1133 Bulgarian Journal of Agricultural Science, 25 (No 6) 2019, 1133–1142 Physiological quality of Tithonia diversifolia (Hemsl.) A. Gray seeds as a function of harvest period and storage conditions Eduardo Pacca Luna Mattar 1* , Tiago Teixeira Vianna 2 , Wander Douglas Pereira 2 , Bruno Portela Brasileiro 3 , Paulo Cesar Hilst 2 , Denise Cunha Fernandes dos Santos Dias 2 1 Federal University of Acre, Rio Branco, Acre 69920-900, Brazil 2 Federal University of Viçosa, Department of Plant Science. Viçosa, Minas Gerais 36570-900, Brazil 3 Federal University of Paraná, Department of Plant Science and Phytosanitation. Curitiba, Paraná 80060-000, Brazil * Corresponding author: eduardo@ufac.br Abstract Mattar, E. (2019). Physiological quality of Tithonia diversifolia (Hemsl.) A. Gray seeds as a function of harvest period and storage conditions. Bulgarian Journal of Agricultural Science, 25 (6), 1133–1142 Tithonia diversifolia is a shrub of the Asteraceae family native to Central America and found on all continents. It has multiple functions with emphasis on use in animal feed and as a medicinal plant. It is usually propagated vegetative, with little information on seed propagation. For this reason, the aim of this study was to define the ideal time for harvesting the seeds and to evaluate the quality of the seeds according to time and storage condition. Therefore, achenes were collected on different days after the anthesis (14, 16, 18, 20, 22, 24, 28, 32, 36 and 40 days) of inflorescence. Following harvesting, the following variables were evaluated: seed dry matter mass, germination percentage, germination speed index, germination speed and percentage of full achenes. Moreover, these variables were analyzed as a function of two storage conditions (refrigerated and non-refrigerated environment) and two storage times (6 and 12 months). The ideal harvest period comprised the period from 28 to 36 days after anthesis, in which seeds with germination percentages exceeding 75% and percentage of full achenes of 100% were obtained. The chilled environment provided the highest percentages of seed germination. Moreover, germination speed increased throughout the storage time. The seeds showed a high percentage of germination after 12 months of storage, both in refrigerated and non-refrigerated conditions. Keywords: Asteraceae; medicinal plant; Mexican sunflower; multipurpose shrub; non-conventional forage; seed production Introduction Tithonia diversifolia (Hemsl.) A. Gray is a species of the Asteraceae family and native to Central America, being found on all continents (Winnifred & Morris, 2014). It is popularly known as daisy, buttercup, honey flower, or Mexi- can sunflower. It is a shrub that can reach 1 to 3 m in height and has multiple functions, especially for use in animal feed and as a medicinal plant. It is forage with a protein content of up to 28% and a digestibility of 65% (Peters et al., 2011) and is recommended as a food component for goats (Wambui, 2006) and dairy cattle (Ribeiro et al., 2016). Moreover, it is used in traditional medicine in several countries to treat diabetes, malaria, snakebite, measles, gastric ulcers, menstrual pain and wounds (Ajao & Moteetee, 2017). Its extracts have an anti-trypanosomal effect (Sut et al., 2018) and its essential oil was active against Staphylococcus aureus (Orsomando et al., 2017). In guinea pigs it improved immune response and reduced cholesterol and triglycerides (Ejelonu et al., 2017). It also has potential for use in plant phytosanitary control (Pulido et al., 2017; Zhao et al., 2017). Even though there is some information, lack of knowl- edge of simple techniques for sexual propagation and the poor supply of cuttings (asexual propagation) are the main