6-benzylaminopurine (BA), which was applied at the 10 mm stage of fruit development at 50 and 100 mg.liter$\sp{-1}$ to 'McIntosh' apples (Malus domestica Borkh), effectively thinned fruit, and increased fruit size and caused seed abortion. Regardless of BA treatment, there were two distinguishable peaks of fruit abscission during 'June drop' on 'Morespur McIntosh' apples. There was a large peak about 14 days after treatment and a second smaller one 24 days after treatment. The first abscission peak was increased by BA, and approximately half of then existing fruit abscised from treated trees between 10 and 14 days after treatment, whereas only one fourth abscised from the control trees. The number of seeds per fruit was lower in abscising fruit than in persisting fruit regardless of BA treatment. Seed number of abscising fruit was increased linearly by BA application. BA enhanced the translocation of $\sp{14}$C-sorbitol from leaves to fruit when applied directly to the fruit, but not when applied directly to the leaves. Therefore, it is unlikely that BA thinned apple fruit directly through restricting the translocation of photosynthates moving from leaves to fruit. Net photosynthesis was decreased and dark respiration was increased when temperature following BA application was high (30$\sp\circ$C), whereas there was no effect when temperature was lower (20$\sp\circ$C). Total nonstructural carbohydrates, total soluble sugars, reducing sugars, and starch in the leaves decreased dramatically over the 12 or 13 day observation period, regardless of BA treatment. These carbohydrate levels were further lowered by BA application. Abscising fruit, based on specific reddening of pedicel, had higher reducing sugars, total soluble sugars, starch, and total nonstructural carbohydrates. The levels of these carbohydrates in fruit from BA treated trees were similar to that from untreated control trees. Foliar application of 5% sorbitol solution had no effect on fruit set. Removal of bourse shoot tip increased fruit set regardless of BA treatment. BA thinned fruit regardless of whether shoot tips were removed or not, and there was no interaction between BA application and shoot tipping. Experiments were conducted to evaluate the effects of BA on fruit set and fruit development on small fruiting branches supported by different numbers of leaves per fruit. BA thinned fruit only when one leaf per fruit was on the girdled small fruiting branch, but not when the leaf number was greater than two. Fruit weight and soluble solids content increased quadratically with increasing leaf number per fruit. BA reduced fruit growth rate when less than 16 leaves were present on the girdled branches between 3 and 7 days after treatment, but it did not affect fruit growth rate when 32 leaves were on the girdled branches. Increasing leaf number also increased normal seed number while decreasing the number of aborted seeds, but it had no effect on the number of total seeds per fruit. BA reduced the number of normal seeds per fruit only when the number of leaves per fruit was less than 4. These results were discussed in relation to carbohydrate supply and source-sink relationships.

Isozyme analysis was used to identify clones, measure levels of genetic variation within groups of clones, and analyze mating systems in two Cactaceae genera--Hatiora and Schlumbergera. Isozymes were extracted from phylloclades and pollen and were separated by polyacrylamide gel electrophoresis. The inheritance of aspartate aminotransferase (AAT), glucose-6-phosphate isomerase (GPI), malate dehydrogenase (MDH), phosphoglucomutase (PGM), and triosephosphate isomerase (TPI) was examined in Hatiora. Six loci (Aat-1, Gpi-1, Mdh-1, Pgm-1, Pgm-2, and Tpi-2) were analyzed, and results were generally as expected for single loci with codominant alleles. For all six isozyme loci segregation distortion was observed in at least one segregating family. Aat-1 was linked with Pgm-1 (26 cM), but the other isozyme loci assorted independently. The inheritance of leucine aminopeptidase (LAP), phosphoglucomutase (PGM), and shikimate dehydrogenase (SKD) was investigated in Schlumbergera. Three loci were analyzed (Lap-1, Pgm-1, and Skd-1), and results were generally as expected for single loci with codominant alleles. Significant segregation distortion was observed in at least one segregating family for all three isozyme loci. Disturbed segregation at Lap-1 was due to tight linkage (7 cM) with the locus controlling gametophytic self-incompatibility (S). All three loci assorted independently of each other. In a third study, a Hatiora germplasm collection composed of 49 clones was assayed for AAT, GPI, LAP, MDH, PGM, SKD, and TPI. Thirteen putative loci and 42 putative alleles were identified, and 9 of the 13 loci (69%) were polymorphic. Twenty-two clones (45%) could be distinguished solely on the basis of their isozyme profiles, but the other 27 clones shared isozyme profiles with one to five other clones. Thirteen modern H. x graeseri cultivars exhibited less genetic diversity than 40 H. gaertneri, H. x graeseri, and H. rosea clones representing older and modern cultivars plus field-collected specimens. The difference in genetic diversity was primarily attributed to a loss of alleles during breeding. In a fourth study, a Schlumbergera germplasm collection composed of 59 clones was assayed for AAT, GPI, LAP, MDH, PGM, SKD, and TPI. Twelve putative loci and 36 putative alleles were identified, and 10 of the 12 loci (83%) were polymorphic. Forty-one clones (69%) could be distinguished solely on the basis of their isozyme profiles, but the other 18 clones shared isozyme profiles with one or two other clones. Forty-two commercial clones of S. truncata, S. x buckleyi, and S. x exotica exhibited less genetic diversity than 14 field-collected clones of S. kautskyi, S. opuntioides, S. orssichiana, S. russelliana, and S. truncata. The difference in genetic diversity was attributed to limited sampling from wild populations and loss of alleles during breeding.

Iron/manganese toxicity disorder in marigold (Tagetes erecta L.) has been related to high concentrations of Mn and low concentrations of Ca and Mg in the affected leaves. Preplant addition of micronutrients in the media combined with constant feed program and low medium pH create favorable conditions for the development of Mn toxicity in greenhouse crops. Deficiency of Ca or Mg is due in part to low medium pH and to a lack of Mg and Ca in many of the fertilizers used in greenhouse production. The objectives of this research were to determine the relationship of Mn toxicity to the incidence of Fe/Mn toxicity disorder in marigold, and to evaluate the effect of low Mg supply and/or low Ca supply on the occurrence of the toxicity. Six experiments were conducted. Plants of Tagetes erecta L. ‘First Lady’ were started from seeds and then grown in solution culture supplying different concentrations of Mn, Ca and Mg depending on the objectives of each experiment. Symptoms were described for each experiment. When the plants were harvested, their dry weights were taken and their tissues were analyzed for Mn, Fe, Ca, and Mg concentrations. The symptoms of Mg deficiency included stunting, chlorotic and necrotic areas on the leaves. The symptoms of Ca deficiency included chlorosis and curling, especially of the new leaves. The symptoms of Mn toxicity included curled leaves, bleached patches and brown spots on the leaves. These symptoms of Mn toxicity are similar to those related to Fe/Mn toxicity disorder. The incipient deficiency solution concentration of Mg was 10 mg/l (internal incipient deficiency concentration was 1.5%). The incipient deficiency solution concentration of Ca was 20 mg/l (internal incipient deficiency concentration was 0.54%). The critical toxicity concentration of Mn was 4.5 mg/l (internal critical toxicity concentration was 270 mg/kg DW). Low Ca in solution (20 mg/liter) increased the sensitivity of marigold to high levels of Mn in solution by reducing the critical toxicity concentration of Mn from 4.5 to 0.5 mg/liter. Similar results were found when both Ca and Mg were low. Iron/manganese toxicity disorder can be attributed to Mn toxicity. Low Ca supply or low Ca and Mg supplies are factors favoring the occurrence of the disorder. Low Mg supply, alone does not seem to affect Mn toxicity in marigold. Based on this research, high Ca supply could alleviate the harmful effects of Mn toxicity in marigold. Low Mn supply could prevent the toxicity problems. Agricultural practices and nutritional regimes that reduce the availability of Mn and increase the availability of Ca could reduce the occurrence of Fe/Mn toxicity disorder in marigold and similar physiological disorders in other bedding plants grown in soilless media. Monitoring Mn supply and fertilizing with Ca could prevent or reduce Mn toxicity to floriculture plants.

No description available.

Digitized by Kansas Correctional Industries

Call number: LD2668 .T4 1979 A432 / Master of Science

Digitized by Kansas Correctional Industries

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

No description available.