Assessing detached onion leaves inoculated with Alternaria porri (Ellis) Cif. through visual and electronic means

Abstract

Spring onions are among the most valuable crops exported from Egypt. Inoculation of detached onion leaves with Alternaria porri (Ellis) Cif. provided an accurate and rapid method of disease severity assessment. This approach is proved superior in maintaining leaf vitality over an extended period compared to the control method. Two assessments of purple blotch disease severity were compared on detached onion leaves inoculated with A. porri, a quantitative assessment made via a visual assessment and a computer-based image analysis made by two raters. The image analysis provided a precise measurement of the percent lesion area of infected leaves. There was a strong positive correlation coefficient between the visual and Digital image raters (DIR) assessment (R2 =0.99). After applying the best sterilization, incubation method, detached leaf, and propagule concentration to 10⁶ml A. porri isolates. The results showed that isolate Ay-03 had higher virulence (3.1 cm ±0.37a), (70%±12.91a), (63.5%±12.31a), (62.5%±20.81a), (100%), and (2 day±0.25a) respectively compared to the other isolates for the assessment of lesion length, disease severity (visual, rater1 and rater2), disease incidence, and incubation duration.