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- Author or Editor: Chemda Degani x
Using a malate dehydrogenase isozyme system, it was possible to identify the pollen donor parent in progenies of avocado (Persea americana Mill.) obtained by enclosing 2 cultivars of complementary flower type in a screenhouse with a beehive. The observed percentage of cross-pollination ranged from 7% to 92%. Isozymes are demonstrated to be a practical way of identifying hybrids.
Cultivars of fruit trees are vegetatively propagated in order to ensure a uniform crop with fruit of consistent quality. Unequivocal identification of the propagation material is essential for assuring the desired quality.
Outcrossing rate in a solid block of ‘Hass’ avocado (Persea americana Mill) was determined using the isozyme systems of malate dehydrogenase (MDH) (EC 126.96.36.199), leucine aminopeptidase (LAP) (EC 188.8.131.52), and triosephosphate isomerase (TPI) (EC 184.108.40.206), for which evidence concerning the genetic control of the latter is presented. Almost all ‘Hass’ mature fruits were found to have resulted from cross-pollination. Among the potential pollen donors—‘Hass’, ‘Ettinger’, and ‘Reed’—‘Ettinger’ excelled, producing almost all of the hybrid fruits.
Outcrossing rates in ‘Hass’ and Fuerte’ avocado (Persea americana Mill.) blocks were determined during fruit development using the isozyme systems of malate dehydrogenase (MDH, EC 220.127.116.11), leucine aminopeptidase (LAP, EC 18.104.22.168), and triosephosphate isomerase (TPI, EC 22.214.171.124) as genetic markers. Abscission of avocado fruitlets was selective and was greatly influenced by the pollen parent. Thus, in ‘Hass’ trees subjected to crosspollination by ‘Ettinger’ and ‘Fuerte’, the population of ‘Hass’ fruitlets 1 month after fruit set consisted mainly of ‘Hass’ selfs; however, during fruit development, the rate of ‘Hass’ selfs decreased and the rate of ‘Hass’ hybrid fruitlets produced by ‘Ettinger’ and ‘Fuerte’ increased. By the end of fruit abscission, the surviving mature ‘Hass’ fruits were mostly ‘Ettinger’ hybrids. The ‘Hass’ fruit yield was found to correlate significantly with the rate of outcrossing with ‘Ettinger’. When ‘Ettinger’ served as a pollen parent for ‘Fuerte’, the outcrossing rate in trees adjacent to ‘Ettinger’ was about 40%, which shows that cross-pollination among avocado cultivars of the same flowering group can be substantial at close proximity. The outcrossing rate in ‘Fuerte’ diminished with increasing distance from ‘Ettinger’, but no effect on yield was observed.
Evidence is presented suggesting that genetic selection could be an important factor in avocado fruitlet abscission. ‘Ettinger’ embryos (Persea americana Mill.) at different stages of fruit development were classified according to their leucine aminopeptidase (LAP) electrophoretic pattern in the Lap-2 locus. Analysis of several fruitlet populations showed significant deviations from the expected Mendelian ratio. The genotypic ratios at the different stages indicate genetic selection during fruitlet abscission.
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.
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.
The effects of various pollen parents on outcrossing rates, yield, and fruit and seed weights were studied in a `Fuerte' avocado (Persea americana Mill.). Isozyme analysis was used to identify the pollen parent of mature fruits. Cotyledons were assayed for five polymorphic enzyme systems: alcohol dehydrogenase, leucine aminopeptidase, malate dehydrogenase, phosphoglucomutase, and triosephosphate isomerase. When sampling of fruits was done to a height of 2 m, percent of hybrids produced by `Teague' and `Topa-Topa' pollenizers was in the range of 30% to 40%. With `Teague' as the pollenizer, `Fuerte' yield increased by 30% in trees adjacent to the pollenizer. With `Tops-Tops' as pollenizer, the yield was increased by 40% for trees adjacent to and at a distance from the pollenizer. `Ettinger' trees planted at a distance of 30 to 50 m from `Fuerte' were found to be the pollen parent of 2% to 14% of the progeny, thus supporting our previous conclusion regarding the high potency of `Ettinger' as a pollen parent. `Tops-Tops', `Teague', and `Ettinger' significantly increased fruit and seed weights of crossed compared with selfed `Fuerte' fruits.
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.
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.