Protease activity for identification of Colletotrichum species causing chilli anthracnose in Thailand
W. Winyarat, R. Pongpisutta, C. Rattanakreetakul
Acta Horticulturae 973: 173-180: 2013.
2013
บทคัดย่อ
Protease activity of Colletotrichum species causing chilli anthracnose was tested on casein hydrolysis medium (CHM) and casein from bovine milk medium (CBM). Fifty eight isolates of Colletotrichum species were identified to three species as C. acutatum, C. capsici, and C. gloeosporioides. Each isolate produced an enzyme digest in both substrates with clear zones developing around the fungal colonies. When the clear zones were assessed on CHM, C. acutatum produced the greatest diameter of 10.10 mm, while C. gloeosporiodes and C. capsici produced clear zones of 2.78 and 1.85 mm diameter, respectively. When the clear zones were assessed on CBM, C. acutatum and C. gloeosporiodes produced clear zones of 4.62 and 0.93 mm diameter, respectively, whereas C. capsici produced no clear zone. Protease activity was detected in 1% CBM. This result indicated that C. gloeosporiodes produced the greatest protease activity of 6.67 units/mg, while with C. capsici and C. acutatum the activity was 4.03 and 3.63 units/mg, respectively. Inoculation tests were carried out on two varieties of chilli fruits, ‘Bangchang’ and ‘Jinda’, with mycelial discs (MD) and conidial suspensions (CS). The results showed that MD inoculation with C. acutatum and C. gloeosporiodes on ‘Bangchang’ fruits resulted in 100% disease incidence, whereas C. capsici showed 96.67%. Inoculation tests on ‘Bangchang’ using MD inoculation with C. acutatum, C. capsici, and C. gloeosporiodes showed diseased areas of 16.55, 16.06, and 3.85%, respectively, while percent of diseased area using CS inoculation was 7.44, 6.27, and 3.76%, respectively. There was no relationship between clear zone production and protease activity, and disease severity. Fungal enzymes may not increase disease severity but may be a minor factor in causing fungal infection in the host plant. Moreover, CHM is recommended to be used for simple identification of the three species of Colletotrichum affecting chilli.