Moreover, synthetic pesticides have been increasing to damage in human or animal body such as neurotoxicity, DNA damages in lymphocytes, leukocytes, and animal reproductive health, and must be metabolized, excreted, stored or bio-accumulated in body fat (McCauley et al. 2008; Nicolopoulou-Stamati et al. 2016; Bjorling-Poulsen et al. 2008; Shafer et al. 2005). Moreover, many researchers reported that these pesticides can be found in several foods and beverages for instance cooked meals, water, wine, fruit juices, refreshments and animal feeds (Cabras & Angioni 2000; Nag & Raikwar 2011; Witczak & Abdel-Gawad 2014). For these reasons, almost agriculturists were thus joined together for rejection of chemical pesticides and have been searching for new generation microcides from the natural sources. One of the natural sources can be found in the edible and medicinal plants as well (Tiwari et al. 2009). Higher plant species have usually comprised secondary metabolites (Jabeen et al. 2014; Cos et al. 1998). Phytochemical constituents are obtained from many parts of plants including flowers, leaves, stems, seeds, roots, barks and fruits (Akinmolandum et al. 2007; Pascaline et al. 2011). Plant extracts have potentially displayed for biological activities, especially; antimicrobial activity against bacteria, fungi and virus has been reported (Shan et al. 2007; Hafidh et al. 2011; Cushnie & Lamb 2005). Classes of natural products affecting on antimicrobial controlling were polyketides, fatty acids, terpenoids, steroids, phenylpropanoids, alkaloids, amino acids, carbohydrates and flavonoids (Jabeen et al. 2014; Schuh & Slater 1995).
Thailand locates in South-East Asia closed in the equinoctial line and has abundant of natural resources. Especially, there is a great diversity of plant species and their bioactivities have just been interested in many field researches. Thai plant species have been studied previously for antimicrobial activity focused mostly on clinical microorganisms (Thammajitasakul et al. 2014; Chomnawang et al. 2009; Kondo et al. 2010; Dholvitayakhun et al. 2012; Jarriyawattanachaikul et al. 2016; Norajit et al. 2007; Pongnaratorn et al. 2017). There have been scantly inclusive studies of Thai plants including Hednocarpus anthelminthicus Pierre ex Laness. (Achariaceae), Crataeva magna (Lour.) D.C. (Capparidaceae), Caesalpinia sappan L. (Leguminosae), Piper sarmentosum Roxb. (Piperaceae), Boswellia carteri Bird. (Bruseraceae) and Acacia farnesiana Linn. (Leguminosae-Mimosoideae) for anti-rice pathogenic bacteria and fungi against Rhizoctonia solani, Bipolaris oryzae, Xanthomonas oryzae pv. oryzae and X. oryzae pv. oryzicola (Jantasorn et al. 2016; Chanprapai & Chavasiri 2017; Udomsilp et al. 2009).
Previous studies focused only on testing on rice pathogenic bacteria or fungi. Moreover, P. sarmentosum was collected from another location that differed from our study (Chanprapai & Chavasiri 2017). Thus, this study was to extensively screen for antimicrobial activities against the important rice pathogenic bacteria and fungi including R. solani, B. oryzae, X. oryzae pv. oryzae and pv. oryzicola from other plants which have not been reported. The significance of this study was to screen for novel antimicrobial agents from extracts and essential oils of fourteen plant families collected from the central part of Thailand. This study could be used as a database or a primary step for selecting the effective extracts of Thai plant species to separate, purify and identify the eco-friendly agrochemical agents against rice pathogenic bacteria and fungi in the future.