OUTCROSSING RATE, YIELD, AND SELECTIVE FRUIT ABSCISSION IN ETTINGER AND ARDITH AVOCADO PLOTS

The reciprocal effect of two avocado (Persea americana Mill.) cultivar s-Ardith and Ettinger-on outcrossing rate and yield was studied in sev eral orchards in Israel. Multilocus estimates of outcrossing rates wer e made using the isozyme loci Mdh-1 (malate dehydrogenase) and Aat-l ( aspartate aminotransferase) for 'Ettinger' progeny and Lap-2 (leucine aminopeptidase), Pgm-1 (phosphoglucomutase) and Tpi-1 (triosephosphate isomerase) for 'Ardith' progeny. When the two cultivars were in close proximity, estimated yields ranged from 10 to 20 t.ha(-1) and outcros sing rates ranged from 0.71 to 0.89 and from 0.87 to 0.90 for 'Ettinge r' and 'Ardith', respectively. The effect of 'Ettinger' as a pollenize r was not restricted to adjacent 'Ardith' trees; it also reached more distant 'Ardith' trees. Thus, outcrossing rate in 'Ardith' was 0.82 at a distance of 30 m from 'Ettinger' in one orchard and 0.91 at a dista nce of 36 m in another orchard. These results confirm previous observa tions that 'Ettinger' is a highly potent pollenizer. Outcrossing rates in 'Ardith' and 'Ettinger' were found to increase from the young frui tlet stage to that of mature fruit. These findings provide evidence fo r selective abscission of selfed fruitlets. In addition, parentage ana lysis of abscised versus retained 'Ardith' fruit showed that 'Ardith' selfed fruit abscised at a much higher rate than outcrossed ones. The survival advantage of outcrossed fruit is probably related to the fact that selfed progeny have less-vigorous embryos than outcrossed progen y due to inbreeding depression.