Abstract
We investigated whether lines of transgenic tomato (Solanum lycopersicum) expressing the Bs2 resistance gene from pepper, a close relative of tomato, demonstrate improved resistance to bacterial spot disease caused by Xanthomonas species in replicated multi-year field trials under commercial type growing conditions. We report that the presence of the Bs2 gene in the highly susceptible VF 36 background reduced disease to extremely low levels, and VF 36-Bs2 plants displayed the lowest disease severity amongst all tomato varieties tested, including commercial and breeding lines with host resistance. Yields of marketable fruit from transgenic lines were typically 2.5 times that of the non-transformed parent line, but varied between 1.5 and 11.5 fold depending on weather conditions and disease pressure. Trials were conducted without application of any copper-based bactericides, presently in wide use despite negative impacts on the environment. This is the first demonstration of effective field resistance in a transgenic genotype based on a plant R gene and provides an opportunity for control of a devastating pathogen while eliminating ineffective copper pesticides.
Highlights
Bacterial spot disease, a complex of four Xanthomonas species, is among the most widespread and destructive diseases of tomatoes and peppers throughout the world, causing lesions on aerial plant parts leading to defoliation and fruit loss [1]
We tested 377 samples collected across all five commercial tomato production regions and made race determinations based on the elicitation of a hypersensitive reaction (HR) on plant genotypes carrying R genes that recognize key effectors present in certain Xanthomonas races (Table S3)
Two of the six known tomato bacterial spot races were found (Table 1). These were the highly related X. perforans strains that are distinguished into separate races based on the presence or absence of the effector AvrXv3
Summary
A complex of four Xanthomonas species, is among the most widespread and destructive diseases of tomatoes and peppers throughout the world, causing lesions on aerial plant parts leading to defoliation and fruit loss [1]. In response to observing increased efficacy when copper was mixed with ethylenebisdithiocarbamate (EBDC) fungicides such as maneb and mancozeb, growers began mixing fixed copper products with EBDC fungicides for improved bacterial spot control [5] Even these copper-fungicide mixes have become ineffective against tomato races of the pathogen, especially under conditions of high levels of disease severity were measured in several lines selected for conventional resistance to Xanthomonas with scores between 3.6 and
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