Use of A ₃ Cytoplasm to Reduce Risk of Gene Flow through Sorghum Pollen

Authors

Jeffrey F. Pedersen, University of Nebraska-LincolnFollow
D. B. Marx, University of Nebraska-LincolnFollow
Deanna L. Funnell, University of Nebraska-LincolnFollow

Date of this Version

5-29-2003

Comments

Published in Crop Sci. 43:1506–1509 (2003).

Abstract

A critical impediment to field testing and deployment of transgenic sorghum [Sorghum bicolor (L.) Moench] is the threat of gene flow to weedy relatives through pollen. A technique using sorghum with A₃ cytoplasmic male sterility to control transgene flow through pollen while using nontransgenic pollinators is described and an experiment was designed to evaluate the risk of viable pollen flow using A₃ hybrids under field conditions. Seed set under pollinating bags (an indicator of fertile pollen) was evaluated at the University of Nebraska Field Laboratory at Ithaca, NE, in 2001 and 2002 on selfed F₂ progeny grown from open pollinated seed of 12 F₁ hybrids produced in A₁ and A₃ cytoplasm. The F₂ seed was produced in hybrid yield trials in 1997 and 1998 at Ithaca, NE. In each evaluation year, the experimental design was a split-split plot with seed production year the main plot factor, hybrid as the subplot factor, and cytoplasm as the sub-subplot factor. Cytoplasm effects were highly significant, with percent seed set on A₁ F₂ individuals averaging 74%, and on A₃ F₂ individuals averaging 0.04%. Upper confidence limits (P = 0.05) for percent seed set were 1.32% or less for the progeny from all A₃ hybrids. Polymerase chain reaction (PCR) analysis confirmed that four male fertile individuals (from a population of 1007) were detected with A₃ cytoplasm. These results support the hypothesis that gene flow through pollen can be severely restricted but not eliminated in sorghum by the use of A₃ cytoplasmic male sterility.