Depression by inbreeding after four sucessive self-pollination squash generations

Antonio Ismael Inácio Cardoso

doi:10.1590/s0103-90162004000200016

Abstract

The strategy for breeding F1 hybrid squash is to develop parental lines through self-pollination. However, it increases plant mean homozygosis, which is not the natural genetic state of a cross-pollinated species, and can cause "inbreeding depression". The objective of this work was to evaluate this depression with sucessive generations of self-pollination (without selection) in Cucurbita moschata, cv. Piramoita. Populations were obtained from lines with one to four generations of self-pollination (obtained by the SSD method), from the original cv. Piramoita (population S0). Randomized blocks were used with five treatments (different generations of self-pollination - S0 to S4), six replicates and five plants per plot. Regression analysis was made by the Wright inbreeding coefficient (F) to measure the homozygosis level effect on vigor loss. There was a linear reduction of mean weight and fruit length, seed production (number and weight) per fruit with the increase of the homozygosis level; however inbreeding did not affect seed quality (weight of 100 seeds and germination).

Highlights

The strategy for breeding F hybrid squash is to 1 develop parental lines through self-pollination (Whitaker & Robinson, 1986; Della Vecchia et al, 1993; Robinson & Decker-Walters, 1999; Cardoso, 2001; Maluf, 2001)
The objective of this work was to evaluate this depression with sucessive generations of self-pollination in Cucurbita moschata, cv
The strategy for breeding F hybrid squash is to 1 develop parental lines through self-pollination (Whitaker & Robinson, 1986; Della Vecchia et al, 1993; Robinson & Decker-Walters, 1999; Cardoso, 2001; Maluf, 2001)

Summary

Introduction

The strategy for breeding F hybrid squash is to 1 develop parental lines through self-pollination (Whitaker & Robinson, 1986; Della Vecchia et al, 1993; Robinson & Decker-Walters, 1999; Cardoso, 2001; Maluf, 2001). Self-pollination increases plant mean homozygosis, which is not the natural genetic state of a crosspollinated species, and it can cause “inbreeding depression”. This is clearly observed in hybrid corn production, when plant size and vigor of self-pollinated inbred lines are drastically reduced as compared to outbreeding cultivars from which they originated (Allard, 1971). Cucurbits, being cross-pollinated, are an example of a group of species in which certain lines seem to lose little vigor by inbreeding (Allard, 1971; Whitaker & Robinson, 1986; Robinson, 1999).

Objectives

Methods

Results