EFFECT OF BION AND SALICYLIC ACID ON PEROXIDASE ACTIVITY AND TOTAL PHENOLICS IN TOMATO AGAINST Alternaria solani

Alternaria solani is the most destructive pathogen of tomato (Solanum lycopersicum L.) in the world (Khan, 2002), causing early blight disease and contributing to a heavy reduction in fruit yield (Abbasi et al., 2002). The Alternaria fungus can damage all plant parts including leaves, stem, twigs and fruits, ultimately affects the plant growth process (Abada et al., 2008). Fungicides are major source to control this disease. Nevertheless, the world is moving towards ecofriendly and less hazardous ways of disease management. Systemic acquired resistance (SAR) is a phenomenon useful against a wide spectrum of infective factors, including viruses, and it is played along with assembly of pathogenesisrelated proteins and facilitated through a salicylic acid (SA) based pathway (Hammerschmidt, 1999). SAR initiation starts from a few hours to few days and strengthens the plant for a long time during its development process. A systemic signal is necessary in fast and efficient response of tissues to the infection caused by some pathogen. This process is usually stated as "conditioning" (Métraux et al., 2002). Consequently, SAR protects the plants against several diseases through various defense related enzyme production and it can replace the typical fungicidal control of diseases, which are harmful to the environment. Benzothiadiazole with the trade name Bion is an ecofriendly and non-toxic resistance inducer effective against many pathogens, including viruses (Anfoka, 2000; Baysal et al., 2005). Bion is less toxic, quickly decomposable in plant tissue and human and nature friendly, thus can be applied in the field or greenhouse (Soylu et al., 2003: Cao et al., 2011). Oostendrop et al. (2001) reported that the Bion is the best abiotic inducer currently known. Salicylic acid (SA) is another key factor in triggering both local and systemic acquired resistance (Pieterse and Loon, 1999). SA application to the plants triggers the resistance induction enzymes and pathogenesis-related proteins that help to activate the resistance genes (Yao and Tian, 2005; Fernandes et al., 2006; Chen et al., 2006). When cucumber leaves were inoculated with some pathogenic microbes capable of SAR induction, amount of SA significantly increased in hypocotyl and roots of the cucumber plant (Kubota and Nishi, 2006). SA found effective in activating SAR in sweet cherry fruit against Penicillium expansum (Xu and Tian, 2008). Biochemical changes involved in initiating SAR by resistance inducers can act as marker of induced resistance (Hashem and Abo-Elyousr, 2011). These include increase of phytoalexins, cross linkages of cell wall with lignin (Thangavelu et al., 2003), and increase in certain defense related enzyme (He et al., 2002). The enzyme peroxidase (POD) has been involved in the program cell death, the formation of papillae, and the polymerization of lignin from monomeric lignols (Shah et al., 2004). Comparison of foliar application and seedling root Pak. J. Agri. Sci., Vol. 57(1), 53-62;2020 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 DOI:10.21162/PAKJAS/20.2020 http://www.pakjas. com.pk