Date of Award

Winter 1993

Project Type

Dissertation

Program or Major

Genetics

Degree Name

Doctor of Philosophy

First Advisor

J Brent Loy

Abstract

This investigation characterized and determined the inheritance of the fused vein trait in Cucurbita pepo L. with the purpose of evaluating its use as a rouging marker for hull-less seeded cultivars.

The trait is characterized by the partial fusion of the primary leaf veins. There is a reduction in the intraveinal leaf blade and the dorsal leaf surface appears wrinkled. Depending on genetic background, fusion begins with the fourth to tenth leaf stage and continues throughout vegetative growth. The extent of fusion also varies from slight (1-5 cm) to pronounced (15-20 cm). Anatomically, fusion results from an interruption of vein formation. In the transition zone between petiole and leaf blade, the normal pattern of vascular coalescence and dispersal is expanded into two cycles.

Analysis of segregating populations demonstrated that the trait is most likely governed by a single recessive gene, fv, linked to the hull-less seed gene, n, with 29.2 map units between them. However, inheritance ratios were distorted, varying with population, environment, and type of cross. A hypothesis of gametophytic subvitality was verified by microscopic examination of co-pollinated, style-partitioned flowers, revealing inferior fused vein gametophyte performance.

The consequences of gametophytic subvitality were shown by manipulating reproductive competition. Fused vein pollen generated significantly fewer seed per fruit in all female genotypes when compared to normal, F$\sb{\rm 1}$, and a 50:50 pollen mix at three different pollen loads. In ensuing F$\sb{\rm 2}$ and testcross populations, a reduction in pollen load and therefore pollen competition significantly increased the number of fused vein individuals in segregating populations. Plant growth was also assessed for negative pleiotropic effects. No significant difference was found between fused vein and normal individuals in segregating populations; both leaf initiation and total leaf area were independent of leaf morphology.

The trait's distinct morphology, recessive inheritance, and linkage relationship make it a suitable rouging marker. However, gametophytic subvitality prescribes fused by normal hybrid cultivars to avoid detrimental effects on yield.

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