Latest update from Google, i just did it to my blog. Details by Blogger team as below:
Bringing Google+ Comments to Blogger
Writing a thoughtful post and seeing how people engage can be really rewarding, so we’ve made it easier to reach a broader audience and see more of their reactions.
Once you enable Google+ Comments, people can share the comments they make on your blog to their circles in Google+, helping you reach people that they know. And there's more: mentions of your posts on Google+ automatically show up right in your blog's comments, so you can see more of people’s public conversations about your content (and private conversations you’re part of).
Here's how to add Google+ Comments to your blog:
|1.||Sign in to Blogger|
|2.||Click on the “Google+” tab in your blog’s Dashboard|
|3.||Upgrade to Google+ if you haven’t already done so|
|4.||Enable Google+ Comments. Comments already made on your posts will keep working in the new widget|