Characterization, pollen behavior and propagation of five selected Hibiscus hybrids (Hibiscus rosa-sinensis Linn.)

Abstract

Breeding and characterization of Hibiscus hybrids in the Philippines was conducted to improve the local varieties for them to have unique flower colors and forms by introducing genes from foreign varieties. The Hibiscus hybrids are important ornamental genetic materials being used to honor outstanding Filipina achievers. The study aimed to characterize 5 new selected hybrids, test their pollen fertility and evaluate their graft compatibility with 2 known rootstock varieties. The important characteristics of the 5 selected hybrids are as follows: The flower of hybrid H. rosa-sinensis 'Accession 20' x H. rosa-sinensis 'Gelia Castillo' is solferino purple or red purple (RHCC 65B) with a ruby red (RHCC 59A) eye surrounded by grayish violet (RHCC N77C) halo, while the bloom of hybrid H. rosa-sinensis 'Tandang Sora' x H. rosa-sinensis 'Connie S. Angeles' is tuscan yellow (RHCC 162C) with ruby red (RHCC 59A) eye surrounded by reddish white (RHCC N1555A) halo. The petal of hybrid H. rosa-sinensis 'Tarantella' x H. rosa-sinensis 'Golden Dubloom' is rose red (RHCC 58B) surrounded with yellow orange (RHCC 20A) edging, while the eye is dark red rose (RHCC 61B). The flower of hybrid H. rosa-sinensis 'Perla Santos-Ocampo' x H. rosa-sinensis 'Loren B. Legarda', is spanish orange (RHCC 26B) with lemon yellow (RHCC 13B) eye and dark orange markings (RHCC N 25B) radiating from the eye going to the petals. In addition, the petal color of hybrid H. rosa-sinensis 'Loren B. Legarda' x H. rosa-sinensis 'Tarantella' is a combination of primrose yellow (RHCC4B) and neyron rose (RHCC 58C). Correlation analysis was conducted for the different floral and leaf traits such as corolla length, width, bloom length, receptacle diameter, style length, calyx lobe width, sepal length, style length, ovary width, petiole length, leaf length and width. Very high positive correlation (r = 0.9428) was detected on corolla length and bloom length. High correlation was observed on bloom length and corolla width (r=0.8663), corolla width and corolla length (r= 0.8727), style length and bloom length(r=0.7136), receptacle diameter and calyx lobe width (r=0.7861). Pollen viability of the 5 different Hibiscus hybrids when used as male parents in hybridization, as shown by potassium iodide structural staining was 61.62 to 70.0%, but significant differences on pollen viability were not detected among the different hybrids. However, significant differences between different sucrose concentrations added to the Brewbaker and Kwack's (BK) medium for pollen germination test of H. rosa-sinensis 'Accession 20' x H. rosa-sinensis 'Gelia Castillo' were detected. Ten percent (v/v) sucrose as additive to BK medium was the optimum concentration for pollen germination at 70%. Good pollen germination, a prerequisite for pollen tube growth in the stigma going to the ovary, hence effective fertilization and development of the zygote and growth of the embryo in the hybrid seed, is necessary for successful hybridization. Furthermore, evaluation of the graft compatibility of the 5 Hibiscus hybrids to known rootstock varieties was conducted as a prerequisite for efficient asexual propagation. Significant difference (p ≤ 0.05) was detected between rootstock varieties H. rosa-sinensis 'Reddy or Not' and H. rosa-sinensis 'Wilcox' when side-grafted with the hybrid H. rosa-sinensis 'Accession 20' x H. rosa-sinensis 'Gelia Castillo'. Rootstock variety H. rosa-sinensis 'Wilcox' promoted better grafting success by 65% when used for side-grafting H. rosa-sinensis 'Accession 20' x H. rosa-sinensis 'Gelia Castillo' compared to rootstock variety H. rosa-sinensis H. rosa-sinensis 'Reddy or Not'. However, no significant difference in the grafting success was detected between H. rosa-sinensis 'Wilcox' and H. rosa-sinensis 'Reddy or Not' when side-grafted with the other Hibiscus hybrids. Overall, it is recommended that the 5 Hibiscus hybrids be used as potted and landscaping materials, and as parents for hybridization with other varieties, while the fertile pollen could be utilized for cross-pollination with other varieties to produce another set of Hibiscus hybrids.