Response of soybean {Glycine max (L.) Merr.} under chronic water deficit to LCO application during flowering and pod filling

There has been extensive research focused on decreasing yield losses during soybean crop production, by increasing water availability through irrigation technologies. However, these techniques are expensive and labour-intensive. There has also been considerable effort to enhance photosynthetic activity in crop plants under water deficit stress. Lipo-chitooligosaccharides (LCOs) are bacteria-to-plant signal molecules essential for the establishment of rhizobia-legume symbioses. LCOs (or Nod factors) are known to invoke a number of physiological changes in the soybean plant. The objective of this study was to evaluate the impact of LCO spray application on the physiology and productivity of "water stressed" soybean plants. A greenhouse experiment was conducted to (i) assess the interactions between chronic moderate-level soil moisture deficit and spray application,of LCOs during flowering and pod filling of soybean plants, and (ii) evaluate changes in canopy spectral reflectance due to LCO application. The treatments consisted of factorial combinations of three levels of moisture availability (control, medium stress and severe stress) and LCO application or not. Chronic moderate-level soil moisture deficit strongly reduced soybean growth and productivity at both water stress levels. Foliar application of LCO affected overall plant physiological activity, increased flower and pod numbers, and accelerated leaf senescence of soybean plants under water stress. LCO affected the spectral reflectance signature at the medium stress level. LCO treatment had most positive effects on the growth pattern of soybean at the medium stress level, which is the stress level most commonly observed in standard farm-field conditions. Copyright (c) 2005 John Wiley & Sons, Ltd.