Area under disease progress curve and apparent infection rate of Alternaria blight disease of Indian mustard (Brassica juncea) at different plant age

Abstract

Plant age has a major influence on the incidence of Alternaria blight disease in Indian mustard crops. Disease progression was monitored twice a week on the two chosen Indian mustard cultivars viz., Varuna and Rohini throughout the season. Severity of blight caused by Alternaria brassicae and Alternaria brassicicola decreased with delay in sowing. Calculation for A-value (Area under disease progress curve – AUDPC) and r-value (apparent infection rate) in crops sown on different dates could identify the speed of progress in the disease on leaves and pods, as the crop does not posses resistance to the pathogen till date. Thus, the probable dates of sowing enabling slow disease progress or the weather conditions coinciding with the different crop phenological stages demarcated the advantageous dates of sowing from the disadvantageous ones. However, cultivar Varuna is more susceptible as compared to the other cultivar Rohini, as apparent infection rate both on leaves and pods was higher in former. Highest per cent disease severity (PDS) for season highly correlated with date of sowing, i.e. delayed date of sowing increased PDS.

Keywords:

• Brassica juncea
• Alternaria brassicae
• AUDPC
• apparent infection rate

Acknowledgement

The authors are grateful to Director, National Research Centre on Rapeseed-Mustard (ICAR), Sewar, Bharatpur, Rajasthan, India for providing facilities to carry out the present study.