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Genetic variability of yield traits in diverse sugarcane ecologies of selection on Réunion Island

Dumont T., Hoarau J.Y., Barau L., Thong-Chane A., Siegmund B.. 2018. In : Book of abstract of the ISSCT Joint 12th Germplasm & Breeding and 9th Molecular Biology Workshops: " Improvement of sugarcane for stress environments". Okinawa : ISSCT, p. 22-22. ISSCT Germplasm and Breeding and Molecular Biology workshops. 12/9, 2018-10-22/2018-10-26, Okinawa (Japon).

eRcane currently operates in Reunion several decentralized concurrent sub-selection progr'ammes located in the major areas under cane differing in their agro-climatic conditions. Each year about 100,000 new seedlings are dispatched among the different sub-programs which receive mainly the same families. This early decentralized scheme of selection corresponds to a selection strategy for local adaptation with the objective of increased genetic gains in each environment. Seedlings enter into the same 14-years selection scheme across all sub-programs: two non-replicated stages followed by three replicated yield trials (RYT) stages dedicated to the _evaluation of cane yield (CY), estimable recoverable sugar (ERS) and an economic index (EI). The selection scheme is strictly the same across all sub-programmes (trial designs, rate of selection between stages, selection criteria and procedures). A __ database of 10 years trial was used in order to compare the genetic variability of agronomic traits of interest (CY, ERS and EI) in the second R YT between four regional sub-programmes. Two selection sites are located in the wet windward coast (La Mare: LM and Saint-Benoit: SB) of the island and two others in the dry leeward coast (Vue-Belle: VB and Etang-Sale: ES). The objective of this retrospective study was to compare the effect of selection pressure exerted on genotypes by the different agro-climatic environments of the selection sites. Mean genetic coefficient of variation (GCV%) across the ten series and range [min-max] of variety performances for CY distinguished clearly SB and VB sites from LM and ES sites: (i) mean GCV% for CY was · higher at SB (15.5%) and VB (15.8%) compared to LM (13.7%) and ES (11.3%); (ii). congruently, the [ min-max] range of CY performance of candidates was wider and better centered on the standard cultivar at SB ([45%-152%]) and VB ([35%-173%]) compared to LM ([42%-123%]) and ES ([50%-116%]). These results reflect higher chances of identifying new cultivars in SB and VB in the subsequent final RYT and in semi-commercial tests before release. These larger genetic variabilities of CY in SB and VB compared to LM and ES could be related to agro-climatic differences between selection sites. As opposed to SB and VB, LM and ES are under irrigation. Moreover, ;LM, SB and ES are at a low altitude synonymous with high temperatures favorable for cane growth. On the contrary, the high altitude of VB site (700 m) implies a seasonal thermal stress (from April to September) less favorable for plant growth. SB has a very stony soil and a relatively fine layer of topsoil (0.25 m) which dries more quickly due to a smaller water reserve. On the contrary LM, VB and ES are not stony and have deeper topsoil layers (>0.50-1.00 m). All these agro-climatic comparisons show that the most favorable environments for cane growth (LM and ES) tend to buffer the differences between candidates for their yield potential. Conversely, in less favorable environments due to water stress (VB, SB) and/or soil characteristics (SB), identification of true superior varieties in cane yield seems easier....

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