vijay.ete, have you utilized the Excel Add-in before? With it, I am able to extract the defect, parent, grandparent data along with the discussions.
Query: Defect Discussions
Query Type: Conversation Post
Order: Creation Date
Columns: CreationDate,PostNumber,Text,Artifact.FormattedID,Artifact.Name,Artifact.Description,Artifact.Requirement.FormattedID,Artifact.Requirement.Name,Artifact.Requirement.Feature.FormattedID,Artifact.Requirement.Feature,User,Artifact.Owner,Artifact.Project,Artifact.ScheduleState,Artifact.State,Artifact.CreationDate,Artifact.InProgressDate,Artifact.AcceptedDate