The rate of 'Mauritius' litchi fruit development and abscission was studied over three consecutive seasons. Two pronounced abscission waves were observed. The first started at the end of the female bloom and ended about four weeks later. Female flowers abscised at a rate of 85-90% during this period. Most of the abscised fruitlets were devoid of embryo and/or endo-sperm. After a lull of about a week, the second abscission wave began, lasting about two weeks. Approximately 5% of the female flowers survived this wave, Most of the abscised fruit-lets had embryos. The second wave coincided with the period of rapid replacement of endosperm by embryo. Auxin (2,4,5-TP) was very effective in increasing marketable fruit yield when applied during the lull between the two abscission waves, At that time fruitlets weighed about 2 g. A longitudinal cut revealed an embryo already visible to the naked eye, at the micropylar end of the seed cavity.
Unpicked avocado fruit showed no response to ethylene treatments given at 50 ppm for 48 hr. Picked ‘Hass’ fruit did not respond to ethylene treatments given immediately after harvest. A good response was observed to treatment given 25 or 49 hr after harvest. This may be explained by assuming the existence of an endogenous factor inhibiting ethylene action.
Seedless fruitlets of ‘Fuerte’ and ‘Ettinger’ avocado (Persea americana Mill.) (5 to 20 mm length) exhibited a typical degeneration pattern of the ovule which began at the chalaza and spread toward the micropylar region but stopped when about half of the integument was still intact. Embryo or endosperm or both were found in many seedless fruitlets. Degeneration was found to start at different stages of fruitlet development, from a proembryo to an embryo starting to develop cotyledons. Typical seedless fruit in ‘Fuerte’ and ‘Ettinger’ avocado appears to be the outcome of seed degeneration (stenospermocarpy) and not parthenocarpy.
Normal, abnormal, and degenerate ovules of avocado (Persea americana Mill.) are described and illustrated. The frequency of occurrence of these ovule types differed among 4 cultivars (‘Fuerte’, ‘Ettinger’, ‘Hass’, ‘Tova’) with a total frequency ranging from 15 to 40%. A higher frequency of apparently degenerative ovules increased the proportion considered defective to 80–98%. No relationship could be discerned between the percentage of normal ovules and the yields of 8 trees differing widely in fruitfulness.
The segregation pattern of individuals originating from selfing of several monoembryonic cultivars and one polyembryonic line indicated that polyembryony in mango was of genetic nature. All the plants originating from monoembryonic cultivars bore monoembryonic fruits. A one-monoembryonic to three-polyembryonic segregation pattern was observed among individuals originated from the polyembryonic line, indicating that polyembryony in mango is under the control of a single dominant gene.
The inheritance of five polymorphic enzyme systems, aconitase (ACO), isocitrate dehydrogenase (IDH), phosphoglucose isomerase (PGI), phosphoglucomutase (PGM), and triosephosphate isomerase (TPI), was studied in selfed progenies of four mango (Mangifera indica L.) cultivars and selections. Only in `Haden' did the allozymes of all of the studied loci segregate in the expected Mendelian ratios. Distorted segregations were present in the other cultivars at some loci; three of the five analyzed in `Edward' showed distorted segregations, as did two of three loci in `13/1', and both loci in `21/6'. The distorted ratios in `Edward', a descendant of `Haden', did not appear to be associated with gametic selection because pollen viability in both of these cultivars was high. The five enzymic loci were not linked to one another in `Edward', `13/1', or `21/6'. In `Haden', however, Pgi-2 and Aco were linked, with a distance of about 19.4 map units.
The reciprocal effect of two avocado (Persea americana Mill.) cultivars—Ardith and Ettinger—on outcrossing rate and yield was studied in several orchards in Israel. Multilocus estimates of outcrossing rates were made using the isozyme loci Mdh-1 (malate dehydrogenase) and Aat-1 (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 outcrossing rates ranged from 0.71 to 0.89 and from 0.87 to 0.90 for `Ettinger' and `Ardith', respectively. The effect of `Ettinger' as a pollenizer 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 distance of 36 m in another orchard. These results confirm previous observations that `Ettinger' is a highly potent pollenizer. Outcrossing rates in `Ardith' and `Ettinger' were found to increase from the young fruitlet stage to that of mature fruit. These findings provide evidence for selective abscission of selfed fruitlets. In addition, parentage analysis 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 progeny due to inbreeding depression.
Shortening the juvenile period is highly important for fruit tree breeding projects. Four girdling dates were tested in an attempt to shorten the juvenile period in 9 crosses of 3-year-old avocado (Persea americana Mill.) seedlings. Early September girdling was more effective than later or no girdling. It increased flowering intensity significantly, increased the percentage of seedlings that set from 15% to 66%, and increased 7-fold the number of fruits harvested per seedling as compared with the ungirdled control.