Recent advancements in the physiological, genetic, and genomic research on Rhododendron s for trait improvement

Abstract

High species diversity, hybridization potential, broad geographical dispersal range and ornamental characteristics (i.e., attractive size, shape, structure, flowers, and evergreen) have fetched a good international market for Rhododendron. However, most species are restricted to specific geographic areas due to their habitat specificity in acidic soil and cold climates, resulting many species being classified under threat categories of the IUCN. In this review, advances in research on Rhododendron for improvement to floral display quality and stress resistance have been described. The low genetic barrier among species has created opportunities for extensive hybridization and ploidy alteration for introducing quality and adaptive traits during the development of new varieties. Recent technological advances have supported investigations into the mechanism of flower development, as well as cold tolerance and pathogen resistance mechanisms in the Rhododendron. However, most of the species have limited adaptability to drought, line-tolerance, pathogen resistance, and high-temperature conditions and this resistance ability present in few species largely remains unexplored. Additionally, the available genetic diversity and genomic information on species, and possibilities for their application in molecular breeding have been summarized. Overall, genomic resource data are scarce in the majority of the members of this genus. Finally, various research gaps such as genetic mapping of quality traits, understanding the molecular mechanism of quality-related traits and genomic assortment in Rhododendron members have been discussed in the future perspective section.

Supplementary information: The online version contains supplementary material available at 10.1007/s13205-024-04006-6.

Keywords: Cold adaptation; Genetic improvement; Genomic resources; Ornamental plant; Quality improvement.

Fig. 1

Diversity in the flower color and shape of Rhododendron of central part of Indian Himalayan region. Species are: a R. arboretum, b R. barbatum, c unidentified species, d R. campanulatum, e R. niveum, f R. dalhousiae, g R. campylocarpum, h R. wightii, i R. grande, j R. cinnabarinum, k R. ciliatum, l unidentified species, m R. maddeni, n R. decipiens, o R. thomsonii

Fig. 2

Tolerance mechanism and response of Rhododendrons against cold and associated stresses at structural, physiological, molecular and metabolic level

Fig. 3

Potential mechanism of drought tolerance of Rhododendron delavayi with the application of external brassinosteroids (Modified from Cai et al. 2021)

Fig. 4

Phylogenetic tree constructed from whole chloroplast genomes sequences of different Rhododendron species