In an experiment, a researcher incubated plant tissue with a bacterial strain for different time durations followed by heat treatment to specifically kill the bacteria. The plant material was analyzed ten days after each experiment for appearance of disease symptoms. Results of this study, which was done in three replicates and with appropriate controls, are tabulated below.
| Duration of bacterial Incubation |
Heat treatment |
Disease symptom |
| 0(minus infection) |
+ |
NO |
| 0(minus infection) |
- |
NO |
| 12 hours |
+ |
NO |
| 12 hours |
- |
Yes |
| 24 hours |
+ |
NO |
| 24 hours |
- |
Yes |
| 48 hours |
+ |
NO |
| 48 hours |
- |
Yes |
| 72 hours |
+ |
Yes |
| 72 hours |
- |
Yes |
Which of the following statement/s is/are likely explanation/s of the above observations?
(i) The bacterium is incapable of causing infection in the absence of heat treatment.
(ii) Continuous contact with live bacteria is not essential to cause disease symptoms.
(iii) The bacterium undergoes spontaneous mutations to become heat-resistant.
(iv) Contact duration of 72 hours with live bacteria is essential to cause disease symptoms.
a. ii and iv only
b. i, iii and iv only
c. ii only
d. i and iii only
