Botanica Marina Vol. 39, 1996, pp. 33-38 © 1996 by Walter de Gruyter · Berlin · New York Effects of Cytokinin-Containing Seaweed Extract on Phaseolus lunatm L.: Influence of Nutrient Availability and Apex Removal S. R. Reitz* and J. T. Trumble Department of Entomology, University of California, Riverside, California 92521, U.S.A. * Corresponding author We examined the effect of a cytokinin-containing extract of the marine alga Ascophylhim nodosnm on the growth of immature Phaseolus lunatus under conditions of high and low nutrient availability, and the response of decapitated Phaseolus lunatus to the extract. Under low nutrient availability, few differences between control and treated plants were found. Therefore the extract did not provide supplementary nutrients to these plants. Under higher nutrient availability, plants receiving the more concentrated extract treatments did not produce as much new growth as control plants and plants receiving lower concentrations. For plants with apical meristems removed, control plants grew taller and produced more new leaf tissue than Ascophyllum nodosum-sxtrvict treated plants. However, treatment with the extract resulted in plants with greater specific leaf mass compared with controls. Given these results, this particular seaweed extract was not beneficial for stimulating the growth of immature Phaseolus lunatus or promoting their compensation for damage. Introduction Liquid extracts derived from marine algae have been used over the past forty years on a variety of crops to promote plant growth and development (Crouch and Van Staden 1994). Interest in these seaweed con- centrates (SWC) in agricultural systems has focused on their use as an inexpensive source of naturally oc- curring plant growth regulators. Because the concen- trations of minerals and nutrients present in these products are low relative to crop requirements, much of the benefit from applications of SWC has been attributed to the presence of plant hormones, es- pecially cytokinins (Blunden 1977, Verkleij 1992). Various seaweed concentrates contain significant am- ounts of cytokinins in addition to other phytohor- mones (Crouch and Van Staden 1993). Endogenous cytokinins are physiologically impor- tant to the growth and development of plants. High levels of cytokinins promote cell division (Weaver 1972, Elliott 1982, Taiz and Zeiger 1991) and delay senescence (Nooden and Leopold 1978). Endogenous cytokinins also occur at high levels in the leaves of plants recovering from herbivory (Trumble et al. 1993) or artificial damage (Wang et al. 1977, Palmer etai 1981). Exogenous applications of cytokinins reportedly improve plant vigor in adverse environmental cpn- ditions (Senn et al. 1961, Mooney and Van Staden 1985, Beckett and Van Staden 1991). Therefore, ex- ogenous applications of cytokinins or cytokinin-con- taining products could increase the growth of nutri- ent stressed plants or recovery of plants from dam- age. However, data on the efficacy of these SWC are conflicting, with exogenous applications of SWC pro- ducing positive, neutral, or inhibitory effects on the plants tested (Humphries 1958, Blunden and Wildgoose 1977, Crouch and Van Staden 1994, Hedin and McCarty 1994). Among the factors that can account for these differences are the source and concentration of products, methods of application, plant species or variety tested, and the plant charac- teristics measured. Our objectives were to compare the growth of nu- trient stressed and unstressed lima beans (Phaseolus lunatus L.) treated with different rates and appli- cation methods of a cytokinin-containing product de- rived from the brown alga Ascophylhim nodosnm (L.) LeJol., and the response of Phaseolus lunatus to ap- plications of that product following removal of the apical meristem (decapitation). Materials and Methods Plant material Seeds of Phaseolus lunatus ('Henderson Bush') were germinated in containers filled with vermiculite. After primary leaf expansion began, individual seedlings were transplanted to 10-cm X ÉÏ-cm pots containing UC soil mix (Matkin and Chandler 1957). Plants were maintained in greenhouses and were watered daily. All experiments began when the first trifoliate leaves had expanded fully. Seaweed concentrate (SWC) We used a commercially available SWC, Cytokin® (Plant Biotech Inc., Corrales, NM, U.S.A.). Cytokin Brought to you by | University of Glasgow Library Authenticated Download Date | 6/29/15 1:27 PM