They would be RR1 beans.


From the link below:


We applaud Kip on demonstrating the yield potential of today's elite soybean varieties," said Paul E. Schickler, president – Pioneer Hi-Bred, a DuPont business.
   "We're especially proud that Kip used a high-yielding Y Series soybean variety from Pioneer. His achievement shows how genetics and crop management play a role in higher yields."

http://www.worldrecordsacademy.org/society/most_bushels_of_soybeans_per_acre_of_yield_Kip_Cullers_sets_world_record_101927.html