Seed treatment with salicylic acid invokes defence mechanism ofHelianthus annuusagainstOrobanche cumana

Abstract

The root holoparasitic angiosperm sunflower broomrape (Orobanche cumana) specifically affects sunflower (Helianthus annuus) growth and causes severe damage all over the world. This investigation was designed to examine the protective effects of salicylic acid (SA) treatment to the seeds of an O. cumana-susceptible cultivar of sunflower (TK0409). Sunflower seeds were pretreated with different concentrations (0, 0.5 and 1 mM) of SA and inoculated with O. cumana for 4 weeks. O. cumana infection resulted in reduction in plant biomass, endogenous SA level, and the expression of SA-related genes including pal, chs and NPR1. By contrast, O. cumana infection enhanced the production of reactive oxygen species, activities of antioxidant enzymes as well as contents of phenolics and lignin. Seed treatment with 1 mM SA increased sunflower biomass in terms of plant height, fresh weight and dry weight by 10%, 13% and 26%, respectively, via reducing the number and biomass of established O. cumana. The increase of hydrogen peroxide contents by 14% in the 1 mM SA treated sunflower plants appeared to be because of the inhibition of ascorbate peroxidase and catalase by exogenous SA. The enhanced expression of pathogenesis-related genes (PR3 and PR12, encoding chitinase and defensin, respectively) after 4 weeks of inoculation indicated that systemic acquired resistance was induced in the SA treated sunflower in which the level of endogenous SA was also elevated in a dose-dependent manner. The increased expression of a hypersensitive-responsive (HR) gene hsr indicated that the resistance of sunflowers might be associated with a hypersensitive reaction which was activated by exogenous SA treatment.(H 2 O 2 ) in O. cumana-infected sunflowers promote an oxidative burst during the interaction of sunflower and O. cumana . Rapid production of ROS is seen as an indicator of successful recognition of infection by plants, leading to the activation of the plants' defence mechanism (Torres et al., 2006;Torres, 2010). Accumulation of H 2 O 2 in peas infected by Orobanche crenata was observed by using both biochemical and cytochemical techniques (Pérez-de-Luque et al., 2006;Mabrouk et al., 2007). However, Mor et al. (2008) found that ROS detected at the interaction site on Arabidopsis thaliana infected by Orobanche aegyptiaca probably originated from the parasite, which was important for 408 Ann Appl Biol 169 (2016) 408-422

Recent research progress in combatting root parasitic weeds

“…However, a foliar application of BTH did not complement the loss of SA in NahG rice plants, suggesting that BTH and endogenous SA may have different effects on S. hermonthica resistance in rice [24]. Sunflower seeds pretreated with SA and then grown in pots containing O. cumana seeds showed an increased biomass via reducing the number and biomass of established O. cumana, suggesting that the treatment invokes a defence mechanism of the host against the parasite [205].…”

Induction of systemic resistance in tomato against broomrape (Phelipanche aegyptiaca)

“…Sunflower seed treatment with SA reduced the Orobanche cumana biomass and improved sunflower growth. Moreover, SA treatment increased hydrogen peroxide content in sunflower by 14% (Yang et al, ). Thereby, there is disagreement in determining the role of signalling pathways against broomrape.…”

“…These cases showed that broomrape does not activate the SA pathway. Interestingly though, the artificial activation of the SA pathway slightly increased the host's resistance to broomrape (Hurtado, 2004 (Yang et al, 2016). Thereby, there is disagreement in determining the role of signalling pathways against broomrape.…”

Plant seeds are primed by herbivore-induced plant volatiles

“…Seed treatment with JA also changes the volatile composition of mature plants, making their blends more attractive to predatory mites (Smart et al , 2013). Similarly, seed treatment with salicylic acid (SA) enhances the expression of SA-related genes and the endogenous SA level against root holoparasite ( Orobanche cumana ) (Yang et al , 2016). Additionally, seed coating with plant growth promoting rhizobacteria (PGPR) and plant growth promoting fungus (PGPF) enhances seed germination, seedling establishment, and boosts induced defenses in future plants in SA-, ET-, and JA-dependent manners (Ryu et al , 2004; Rudrappa et al , 2010; Sharifi & Ryu, 2016).…”