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Raphael A. Stern and Shmuel Gazit

The lychee (Litchi chinensis Sonn.) has two types of pollen-releasing flowers—M1 and M2. We compared the morphology and viability of these two pollen types, mainly for the two commercial cultivars in Israel: `Mauritius' and `Floridian'. Observation by scanning electron microscope did not reveal any consistent morphological differences between the two pollen types. However, M2 pollen was found to have a consistent and significant advantage over M1 pollen in in vitro germination tests. M2 pollen from `Mauritius', `Floridian', `No Mai Chee', `Wai Chee', and `Early Large Red' had a much higher germination rate at 15, 20, 25, 30, and 35 °C than M1 pollen from those same cultivars. The optimal incubation temperature for in vitro pollen germination was 30 °C for M2 pollen of all five cultivars studied; adequate germination rates were also found at 35 and 25 °C. The optimal temperature for M1 pollen germination was also 30 °C for `Mauritius' and `No Mai Chee', but was not well defined for the other three cultivars. No pronounced advantage of M2 pollen-tube growth could be discerned 48 h after hand pollination. However, final fruit set was consistently and significantly higher after hand pollination with M2 pollen, relative to M1 pollen. Hot (32/27 °C) and warm (27/22 °C) regimes during flower development had a pronounced detrimental effect on pollen viability compared to a cool (22/17 °C) regime. `Floridian' was much more susceptible than `Mauritius' in this respect.

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Raphael A. Stern and Shmuel Gazit

Pollination of lychee (Litchi chinensis Sonn.) by the honeybee was studied in Israel's two commercial cultivars, `Mauritius' and `Floridian'. Pollination rate, which was determined in a mixed `Mauritius' and `Floridian' plot, followed a consistent pattern: it was low at the first male (M,) `Mauritius' bloom and reached a high value only when the pseudohermaphroditic (M2) `Mauritius' bloom started. Pollen density on bees collected from `Mauritius' inflorescences was very low during the M, bloom and increased to very high values during the M2 bloom. These results indicate that the `Mauritius' M, bloom does not play an important role as a source of pollen for pollination. Pronounced, significant, and consistent differences in nectar volume per flower and sugar concentration in the nectar were found between M1, M2, and female (F) `Mauritius' flowers. Values were very high in F flowers, medium in M2 flowers, and low in M, flowers. Accordingly, the density of bees found on inflorescences was high during the F bloom, intermediate during the M2 bloom, and low during the M1 bloom. The positive correlation between bee density and sugar concentration in the nectar was highly significant for M2 and F `Mauritius' flowers. The nectar contained three sugars: glucose (43%), fructose (39%), and sucrose (18 %). This ratio was the same in nectar from M1, M2, and F `Mauritius' flowers.

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Chemda Degani, Ruth El-Batsri and Shmuel Gazit

Forty-one (Mangifera indica L.) cultivars were characterized electrophoretically using the isozyme systems aconitase, isocitrate dehydrogenase, leucine aminopeptidase, phosphoglucose isomerase, phosphoglucomutase, and triosephosphate isomerase. The outcross origin of some of the mango cultivars was supported by the isozymic banding patterns. Reported parentage of some other cultivars was not consistent with their isozymic banding patterns.

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Chemda Degani, Ruth El-Batsri, Raphael A. Stern and Shmuel Gazit

Fruits produced in two commercial lychee (litchi chinensis Sonn.) orchards consisting of adjacent blocks of `Floridian' and `Mauritius' were analyzed for pollen parentage by phosphoglucose isomerase (PGI) isozyme system. 'Mauritius' and `Floridian' were found to possess distinguishable homozygous isozyme phenotypes in PGI, thus allowing the unequivocal identification of their progenies as originating from self- or cross-pollination. The rates of hybrids produced in the two orchards were 69% and 87% for `Floridian' and 17% and 65% for `Mauritius'. In both cvs a significant correlation was found between pollen parent and the weights of fruits and seeds. Fruits originating from cross-pollination were heavier and contained heavier seeds than selfed fruits. The most pronounced effect of the pollen parent on seed weight was found in `Floridian, which appears to exhibit inbreeding depression.

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Chemda Degani, Menashe Cohen, Ruth El-Batsri and Shmuel Gazit

Leaf phosphoglucose isomerase (PGI) isozymes from 139 cultivars and seedlings of mango (Mangifera indica L.) were analyzed by starch gel electrophoresis. Six distinct banding patterns of PGI-2 consisting of single- and triple-banded phenotypes were detected. The genetic control of PGI-2 isozymes were inferred from segregating progenies of self-pollinated parent cultivars having triple-banded phenotypes. Comparison of the banding patterns of PGI-2 isozymes extracted from the pollen and the leaf of the same heterozygous cultivar demonstrates the allelism of the Pgi-2 locus.

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Catherine M. Ronning, Raymond J. Schnell and Shmuel Gazit

The native American genus Annona contains many species that are cultivated in the tropics and subtropics for their edible fruit, including the custard apple (A. reticulata), soursop (A. muricata), cherimoya (A. cherimola), sugar apple (A. squamosa), and the interspecific hybrid, Atemoya. Random Amplified Polymorphic DNA (KAPD) analysis of the A. cherimola cultivars `Jete' and `Campa, 1A. squamosa `Lessard', and the Atemoya cultivars `Ubranitzki', `Mallali', and `Kaspi' resulted in very distinctive patterns, indicating that RAPD markers are an easy, efficient method of fingerprinting Annona species. Thirteen of 15 primers gave repeatable, polymorphic patterns. An F1 population of `Jete' × `Lessard' as well as selfed populations of `Jete' and of `Lessard' were analyzed to determine the inheritance of the KAPD banding patterns. The results indicate that PAPD analysis can be used in genetic and phylogenetic studies of Annona species.

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Raphael A. Stern, Daniel Stern, Moshe Harpaz and Shmuel Gazit

Application of TP as Tipimon® or TPA as Maxim® at the young fruitlet stage significantly increased yield in three lychee (Litchi chinensis Sonn.) cultivars: `Mauritius', `Floridian', and `Kaimana'. Application of TP followed by TPA a week later increased yield more than did either substance alone. In all experiments, TPA increased fruit size and weight, relative to both controls and TP-treated trees. The increased yield did not prevent the increase in fruit size. Use of sprays of TPA may be an effective way of satisfying the market demand for large lychee fruit. Chemical names used: 2,4,5-trichlorophenoxypropionic acid (TP); 3,5,6-trichloro-2-pyridyloxyacetic acid (TPA).

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Emanuel Lahav, Eli Tomer, Shmuel Gazit and Uri Lavi

Most fruit-tree breeding projects are based on selection of seedlings in regard to their performance. The selected seedlings are vegetatively propagated, usually by grafting. It is highly important for the breeder to know whether the performance of the grafted tree will resemble the performance of the original seedling. In this study the performance of avocado and mango seedlings was compared with that of their grafted duplicates. Significant differences were found in only 8 out of 36 avocado traits and 2 out of 10 mango traits. Significant seedling x graft interaction was detected in 10 other avocado traits. These differences were considered of no practical significance, since their magnitude was of minor importance for the breeder. The conclusion for avocado and mango breeders is that for most traits selection could be carried out on ungrafted seedlings.

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Uri Lavi, Emanuel Lahav, Chemda Degani and Shmuel Gazit

Avocado (Persea americana Mill.) progeny that originated from 11 crosses (both self-pollinations and crosses between cultivars) were evaluated for the length of their juvenile period. Time to first flowering, “flowering age,” and time to first fruit production, “fruiting age,” were recorded for each progeny. The mean values for both ages, the sd, and the progeny distribution were calculated. Significant statistical differences in flowering age and fruiting age between various progeny populations were detected. No differences were detected between self-pollinated plants and crosses. The time until first flowering was found to be the limiting factor in evaluation of seedlings.

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Uri Lavi, Emanuel Lahav, Chemda Degani, Shmuel Gazit and Jossi Hillel

Genetic variance components for avocado (Persea americana Mill.) traits were estimated to improve avocado breeding efficiency. The additive and nonadditive genetic variance components were calculated from the variances between and within crosses. In all nine traits examined, i.e.-anise scent, fruit density, flowering intensity, fruit weight, harvest duration, inflorescence length, seed size, softening time, and tree size-a significant nonadditive genetic variance was detected. Additive genetic variance in all traits was lower and nonsignificant. The existence of major nonadditive variance was indicated also by narrow-sense and broad-sense heritability values estimated for each trait. Therefore, parental selection should not be based solely on cultivar performance. Crosses between parents of medium and perhaps even low performance should also be included in the breeding program.