Pretreatment with Chitosan Prevents Fusarium Infection and Induces the Expression of Chitinases and Β-1,3-glucanases in Garlic (allium Sativum L.)

Fusarium infection decreases the yield of garlic (Allium sativum L.); however, the knowledge about garlic response to fungal attack is limited. Chitosan induces plant defense response to stress conditions. Here, we analyzed the effects of chitosan with low (Ch1, 39 kDa) and medium (Ch2, 135 kDa) molecular weight on Fusarium infection in garlic. Ch1 and Ch2 at concentrations 0.125–0.400 mg/mL suppressed the growth of Fusarium proliferatum cultures in vitro. Pretreatment of garlic bulbs with Ch1 or Ch2 prevented disease symptoms after F. proliferatum inoculation, while exerting early inhibitory and late stimulatory effects on chitinase and β-1,3-glucanase activities. Ch1/Ch2 treatment of garlic already infected with F. proliferatum caused transcriptional upregulation of chitinases and β-1,3-glucanases at the early stage, which was maintained at the late stage in Ch2-treated samples, but not in Ch1-treated samples, where transcriptional inhibition was observed. The stimulatory effect of Ch2 pretreatment on the expression of chitinase and endo-β-1,3-glucanase genes was stronger than that of Ch1 pretreatment, suggesting that Ch2 could be more effective than Ch1 in pre-sowing treatment of garlic bulbs. Our results provide insights into the effects of chitosan on the garlic response to Fusarium, suggesting a novel strategy to protect garlic crop against fungal infection.