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Potential contribution of dwarf and leaf longevity traits to yield improvement in photoperiod sensitive sorghum

Kouressy M., Dingkuhn M., Vaksmann M., Clément-Vidal A., Chantereau J.. 2008. European Journal of Agronomy, 28 (3) : p. 195-209.

Sorghum breeders in West Africa seek to combine photoperiod-sensitivity with short-stature, stay-green and high-yield potential. A field study explored physiological interactions among these traits. Three genotypes were compared by growth analysis, V1 (tall, traditional, photoperiod-sensitive), V2 (dwarfed, photoperiod-sensitive descendant of V1) and V3 (photoperiod-insensitive, stay-green, dwarf hybrid). Seed was sown in fields near Bamako (Mali) with supplemental irrigation in 2004 and 2005 on three dates (D1, 22 June; D2, 16 July; D3, 15 September). Measurements included phenology (leaf number and life span; reproductive development), leaf length/width and internode length distribution on main stems, leaf area index (LAI), fertile tiller number, dry wt of green and senescent aboveground organs, and yield. Crop growth rate (CGR) was calculated from dry wt dynamics. Stem sugar reserves were analyzed on stems at flowering and maturity. Photoperiod-sensitive V1 and V2 showed variable crop duration among dates but not years, whereas V3 had nearly constant duration. Dwarfing of V2 was due to shorter internodes but did not affect leaf length, width and specific leaf area. V3 had higher LAI than V1 and V2 after flowering due to greater leaf longevity. Leaf senescence was substantial even before flowering in V1 and V2, causing reduced CGR at flowering. Grain yield of V1, up to 3.7 m tall, was 1.0 t ha?1 and varied little whereas stem dry wt varied between 4 and 14 t ha?1. V2 attained only half the height of V1 and had smaller stem dry wt, but 2¿3-fold greater yields. Yield of V3, which had the same height as V2, averaged 4.5 t ha?1. Only V2 showed a positive yield response to crop duration (sowing date) due to variable panicle number plant?1 and yield panicle?1, which were correlated (P < 0.001). In all cultivars, large stem sucrose reserves remained constant from flowering to maturity, indicating that sugars were not mobilized and did not limit grain filling. It is concluded that the dwarf habit of V2, compared to V1, reduced competition for assimilates among sinks during stem elongation and thus enabled survival of more productive tillers and development of larger panicles. Dwarfing and compensatory tillering thus benefited yield potential. Introduction of stay-green to increase assimilates for grain filling would theoretically not improve yield because yield was sink limited. Expression of stay-green before flowering, however, might alleviate source restrictions to sink capacity development. (Résumé d'auteur)

Mots-clés : rendement; dimension; photopériodicité; glucide; tige; feuille; croissance; nanisme; phénologie; expérimentation; génotype; sorghum bicolor; afrique occidentale; mali

Thématique : Physiologie végétale : croissance et développement; Génétique et amélioration des plantes

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