Shmuel Gazit

In vitro somatic embryogenesis from Mangifera indica L. callus

Abstract The nucellus and globular adventitious proembryos were removed from 2-month-old fruits of mango (Mangifera indica L.) cultivars ‘Ono’ and ‘Chino’, and were cultured on sterile, solid Murashige and Skoog (MS) medium that had been modified as follows: half-strength major salts and chelated iron; 20% (v/v) coconut water (CW); 6% sucrose; 100 mg l−1 ascorbic acid and 400 mg l−1 glutamine. Embryogenic explants were sub-cultured after 4–6 weeks in liquid modified MS medium containing 2 mg l−1 2,4-dichlorophenoxyacetic acid (2,4-D) instead of CW. Rapidly growing cultures were established and were sub-cultured monthly. Somatic embryogenesis was induced following sub-culture from MS medium with 2,4-D to MS without growth regulators and with or without activated charcoal (0.5%). Germination of somatic embryos appeared to be enhanced by 1 mg l−1 benzyladenine (BA); however, most of the germinating embryos became embryogenic.

Effects of autumnal water stress on litchi flowering and yield in Israel

Abstract Four experiments were conducted over a 3-year period (1988–1991) to evaluate the use of autumnal water stress in alleviating low flowering and yield in Israeli litchi orchards. In all experiments, autumnal water stress significantly increased flowering intensity and yield in Litchi chinensis Sonn., cultivars ‘Mauritius’ and ‘Floridian’. Six weeks of autumnal water stress, terminated by winter rains, were sufficient to effect these changes.

Effect of temperature regime on pollen and the effective pollination of ‘Kent’ mango in Israel

‘Kent’ mango (Mangifera indica L.) flowers were sampled in an orchard in the coastal plain of Israel during the 1997 flowering season. Effective pollination rate was determined at two stages of the fertilization process: (a) pollen germination on the stigma; (b) pollen-tube penetration into the ovule. Pollination rates were negligible during the first part of the flowering season (31 March to 18 April), reaching a high value only at the end of the season (21 May). The same phenomenon also occurred, albeit with consistently higher rates of effective pollination, when detached flowers, taken from the orchard during the flowering season, were pollinated and incubated for 24 h at the presumed optimal temperature of 308C, indicating that the reproductive organs were not fully functionally viable. At the start of the flowering season, all the pollen was deformed, and later (16 April 1997), when pollen grain shape was normal, only 23% of it was found to be viable by Alexander’s staining. The functional viability of the pollen and pistils of orchard- and phytotrongrown (22/278C, night/day) flowers was determined in detached flowers. At the beginning of the flowering season, both orchard pollen and pistils tended to be defective. Orchard pollen germinated poorly, even on phytotron adapted stigmas. Ovule penetration was hampered in orchard pistils, even when phytotron pollen was used for pollination. Chilling injury appeared to be responsible for the damage to the reproductive organs of the orchard flowers. The negligible rate of effective pollination found in mango orchards in Israel during a significant part of the flowering season therefore appears to be due to the detrimental effect of cold weather on the pollination and fertilization processes as well as on the functional viability of the male and female reproductive organs. # 2000 Elsevier Science B.V. All rights reserved.

Flower development in the passion fruit Passiflora edulis requires a photoperiod‐induced systemic graft‐transmissible signal

Different organisms use gradual seasonal changes in photoperiod to correctly time diverse developmental processes, such as transition to flowering in plants. Florigen is a systemic signal formed in leaves exposed to specific environmental cues, mainly photoperiodic, and capable of triggering flower induction in several species. Here we show that in Passiflora edulis, a perennial climbing vine, flower initiation occurs throughout the year; however, without long photoperiods, flower primordia show arrested growth and differentiation at an early stage. Our results support the existence of a positive, systemic, graft-transmissible signal, produced in mature leaves under LDs, that is required for normal flower development beyond sepal formation. Our results also suggest that Gibberellin acts to inhibit flower development. We provide evidence for genetic variation in the response to short photoperiods. A genotype capable of forming developed flowers under short photoperiods produces a positive graft transmissible signal allowing normal flower development under short days in a cultivar which normally aborts flower development under these conditions. We believe these findings contribute towards discovering the chemical nature of this interesting mobile signal involved in flower development.

Isolation and identification of a plant growth inhibitor from avocado

Abstract A compound was isolated from avocado mesocarp and identified as 1-acetoxy-2,4-dihydroxy- n -heptadeca-16-ene. The new compound inhibits soybean callus growth and elongation of wheat coleoptiles.

Xylem-sap zeatin-riboside and dihydrozeatin-riboside levels in relation to plant and soil water status and flowering in ‘Mauritius’ lychee

Abstract The effects of autumnal water stress on the levels of zeatine-riboside and dihydrozeatin-riboside in the shoot xylem-sap and on the intensity of flowering in the following year were studied in commercial lychee ( Litchi chinensis Sonn.) during the 1995/1996 season. Four irrigation treatments were initiated at the beginning of October coinciding with the end of the second vegetative flush after harvest as follows: 0.5, 0.25, 0.125 and 0 Class A pan evaporation coefficient, designated as 100, 50, 25 and 0%, respectively, were applied. Soil and midday stem water potentials were determined several times during October, after the beginning of treatment. Xylem-sap concentrations of trans -zeatin-riboside ( t -ZR) and dihydrozeatin-riboside (DHZR) were determined 20 days after the start of the irrigation treatments. Both soil and midday stem water potentials decreased with the decrease in the irrigation levels. Flowering intensities in the following spring were higher after the reduced irrigation treatments than in the control (100%). DHZR and t -ZR concentrations in the xylem-sap increased with decreasing irrigation level, down to the 25% irrigation level. Cessation of irrigation (0%) resulted in a steep decrease in the t -ZR concentration and a further increase of DHZR. The relationships between plant and soil water status, cytokinin xylem-sap content and flower bud differentiation reported herein suggest that moderate water stress is sufficient to induce fruit bud differentiation without any visible damage to the trees.

Components of the genetic variance and genetic correlations between traits in Mango

Phenotypic and genetic variance components for mango (Mangifera indica) traits were estimated. The analyzed population composed of 745 progeny derived from both controlled crosses and open pollination. The average percent of selfing was estimated from the statistical model to be 50%. Both the additive and the dominance (non-additive) genetic variance components were calculated. In all 13 traits analyzed, the additive genetic variance components were not statistically significant while in eight of the traits the dominance genetic variance was significant. In three pairs of traits, significant phenotypic correlation was detected and in one pair of traits, significant genetic correlation was found. Conclusions for mango breeders are discussed with the main recommendation being to widen the genetic background of the breeding population.

Outcrossing rate in adjacent ‘Maya’ and ‘Tommy Atkins’ mango blocks

Abstract Outcrossing rate in mango ( Mangifera indica L.) mature fruit was studied for the first time in an orchard consisting of two adjacent blocks of ‘Maya’ and ‘Tommy Atkins’. Few polyembryonic rootstocks were detected in the blocks. Outcrossing rates were determined at different distances from the pollenizer block using the polymorphic enzyme systems triosephosphate isomerase and isocitrate dehydrogenase. The Outcrossing rate was measured in ‘Maya’ for two consecutive years and in ‘Tommy Atkins’ for one year. In all three cases, a pronounced decrease in hybrid rate was found between fruit sampled from the row bordering the second cultivar and that from the most distant row sampled (108 m and 96 m for ‘Maya’ in 1992 and 1993, respectively, and 80 m for ‘Tommy Atkins’). Outcrossing rates were: 63% and 34% for ‘Maya’ in 1992; 57% and 39% for ‘Maya’ in 1993, and 79% and 24% for ‘Tommy Atkins’, for fruit sampled from the row closest to and most distant from the pollenizing cultivar, respectively.