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Co-expression of Bs2 and EFR Genes in Tomato Provides Effective Broad-spectrum Field Resistance Against Bacterial Wilt and Bacterial Spot of Tomato

Sanju Kunwar: University of Florida

<div>Field trials were conducted at two locations in Florida to evaluate transgenic tomatoes expressing the <em>EFR</em> gene from <em>Arabidopsis thaliana</em>, the <em>Bs2</em> gene from pepper, or both <em>Bs2/EFR</em> for managing bacterial wilt caused by <em>Ralstonia solanacearum</em> and bacterial spot caused by <em>Xanthomonas perforans</em>. Expression <em>of </em><em>EFR </em><em>or </em><em>Bs2/EFR</em><em>, in the susceptible genotype, Fla. 8000, significantly reduced bacterial wilt incidence</em><em> (50-100%) </em><em>and increased total yield</em> (57-114%) <em>relative to</em> lines expressing only <em>Bs2</em> or non-transgenic Fla. 8000 control, although the marketable yield was not statistically affected. Following harvest, the surviving plants in the fields were assessed for colonization by <em>R. solanacearum</em>. There were no significant differences in the population at the lower stem. Interestingly, in the middle stem, no bacteria could be recovered from <em>EFR</em> lines or <em>Bs2/EFR</em> lines, but viable bacterial populations were recovered from <em>Bs2</em> and non-transformed control lines at 10<sup>2</sup>-10<sup>5</sup> CFU/g tissue. <em>EFR</em> transgenic tomato lines were effective against several <em>R. solanacearum </em>strains isolated from the southeastern U.S. indicating utility in a broad geographical area. I<em>n all three bacterial spot trials, </em><em>EFR</em> and <em>Bs2/EFR</em> lines significantly reduced <em>disease severity </em>compared to Fla. 8000 <em>(22-98%)</em><em>. The </em>marketable and total yield of <em>Bs2/EFR</em><em> were </em>significantly higher than Fla. 8000 (43 -170%) in three the of four field trials. These results demonstrate the potential of stacking <em>Bs2</em> and <em>EFR </em>genes for durable field resistance to bacterial wilt and bacterial spot of tomato.</div>

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