SPREAD OF ENDOSEPSIS IN CALIMYRNA FIG ORCHARDS

Pollination of the edible fig (Ficus carica cv. Calimyrna) is mediated by a small symbiotic wasp, Blastophaga psenes, that inhabits the syco nium cavity of the spring crop of fig pollinator trees (caprifigs). Th ese fig wasps also carry propagules, mainly of Fusarium verticillioide s (formerly F. moniliforme) and other Fusarium spp., which cause endos epsis, from pollinator figs to the edible Calimyrna figs in California . Spread of endosepsis was studied in one experimental and up to four commercial Calimyrna fig orchards from 1989 through 1995. The incidenc e of endosepsis in fruit collected from the tree canopy at either <2.0 m (low) or >2.0 m (high) height, from the north and south of the tree canopy, and from the outer (direct sunlight) and inner (shaded) canop y were similar. More wasps were captured in fig trees located 3.5 to 1 0 m east or west of the source than in trees 48 to 63 m from the sourc e. In addition, significantly more wasps entered the syconia of trees closest (9 to 12.7 m) to the source than the syconia of the second or third trees (18 to 38.2 m) from the source. Endosepsis decreased with distance from the source, decreasing faster to the south than in other directions from the source. In addition, the disease-vectoring wasps decreased with increased distance from the source, which also describe d the disease spread from the contamination source for most directions , with a sharper decline south of the source. A 3-year study in three commercial Calimyrna orchards showed there is no secondary spread of f ig endosepsis in the field. Although endosepsis can complete as many c ycles (three to four) as its vector in fig pollinator trees, in Calimy rna figs it is considered a monocyclic disease. Because fig wasp polli nators prefer to stay close to the contamination source when receptive Calimyrna figs are available in close proximity, only disease sources (caprifigs trees) found among Calimyrna trees or at a distance less t han 50 m from the borders of Calimyrna orchards affect endosepsis inci dence in commercial orchards.