Date of Award

Spring 1982

Project Type


Program or Major

Plant Science

Degree Name

Doctor of Philosophy


The productivity of a new bush winter squash cultivar ('Autumn Pride') was compared to that of 'Blue Hubbard', a high-yielding vine cultivar. Yields of 'Autumn Pride' increased with increasing plant density and, at high plant densities, were greater than yields of 'Blue Hubbard' at its near optimum plant density.

Several factors could have contributed to the higher yield potential of 'Autumn Pride'. CO(,2) compensation points were determined to be 38 ppm and 77 ppm CO(,2) for 'Autumn Pride' and 'Blue Hubbard', respectively, at 30(DEGREES)C. 'Autumn Pride' had two layers of palisade parenchyma cells, occupying 74 percent of the mesophyll. In 'Blue Hubbard' leaves, the second layer of palisade parenchyma was often incompletely formed, so that palisade cells occupied only 52 percent of its mesophyll thickness. Leaf thickness was not found to be significantly different between 'Autumn Pride' and 'Blue Hubbard'.

Due to its dwarf stem, all 'Autumn Pride' organs were more proximal to their leaves. Furthermore, stems and petioles of 'Autumn Pride' were larger in diameter and contained larger vascular bundles. ('14)C-sucrose label studies showed that translocation into sink organs over 24 hours was significantly higher in 'Autumn Pride' than in 'Blue Hubbard'.

Greenhouse and field studies of partitioning showed that total biomass produced by bush ('Autumn Pride') and vine ('Blue Hubbard') plants were equal during the first eight weeks of growth. 'Blue Hubbard' plants partitioned a higher proportion of their dry weight into stems, while 'Autumn Pride' plants had more in leaves and roots. After the eighth week, 'Blue Hubbard' plants became significantly larger than 'Autumn Pride' plants, but 'Autumn Pride' plants had higher harvest indices throughout fruit development. Twelve weeks after transplanting, harvest indices were 70 per cent for 'Autumn Pride' and 57 per cent for 'Blue Hubbard' at low density planting. 'Autumn Pride' plants had a higher specific leaf weight (SLW), a lower leaf area ratio (LAR), and a higher cumulative net assimilation rate (NAR) than those of 'Blue Hubbard'.