Hybridization and Cutting of Buddleja Genus

Buddleia davidii, also known as butterfly bush, is a unique species in China, with extensive cultivation and promotion values. The purpose of cross-breeding is to promote environmental adaptation and improve its economic benefits as a garden plant.. As Buddleja is asexual, cutting can aid in mass production of the hybrid offspring, thus stabilising local ecosystem.


Introduction
Buddlejoideae, under the family of Scrophulariaceae, is a widely cultivated and extremely popular flowering shrub with attractive foliage, diverse colours and strong aroma. As a member of Buddlejaceae, the genus Buddleja has about 100-150 subspecies (e.g. Buddleja davidii, B. lindleyana, B. japonica, B. × weyeriana) that is distributed in north andsouth America, south and east Africa, as well as south-central and southeast Asia (Sandra B. Wilson et al. 2004). There are about 100 species in the world and about 23 species in Asia, of which 21 species are distributed in China (Chen et al., 2007). Out of these species, B. davidii Franchet is the most common.
B. (Synonyms. Buddleia davidii; also known as butterfly bush) is a perennial, semi-deciduous, multistemmed shrub that readily establishes in disturbed areas of temperate, subtropical, and tropical climates. Native to central and southwestern China The use of native plants as ornamental would help avoid invasions from exotic species. The local ecosystem of China as a whole consists of biocenosis and the environment they live in, which could adjust and organize itself to maintain balance through adaptation and development. Failures of introduced species to adapt to the local ecosystem and potential unrestricted growth factors may eventually threaten other species, breaking down balance of the local ecosystem (Shi & Liu, 2013).

Aim of the research
The idea of using native plant is important. Therefore, Buddleia davidii, as a local species of China, is worth promoting. The paper also I focused on cross-breeding of this genus and asexual reproduction through hybridization and cutting.
The purpose of cross breeding aims at facilitating the adaption to the external environment and improve its economic benefits as a garden plant by perfecting its appearance. Cutting can help mass-produce hybridization as it is asexual, thus stabilising the local ecosystem.

The previous research and development of the breeding and cutting of Buddleja genus:
Breeding: Starting as early as 1920, Buddleja davidii breeding programs have been focusing on the scale of breeding and diverse colours under harsh conditions for plantation (Tallent-Halsell & Watt, 2009). Meanwhile, the hybridization programs are concentrating on the traits of flower colours, inflorescence morphology, compact growth habits and grey pubescent foliage.
These breeding programs generally include intergeneric hybridization, physical breeding, bioengineering, and chemical breeding. Thirdly, bioengineering has played a significant role in breeding development. Researchers used genetic engineering techniques to create hybrids with dwarf or non-functional reproductive organs or heavier seeds that are not carried by the wind. In addition, Lindstrom have sought to reduce potential invasions by producing hybrid varieties that either alter plant morphology or have an odd ploidy number (Tallent-Halsell & Watt, 2009). Introgression of flower colour in B. davidii is made possible by polyploidisation and interspecific hybridisation. There was an interspecific breeding programme with B. globose that introduced yellow in the commercial B. davidii assortment through introgression.
Interspecific crosses between chromosome doubled B. globosa genotypes and B. davidii produced a progeny with yellow flower colour resembling B. davidii, which offers new opportunities for Buddleja breeding programmes (Laere et al., 2011).
Finally, for chemical breeding, a study in 2007 determined that oryzalin could be used to restore fertility and alter morphological traits such as flower size or growth habit of other Buddleja species as longer and more intense exposure could lead to greater chromosome doubling potential (Dunn & Lindstrom, 2007) Cutting: There are a number of cutting programs of Buddleja in China. Liu et al. (2008) conducted orthogonal experiments on cutting propagation of four B. davidii breeding lines. The result showed that all the four lines belonged to the lenticel rooting family. In the two media, the soil mixture composed of clay and sand in equal proportion + perlite had a positive effect on rooting rate while peat soil+ perlite had a positive effect on rooting number. The study shows that the root number is positively correlated with rooting length.
Xu (2015) investigated three substrates and two rooting agents, and carried out cutting experiments on B. davidii by random combination. The results showed Peat soil: sand (1:1) matrix and Guoguang rooting agent works more effectively for cuttings breeding of B. davidii. Zhang et al. (2017) studied the suitable cutting matrix of Buddleja by experimenting with different ratios of vermiculite, perlite, sand and soil. The results showed that the strong permeability of sand is beneficial to the growth of root elongation due to strong permeability of perlite and strong water conservation in soil. The combination of the two can increase the number of rooting and maintain moisture to increase the survival rate.

Research Hypothesis
• Hybridization of Buddleja

Conclusion
The table of results shows that as of August 22, 2018, 62% of the pollinated ovaries had expanded, as expanded. However, weather conditions and unavoidable states of the flowers could hinder pollination. Therefore, Buddleja is likely to expand further in more parts of China. This process of crossbreeding could facilitate Buddleja's adaption to the environment and boost its economic use as a garden plant, thus stabilising the local ecosystem.