Leaf edge senescence on watercress crops in southern Spain; cause and potential solutions : Industry Report

Lascelles, Damien Mark and Roberts, Mike (2019) Leaf edge senescence on watercress crops in southern Spain; cause and potential solutions : Industry Report. Masters thesis, Lancaster University.

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Watercress grown in Spain can be adversely affected during the winter from driving rain, hail or other weather events including low temperature (especially when frosts are experienced over a number of days). Leaf edge senescence is observed on crops during mild and humid periods and is exacerbated following abiotic stress. Here we look at causes of leaf edge senescence and evaluate potential control methods. Influencing factors may be both physiological and pathogenic. As such, factors including humidity and leaf structure are looked at as is nutritional status of healthy leaves and leaves showing symptoms. Crops affected are screened for pathogens and pathogenicity. Bacterial pathogens are investigated since symptoms seen on crops in Spain are similar to those cited as being caused by bacterial infections in watercress crops. Symptoms cited are those starting on the leaf edge as seen on watercress crops in Hawaii, McHugh and Constantinides (2004). Roberts (1999) describes symptoms of bacterial infection as wedge shaped necrotic patches originating from the leaf margin. Potential control methods are reviewed. Xanthomonas nasturtii, not previously recorded in Europe was isolated from crops in Spain showing symptoms of leaf edge breakdown at 3 separate institutions; Fera (York), Cambrico Biotech (Seville) and The University of Warwick. Pure isolates from Warwick were used to test for pathogenicity on watercress plants in Spain and at Warwick University. Xanthomonas nasturtii was also identified on seed (seed produced in Spain) and Xanthomonas spp. in water recirculating through the beds. Leaf edge breakdown was found to start at the leaf edge hydathodes and initial damage appears to be exasperated by humid conditions. Following identification, potential control options for Xanthomonas nasturtii were looked at both in vitro as well as in field trials. Control using the sterilant hydrogen peroxide on seed was assessed as was Ultraviolet (UV) water treatment of recirculating water. Xanthomonas nasturtii showed symptoms of pathogenicity following inoculations on watercress plants; a higher level of pathogenicity noted on crops untreated against those treated with copper gluconate. Copper gluconate inhibited bacterial growth in vitro to varying degrees. Crops treated during field trials showed reduced disease incidence at times of year when crops have experienced abiotic stress, humidity is high and/ or rainfall noted and temperatures are mild. Hydrogen peroxide reduced levels of E. coli and pseudomonas on seed. UV affected E. coli levels in recirculating water but had no effect on Xanthomonas spp. It would be useful to look specifically at Xanthomonas levels pre and post sterilant application on seed and investigate further why UV had no effect on Xanthomonas spp. in water.

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19 May 2022 11:25
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16 Mar 2024 00:05