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Title: ESTIMATION OF 2N MEGAGAMETOPHYTE HETEROZYGOSITY IN A DIPLOID BLUEBERRY, V. DARROWI CAMP, CLONE USING RAPDS

Author
item VORSA, NICHOLI - RUTGERS UNIVERSITY
item Rowland, Lisa

Submitted to: Journal of Heredity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: A Vaccinium darrowi selection from the wild called Fla4B (collected in Ocala, Florida) has been used extensively in the USDA blueberry breeding program to introduce low chilling requirement into the typically high chilling V. corymbosum background. This plant generates 2n gametes (eggs that carry twice the normal amount of DNA) at a relatively high frequency. Thus, although V. darrowi is a diploid species (2x the basic chromosome number) and V. corymbosum is a tetraploid species (4x the basic chromosome number), Fla4B can be crossed to V. corymbosum cultivars to produce tetraploid offspring for use in blueberry breeding programs. We have examined the transmission of molecular markers called RAPDs from Fla4B to these 4x type offspring to determine the mechanism of 2n gamete formation in Fla4B. Our results suggest that the majority of 2n eggs produced by Fla4B are a result of a defect occurring at the first meiotic division (First Division Restitution or FDR). The predominance of 2n eggs genetically equivalent to FDR is generally considered desirable for breeding because more of the genetic diversity (genetic heterozygosity) will be transmitted to offspring.

Technical Abstract: To determine the mode(s) of 2n gamete formation in a V. darrowi (2n = 2x = 24) clone Fla4B, the transmission of parental heterozygosity was estimated in 2n eggs through randomly- amplified polymorphic DNA (RAPD) analysis of 41 progeny from crosses of Fla4B to tetraploid V. corymbosum (2n = 4x = 48). The level of estimated heterozygosity transmitted range from 5.3% to 100%, with an overall mean heterozygosity of 72.7%, which suggests that first division restitution (FDR) type 2n gamete forming mechanisms were operating in this clone. However, there was evidence that 17% of the 2n eggs had less than 50% estimated heterozygosity, which supports second division restitution (SDR) mechanisms operating as well. Both SDR and FDR modes of 2n egg formation are also supported by a non-normal, bimodal frequency distribution of estimated heterozygosity transmission. Recombination also appears to be prevalent. The predominance of 2n gametes genetically equivalent to FDR is generally considered desirable for breeding autotetraploid crops.