Brown Spot of Potato Caused by Alternaria alternata: an Emerging Problem of Potato in Eastern India

Several black to brown colored spots especially on leaf lamina were noticed on the potato crop at an experimental field of Banaras Hindu University, Varanasi (India) during 2015. Such symptoms were reported as brown spot of potato caused by Alternaria alternata elsewhere in the world. To understand the extent of such symptoms, a roving survey was carried out during the 2016 cropping season in thirteen districts of Uttar Pradesh and two districts of Bihar and the presence of brown spot symptom across the region with the percent disease index (PDI) ranging from 17.77 to 40.00% was observed. Forty isolates obtained from surveyed locations grouped into four categories viz., non-pathogenic (10), low pathogenic (09), moderately pathogenic (08) and highly pathogenic (13) based on the pathogenicity test. However, morphologies of 30 pathogenic isolates were found to be similar with A. alternata. The identity of those 30 isolates was further confirmed by PCR using A. alternata specific primers. On the other hand, phylogenetic analysis of rDNA sequence of 13 pathogenic isolates from the present study and published sequences of A. alternata and other related fungi retrieved from GenBank, NCBI has confirmed the identity of brown spot of potato from the surveyed location as Alternaria alternata.