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.
C. Degani, R. El-Batsri and S. Gazit
R.J. Schnell, C.M. Ronningl and C Degani
To investigate the usefulness of RAPDs for determining parentage in mango, progeny arising from caged trees of the cultivars Keitt (FS1) and Kent (FS2) were analyzed. In the FS1, 110 bands were generated, of which 78 (70.2%) were repeatable. Of these 78 loci, 23 were variable and segregated 3:1 as expected. In the FS2, 142 bands were generated, of which 57 (40%) were not repeatable, 6 (4.2%) were present in the progeny but not in the parent, and 79 (56%) were repeatable. Thirty-nine of these loci were variable; however, only 21 segregated as expected. Apparently, the progeny arising from the caging of `Keitt' are the result of self-pollination, while those arising from caged `Kent' are not. The six bands found in the FS2 but not in `Kent' are reproducible and, along with the 46% anomalous segregation, indicate that cross-pollination did occur. The implications for mango breeding efforts are discussed.
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.
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.
E. Lahav, U. Lavi, C. Degani, D. Zamet and S. Gazit
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 22.214.171.124) 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.
E. Tomer, U. Lavi, C. Degani and S. Gazit
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.
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 126.96.36.199) 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.