Screening of onion accessions for Stemphylium blight resistance under artificially inoculated field experiments

Onion ( Allium cepa L.) contributes more than 50% of the net export earnings among fresh vegetable exports in India. Stemphylium blight and purple blotch are the most destructive fungal diseases in the tropics and cause 80–90% losses in bulb and seed crop. Our aim was to screen multiple onion accessions against Stemphylium blight under artificially inoculated conditions, assess morphological and biochemical traits and correlate the observed trait with disease incidence. Screening of fifty-nine accessions resulted in identification of ‘Pusa Soumya’ ( A. fistulosum L.) and ‘Red Creole2’ ( A. cepa L.) as moderately resistant and ‘Red Creole1’ as susceptible. Highest marketable yield was recorded in ‘AFW’ (28.00 t/ha) followed by ‘Punjab Naroha’ (25.85 t/ha) in New Delhi, whereas in Karnal, ‘AKON555’ (45.85 t/ha) performed best. Pooled analysis revealed highest marketable yield in ‘PWF’ (44.56 t/ha). These varieties have exhibited field tolerance and in the absence of credible resistance can be recommended for areas where Stemphylium blight is the major problem. Significant variation in foliage weight, gross yield, marketable yield, dry matter, total soluble solids, total phenolic content and pyruvic acid content were recorded between non-inoculated and inoculated field trials which suggests the devastating effect of this disease on onion crop. Pearson’s correlation coefficient exhibited that percent disease index (PDI) was significantly and positively correlated with average bulb weight, gross yield, marketable yield. Significant negative correlation ( r = −0.30) between dry matter and PDI ( p < 0.05) and significant negative correlation ( r = −0.35) between ATP (total foliar phenols after inoculation) and PDI were observed. This signifies that dry matter and total foliar phenol content can be used as a biochemical marker for high throughput screening against Stemphylium blight at preliminary screening stage. Further, ‘Pusa Soumya’ and ‘Red Creole2’ can be used as parent material to study the inheritance mechanism and for breeding of Stemphylium blight resistant onions under short day tropical conditions.