The Breeding for Development of Rhododendrons and Azaleas with Heat Resistance and New Flower Colors

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Some lepidote rhododendrons (LR) which have morphological characteristics similar to Evergreen Azaleas (EA) have excellent blue flower colors. Their fundamental defect is, however, their lack of heat resistance. Moreover, cross-incompatibility and/or hybrid sterility are frequently encountered. Incomplete diallele crosses using 26 species and cultivars were conducted. Two species and 7 cultivars were selected as promising breeding materials from their cross-ability, heat resistance, and ornamental characteristics. Further crosses using these materials were conducted, in which initial crosses between some LR and R. Eriocarpum, a heat resistant EA from Tokara Archipelago, were successful.Pigment components of blue, purple, pink, rose and red rhododendrons were compared using HPLC. Hydroxylation and methylation of anthocyanin, total amount of flavonol and its methylation, and copigmentation between anthocyanin and flavonol were important factors towards development of bluer hues, although … More action of hydroxylation of anthocyanin seemed to be most prominent. In the course of this analysis, an unknown yellow pigment was also revealed to be present in some rose and red rhododendrons, The possibility for another breeding approach to intensify yellow flower color was thus suggested.Intersubgeneric crosses among EA/Deciduous Azaleas (DA) and LR/Elepidote Rhododendrons (ER) were implemented to develop hybrids with intense yellow color and other ornamental characteristics. Hybrid seeds from ER x DA and ER x LR germinated, but normal sized hybrid seeds from LR x DA, EA x DA and LR x ER did not germinate. In addition, a fairly severe interspecific barrier was found in crosses within yellow LR. The necessity for polyploid breeding is suggested.About 44,665 ER seedlings were screened for heat resistance in a plastic house. It was suggested that improvement of heat resistance is possible through selection of appropriate parental materials, repetition of crosses, and strict progeny selection. Less