The objective of this study was to select the most dependable soiltest criterion for determining whether potato (Solanum tuberosum L.) yields might be increased by liming soils. To achieve this end, the crop was grown in unlimed and limed treatments of eight coarsetextured soils (Spodosols), with initial pH values ranging from 4.62 to 5.02 (H2O) and 4.32 to 4.76 (0.01 M CaCl2), in a greenhouse experiment. Liming at 8 g CaCO3/8 liter soil (≃ 2,000 kg/ha) increased the average tuber yield of three soils by 40%. No yield increases were, however, produced by liming soils which had pH values higher than 4.6 (0.01 M CaCl2) or 4.9 (H2O). Extractable soil Al (I N KCl) was as good an indicator as soil pH for predicting crop response to liming. Yields were generally not increased by liming when the concentration of extractable soil Al was < 0.90 meq/100 g. Manganese concentrations in soil or plants were not reliable indicators for predicting the response of this crop to liming. A relationship was found between the concentration of soil Mn extracted with either 1 N NH4OAc or 1 N KCl and the concentration of this element in plant tops (r ≃ 0.75**, significant at the 0.01 level); furthermore, the concentrations of Mn extracted by these solutions were related (r = 0.92**. The Mn content in plant tops also tended to decrease exponentially as soil pH increased (R2 = 47%). Finally, no Ca‐deficiencies were observed on these soils; apparently this crop can absorb sufficient Ca when soils contain as little as about 0.7 meq Ca/100 g (140 µg/g).
Escherichia coli TB1 was transformed with pUC9 containing fragmented DNA (4–10 kilobases (kb)) from Corynebacterium sepedonicum. The resulting genomic bank was screened by a dot blot assay to identify clones specifically hydridizing to C. sepedonicum DNA and not to the DNA of several other Gram-positive and Gram-negative bacteria. Two clones (III24 and III31) were selected because of their ability to strongly hybridize to C. sepedonicum DNA and weakly hybridize to the DNA of C. michiganense, Erwinia carotovora, Agrobacterium tumefaciens, Bacillus subtilis, Pseudomonas solanacearum, Micrococcus luteus, and Arthrobacter globiformis. These two clones were also specific for C. sepedonicum DNA when tested against the DNA from 30 isolates of soil bacteria. Restriction enzyme analysis has shown that the two clones have an insert of 8 kb (III24) and 4 kb (III31). On the basis of restriction enzyme patterns, one clone (III24) does not correspond to plasmid pCL 50, a cryptic plasmid found in several C. sepedonicum isolates. Because purified III24 and III31 DNA can be used to detect approximately 1 ng of C. sepedonicum genomic DNA, the two clones can complement serological or biological detection methods. This could be useful, especially when a high degree of specificity is required for detection or identification of this plant pathogen.
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