Received: 11 June, 2012. Accepted: 3 October, 2012. Original Research Paper Medicinal and Aromatic Plant Science and Biotechnology ©2013 Global Science Books Effect of Foliar Application of Diammomium Phosphate on Morphological Characteristics and Constituents of Essential Oil of Mexican Marigold (Tagetes minuta L.) Marzieh Negahban 1 • Kamel Msaada 2* • Enayatollah Tafazoli 3 • Abdolrasool Zakerin 4 1 Islamic Azad University, Unit Jahrom, Jahrom, Iran and Young Researchers Club of Jahrom University, Iran 2 Laboratory of Bioactive Substances, Biotechnology Center in Borj-Cedria Technopol, BP. 901, 2050 Hammam-Life, Tunisia 3 Department of Horticultural Sciences, College of Agriculture, Shiraz University, Shiraz, Iran 4 Department of Horticultural Sciences, Islamic Azad University, Unit Jahrom, Jahrom, Iran Corresponding author: * msaada_kamel@hotmail.com ABSTRACT Pot trials were carried out in a greenhouse in Shiraz, Iran to determine the effect of foliar application of diammonium phosphate (DAP) on morphological characteristics and quality of essential oil (EO) of Mexican marigold (Tagetes minuta L.). DAP was applied at 0, 2.4, 4.8, 7.2, 9.6 and 12% (w/v). Growth parameters increased as DAP levels increased. The dry weight of shoots increased at 2.4% DAP. At 7.2% DAP, the height, leaf area, length of axillary shoots and fresh weight of aerial parts peaked. Moreover, the number of axillary shoots, number of flowers per plant and the EO yield reached a maximum at 9.6% DAP. Regarding the EO constituents, the content of dihydro tagetone and Z-tagetone increased as DAP level increased while Z--ocimene and Z-ocimenone content decreased as the DAP level increased. The role of phosphorus as a central and pivotal metabolic and regulatory nutrient element is discussed. _____________________________________________________________________________________________________________ Keywords: Asteraceae, essential oil composition, growth parameters Abbreviations: DAP, diammomium phosphate; EO, essential oil INTRODUCTION Asteraceae is the largest family of vascular plants with more than 23,000 species (Jeffrey 2007), rich in secondary metabolites and essential oils (EOs) (Teixeira da Silva 2003, 2004; Teixeira da Silva et al. 2005). The genus Tagetes, with the common name of marigold, consists of 30-40 spe- cies that are endemic from Arizona to Argentina (Sefidkon et al. 2004). Mexican marigold (Tagetes minuta L.) is an annual plant belongs to the Asteraceae family. It is native of grasslands and mountainous regions of South America (Dole 1999), including Argentina, Chile, Bolivia, Peru, and in the Chaco region of Paraguay (Reiche 1903; Perkins 1912; McVaugh 1943; Soule 1993). T. minuta grows wild from spring to early winter when it completes its life cycle (Babu and Kaul 2007). The plants reach 1 to 2 m in height. Leaves are slightly glossy green, and are pinnately dissected into 4 to 6 pairs of pinnae. The undersurface of leaves bear a number of small, punctuate, multicellular glands, orangish in color, which exude a licorice-like aroma when ruptured. Glands may also be found on the stems and involucre bracts (Dole 1999). Fractions of T. minuta EO have the potential for aphid control and the EO also has the potential as a natural herbicide for managing rice weeds (Singh et al. 2003; Tomova et al. 2005; Batten et al. 2006; Pritekel et al. 2006; Batish et al. 2007). Due to its competitive nature, T. minuta is resistant to natural drought and survives easily on poor soils as a weed, although it is now also cultivated as a crop for agrochemical and pharmaceutical purposes (Hulina 2008). T. minuta plant organs contain allelochemicals that inhibit the germination and root growth of Acacia asak seeds (Arif and Alhammadi 2008). “New World” people were said to use T. minuta as a flavorful beverage, medici- nal tea, and a condiment since pre-contact times (Rees 1817). T. minuta is commercially grown and harvested for its EOs which are used in the flavor and perfume industry as “Tagetes oil”. The EO is used in perfumes, and as a flavor component in most major food products, including cola beverages, alcoholic beverages, frozen dairy desserts, candy, baked goods, gelatins, puddings, condiments, and relishes (Craveiro et al. 1988). Tagetes EO is used to treat chest infections, coughs and catarrh, dilating bronchi, facili- tating the flow of mucus and dislodging congestion and can be used in cases of skin infections (Chamorro et al. 2008; Meshkatalsadat et al. 2010). It has a healing effect on wounds, cuts, calluses and bunions (Singh et al. 2002). T. minuta is rich in many secondary metabolites, including acyclic, monocyclic and bicyclic monoterpenes, sesquiter- penes, flavonoids, thiophenes, and aromatics (Rodriguez and Mabry 1977). Various studies on T. minuta reported that there are variations in the EO composition according to the harvesting location, the growth stage and the different parts of the plant (Ester et al. 2008). EO compositions of T. minuta L. have biological activities against certain patho- gens (Kéita et al. 2000) and are well known for their bio- cidal properties (Gillij et al. 2008). Also, T. minuta has been reported to have antimicrobial activity against Staphy- lococcus aureus and Staphylococcus epidermidis (Katerere et al. 2012). It is used in the treatment of colds, diarrhoea and suspected liver ailments (Rios and Recio 2005). A. spi- nosus was used in the treatment of menorrhagia, gonorrhoea, eczema and colic (Azhar et al. 2004) and is also cited in the treatment of diabetes (Katerere and Eloff 2005). Previous studies showed that the secondary compounds in Tagetes are effective deterrents of numerous organisms, including fungi, fungi pathenogenic on humans, bacteria, round worms in general, trematodes (Wang et al. 2003), nema- todes (Hamawi et al. 2004), and numerous insect pests through several different mechanisms (Scrivanti et al. 2006; Krueger et al. 2010; Meshkatalsadat et al. 2010). The anti- ®