The Horner rootstocks originated about 30 years ago when nurseryman David Horner developed more than 500 selections in a remote area of western Oregon. They were open-pollinated crosses of OHxF 40, 51, 87, 333, and 339. Dr. Bill Proebsting, horticulturist with OSU in Corvallis, evaluated them initially for their ease of propagation. Those that were difficult to bulk up were discarded. In 1995, horticulturists at the Hood River station began to prescreen 13 of the rootstocks for tree size, yield, and fruit size. They also looked for 'fatal flaws' such as too much root suckering and susceptibility to fire blight or Pseudomonas. The scion was d'Anjou, and the trees were spaced 8 by 18 feet. The control was OHxF.97, which Auvil said is similar to seedling. During the seven-year study, two of the rootstocks-Horner 4 and 10-were more productive than OHxF.97 and produced larger fruit.
From: GoodFruit Grower, September 2007