Distribution of phytopathogenic bacteria in infested seeds
Phytobacterial populations from naturally-infested seeds of cowpea, pepper, tomato, watermelon and corn were assessed to determine if there was a common mathematical relationship across seedborne bacterial diseases. Numbers of viable colony-forming units (CFU) of Xanthomonas axonopodis pv. vignicola (Xav) and Clavibacter michiganensis subsp. michiganensis (Cmm) were estimated from cowpea and tomato seeds by soaking individual seeds in phosphate-buffered saline followed by dilution-plating onto MXP and CNS semi-selective agar medium, respectively. Xanthomonas euvesicatoria and Acidovorax citrulli populations were estimated by crushing individual seeds in buffer followed by plating of seed macerates onto appropriate media. For Pantoea stewartii subsp. stewartii, bacterial populations were estimated by comparing ELISA absorbance values from naturally-infested corn seed to standard curves created from a serial dilution of P. stewartii. Among the four vegetable bacterial pathogens (Xav, Cmm, X. euvesicatoria and A. citrulli), the population ranged from 10 to 4.1 × 108 CFU per seed in subsets of ∼30 infested seeds. Bacterial populations of P. stewartii ranged from 1.6 × 105 to 8.5 × 108 CFU per seed. Based on the Shapiro-Wilk test, none of the bacterial populations were adequately described by a normal or log-normal distribution. No single distribution provided a good fit to all data sets, but most of the bacterial populations were adequately fit by the inverse Gaussian or Pearson (type 5) distributions that are highly and positively skewed. The highly skewed distributions of bacteria in infested seeds could have implications for determining appropriate sample sizes and statistical analysis methods for seed health testing.
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Document Type: Research Article
Publication date: December 1, 2013
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