A Preliminary Study on Genetic Characteristics of Inter-specific Hybrids of Camellia amplexicaulis

Liu Xinkai, Zhong Naisheng, Feng Guimei Yan Danfeng and Gao Jiyin

The Department of Plant Resources Research and Development, Palm Landscape Architecture Co., Ltd., Guangdong 510627, China.
E-mail: y25006@163.com.

Introduction

Camellia amplexicaulis is distributed in the contiguous areas North Viet Nam and Hekou County, Yunnan Province, China (Chang,1981). The local people have used the species as cut flowers or planted it in temples as ornamental plants since it was discovered in 1916 (Ming, 2000). Even so, insufficient attention has been paid to the development and utilization of this unique species in the Camellia World until now.

The flowers of C. amplexicaulis are purplish red, single and crabapple flower-shaped, small to medium, petals 7-11, fleshy, broadly ovate with rounded tips and concave; stamens are numerous, filaments fused at the base, style glabrous, three freely un-fused, anthers yellow. Pedicels longer. Leaves large, long-elliptic in shape, upper surface with venation slightly impressed, petioles short and held by the base of their leaves. Plants upright, growth vigorous and big trees can be grown, but it is not cold-hardy (below -30). Blooming season: autumn to following spring or year-round .(Gao, 2005). From the above, we can see that this species has very special characteristics and has great potential as an ornamental plant in the future.

With the development of camellias around the world, the species is starting to be noticed by camellia people. A photograph and description of C. amplexicaulis was published on the cover of No.133 of 1999 ‘New Zealand Camellia Bulletin’ by Mr. Neville Haydon (Haydon, 1999). A detailed introduction for this species was reported by Mr. Gao Jiyin in 2002 (Gao, 2002). Molecular and morphological comparisons of C. amplexicaulis with its different sources and some interspecies hybrids were made by Dr. George Orel et al in 2010 and 2012 respectively (Orel et al, 2010 and Orel et al, 2012). A significant research result in recent years is that Yellow hybrids can be bred from cross-combination between C. japonica cultivars and C. amplexicaulis (Liu et al, 2012).
Anyway, C. amplexicaulis also is an important breeding material in the Genus Camellia for creating more unique hybrids to be used for gardening. There is, however, virtually no reporting on hybridization of C. amplexicaulis in the camellia world.

Based on above, we have used C. amplexicaulis as a parent and crossed with other camellia cultivars since 2006 and some new hybrids of it have been obtained. Here we would like to share our preliminary research results of this species with the world’s camellia people.

Materials and methods

Basic situation

The hybridizations were done at the Camellia Breeding Base, Gaoyao City, Guangdong Province, China in 2006 and 2007. C. amplexicaulis was selected as a main cross-parent and other camellia species or cultivars were selected as the other cross-parent in a cross-combination. The cross-pollinations were artificially controlled from autumn to the following spring. More than 200 flowers were pollinated for each cross-combination. The mature capsules that had been pollinated were collected in the autumn and the hybrid seeds were taken from the capsules. The seeds were sown in pots and the hybrid seedlings were cultivated for growing on. One hundred and twenty individual plants of these kinds of hybrids started to bloom from 2010. Sixteen typical plants were selected for the study in the Camellia Breeding Base.

Cross-combinations

C. amplexicaulis was the main cross-parent and crossed with other camellia cultivars or species. Nine cross-combinations were done. They are shown in Table 1.

Table 1. Inter-specific cross-combinations of C. amplexicaulis

Observation, measurements and statistics

a) With the development of flower buds, over five flower buds selected from each tested plant were observed, measured and photographed during the blooming period of the hybrids. The flower characteristics, including color, size, form, petals, and stamens, were measured when the flowers were fully opening.
b) For comparing the differences between hybrids and their parents in plant morphology and growth habits, leaf characteristics, such as leaf color, leaf length and width, leaf thickness etc., were determined in the spring.
C) For estimating growth vigor, ten new shoots were measured from each hybrid plant when growing stopped in winter.
D) The data obtained from above determinations were statistically analysed using Microsoft Office Excel 2007. According to results of statistical analysis, genetic expressions of the hybrids were evaluated.

Results and Discussion

Flower showing of the hybrids

Eighteen distinct plants were selected from 125 individual hybrid plants that had bloomed. Two photos were taken from a normal flower of each hybrid during the blooming season. The flowers of the hybrids are listed in table 2.

Table 2. Flowers of Inter-specific hybrids of C. amplexicaulis

From the above, the general outlines of the flowers of C. amplexicaulis hybrids can be clearly seen. It seems that most of the hybrids’ flowers in the nine cross-combinations are beautiful and they certainly all are of ornamental value.

Flower characteristics of the hybrids

Let us firstly look at the flower characteristics of the hybrids and their relationship to cross-parents. See Table 3 below:

Table 3 Flower characteristics of the hybrids

*Flower bud density was calculated with the formula, ( Total quantity of the flower buds from first leaf axil at the tip of a shoot to third leaf axil of the shoot) ÷3

From the above, we can see that in flower bud density, hybrids are more similar to C. amplexiecaulis in which flower buds are very dense. In flower color, most of the hybrids are light pink to deep-pink, which is similar to C. amplexicaulis, but one exception is that yellow to pink flowers appeared in the three hybrids within cross-combination HB8. This occurrence, perhaps, is because of gene recombination during hybridization between C. japonica cultivar, ’Tama Beauty’ and C. amplexicaulis. In flower form, most of the hybrids, in a high degree, tend towards the other cross-parent within a cross-combination. In flower size, all of the hybrids are larger than C. amplexicaulis and tend towards the other cross-parent as well. We also can see that petal quantity in most of the hybrids is increased, which tends towards the other cross-parent. In pedicel length, it very obvious that this is increased in the hybrids,  which tends towards C. amplexicaulis. In blooming period, most of the hybrids tend towards C. amplexicaulis:  only a few of the hybrids tend towards their other cross-parent.

In conclusion, the genetic characteristics of C. amplexicaulis hybrids in flower buds, flower color, pedicel length and blooming period are more like C. amplexicaulis and in flower form and petal quantity are more like their other cross-parent in a cross-combination.

Leaf characteristics of the hybrids

The leaf characteristics of the hybrids mainly follow C. amplexicaulis, even though there are some differences in a few cross-combinations. See Table 4.

Table 4. Comparisons on leaf characteristics of the hybrids with their cross-parents

From the table, we can see that the leaves of the hybrids are mainly light-green to green, which is inclined towards C. amplexicaulis; the leaf length and width of the hybrids are significantly similar to C. amplexicaulis and smaller than their other cross-parents. However, the data of Length / width is about 2.0, which shows that the leaves of both cross-parents and hybrids all are elliptic in shape and also that hybrids’ leaves are thicker, which tends to C. amplexicaulis, but petiole length is similar to their other cross-parents.

The above results show that the genetic expressions of the hybrids on leaf characteristics obviously tend to C. amplexicaulis, except for petiole length. The larger leaves of the hybrids are of ornamental value in gardening.

Plant characteristics of the hybrids

The hybrids all grow upright, very strongly and quickly. From Fig. 1, we can see that both new shoot growth and three-year plant growth in the hybrids are significantly higher than C. amplexicaulis, but very much greater than that of their other cross-parents. The new shoot growth of the hybrids is about twice that of C. amplexicaulis and about five times that of their other cross-parents. The hybrids have demonstrated an obviously heterotic vigor in growing. C. amplexicaulis has the habit of growing quickly, and the hybrids genetic expression has confirmed that the hybrids have gained some quickly growing genes from the species. This habit of the hybrids will be very useful for the rapid cultivation of large camellia trees for gardening purposes.

Fig. 1. Growth comparisons of the hybrids with their cross-parents

Resistance of the hybrids

It has been shown that C. amplexicaulis is not cold hardy but can grow well in hot climates (Gao, 2002 and Gao, 2005). The other cross-parents used in our study belong to C. japonica or C. chekiangoeosa which are both very cold hardy. From Table 5, we can see that the resistance of the hybrids to extreme temperatures is greatly increased in southern China and eastern China. This shows that, because of the cold resistant genes that have been gained from the other cross-parents, the hybrids have overcome the defect by which C. amplexicaulis is not cold hardy and, because of the heat-resistant genes that have been acquired from C. amplexicaulis, the hybrids have inherited the advantage of C. amplexicaulis, being resistant to hot temperatures. It is very important that the adaptability of the hybrids has obviously been increased and it could be expected that the hybrids will be widely used for gardening in subtropical and tropical areas.

Table 5. Resistant comparisons of the hybrids with their parents on leaf and plant under extreme temperature in southern and eastern China

Conclusion

As a result of the crosses between C. amplexicaulis and other camellias from 2006, a series of inter-specific hybrids of C. amplexicaulis had been obtained. After observation and determination of flowers, leaves, growth and resistance, we confirmed that the hybrids have many special and unique characteristics. Flowers of the hybrids mainly tended towards C. amplexicaulis in flower bud density, color, pedicel length and blooming period: in flower form, size and petal quantity they tended towards their other cross-parents. Leaves of the hybrids in color, shape, size and thickness all tended towards C. amplexicaulis, but in petiole length tended to other cross-parents. Plant growth of the hybrids was very strong and had an obvious heterotic vigor. The resistances of the hybrids to hot and cold temperatures were greatly increased, compared to their cross-parents. It could be expected that not only the characteristics of the hybrids would be useful for gardening in the future, but also a reference could be provided for future breeding using C. amplexicaulis as a major cross-parent.

Acknowledgments

The authors would like to thank the managers of the Palm Landscape Architecture Co. Ltd. for financial support and to thank the project, Research on Flower Breeding and Regulate & Control of Blooming Period, Guangdong, China (Project Number: 2011A020102007) for its the strong support on techniques.

References

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