Screening and Physiological Characterization of Lime-induced Iron Deficiency Chlorosis (IDC) Tolerance in Rhododendron Genotypes (RHODOLIME)

The aim of the RHODOLIME project is a research tool for a more efficient, faster breeding of the popular rhododendron garden plant (Rhododendron spp.). Rhododendrons, including pot azaleas, require acidic soils to grow. Because low soil pH does not occur in many gardens, development of rhododendron types adapted to a higher pH would help them to find their way into the average garden. In the context of breeding and selection, ILVO is looking for a good testing method for the development of adapted rhododendron types. In addition, we are investigating why rhododendron plants prefer acidic soil. The answer to that question can support the development of rhododendrons for less acidic soils.

A bioassay is being developed to help select rhododendron genotypes that can also grow on less acidic soil. The intention is to be able to carry out the selection according to suitable genotypes at the seedling stage. The parent plants are also tested in order to make cross combinations; their seedlings are expected to grow well in a soil with a higher pH. The tests are developed and executed in plant tissue culture and subsequently validated for rhododendron plants under normal growing conditions. The underlying mechanism for pH preference is also unraveled. There are already indications that the iron and calcium uptake of the plant are involved. When the pH changes, the absorption of these elements changes. The hypothesis to be tested is that rhododendron does not like calcareous soils (high pH) because it prevents the absorption of iron.

Rhododendron is an important ornamental shrub for garden use. Every year 35 million young rhododendron (and pot azalea) plants are produced at Flemish companies and sold worldwide. Rhododendrons, including pot azaleas, require acidic soils to grow. Development of rhododendrons that can also be used in non-acidic soils would help to expand this market. The results of this project will add valuable fundamental knowledge and applied knowledge regarding cultivation and breeding of rhododendron species, including pot azalea, in less acidic soils.