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R.A. Stern and S. Gazit

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.

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C. Degani, R. El-Batsri, and S. Gazit

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.

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C. Degani, R.A. Stern, R. El-Batsri, and S. Gazit

Fruit produced by adjacent blocks of `Mauritius' and `Floridian' lychee (Litchi chinensis Sonn.) were sampled at four different stages of development and the embryos were analyzed for pollen parentage by phosphoglucose isomerase (PGI; EC isozyme system. Hybrid percentage increased significantly from ≈5 weeks after fruit set to maturity as follows: from 29.5% to 76.3% in `Mauritius' and from 74.2% to 92.5% in `Floridian'. These findings clearly indicate selective abscission of selfed fruitlets. In `Mauritius', yield was not related to the distance from the pollenizer block or hybrid percentage. In `Floridian', yield of trees adjacent to the `Mauritius' pollenizer was higher by 36% than that of trees at a distance of 24 m. The correlation between `Flordian' yield and hybrid percentage tended toward significance (r= 0.64, P = 0.08). In addition, in both cultivars, fruit and seed weights were affected by the pollen parent: outcrossed fruit were heavier and contained heavier seeds than selfed ones.

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C.M. Ronning, R.J. Schnell, and S. Gazit

The native American genus Annona contains many species that are cultivated for their edible fruit, including the custard apple (A. reticuluta L.), soursop (A. muricata L.), cherimoya (A. cherimola L.), sugar apple (A. squamosa L.), and interspecific hybrids, the atemoyas. RAPD analysis of A. cherimola. `Campa' and `Jete,' A. squamosa `Lessard,' and the atemoyas `Ubranitzki,' `Malali,' and `Kaspi' resulted in very distinctive patterns, indicating that RAPD markers, may be an efficient method of fingerprinting genotypes within and between Annona species. All 15 primers used generated repeatable, polymorphic patterns. An F1 population of `Jete' × `Lessard' was analyzed to determine the inheritance of the RAPD banding patterns. Fifty-two polymorphic loci were identified, which segregated in an expected Mendelian fashion.

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R.A. Stern, J. Kigel, E. Tomer, and S. Gazit

Fruit development and abscission in `Mauritius' lychee (Litchi chinensis Sonn.) were studied over three consecutive seasons. Each season, two distinct abscission periods were observed. The first started at the end of full female bloom and continued for ≈ 4 weeks. Of the initial number of female flowers, 85 % to 90 % abscised during this period. The second period began after a lag period of≈ 1 week and lasted ≈ 2 weeks. About half of the remaining fruitlets abscised during this wave. AU of these fruitlets contained an embryo. The second wave coincided with a period of rapid embryo growth and endosperm loss. Tipimon (a commercial product containing the triethanolamine salt of the synthetic auxin 2,4,5-TP) consistently and significantly increased marketable fruit yield when applied between the two abscission periods. Chemical name used: 2,4,5 -trichlorophenoxy propionic acid (2,4,5 -TP).

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A. Adato, D. Sharon, U. Lavi, J. Hillel, and S. Gazit

DNA fingerprint information was used for identification of mango (Mangifera indica L.) cultivars for genetic relatedness analysis of20 mango cultivars and for genetic analysis of a family structure. Genomic DNA was extracted from young leaves, digested with Hind III or Dra I, and hybridized with 10 different DNA probes. Jeffreys' minisatellite probe 33.6 was the most useful, resulting in well-resolved bands representing highly polymorphic loci. Specific patterns were obtained for each cultivar. The probability of obtaining a similar pattern for two different cultivars was 9.4 × 10-6. Based on DNA fingerprint information, genetic distances between 20 mango cultivars were evaluated and an evolutionary tree was established. Analysis of DNA fingerprint band patterns of 12 progeny resulting from a cross between `Tommy Atkins' and `Keitt' mango revealed neither linked nor allelic bands. Application of the reported results for identification, genetic analyses, and mango breeding is discussed.

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E. Tomer, U. Lavi, C. Degani, and S. Gazit

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C. Degani, E. Lahav, R. El-Batsri, and S. Gazit

Single trees of several avocado (Persea americana Mill.) cultivars were caged with a beehive for the production of selfed progeny. Isozyme analysis was used to identify undesirable outcrosses in the planted progenies. Outcrossing rates were found to be highly variable, ranging from 0 to 0.86. Short accidental breaches in the net's integrity were suspected to be the main cause for the haphazard appearance of hybrids. Indeed, when `Tova', which consistently had progenies with a high rate of hybrids (averaging 0.58) was caged very meticulously, outcrossing rate was consistently low, averaging only 0.07. Apparently, short periods of accidental exposure to open pollination can result in a high percentage of outcrossed progeny, due to the higher survival rate of outcrossed fruitlets compared to selfed ones. The residual low outcrossing rate found with meticulous caging probably occurred through the penetration of floating foreign pollen from adjacent trees. Thus, the production of pure selfed progeny in avocado requires meticulous caging and the absence of foreign cultivars around the caged trees. In general, the fact that net caging was not fully effective in excluding foreign pollen should encourage the performance of parentage analysis to confirm the purity of progenies produced in net cages.

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Y. Aron, H. Czosnek, S. Gazit, and C. Degani

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.

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Y. Aron, S. Gazit, H. Czosnek, and C. Degani

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.