A study of heterotic relationships in sorghum

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Title: A study of heterotic relationships in sorghum
Author: Gabriel, Krishnamoorthy
Abstract: In sorghum , a predominantly self -pollinated crop , hybrid seed production relies exclusively on the cytoplasmic -genetic male sterility system . The system of hybrid development has caused sorghum breeding programs to develop two breeding groups : a male -parent group (R -line / fertility -restorer ) and a female -parent group (an A /B line , lacking the fertility -restoring gene of the A1 male -sterility system ) . These have served as heterotic groups in the absence of more information with reference to genetic diversity . Efforts to determine heterotic groups in sorghum have not been successful in clearly delineating any patterns . However , in a recent molecular marker -based study of 50 elite sorghum parental lines , groups similar to the working group system were observed , as was an absence of a consistent delineation , characteristic of heterotic groups , between the A /B - and R -lines . This study was conducted with the objective of evaluating the groups observed and assessing their potential as heterotic groups . Two parental lines from each of the five groups , and two lines from those not conforming to any group , were chosen and crossed in a half -diallel . The twelve parents , sixty -six diallel hybrids and three commercial hybrid checks were evaluated for grain yield and other agronomic traits in five environments' College Station , TX in 2003 and 2004 , Weslaco , TX in 2003 , and Halfway , TX in 2003 and 2004 . Within -group crosses exhibited inferior heterotic expression , for grain yield and other traits , in comparison with across -group crosses . Furthermore , genetic similarity estimates for parental line pairs obtained from the molecular study were significantly correlated with specific combining ability and heterosis for yield of the corresponding hybrid combinations , revealing a pattern of correspondence between molecular data and heterosis . Hybrids made among R -lines and among B -lines were significantly lower in yield compared to AxR hybrids , likely to be a result of decades of breeding efforts to develop inbreds within the mutually isolated groups , rather than a consequence of phylogenetic divergence . An examination of the heterotic effects manifested in hybrid combinations reveals a pattern of interactions broadly in agreement with the molecular data , but differential responses between individual members of the proposed groups make it difficult to define distinct heterotic groups .
URI: http : / /hdl .handle .net /1969 .1 /3226
Date: 2006-04-12

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A study of heterotic relationships in sorghum. Available electronically from http : / /hdl .handle .net /1969 .1 /3226 .

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