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

Fruits produced in two orchards, each consisting of adjacent blocks of `Floridian' and `Mauritius' lychee (Litchi chinensis Sonn.), were unequivocally identified as selfed or outcrossed by phosphoglucose isomerase (PGP; EC 5.3.1.9) isozyme analysis. The average rate of hybrid production in each orchard was 69% and 87% for `Floridian' and 17% and 65% for `Mauritius', respectively. The percentage of hybrids produced on trees adjacent to those of the other cultivar was invariably significantly higher than that produced on the more distant trees. However a significant correlation between hybrid percentage and proximity to the other cultivar, as well as between hybrid percentage and yield, was found only for `Floridian' in one of the orchards. A significant correlation was found between pollen source and the weights of fruits and seeds in both cultivars. Fruits originating from cross-pollination were heavier and contained heavier seeds than selfed fruits. The most pronounced effect of pollen parent on seed weight was found in `Floridian', which appears to exhibit inbreeding depression.

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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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A. Dag, D. Eisenstein, S. Gazit, R. El-Batsri and C. Degani

Postzygotic self-incompatibility has been reported in several Indian mango (Mangifera indica L.) commercial cultivars. Floridian cultivars, on the other hand, have been planted in solid blocks and seem to be self-fertile. Isozyme analysis enabled us to determine outcrossings rates at the fruitlet and fruit stages in the Floridian `Tommy Atkins' (`Tommy'). Two commercial mango orchards consisting of adjacent solid blocks of `Maya' and `Tommy' were studied. This combination offered a unique opportunity to identify each individual fruitlet or fruit as selfed or outcrossed by TPI isozyme analysis. A consistent and significant increase in outcrossing rate during fruit development was found: the average outcrossing rate increased from 10% and 13% in fruitlets to 66% and 73% in mature fruit in the two `Tommy' blocks surveyed. This 6-fold increase is the result of selective abscission of selfed progeny. A significant inverse correlation was found between the distance of `Tommy' trees from the `Maya' block and the outcrossing rate in mature fruit. No significant correlation between distance from `Maya', or outcrossing rate, and yield was observed, suggesting that the practice of planting `Tommy' in solid blocks is sound.

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C. Degani, A. Beiles, R. El-Batsri, M. Goren and S. Gazit

Leaf isozyme banding patterns were studied in 30 cultivars and selections of lychee (Litchi Chinensis Sonn.) by means of starch gel electrophoresis. Polymorphism in aconitase, aspartate aminotransferase, isocitrate dehydrogenase, phosphoglucomutase, shikimate dehydrogenase, superoxide dismutase and triosephosphate isomerase is demonstrated for the first time and observations are extended for the previously described polymorphism in phosphoglucose isomerase. In this study we found five groups of cultivars with identical electrophoretic genotypes. The 18 different cultivars were clustered by the UPGMA method into two large clusters and three pairs of similar cultivars. Three cultivars were relatively separate from the clusters. This study shows that isozyme polymorphism is a prevalent phenomenon in lychee, and that isozymes can provide useful genetic markers for lychee cultivar identification and parental analysis.