Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Eighteen progenies of the octoploid cultivated strawberry (Fragaria x ananassa Duch.) and their parental clones were studied, with selection of parental clones based upon phenotypic performance regarding characters related to mechanical harvesting. Matings were made at random between all parents. Progenies and their parents were evaluated, through 4 harvesting periods at 3-day intervals, for yield, concentration of fruit ripening, berry firmness, and easy-cap traits as related to mechanical harvesting;Results indicated that mating of chosen parents affected these characters. Moderate increases in mean yield were obtained in some progenies; however, some progenies were not significantly affected or had lower average number of berries per plant than their own parents. Moreover, concentration of fruit ripening reached a peak during the second and third harvests. It was found that the high yielding genotypes usually concentrated high percentages of berry ripening within a short period of time;Average berry firmness as well as easy-cap traits were also affected by crosses between selected parents. In many cases, average berry firmness and average force required for berry detachment for the progeny exceeded mean averages of both parents. However, other matings decreased berry firmness and average capping force, or showed no differences between the progeny and its parents. Both traits decreased with the progression of the harvest dates. It was found that easy-cap types usually had soft berries and vice versa. These findings are important as criteria for detecting and selecting clones adapted to mechanical harvest;Cytogenetical studies were made on four progenies and their parents. For all genotypes studied, chromosomes were associated as bivalents during diakinesis and metaphase I at high frequency. Secondary associations between bivalents were observed in both stages for all genotypes. During diakinesis, loose bivalents and/or univalents were observed in some pollen mother cells (PMCs), and two nucleoli were observed in a few PMCs. Different numbers of bivalents associated with the nucleolus of the diakinesis were observed. The cytological study of meiosis and mitosis revealed that all genotypes are octoploid with 2n = 56 chromosomes. Two satellite chromosomes were detected for all genotypes. One to 8 nucleoli per nucleus were observed during interphase. This study generally revealed that both meiosis and mitosis of all genotypes studied were normal.



Digital Repository @ Iowa State University,

Copyright Owner

Atef Mohamed Ibrahim



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160 pages

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Genetics Commons