Abstract:

In order to learn the seed hardness of pomegranate during development，the soft seeds cultivar‘Tunisia’，the semi-soft seeds cultivar‘Israel Sour’and the hard seeds cultivar‘Qingpi’were used in this research. The seed hardness，aril weight and total soluble solids in pulpa were tested during development. The cell microstructure and lignifying conditions in seed coat were also observed during fruit ripening，under microscope by phloroglucinol-HCl and safranine staining. The seed hardness of  ‘Tunisia’growing at different places was also compared. Results showed that the seed hardness of pomegranate increased progressively during ripening. The maximum hardness stage was presented at the later stage of fruit ripening but not at the completely ripened time. On the 97th d after flowering，the seed hardness of‘Tunisia’arrived its maximum，（2.939 ± 0.895）kg，while‘Israel Sour’and‘Qingpi’got their maximum seed hardness，with being（5.571 ± 2.109）and（9.203 ± 3.006）kg，respectively，on the 106th d after flowering. On the 124th d after flowering，the maturity，the seed hardness of‘Tunisia’，‘Israel Sour’and‘Qingpi’was（2.887 ± 0.735），（4.242 ± 1.036）and（8.192 ± 2.561）kg，respectively. The seed hardness of the 3 cultivars showed significant difference. The correlation between seed hardness and total soluble solids and aril weight varied in a large range with TNS being the highest of them. No significant difference of seed hardness was detected among the seeds of TNS growing at different places at mature time. Micro-examination revealed that the cell wall of seed coat was highly lignified in the cultivars. According to the cell wall thickness of outer integument，order of the 3 cultivars was ranked as‘Tunisia’>‘Israel Sour’>‘Qingpi’. The significant differences were detected among the cultivars by ANOVA. In summary，TNS was a soft-seeded cultivar of pomegranate with significant lower cell wall thickness. The seed hardness was independent to the growing conditions.

Key words: pomegranate, soft seed, seed hardness, seed coat, lignifying, cell wall of seed coat