Two diterpenoids produced in rice leaves upon Magnaporthe grisea infection, momilactones A and B have received particular attention for their antifungal activity against this fungus, the casual agent of the devastating rice blast disease [27-29]. Another group of similar diterpenoids named oryzalexin A–D were identified as rice phytoalexins also in M. grisea infected leaves [30-33]. Later, orzyalexin S and orzyalexin E and F were discovered as additional diterpenoids with potent antifungal

activity [34-37]. Five cassane diterpenoids phytocassane A-E were found to increase upon M. grisea infection and Inhibitors,research,lifescience,medical present at higher concentrations in resistant strains in addition to having antifungal activity against another pathogenic fungus Rhizoctonia solani [38]. A recent study collected volatile organic compounds (VOCs) released by oat, barley and wheat in response to infection by three Fusarium species including two species that cause cortical Inhibitors,research,lifescience,medical rot disease of wheat. Piesik et al., measured

the VOCs using GC-MS identifying two terpenes linalool (Figure 1) and β-caryophyllene to be present at higher concentrations in infected tissue than controls [39]. The same authors carried out a similar study in maize identifying three additional terpenes induced Inhibitors,research,lifescience,medical upon infection, β-pinene, β-myrcene and Nutlin3 Z-ocimene [40]. A substantial amount of research into linalool synthesis and natural production has been undertaken due to its aroma and flavour in flower and vegetables for the application of perfume manufacture to metabolic engineering in tomatoes [41,42]. However, little is known Inhibitors,research,lifescience,medical regarding its involvement in plant pathogen interactions and the mechanism is assumed to be similar to other terpenoids for which evidence suggests interference and disruption of membranes [43-46].

Piesik et al. also demonstrated Inhibitors,research,lifescience,medical the ability of infected plants to lead to an increase in VOCs in uninfected neighbours. Control of VOC release in plants has significant potential for the management of crop pathogens. An early study of volatiles in wheat showed it contained the same major terpenoid species as oat and barley [47]. The utility of recent technological advances analysing VOCs using solid phase microextraction (SPME) and headspace techniques for the analysis of terpenes and other volatiles has been demonstrated over [48]. Investigation into terpenoids with antifungal activity against two maize pathogens Fusarium graminearum and Colletotrichum graminicola identified geranic acid (Table 1), which had a minimal inhibitory concentration of 7.8 μg/mL and is the most potent antifungal towards these two pathogens discovered [49]. In an attempt at metabolic engineering to increase resistance of maize to these pathogens, the enzyme geraniol synthase was cloned and overexpressed.