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Improving Persistence in Red Clover: Insights from QTL Analysis and Comparative Phenotypic Evaluation

Agroscope Reckenholz-Tänikon Research Station ART, Reckenholzstrasse 191, 8046 Zurich, Switzerland

^* Corresponding author (roland.koelliker{at}art.admin.ch).

Cultivars of red clover (Trifolium pratense L.) often suffer from low persistence, leading to insufficient legume proportions in pluriannual forage stands. Persistence is a complex trait often negatively correlated with other important traits and its phenotyping is laborious. Consequently, persistence is difficult to improve. The objectives of this study were to optimize the phenotypic evaluation of persistence, to identify quantitative trait loci (QTLs) for this important trait, and to investigate the association of persistence with other important traits. A weighted average of vigor scores assessed during two winters and three growing seasons was identified as the optimal method to phenotype persistence. For this index, one QTL explaining 12.2% of the total phenotypic variation was identified. While there was no negative correlation between persistence and seed yield, persistence was positively correlated with length of stem, which in turn was positively correlated with seed yield. Furthermore, QTLs for persistence, length of stem, and seed yield were detected in the same genome region. Improvement of persistence should therefore be possible without adverse effects on seed yield. Moreover, length of stem may present a candidate character for indirect selection of these two traits. The QTLs and the indirect selection criteria identified in this study may substantially assist future breeding efforts for the improvement of persistence in red clover.

Abbreviations: AP3, absolute persistence • DS, difference of vigor scores before and after seed harvest • DV3, difference of vigor scores between the third and the first two growing seasons • LG, linkage group • LL, length of medial leaflet • LS, length of stem • QTL, quantitative trait locus • SYP, seed yield per plant • TOF, time of flowering • TSW, thousand-seed weight • V1, V2, V3, V4, average vigor scores of growing seasons 1 to 4 • WL, width of medial leaflet • WV3, weighted vigor score across three growing seasons

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Received for publication March 13, 2007.