterial blight, predominantly in a single variety, suggests a different mechanism of transmission is more likely involved.  It is most likely that the items listed above serve as a secondary source to spread the disease.  In addition, it is possible that damage to leaves by insects could result in easier entrance of the bacterium into the plant for infection but much of the work that has been conducted in this area occurred in parts of the world where insects are not managed as carefully as they are in MS.  Moreover, some of the studies that were conducted on insect transmission and the role of insect injury in the development of the disease have dealt with insects that are not present in our production system.  In short, insects didn’t put the disease in the infected cotton fields.  The information to support this section was obtained from several references including:

   Verma, J.P. 1986. Bacterial blight of cotton. Pages 149-155, CRC Press, Boca Raton, FL.       

   Wheeler, A.G., Jr. 2001. Biology of the plant bugs (Hemiptera:Miridae): Pests, predators, opportunists. Ithaca, New York, Cornell Univ. Press.

3. Several people have inquired as to whether or not the organism survives in soil.  Phytopathogenic bacteria, the bacteria that cause diseases of plants, are typically not soilborne (but there are a few exceptions; however, the bacterium that causes bacterial blight of cotton is not one of them).  Published articles suggest that the bacterial blight of cotton bacterium will not survive in the soil for extended periods of time unless a field has had a continuous history of cotton and plant stubble is present at that particular location.  Thus, this limits the potential of the disease being initiated by the sand blasting that occurred earlier in the year.  Sand blasting could have opened wounds, making it easier for the organism to gain entry into weakened plants but the bacterium was likely present on plant material prior to injury. The information to support this section was obtained from:

   Verma, J.P. 1986. Bacterial blight of cotton. Pages 143-144, CRC Press, Boca Raton, FL.

4. Questions have been posed as to the role of the bacterium in disease on additional host plants.  Research into the role of additional plant hosts in disease incidence and progression has been conducted and while there are some additional hosts, most of them are various species of Gossypium (cotton relatives) as well as host plants that are not present in MS.  The information to support this section was obtained from:

   Verma, J.P. 1986. Bacterial blight of cotton. Pages 149-155, CRC Press, Boca Raton, FL.

5. Bacterial blight is predominantly a seed transmitted disease especially in situations where cotton has not been grown in a particular field in the recent past.  While the inoculum can overwinter on stubble that remains in the field, unless a particular field has had a problem with the disease in the past it is unlikely to originate from stubble.  In addition, even in situations where the stubble from infected plants remains in a given field, survival of the organism on this material in the soil is short lived.  With that in mind, ideally, any process whereby infected material passed through a gin, even seed that was “clean” could become infested by material that contained the bacterium.  The information to support this section was obtained from:

   Verma, J.P. 1986. Bacterial blight of cotton. Pages 145-147, CRC Press, Boca Raton, FL.