Pollinator Effects on Genotypically Distinct Soybean Cytoplasmic Male Sterile Lines

Poor seed-set limits potential for soybean hybrid seed production. The objective of this study was to evaluate effects of different pollinators on the rate of seed set in three soybean cytoplasmic male sterile (CMS) lines, JLCMS9A, JLCMS82A, and JLCMS89A. The following five treatments were applied under net room isolation-conditions: (i) insecticide application and release of alfalfa leafcutter bees (Mega-Chile rotundata) during flowering; (ii) insecticide application in the absence of leafcutter bees; (iii) release of alfalfa leafcutter bees during flowering without insecticide application; (iv) the absence of insecticide or alfalfa leafcutter bees during flowering; (v) plants without a net cover and pesticide application. Results indicated that the rate of pod production and seed set differ significantly between CMS lines and between treatments. Alfalfa leafcutter bees were an effective pollinator as evidenced by increases in pod-bearing rate and seed-set rate respectively from 21.35 to 53.22% and from 19.91 to 58.77% in the three CMS lines. The three CMS lines also showed significant differences in seed set, with JLCMS82A exhibiting the highest rate in all five treatments, followed by JLCMS9A and then JLCMS89A. These results suggested that thrips (Sericothrips variabilis) might have some effect on soybean pollination, but did not elicit a major influence based on the low increases in seed production. The natural insect population served an important role in outcrossing and seed set in soybean.