Will people be eligible to apply for PGDM BM at XLRI, Jamshedpur if one has secured less than 50% in their graduation?

Having friends at XLRI, I can only suggest you keep in mind these few facts if you're passionate about getting into any high-quality B-School. 

• Understand that people at B-Schools care about your marks very seriously.
• The competition level at any B-School would be so intense that the panel would not just consider people with a great academic background. They would take a month/year's work experience into consideration, too.

The status that XLRI or any great B-School carries would not be put at risk by admitting candidates who do not have a quality academic background. You have to at least maintain a minimum of the criteria that these institutes demand. 

• Recruiters that approach these reputed B-Schools for placements belong to different firms. For instance- Finance (Citibank, SoftBank, Goldman Sachs Group); Consulting (PWC, BCG, McKenzie); Marketing (P&G, Nestlé, HUL), and others. 
• These companies check the candidate's academic background. 
• The minimum percentage level they take into consideration for shortlisting is 60% at the graduation level. If your score is beyond that and you have been a university topper, it would be a plus.

Because of the reputation factor, FMS/XLRI/SPJIMR, etc. would not put their reputation at stake by admitting students with a poor academic background. Therefore, instead of focusing on that, it will be wise to focus and perform well in other exams like - MICAT, NMAT, SNAP, IIFT, CAT, XAT so that you can get a call from any one of the top 20 B-Schools of India. 

Despite a 50% score in your graduation, you still think about getting into a reputed institute like XLRI. This shows how much faith you carry in yourself.