Effect of cotton root exudate constituents on growth and pectolytic enzyme production by Verticillium albo-atrum

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Abstract
New Mexico Acala cotton cultivar 8229 (Verticillium tolerant) exuded 3.5 times more choline from roots than did susceptible 1517-C cultivar. Other exuded growth factors were not significantly different between cultivars. The choline difference and the earlier discovery that alanine is exuded in greater quantities by the susceptible cultivar prompted an investigation into the effects of these metabolites on growth and pectic enzyme production by the pathogen. L-Alanine (0.002 M) increased Verticillium growth 320% (dry weight basis), but when 2.0 μg/ml choline was also added, growth was reduced to 41% of control cultures. Polygalacturonase activity was also stimulated by 0.002 M L-alanine (17.2 units/mg dry weight of growth vs. 10.4 units for control cultures). When choline was added, the activity was suppressed (7.4 units). Choline without L-alanine had little effect on growth or polygalacturonase production. When alanine was taken up by excised cotton seedlings or supplied in nutrient solution supplied to older plants before inoculation, the tolerance characteristic of cultivar 8229 was reversed.
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