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Stolbur Phytoplasma Transmission to Maize by Reptalus panzeri and the Disease Cycle of Maize Redness in Serbia

First, second, third, fourth, and fifth authors: Institute for Plant Protection and Environment, Department of Plant Pests, Banatska 33, 11080 Zemun, Serbia; sixth author: United States Department of Agriculture--Agricultural Research Service, Corn and Soybean Research and Department of Plant Pathology, The Ohio State University/Ohio Agriculture Research and Development Center (OSU/OARDC), Wooster 44691; seventh, author: Department of Horticulture and Crop Science, OSU/OARDC, Wooster, OH 44691; eighth author: Department of Disease and Stress Biology, The John Innes Centre, Norwich Research Park, Colney Lane, Norwich NR4 7UH, UK; and ninth author: CABI Europe--Switzerland, 1 Rue des Grillons, 2800 Delémont, Switzerland.

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 to 90% in South Banat District, Serbia. Potential vectors including leafhoppers and planthoppers in the order Hemiptera, suborder Auchenorrhyncha, were surveyed in MR-affected and low-MR-incidence fields, and 33 different species were identified. Only Reptalus panzeri populations displayed characteristics of a major MR vector. More R. panzeri individuals were present in MR-affected versus low-MR fields, higher populations were observed in maize plots than in field border areas, and peak population levels preceded the appearance of MR in late July. Stolbur phytoplasma was detected in 17% of R. panzeri adults using nested polymerase chain reaction but not in any other insects tested. Higher populations of R. panzeri nymphs were found on maize, Johnsongrass (Sorghum halepense), and wheat (Triticum aestivum) 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%, respectively, became infected. These results suggest that the MR disease cycle in South Banat involves mid-July transmission of stolbur phytoplasma to maize by infected adult R. panzeri. The adult R. panzeri lay eggs on infected maize roots, and nymphs living on these roots acquire the phytoplasma from infected maize. The nymphs overwinter on the roots of wheat planted into maize fields in the autumn, allowing emergence of phytoplasma-infected vectors the following July.

Additional keywords:epidemiological cycle, hemipteran vectors, Mollicutes, Zea mays.