First Record of Black Dot Disease Caused by Colletotrichum coccodes on Potato Plants in Egypt

Black dot is an important disease of potato that affects all plant parts. The disease was observed for the first time at Salhiya and Abo Swair locations in potato fields irrigated with pivot system during 2009/2010 season. Therefore, this study was initiated to investigate the ability of black dot disease to develop and spread on potato plants grown under Egyptian field conditions. Six fungal isolates were identified as Colletotrichum coccodes ((Wallr.) S. Hughes), obtained from two locations in Ismailia Governorate. Pathogenicity tests with the six isolates indicate that isolate CCS-3 was the most virulent one, recorded 100 % wilt of potato plants, while isolate CCA-3 was the weakest one recorded 50.4%. The virulent isolate CCS-3 showed the highest number of sclerotia compared with other isolates. The optimum growth temperature for C. coccodes isolates was 30oC. At low temperatures (5 to 10 °C), the fungal growth was very limited after 8 to 14 days of incubation. Number of acervuli or sclerotia was observed during the first 8 days of incubations at 5, 10, 15 and 20°C. Abundant acervuli and sclerotia were formed during 20-30 days after incubation at 15 to 20 °C. The sensitivity of C. coccodes to eight fungicides in vitro revealed that the fungicides Octave WP, Euparen M50% and Switch M were the most effective ones as no fungal growth was observed at all tested concentrations.The survival percentage of C. coccodes sclerotia decreased above soil surface as compared to those burred below soil surface at 10 and 20 cm depth during June 2010 till June 2011. The obtained results indicate that sclerotium was able to survive in soil for at least one year. This is the first report of black dot disease caused by C. coccodes in Egypt.