This project was designed to determine if 4. hindsii (Northern California black walnut) pollen could be used to pollinate 4. regia to enhance set without risking the transmission of the virus causing walnut blackline disease. Pollen from 4. hindsii was applied to young 'Chandler' orchards in Tulare county in 1989 and 1990 and in Butte County in 1990. In each case, no or minimal catkin bloom was present on the 'Chandler' trees and no catkins were present on the 'Franquette' trees planted as pollinizers in the orchards. The experimental trees in the Tulare county experiment were separated by at least 9 trees and by 11 trees in the Butte county orchard. Pollen was applied at the rate of 2 grams per tree per treatment with 4 or 5 treatments every other day to cover the period of pistillate bloom. Flowers tagged prior to their receptive period were scored for fruit set. In 1989, trees that received the black walnut pollen had a statistically significant 15% increase in set over control trees. In 1990 no increases over controls occurred in either Tulare or Butte. Isozyme analysis of the 1989 samples indicated that the nuts obtained from the experimental trees did not have ,J. hindsii as the pollen parent. Only four nuts from the 1989 experiment have been analyzed by RFLPat this time. These results are consistent with selfing by 'Chandler.' In one of the four cases, the results are consistent with apomictic set. Further analysis is currently underway to determine the extent to which apomixis, induced by the 4. hindsii pollination stimulus, is a factor.