Soybean Pod Set Enhancement with Synthetic Cytokinin Analogs

Abstract

The previously reported activity of benzyladenine and selected other cytokinin analogs to increase pod set in soybean (Glycine max [L.I Merr.) was further investigated to define the structure-activity relationship and evaluate the effects of the cytokinins on yield parameters. Enhancement of pod set was found to be greatest with N-6 saturated alkyl substituted analogs, and was only weakly associated with activity in a callus growth bioassay. The response of yield parameters to increasing pod load was evaluated by applying various cytokinin analogs having a range of pod set enhancement activity. The increased pod load at the treated nodes was not compensated by a reduction in pod number on the remainder of the plant. However, there was a compensatory decrease in seed size.Overall, a significant trend to greater total seed weight per plant was associated with the increased pod number. Initial evaluations indicated that foliar applications of select cytokinins could temporarily increase pod number. However, the increases in pod number obtained with foliar treatments were too small to be of practical utility and were not maintained to maturity.In the companion paper (1), we describe the relationship of cytokinin flux to pod set in soybean, and the use of BA as an externally supplied synthetic cytokinin to alter pod set patterns. BA has previously been reported to increase pod number of soybeans under field conditions (4, 10), as well as to increase fruit set in other species (2, 7). The close association between cytokinin flux and pod set in soybean, and the ability to enhance pod set through exogenous applications of BA, make this system especially useful for studying the natural regulation of pod set.Very few cytokinin analogs have been evaluated for pod set enhancement activity, so little is known regarding the optimum chemical structure to obtain maximal response. A diversity of cytokinin analogs have been reported in the literature (9). The activity of these compounds has usually been tested in tissue or organ bioassays, such as callus growth. Whether the activity in those assays is related to the pod set enhancement activity for the same compounds is not known.In this paper we report on the results of evaluations comparing the pod set enhancing activity of naturally occurring cytokinins to that of BA. In addition, we characterized the relative activity of a number of synthetic cytokinins, and defined chemical attributes associated with high pod set enhancing activity. Finally, by utilizing several cytokinin analogs which varied in pod set en- Plants were grown in a greenhouse with a 13.5 h photoperiod maintained with supplemental metal halide lamps, which supplied a photosynthetic photon flux density of 300 ,uE m-2 s-' PAR, and temperature was regulated to 28°C day/22°C night.Seeds were inoculated with Bradyrhizobium japonicum (Nitragin, Nitragin Co., Milwaukee, WI) at the time of planting. Plants were thinned to one plant per pot at the unifoliate leaf stage (VI according to Fehr et al. [5]). All b...

Effects of Source/Sink Ratio and Cytokinin Application on Pod Set in Soybean

“…Several previous studies indicated that cytokinin plays a critical role in pod set (Crosby et al, 1981;Dyer et al, 1987;Peterson et al, 1990;Mosjidis et al, 1993;Kokubun and Honda, 2000;Nagel et al, 2001). Therefore, we examined whether pod number can be increased by applying cytokinin to the plants with a high source/sink ratio.…”

“…Endogenous cytokinins detected in exudate showed a maximum concentration during a period from 0 to 9 days after anthesis, when most fl owers are destined to either initiate or abort pods (Heindl et al, 1982;. The application of BA to racemes reduced abortion and increased pod number (Crosby et al, 1981;Carlson et al, 1987;Dyer et al, 1987;Peterson et al, 1990;Mosjidis et al, 1993;Reese et al, 1995;Nagel et al, 2001). Within individual racemes, pod set probability at different fl oral positions was closely associated with the cytokinin concentration (Kokubun and Honda, 2000).…”

Cinetina e nitrato de potássio em características agronômicas de soja

“…Alguns estudos têm mostrado uma forte tendência tecnológica para o uso de citocininas sintéticas, aplicadas via foliar, associadas ou não a nutrientes, como formas de manejo para aumentar a produtividade da soja (Crosby et al, 1981;Carlson et al, 1987;Dyer et al, 1987;Mosjidis et al, 1993;Nagel et al, 2001;Cho et al, 2002;Liu et al, 2004;Yashima et al, 2005;Nonokawa et al, 2007). Nessa leguminosa, um elevado número de flores e de legumes jovens é abortado naturalmente, o que representa um impacto negativo na produtividade (Nonokawa et al, 2007).…”

“…Os principais fatores envolvidos na fixação de legumes de soja são a disponibilidade de nutrientes e de fotoassimilados destinados a esses legumes, quando em desenvolvimento (Wiebold, 1990), assim como a disponibilidade de algumas classes de hormônios nas sementes (Crosby et al, 1981;Carlson et al, 1987;Kokubun & Honda, 2000;Yashima et al, 2005). Pesquisas indicam a existência de deficiência de citocinina endógena, no terço superior do racemo em plantas de soja, que se encontra correlacionada ao maior aborto das partes reprodutivas da planta (Kokubun & Honda, 2000;Nonokawa et al, 2007).…”

The Effects of Figaron and Water Deficit on Seed Yield of Two Soybean Cultivars

“…Management practices such as the application of Figaron may minimize the loss of soybean yield caused by water deficit. Cytokinins are reported to increase pod set in soybean Dyer et al, 1987;Kokubun and Honda, 2000). The combined effects of cytokinins and water deficit on pod retention and yield in soybean should be examined in future.…”