VIEW ARTICLE

Physiology and Biochemistry

Cytokinin Levels and Kinetin-Virus Interactions in Tobacco Ringspot Virus-Infected Cowpea Plants. W. E. Kuriger, Former Graduate Research Assistant, Department of Plant Pathology, University of Massachusetts, Amherst, MA 01003, Present address of senior author: Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061; G. N. Agrios, Professor, Department of Plant Pathology, University of Massachusetts, Amherst, MA 01003. Phytopathology 67:604-609. Accepted for publication 1 November 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-604.

Tobacco ringspot virus was detected in cowpea root tips 3 days after leaf inoculation and reached its highest concentration 2 days later. Cytokinin levels in root exudate and root tissue extracts were lower in TRSV-infected cowpea plants 7 days after inoculation than in healthy plants. Purified extracts from healthy and TRSV-infected root tissue collected at that time and separated by paper chromatography showed a minor peak of cytokinin activity at R_t 0.5 and a major peak at R_t 0.8 in the tobacco stem pith callus tissue bioassay. The peak at R_t 0.8 from TRSV-infected root tissue was 31% less than that produced by healthy extracts. Daily treatment of primary leaves of cowpea plants with 10^–4 M kinetin had no effect on shoot growth but reduced the growth of roots. Kinetin treatment of cowpea plants inoculated with TRSV had no effect on either shoot or root growth. Cowpea primary leaves treated with kinetin and inoculated with TRSV produced 75% fewer local lesions than untreated, inoculated leaves. Virus production in roots of kinetin-treated plants was lower and delayed compared to untreated plants. Yellowing and abscission of inoculated, kinetin-treated leaves was also delayed and the rate of yellowing of individual leaves was slower than in inoculated, untreated leaves.