Studies on the Blackleg Disease of Potato in the Libyan Jamahiriya

Abstract

Symptoms of blackleg disease have been found recently on potato (Solanum tuberosum L.) in the Libyan Jamahiriya. These symptoms occur at different parts of the country’s north-west region where most of potato plantations are located.
Isolation trials of the causal organism revealed the presence of a Gram-negative, non-spore former, motile, rod-shaped bacterium, 0.5 — 0.7 x 1 — 2/x. Its colonies on nutrient agar were round, white, smooth, glistening and butyrous. It grew at 25°Cbut not at 37°C, liquified gelatin, utilized citrate as a sole source of carbon, reduced nitrate to nitrite and was able to produce hydrogen sulfide but not indole or phenylpyruvic acid. Also it was able to ferment glucose, sucrose, fructose, maltose, mannito, with the production of acid only. Voges Proskauer test was positive while the methyl red test was negative.
The isolated bacterium was able to rot potato tubers and to cause the development of blackleg symptoms when stems of vigorously growing plants were inoculated under green house conditions. The symptoms developed after 4-5 days of inoculation.
The results obtained indicate that the isolated organism was the blackleg bacterium, Erwinia carotovora var. at rosept ica (Hellmers and Dowson) Dye, 1969.
The sensitivity of two isolates of the causal bacterium to different antibiotics was also studied. Both isolates were found sensitive to tetracyclin, gentamycin, ampicillin, kanamycin, neomycin. However, one isolate was resistant to penicillin and chloramphenicol, and the other one was resistant to penicillin and streptomycin.