Leptosphaeria maculans semi-quantitative disease scale (LeMaSQ)

This scale includes nine categories of symptoms referred to as disease scores of L. maculans on B. napus or B. carinata. Category 1 includes isolates displaying non-adapted phenotypes, unable to infect the plant efficiently, Category 2 includes isolates displaying intermediate phenotypes, that are able to cause symptoms but with a late resistance response from the plant; and Category 3 represents isolates displaying adapted phenotypes, able to infect the plant efficiently. The first category, “non-adapted”, covers the phenotypic lesions caused by non-adapted isolates on the infected plant cotyledons (the plant is resistant) and encloses scores 1, 2, and 3. Score 1 corresponds to a hypersensitive response (HR), i.e. the isolate was not able to colonize the plant and the infection was stopped at the inoculation site; Score 2 corresponds to a small necrotic lesion (slightly larger than a HR), very dark in colour and limited just around the infection site; Score 3 corresponds to a medium-size necrosis, very dark with a bit of grey which shows a tissue collapse. The second category, “intermediate”, covers the phenotypic lesions caused by intermediately-adapted isolates on the infected plant cotyledons (the plant displays an intermediate resistance phenotype) and encloses scores 4, 5 and 6. Score 4 corresponds to medium-size necrosis, very dark with a bit of grey showing collapsing tissues but with the appearance of a few pycnidia (this could highlight a situation of stress in which the fungus is attempting to survive by producing pycnidia despite the induction of plant defences); Score 5 represents a medium-size macule (necrosis) with a light grey centre and a dark edge, showing a black margin corresponding to a late defence reaction of the plant; Score 6 represents a medium-size macule with a light grey centre and a dark edge, showing a black margin corresponding to a late defence reaction of the plant with the appearance of a few pycnidia (suggesting that the fungus is attempting to survive on the plant). Finally, the third category, “adapted”, covers phenotypic lesions caused by adapted isolates on the infected plant cotyledons (the plant is susceptible), and encloses scores 7, 8 and 9. Score 7 corresponds to a weak light grey symptom, meaning the fungus is aggressive on the plant; Score 8 represents a medium to large macule of light grey colour, and Score 9 represents a large macule of light grey colour carrying numerous pycnidia.