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Detection of QTAs for agronomic traits across crop-cycles and seasons in two segregating populations

Forget L., Hoarau J.Y., Mungur H., Payet J., Badaloo G., Hellmann M., Ramdoyal K., Wong Sak Hoi L., Raboin L.M., Dookun-Saumtally A., Offmann B.G.. 2003. In : IVth Molecular biology workshop, Montpellier, France, 7-11 April 2003 [Abstracts]. Montpellier : CIRAD-CA, p. 23-23. Molecular Biology Workshop. 4, 2003-04-07/2003-04-11, Montpellier (France).

Two segregating populations (P1 and P2) were evaluated for several agronomic traits related to the milling process in view of detecting QTAs controlling these traits. P1 was evaluated at CERF and consisted of 80 progenies, derived from a selfing of cv. R570, representing both extremes of a larger segregating population of 300 individuals evaluated for brix. P2 was evaluated at MSIRI and consisted of 170 progenies randomly derived from a cross between M 695/69 and R570. Both trials were planted in a randomized complete block design with four replications. P1 and P2 were evaluated for 5 and 10 agronomic traits respectively including Brix%-juice, Brix%-cane, Pol%-cane, Purity, Fiber%-cane, Cane-yield, Field-brix, Brix%-dry-matter, Pol%-dry-matter, Dry-matter%-cane and Kilo-brix. Measurements in both populations were carried out over two seasons in plant cane [May/June (pre-harvest); August/September (middle-harvest)] and over one season in the first ratoon [June/July (earlyharvest)]. A map spanning over 5850 cM (120 cosegregation groups-CGs-) was constructed from P1 using 939 simplex AFLP markers (LOD=5; 0=0.35). Two maps (2570 cM / 49CGs for R570 and 2578 cM / 64CGs for M 695/69) were constructed from P2 using 603 simplex AFLP and microsatellite markers. ANOVA analysis allowed the identification of 168 QTAs at P=0.005 (54 were still significant at P=0.001) for all the 45 traits (15 variables x 3 seasons) investigated, each of which explained between 3 -11% of the variation of individual trait. The consistency of the QTAs across the 3 environments appeared rather low as 80% of the QTAs were detected only once. This was due to the high genotype x environment interaction for most traits. However the direction of the effect of the QTAs was conserved over the years, whether the effect was significant or not. A positive correlation [+0.06;+0.46] was observed between all sucrose-related parameters and fiber content in both experiments in pre- and early-harvest seasons (the sign of the correlation being reversed in middle-harvest in P2 experiment [-0.08;-0.21]). These unusual positive correlations suggest that variation in growth and development existed in the two progenies: At the time data for the various traits were recorded, less vigorous clones might still have been in an active growth process unlike faster clones which had reached their full development. These findings revealed a mixture of two sorts of QTAs, i.e some related to early growth development and involved in the control a several traits and others governing more specifically the ultimate potential of a single trait. (Texte intégral)

Mots-clés : saccharum; caractère agronomique; gène; ségrégation

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