PATHOGENIC VARIATION IN USTILAGO SCITAMINEA CAUSING SUGARCANE WHIP SMUT IN EGYPT

Abstract

1- The main symptom of sugarcane whip smut disease is characterized by production of a long whip –like structure from the apex of the affected stalk plant . The whip length vary from several centimeters to more than one meter and the short ones are straight or slightly curved. The structure is pencil – like in thickness , unbranched and is made up of a fairly hard core of parenchyma and fibrovascular elements surrounded by millions of black teliospores enclosed in earlier stages within a thin silvery membranous sheath.

2- Disease survey in Minya , Sohag , Qena and Luxor governorates showed that, the highest incidence (5.5%)was observed in Minya (Abu Qurqas county ) in sugarcane crop season 2010, the lowest incidence (0.25% ) was observed in Sohag (EL Balyana county )in 2012. Generally the disease incidence was lesser in sugarcane crop season 2012 than others.

3- Teliospores of the four isolates was morphologically similar in shape and color using light microscopy . Spore diameter located between 7.2 to 7.9 µm.

4- Teliospores of the four isolates was morphologically similar in shape, outer surface using scanning electron microscopy. Spore diameter located between 5.6µm to 6.5 µm.

5- Growth of the four isolates of Ustilago scitaminea on four different agar media , PDA, YGC , Malt extract and Sugarcane juice was similar in each medium ( sector , color and edge shape ) but differ from each other on radial growth on various media . Luxor isolate differed from Sohage isolate on PDA . Qena isolate differed from Minya , Sohag and Luxor isolates on YGC . Qena isolate differed from Sohag and Luxor isolates on Malt extract medium . Finally , Luxor isolate differed from Minya isolate on sugarcane juice agar medium . 6- Pathogenicity test was carried out in green house , the more virulent isolate ( on GT54-C9 variety ) was Luxor where disease incidence was 28% followed by Minya isolate 21% , Qena isolate 20%and finally Sohag isolate was 7%.