Foliar application of lipo-chitooligosaccharides (Nod factors) to tomato (Lycopersicon esculentum) enhances flowering and fruit production

Lipochitooligosaccharides (LCO) or Nod factors, which are rhizobia-produced signal molecules, induce deformation of legume root hairs. In addition to triggering legume plant nodulation, Nod factors influence cell division and promote somatic embryo generation in non-legume plants. This suggested to us the potential of using LCO to stimulate the development of tomato flowers and fruit. This study indicated that the foliar application of LCO to tomato plants during the appropriate stages increased flower numbers and early fruiting in greenhouse trials. Flower stimulation by LCO occurred 1-2 wk after application and fruit numbers increased 2-4 wk after application. The accelerated flowering and fruiting resulted in an increase in tomato fruit yield. The most effective concentration of LCO was 50 ng per plant applied twice in the greenhouse, initially during the early flowering stage and again in the late flowering stage. A field trial in 2002 indicated that the optimal LCO application concentration was 10 ng per plant applied at the early flowering stage, which increased fruit yield and number by up to 29.8 and 29.4%, respectively. When plants received a second LCO application at the early fruiting stage, the fruit yield increased, but most were unmarketable green fruits. Analyses of yield data showed that the yield increase in field-grown tomatoes was due to an increase in the fruit number per plant, but not to individual fruit weight or fruit size. The average weight per fruit due to the treatment was not different from the control. A second field trial, carried out in 2003, showed that a foliar application of LCO at 50 ng per plant produced the best tomato yield. Our studies indicate that an LCO foliar application to tomatoes in the range of 10-50 ng per plant can increase early flowering and fruiting, which results in improved fruit yield.