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Occurrence and extent of pistillate flower abscission (PFA) in persian walnut were investigated during 1996-1997 at the walnut genotype collection station, Seed and Plant Improvement Institute in Karaj. Similar observations were made in 1996 for PFA occurrence in walnut genotype collections in Mashhad, Shahrood and Oroumie. PFA occurred at very high levels in all orchards with considerably different levels of
occurrence among genotypes. The range of recorded PFA for genotypes was from 0 to 98%.The average PFA for genotypes significantly differed among different sites in 1996. Mean PFA for the same genotypes differed significantly from year to year for the two years 1996 and 1997 in Karaj. No relationship was found between the extent of PFA and any of the minerals. Thus, the nutritional conditions as indicated by standard
midsummer sampling did not appear to be related to PFA. Low positive correlations were found between PFA and pistillate flower density, flowering index, catkin density and vegetative points density.