Abstract
Six isolates of Colletotrichum gloeosporioides f.sp. manihotis obtained from anthracnose-infected cassava stems in six different cassava-growing locations of Akwa Ibom State were examined in the laboratory for morphological and physiological differences. The isolates were then screened in the greenhouse for virulence on cassava variety NR 8083 widely grown in Akwa Ibom State. Six-week old cassava plants were inoculated with 1ml of the spore suspension of each isolate of the pathogen at a concentration of 104 conidia/ml using a sterile hypodermal needle. One injection of inoculum was made at five different internodes of each cassava stem at an ambient temperature of 300C and relative humidity of 80%. Results of laboratory examinations showed that mycelial growth on potato dextrose agar (PDA) medium was fastest (10.65mm/day) in isolate CGM 2 from Ikono and slowest (7.29mm/day) in isolate CGM 6 from Uyo. Sporulation of the isolates on PDA medium under alternate light and dark regimes was highest (9.30 x 106 spores/ml) in isolate CGM 4 from Nsit Atai and lowest (1.23 x 106 spores/ml) in isolate CGM 5 from Oruk Anam. Percentage spore germination and conidia length were highest (85.64% and 23.55µm) respectively in isolates CGM 4 from Nsit Atai and CGM 1 from Essien Udim and lowest (49.86% and 13.75µm) in isolate CGM 3 from Itu and isolate CGM 2 from Ikono, respectively. Results of greenhouse inoculations showed variations in lesion size for the different isolates. The largest (15.30mm) lesion was produced by isolate CGM 4 from Nsit Atai, followed by isolate CGM 1 (12.60mm) from Essien Udim. There were no significant (p> 0.05) differences in lesion size for isolates CGM 3 (8.63mm) from Itu, CGM 2 (8.45mm) from Ikono and CGM 6 (8.41mm) from Uyo. Lesion size was smallest (5.00mm) in isolate CGM 5 from Oruk Anam. Isolate CGM 4 of C. gloeosporioides f.sp manihotis from Nsit Atai which showed the highest sporulation density and percentage spore germination, one of the longest conidia and largest lesion size on inoculated cassava stems, appeared to be the most virulent of the six isolates of the pathogen in Akwa Ibom State during this investigation. Key Words: Fungal variability, fungal virulence, C olletotrichum gloeosporioides f.sp. manihotis, cassava, anthracnose
Highlights
The cassava anthracnose disease (CAD) caused by Colletotrichum glocosporioides f.sp manihotis is one of the most important and widely distributed fungal diseases of cassava, worldwide (Lozano et al; 1981; Daudi and Saka, 1995)
This study shows that isolate CGM 4 (Nsit Atai) was the most pathogenic on cassava variety NR 8083 among the six isolates tested
Alvarez et al (2005) in their studies on soursop anthracnose disease caused by C. gloeosporioides, reported that slow growing isolates of the pathogen were more pathogenic than isolates with higher mycelia growth rates
Summary
The cassava anthracnose disease (CAD) caused by Colletotrichum glocosporioides f.sp manihotis is one of the most important and widely distributed fungal diseases of cassava, worldwide (Lozano et al; 1981; Daudi and Saka, 1995). In Nigeria, incidence of the disease has been reported in Ibadan in Oyo state, described by Owolade et al; 2005 as a high infection zone for CAD. The disease has been reported from Kwara, Ogun, Ondo, Plateau, Osun and Cross River States (Fokunang, 1995). In Africa, the CAD is of major importance because of its ability to cause stem damage in cassava. In Nigeria, the disease was reported to have so reduced the amount of healthy plantable stems available to farmers, that a search for resistant cassava varieties was embarked upon (Ikotun and Hahn, 1994)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
