Pathogenic stability of Alternaria longipes (Ell. & Ev.) Mason subjected to different methods of isolation,storage and inoculum production

Summary The pathogenic stability ofA. longipes was greatest when the composition of the medium promoted maximum sporulation and minimal mycelial proliferation.A Whatman No. 17 filter paper disc saturated with an 0.1 % dextrose infusion medium from carrots and potatoes minimised mycelial proliferation, and promoted rapid and extensive spore production in two to four days at 25° C. Approximately 75% of the cultural period on 2% PDA was devoted to mycelial proliferation. The difference in extent of mycelial growth in the filter paper and standard methods was apparently instrumental in eliminating a decline in pathogenicity when using the former method. Weekly mycelial subculturing on 2% PDA caused rapid drop in pathogenicity and a total loss of pathogenicity and sporulative ability between the 62nd and 76th day.The use of a modified filter paper method for large scale inoculum production for greenhouse and field variety trials is discussed.