English

Abstract

Azaleas are among the most important ornamental shrubs in Europe (Scariot, 2007), America and East Asia, which contain thousands of cultivars with various flower morphotypes and flowering patterns. In China, it could be chased back to the Tang Dynasty when our ancestors started to enjoy its beauty (Zhou, 2013a). Nowadays, the areas of commercial production for azaleas have been expanded to more than 2500 hectares in China and over 350 million cuttings are propagated every year to meet the needs of landscaping and home cultivation (Zhou, 2010). In natural conditions, flower buds of azalea enter dormancy in winter to overcome the low temperature and usually bloom in April to May (Meijon, 2009). However, almost 80% to 85% floral products are sold during the Chinese New Year (Wang, 2014), which is mainly in January or February, the coldest month in a year. Thus, it is crucial to regulate the timing of flowering in azalea. It has been studied previously to find various ways to regulate dormancy and bud break by using different chemicals in the last few decades (Arora, 2003). Among these chemicals, gibberellic acid (GA) applications were proved to be efficient on dormancy-breaking by partly substituting the cold requirements in azaleas and other woody plants (Bodson, 1986; Chang and Sung, 2000; Yeo et al., 2012; Christiaens et al., 2012). It is also reported that DNA demethylation is involved during vernalization (Demeulemeester, 1999). The usage of 5-azacytidine (5-azaC) could lower the DNA methylation level by merging analogue in place of cytosine (Jones, 1985) and inhibiting the action of methyltransferase enzyme (Bouchard, 1983). In Burn’s (1993) experiment, Arabidopsis thaliana and Thlaspi arvense treated with 5-azaC turned up with an early flowering on nonvernalized plants, just reacted the same as those treated with cold. In some short-day plants, DNA demethylation caused by 5-azaC could also induce flowering (Kondo, 2006, 2007, 2010). As far as our understanding, 5-azaC has never been used to manipulate flowering in azaleas. In China, on a regular basis, flowering of azaleas is usually forced by temperature control (high temperature) or photoperiod manipulation. When the flower buds become dormant, only be released if their chilling requirements are satisfied (Christiaens, 2015). In view of global warming and expansive costs, cold storage is hard to accomplish in most of the production areas. We tried different combinations of 5-azaC and GA3 in this study to 1) document the morphological changes and flowering patterns of azalea under different treatments; 2) evaluate the effect of each treatment on promoting flowering; 3) analyze the endogenous hormones and global DNA methylation during Pak. J. Agri. Sci., Vol. 53(1), 1-6; 2016 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 DOI: 10.21162/PAKJAS/16.4717 http://www.pakjas.com.pk