VIEW ARTICLE

Multiple Regression of Tobacco Black Shank, Root Knot, and Coarse Root Indexes on Soil pH, Potassium, Calcium, and Magnesium. Randall R. Kincaid, Professor (Plant Pathologist), Institute of Food and Agricultural Sciences, North Florida Experiment Station, Quincy 32351; Frank G. Martin(2), Nathan Gammon, Jr.(3), Herman L. Breland(4), and William L. Pritchett(5). (2)(3)(4)(5)Associate Professor (Associate Statistician), Professor (Soil Chemist), Associate Professor (Associate Soil Chemist), and Professor (Soil Chemist), IFAS, Florida Agricultural Experiment Station, Gainesville, 32601. Phytopathology 60:1513-1516. Accepted for publication 13 May 1970. DOI: 10.1094/Phyto-60-1513.

Multiple-regression analysis offers an opportunity to obtain more reliable information on root disease-soil analysis relationships than does simple correlation. Data on incidence of tobacco black shank (Phytophthora parasitica var. nicotianae), root knot (Meloidogyne incognita acrita), and coarse root (Pratylenchus penetrans and P. brachyurus) and soil pH, K₂O, CaO, and MgO for 13 crop years were analyzed. The relative reliability of the following conclusions is judged by the consistency and magnitude of the responses: (i) black shank: pH, strong positive linear; K₂O, moderate quadratic, min 500 lb./acre; CaO, inconclusive; MgO, weak positive linear; (ii) root knot: pH, moderate negative linear; K₂O, moderate quadratic, max 800 lb./acre; CaO, moderate quadratic, min 1,300 lb./acre; MgO, weak quadratic, min 300 lb./acre; (iii) coarse root: pH, moderate quadratic, min 6.0; K₂O, strong positive linear; CaO, weak quadratic, min 1,200 lb./acre; MgO, weak negative linear. Fortunately, soil analyses found in cigar-wrapper tobacco fields in north Florida and southwest Georgia are mostly favorable to control of diseases, with the exception of black shank, which is aggravated by liming but controlled rather well by other means.