Determination of effective nodulation in early juvenile soybean plants for genetic and biotechnology studies

Abstract

Symbiotic fixation of atmospheric nitrogen (N2) is a complex physiological process influenced by the 
interaction of genetic elements in the higher plant species and rhizobia. No standardized, efficient 
method is available to critically examine the effect of altering the genetic elements in either component 
by selection and/or genetic engineering. At planting, seeds of a tropical (‘TGX-4E’) and non-tropical 
(‘Soma’) soybean cultivar were inoculated individually in sand-filled Conetainers® in a greenhouse with 
each of two strains within two rhizobial types (Bradyrhizobium japonicum and cowpea). Six weeks after 
inoculation, each plant was classified into one of two categories; vigorous plant with dark green leaves 
indicating effective nodulation and N2-fixation (+), and stunted plant with chlorotic yellow leaves 
indicating ineffective nodulation and no N2-fixation (-). The results indicated that this non-destructive 
method could be used to identify major genetic differences in the soybean and inoculant. Therefore, 
this method could be used to rapidly identify genetic segregants resulting from selection in plant 
breeding programs and/or genetic engineering.