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Cotyledons and embryonic axes of Pistacia vera L. `Kerman' were cultured on modified DKW or MS media. Cotyledonary petioles regenerated shoots when cultured on DKW medium supplemented with (in g/liter) 2.5 Zn(NO3)2, 0.48 H3BO3, 100 KNO3 and (in mg/liter) 1 BA, 0.01 IBA, 2 kinetin and 250 glutamine whether under light (80 μmol·m-2·s-1) or dark conditions. Cotyledons regenerated floral parts from their abaxial surfaces when cultured on (1) DKW or MS, both supplemented with (in mg/liter) 600 glutamine, 300 glycine, 200 asparagine, 50 arginine, 20 ascorbic acid and 0.05-0.1 2,4-D plus 0.1 BA or 0.1 zeatin under light or dark conditions or (2) DKW medium supplemented with (in g/liter) 2.5 Zn(NO3)2, 0.48 H3BO3, 100 KNO3 and (in mg/liter) 0.002 thidiazuron plus 0.2 2,4-D under light conditions.
RFLP markers were used to investigate genetic diversity among California walnut (Juglans regia) cultivars and germplasm collected worldwide. Sixteen of 21 RFLP markers were polymorphic in the 48 walnut accessions tested. RFLP markers were useful for identifying walnut cultivars. All genotypes were heterozygous at ≈20% of the loci for both California and worldwide germplasm. California walnut germplasm contained 60% of the worldwide allelic diversity. Cluster analysis of genetic distance between accessions and principal component analysis of allelic genotypes showed two major groups of walnut domestication. California germplasm was associated with germplasm from France, central Europe, and Iran and had less genotypic similarity with germplasm from Nepal, China, Korea, and Japan.
RFLP markers were used to study genetic diversity among California walnut (Juglans regia L.) cultivars and germplasm collected worldwide. 16 of 21 RFLP markers were polymorphic in the 48 walnut accessions tested. Seven RFLP markers permitted unique identification of all walnut cultivars. All genotypes were heterozygous at approximately 20% of the loci for both California and worldwide germplasm. California walnut germplasm contained 65% of the worldwide allelic diversity. Cluster analysis of genetic distance between accessions and principal component analysis of allelic genotypes showed two major groups of walnut domestication. California germplasm was associated with germplasm from France, Central Europe, and Iran, and had less genotypic similarity with germplasm from Nepal, China, Korea, and Japan.
The role of pollen in abscission of pistillate flowers of Persian walnut (Juglans regia L.) cv. Serr was investigated over a 4-year period by controlled pollinations and pollen counts. Self-pollen, pollen from other walnut selections or cultivars, or dead pollen was applied at high and low doses to pistillate flowers enclosed in pollination bags. Unbagged, open-pollinated flowers and bagged, nonpollinated flowers served as controls. In all cases, presence of pollen significantly increased the probability of pistillate flower abscission (PFA). Dead pollen resulted in as much PFA as live pollen. Counts of pollen grains confirmed that PFA-type flowers had significantly more pollen than normal flowers. In the fourth year `Serr' pollen was applied to unbagged flowers of `Serr' and ten other Persian walnut cultivars, and the amount of PFA on the artificially pollinated flowers was significantly higher than on the open-pollinated flowers, while the control flowers dusted with talc or pine pollen had almost no PFA. These results clearly indicate that excess pollen is involved in pistillate flower abscission in `Serr' walnut and suggests that other cultivars may also be sensitive to pollen load. This phenomenon may have implications in the biology of selfing and evolution.
Abstract
Intergeneric hybrids between wingnut (Pterocarya sp.) and walnut (Juglans regia) were developed by regenerating plants from somatic embryos produced on immature cotyledons of seed from control-pollinations. Hybridization was confirmed by isozyme analysis using starch gel electrophoresis. To the best of our knowledge, this is the first report of hybrids between wingnut, which has a high level of resistance to Phytophthora spp. and nematodes, and walnut. Wingnut may now be used as a source of germplasm for improving walnut rootstocks.
Somatic embryos derived from walnut (Juglans regia L.) ovule tissues were evaluated to determine whether they were of zygotic or maternal origin. Molecular markers were used to permit evaluation at an early stage, before whole plant development. Somatic embryos developed from potentially apomictic `Sunland' and `Cisco' ovule tissue isolated from bagged putatively unpollinated flowers. Phosphoglucomutase (PGM) isozyme analysis showed that all of these embryos, except one from each cultivar, carry the same zymotype as the maternal tissue. However, restriction fragment length polymorphism (RPLP) analysis combined with isozyme evaluation demonstrated that the tested embryos originated from zygotic rather than maternal tissues. This study demonstrates the application of molecular marker analyses, particularly RFLPs, evaluation of somatic embryo origin.
In both laboratory and field experiments, excessive pollen has been found to be a major cause of pistillate flower abscission (PFA) and reduced yields of sensitive English Walnut cultivars (CVs) (especially “Serr”). In the field, PFA and reduced yields develop when substantial overlap of male and female walnut bloom occurs. PFA and poor yields can be further aggravated when pollenizing CV's have been included into an orchard to maximize pollen availability for the commercial CV Field experiments, conducted in 1992 and 1993, demonstrated that mechanically shaking trees to remove male flowers pre-bloom from either pollenizer CV's or the main CV reduced pollen load, PFA, and substantially improved yields.