Table 1 Overview of disease components used to target different stages of northern leaf blight (NLB) development.

Incidence of multiple

appressoria^a

The incidence of > 1 appressorium

developed from each germinated

conidium (%)

Pre-penetration

Trypan blue staining and

microscopy

[25, 42]

Infection efficiency

The incidence of successful

infection per germinated

conidium (%)

Penetration into the epidermal cell

Trypan blue staining and

microscopy, KOH-aniline blue

fluorescence microscopy

[25, 42, 94]

Accumulation of

callose and

phenolics^a

Diameter of enhanced fluorescing

area surrounding the infection

site (μm)

Intercellular and intracellular hyphal

growth from primary infected cell

to surrounding mesophyll cells

KOH-aniline blue fluorescence

microscopy

[43]

Vascular invasion

efficiency^a

The incidence of hyphae entering

vascular bundles per

infection site (%)

Hyphal growth into the vasculature

KOH-aniline blue fluorescence

microscopy

[43]

Fungal biomass ratio^a

The percentage of fungal DNA

divided by the total DNA in the

infected leaf tissues (%)

Overall fungal growth in leaves before

the appearance of necrotic lesions

DNA-based real-time

quantitative PCR

[44]

Incubation period (IP)

The number of days from

inoculation to the appearance of

the first lesion on a plant (days)

Xylem plugging due to extensive

hyphal growth in the vascular veins

Visual examination

[73, 74, 76–78, 95]

Lesion expansion (LE)

The longitudinal expansion of a

lesion per day (mm)

Destructive hyphal growth in primary

inoculated leaves

Digital caliper measurement

[78, 96]

Diseased leaf

area (DLA)

The percentage of infected leaf

area of the entire plant,

disregarding decayed bottom

leaves (%)

Destructive hyphal growth on the

leaves of a entire plant, caused by

primary and secondary inoculum

Visual examination

[73, 76, 77, 94, 97]

Disease severity^b

The severity of infected leaf area

of the entire plant (scale 1-10, 1:

little diseased area)

Destructive hyphal growth on the

leaves of a entire plant, caused by

primary and secondary inoculum

Visual examination

[98]

Area under the

disease progress

curve (AUDPC)

Total area under the graph of DLA

or other disease severity rating

(area unit)

An overall destructive hyphal growth

on a plant throughout the season

Calculated from visual

examination scores

[76, 77]