Rhizosphere Acidification and Iron Deficiency Chlorosis in Deciduous Azalea (Rhododendron Sect. Pentanthera) Offer Insight on pH Adaptability

The genus Rhododendron (Ericaceae), and many other Ericaceous horticultural crops, are not readily amenable to cultivation on high pH and/or calcareous soils.  Rhododendrons display symptoms of iron deficiency chlorosis when grown under such conditions due to the the lack of soluble iron in the soil.  In many landscape situations where high pH soils abound, this translates to decreased plant vigor and performance in the landscape.  We measure rhizosphere acidification, or the acidification of root apoplast tissue and surrounding soil, as a candidate trait that potentially mitigates iron deficiency chlorosis by increasing iron solubility for root uptake.  Presented is an application of the authors’ previously developed methods for phenotyping rhizosphere acidification in vitro at high throughput using a MATLAB script (MathWorks, Inc). We estimate genetic variances for rhizosphere acidification in two breeding populations: a factorial mating design comprising 10 advanced Rhododendron sect. Pentanthera cultivated selections and a maternal half sib mating design containing 28 wild, Rhododendron viscosum parents occurring in subpopulations across the southern United States.  Additionally, we describe new high throughput methods for quantifying iron deficiency chlorosis using MATLAB to phenotype leaf color on seedling azalea progeny from the aforementioned mating designs.  Finally, we present family level correlations between the degree of rhizosphere acidification measured in vitro and chlorosis severity on greenhouse grown azalea seedlings after subjecting progeny to varying liming (calcium carbonate) rates.