An olive rootstock planting was established in Tulare County, California in 1954 using 10 different rootstocks with ‘Sevillano’ as the scion variety. Verticillium wilt, a major problem in California olive production, became strongly established in this planting, affecting trees on the different rootstocks to a markedly different degree. All trees on 2 of the rootstocks, Olea ferruginea Royle and Forestiera neo-mexicana Gray were killed. No trees on a clonal rootstock, Olea europaea, ‘Oblonga’ were affected, while trees on the 7 other rootstocks showed intermediate survival percentages. Over a 15-year period, tree size and yields were influenced by the rootstock. ‘Sevillano’ trees, on their own roots, were the smallest as measured by trunk cross section area. There was no pronounced effect of rootstock on fruit size.
In another olive planting in Tulare County, California, the effect of various interstocks, inserted during a top-working operation, on the behavior of the scion cultivar was determined. No Verticillium wilt was apparent in any of the trees in this experiment. Each of 3 genetically dwarfed clonal stocks caused a significant dwarfing influence on the scion cultivar and a reduction in yields, in comparison with the scion cultivar itself used as an interstock. No influence on fruit size occurred. Similar results were noted with Olea chrysophylla Lamk. as an interstock but with severe constriction of the interstock tissue.
Controlled low temperature chilling caused flower initiation in container-grown olive (Olea europaea L.) trees at any time of the year. Optimum inflorescence production under controlled conditions occurred after exposure for 70 to 80 days to a diurnal sine wave temperature pattern, with a 2°C minimum and a 15°C maximum. These same temperatures, but changing abruptly from one to another failed to cause inflorescence formation. A constant intermediate temperature of 12.5°C was also effective in causing flower formation, but a continuous constant low temperature (7°C), or continuously high temperatures above 15°C failed to cause infloresence formation. The cv. Ascolano produced inflorescences under a wider range of temperature patterns than did ‘Manzanillo’.
Irregular bearing behavior of olives in California's Central Valley could not be attributed to varying winter chilling patterns. There was no correlation over a 7-year period between amount of winter chilling and subsequent crop size. Sufficient chilling occurs even in warmest winters there for ample flower initiation.