|Redinbaugh, Margaret - Peg|
Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2009
Publication Date: 8/27/2009
Publication URL: http://hdl.handle.net/10113/35179
Citation: Jovic, J., Cvrkovic, T., Mitrovic, S., Krnjajic, S., Petrovic, A., Redinbaugh, M.G., Pratt, R.C., Hogenhout, S.A., Tosevski, I. 2009. Stolbur Phytoplasma Transmission to Maize by Reptalus panzeri and the Disease Cycle of Maize Redness in Serbia. Journal of Phytopathology. 99(9):1053-1069. Interpretive Summary: Maize redness (MR) has been reported periodically in the Banat regions of Serbia, Romania and Hungary over the past 50 years, but the incidence and intensity of the disease has increased dramatically over the past several years. In 2002 and 2003, the disease caused 10-90% yield reduction in the corn crop in and around the South Banat District of Serbia. MR is caused by a bacterial pathogen, the stolbur phytoplasma, that is moved between plants by insects. We determined that the leafhopper, Reptalus panzeri, is the major insect transmitting MR, and that developing leafhoppers acquire the pathogen from maize roots as nymphs. Our results indicate that large populations of the leafhopper can develop on winter wheat that is planted into corn fields in autumn in this part of Serbia, and emerge from wheat fields in early July able to transmit the bacteria to maize. Wheat and Johnsongrass were found to also be hosts of the pathogen. These results are critical for designing and testing cultural approaches for controlling the disease, such has alternative crop rotations and more aggressive weed control.
Technical Abstract: Maize redness (MR), induced by stolbur phytoplasma (Candidatus Phytoplasma solani, subgroup 16SrXII-A), is characterized by midrib, leaf and stalk reddening and abnormal ear development. MR has been reported from Serbia, Romania and Bulgaria for 50 years, and recent epiphytotics reduced yields by 40-90% in South Banat District, Serbia. Potential vectors including leafhoppers, planthoppers and psyllids in the order Hemiptera, suborder Auchenorrhyncha were surveyed in MR affected and control fields, and 33 different species were identified. Of these, only Reptalus panzeri populations were characteristic of a major vector with significantly more R. panzeri individuals in MR affected fields, higher populations in maize plots than in field border areas, and peak population levels preceding the appearance of MR in late July. Stolbur phytoplasma was detected using nested PCR in 17% of R. panzeri adults, but not in any of the other insects tested. Higher populations of R. panzeri nymphs were found on maize, Johnsongrass (Sorghum halpense) and wheat (Triticum aesvetium) roots. Stolbur phytoplasma was detected in roots of these three plant species, as well as in R. panzeri L3 and L5 nymphs. When stolbur phytoplasma-infected R. panzeri L3 nymphs were introduced into insect-free mesh cages containing healthy maize and wheat plants, 89% and 7% of plants became infected, respectively. A model for interactions between stolbur phytoplasma, R. panzeri, maize and wheat that explains the source of infected vectors as well as their relatively high population numbers in maize in South Banat is proposed. IMPACT STATEMENT: Recent outbreaks of maize redness have reduced corn yields in parts of Serbia by 40 to 70%. We identified the insect that is the most important transmitter of maize redness, and found out that it picks up the maize redness pathogen from corn roots remaining in the field after harvest. We found that the insects develop and overwinter on roots of winter wheat that is planted over the corn stubble in the fall, and emerge able to transmit the pathogen in the spring. We also found that wheat and Johnsongrass are hosts of the maize redness pathogen. Scientists and extension agents will use these results to investigate and develop methods for control of maize redness, potentially including changing crop rotations and weed control. In the long term, this research will improve the security of the corn crop in Serbia and other parts of Eastern Europe, and will prevent similar disease problems in the U.S. crop.