Abstract:
The qTSN4 was identified as rice QTL (Quantitative Traits Locus) increasing total spikelet
number per panicle and flag leaf area but potentially reducing panicle number depending
on the environment. So far, this trade-off was mainly observed at grain maturity and
not specifically studied in details, limiting the apprehension of the agronomic interest of
qTSN4. This study aimed to understand the effect of qTSN4 and of the environment
on panicle sizing, its trade-off with panicle number, and finally plant grain production.
It compared two high yielding genotypes to their Near Isogenic Lines (NIL) carrying
either QTL qTSN4 or qTSN12, two distinct QTLs contributing to the enlarged panicle
size, thereafter designated as qTSN. Traits describing C sink (organ appearance rate,
size, biomass) and source (leaf area, photosynthesis, sugar availability) were dynamically
characterized along plant and/or panicle development within two trials (greenhouse,
field), each comparing two treatments contrasting for plant access to light (with or without
shading, high or low planting densities). The positive effect of qTSN on panicle size
and flag leaf area of the main tiller was confirmed. More precisely, it could be shown
that qTSN increased leaf area and internode cross-section, and in some cases of the
photosynthetic rate and starch reserves, of the top 3–4 phytomers of the main tiller.
This was accompanied by an earlier tillering cessation, that coincided with the initiation
of these phytomers, and an enhanced panicle size on the main tiller. Plant leaf area at
flowering was not affected by qTSN but fertile tiller number was reduced to an extent
that depended on the environment. Accordingly, plant grain production was enhanced by
qTSN only under shading in the greenhouse experiment, where panicle number was not
affected and photosynthesis and starch storage in internodes was enhanced. The effect
of qTSN on rice phenotype was thus expressed before panicle initiation (PI). Whether
early tillering reduction or organ oversizing at meristem level is affected first cannot be
entirely unraveled. Further studies are needed to better understand any signal involved in
this early regulation and the qTSN × Environment interactions underlying its agronomic
interest.
