Glucosinolates in cauliflower as biochemical markers for resistance against downy mildew

Abstract

Glucosinolate contents were quantified by HPLC in three susceptible (Billabong, Fanch and Jakavan) and two resistant (C300 and Maudez) cauliflower plants (Brassica oleracea var. botrytis) infected by Peronospora parasitica to determine a possible correlation between glucosinolates and resistance against downy mildew. Uninfected plants were used as controls. Three aliphatic (glucoı̈berin, sinigrin and glucoı̈berverin) and four indole glucosinolates (glucobrassicin, 4-methoxyglucobrassicin, 4-hydroxyglucobrassicin and neoglucobrassicin) were detected. Six days after inoculation with downy mildew spore suspension, the glucosinolate pattern of susceptible and resistant varieties differed. Sinigrin content was higher in resistant varieties than in susceptible ones. Glucobrassicin and methoxyglucobrassicin amounts expressed as a percentage to total indole glucosinolates were compared in infected and healthy seedlings. The susceptible seedlings exhibited a 12% decrease in glucobrassicin and a 25% increase in methoxyglucobrassicin when compared with healthy ones six days after treatment whereas no difference in glucobrassicin and a 10% increase in methoxyglucobrassicin were observed between healthy and inoculated resistant seedlings. Based on the ratio between methoxyglucobrassicin and glucobrassicin, resistant varieties were distinguished from susceptible ones. The susceptible varieties had a ratio greater than 1.5 but the resistant varieties showed a ratio of less than 1. This feature can be readily utilised as a biochemical inducible marker in screening seedlings resistant/susceptible to P. parasitica.