Rice panicle plasticity in Near Isogenic Lines carrying a QTL for larger panicle is genotype and environment dependent.

Dewi Erika Adriani,Hélène Adam,Audrey Dardou,Delphine Luquet,Michael Dingkuhn,Tanguy Lafarge

doi:10.1186/s12284-016-0101-x

Abstract

BackgroundPanicle architectural traits in rice (branching, rachis length, spikelet number) are established between panicle initiation and heading stages. They vary among genotypes and are prone to Genotype x Environment interactions. Together with panicle number, panicle architecture determines sink-based yield potential. Numerous studies analyzed genetic and environmental variation of plant morphology, but the plasticity of panicle structure is less well understood. This study addressed the response of rice panicle size and structure to limited light availability at plant level for near-isogenic lines (NILs) with IR64 or IRRI146 backgrounds, carrying the QTL qTSN4 (syn. SPIKE) for large panicles. Full light and shading in the greenhouse and two population densities in the field were implemented. The image analysis tool P-TRAP was used to analyze the architecture of detached panicles.ResultsThe qTSN4 increased total branch length, branching frequency and spikelet number per panicle in IRRI146 background in the field and greenhouse, and in IR64 background in the greenhouse, but not for IR64 in the field. In the field, however, qTSN4 reduced panicle number, neutralizing any potential yield gains from panicle size. Shading during panicle development reduced spikelet and branch number but qTSN4 mitigated partly this effect. Spikelet number over total branch length (spikelet density) was a stable allometry across genotypes and treatments with variation in spikelet number mainly due to the frequency of secondary branches. Spikelet number on the main tiller was correlated with stem growth rate during panicle development, indicating that effects on panicle size seemed related to resources available per tiller.ConclusionsThe qTSN4 effects on panicle spikelet number appear as indirect and induced by upstream effects on pre-floral assimilate resources at tiller level, as they were (1) prone to G x E interactions, (2) non-specific with respect to panicle architectural traits, and (3) associated with pre-floral stem growth rate.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-016-0101-x) contains supplementary material, which is available to authorized users.

Highlights

IntroductionPanicle architectural traits in rice (branching, rachis length, spikelet number) are established between panicle initiation and heading stages
Panicle architectural traits in rice are established between panicle initiation and heading stages
This was recently confirmed by Adriani et al (2016) analyzing near isogenic lines (NILs) with larger panicles developed by Qi et al (2008) and Fujita et al (2009, 2012) carrying qTSN4 on the long arm of chromosome 4, a QTL identified for high total spikelet number (TSN)

Summary

Introduction

Panicle architectural traits in rice (branching, rachis length, spikelet number) are established between panicle initiation and heading stages. Shiratsuchi et al (2007) revealed that yield is correlated with the ratio of spikelet number to tiller dry weight after spikelet differentiation, and Endo-Higashi and Izawa (2011) suggested that pre-floral photosynthate accumulation determines reproductive sink capacity This was recently confirmed by Adriani et al (2016) analyzing near isogenic lines (NILs) with larger panicles developed by Qi et al (2008) and Fujita et al (2009, 2012) carrying qTSN4 on the long arm of chromosome 4, a QTL identified for high total spikelet number (TSN). Adriani et al (2016) reported that panicle size was strongly affected by (i) shading imposed during the reproductive phase in the greenhouse or (ii) change in plant density in the field These authors revealed that the effect of qTSN was associated with an earlier tillering cessation and the development of subsequent larger internodes and leaf blades and so was already visible before panicle initiation. It highlights that there is a direct response of panicle development to tiller and plant vigor that can be related, either directly to a reduction in light access and C acquisition through cloudiness or planting density, as reported on sorghum (Lafarge et al 2002), or indirectly to another abiotic constraint affecting C sourcesink balance in the plant, for example drought (Luquet et al 2008; Pallas et al 2013)

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