First steps to understand heat tolerance of temperate maize at adult stage: identification of QTL across multiple environments with connected segregating populations
Theor Appl Genet
First steps to understand heat tolerance of temperate maize at adult stage: identification of QTL across multiple environments with connected segregating populations
Felix P. Frey 0 1 2 3 4
0 Communicated by N. de Leon
1 Group Limagrain , Fehrpart u. 80, 6710 Szeged , Hungary
2 Group Limagrain , Am Eggenkamp 1, 48268 Greven , Germany
3 KWS SAAT SE , Grimsehlstrasse 31, 37555 Einbeck , Germany
4 Max Planck Institute for Plant Breeding Research , Carl-von-Linné-Weg 10, 50829 Cologne , Germany
High temperatures have the potential to cause severe damages to maize production. This study aims to elucidate the genetic mechanisms of heat tolerance under field conditions in maize and the genome regions contributing to natural variation. In our study, heat tolerance was assessed on a multi-environment level under non-controlled field conditions for a set of connected intra- and interpool Dent and Flint populations. Our findings indicate that Dent are more heat tolerant during adult stage than Flint genotypes. We identified 11 quantitative trait loci (QTL) including 2 loci for heat tolerance with respect to grain yield. Furthermore, we identified six heat-tolerance and 112
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* Benjamin Stich
heat-responsive candidate genes colocating with the
previously mentioned QTL. To investigate their contribution to
the response to heat stress and heat tolerance, differential
expression and sequence variation of the identified
candidate genes should be subjected to further research.
Maize (Zea mays L.) was grown on 184 million hectares
in 2013 and was, thus, the second most widely cultivated
crop after wheat (FAOSTAT 2014). In temperate regions
of Europe, maize is of increasing importance as fodder
for animal production and, lately, for biogas production
(Deutsches Maiskomitee 2013).
With the progress of climate change, the global mean
temperature and variance are expected to increase in the
future (IPCC 2013). Lobell and Field (2007) observed a
negative correlation of the yields of major crops,
including maize, and an increasing global mean temperature. The
effects of heat stress on plants are yield losses, growth
inhibition and leaf scorching (Wahid et al. 2007), which was
also reported for maize in temperate regions (Giaveno and
Ferrero 2003). Especially during flowering and grain
filling, heat stress has severe impacts on maize plants
(Barnabás et al. 2008). Thus, breeding heat-tolerant cultivars is
crucial to sustain crop production in the future (Chen et al.
2012).
Two complementary approaches are conceivable to
increase heat tolerance in European maize germplasm.
One possibility is to introgress exotic germplasm as
described by Giaveno and Ferrero (2003). The second
approach, which is described in this present study, has the
potential to reduce the introgression of alleles which are
associated with non-adaptedness to a temperate climate.
It consists in assessing heat-tolerance variation in local
germplasm and enhancing the frequency of the present
positive alleles.
The molecular and physiological basis of heat tolerance
in maize was studied intensively by Crafts-Brandner and
Salvucci (2002), Ashraf and Hafeez (2004) and Sinsawat
et al. (2004). Further, Ottaviano et al. (1991), Frova and
Sari-Gorla (1994), Reimer et al. (2013) and Frey et al.
(2015) investigated this question with a focus on natural
variation. All these mentioned studies examined the heat
tolerance of seedlings or pollen grains grown under
controlled conditions. Nevertheless, experiments on seedlings
can never substitute experiments on adult plants grown
under field conditions (Roy et al. 2011) and can only be
an auxiliary means to study the phenotypic and genotypic
response to heat stress. Chen et al. (2012), Cairns et al.
(2013) and Rattalino Edreira and Otegui (2013)
examined heat tolerance of maize in adult stage and measured
yield potential under field conditions. However, to the
best of our knowledge, no previous study has used natural
variation to genetically dissect heat tolerance under field
conditions.
Earlier studies used different approaches to quantify
the effect of a certain level of heat stress on the
occurrence of phenotypic heat stress symptoms. Chen et al.
(2012) and Cairns et al. (2013) described the heat
tolerance of a genotype as the performance at high
temperature conditions, without considering the relation of the
performance at heat conditions to a control environment.
Fokar et al. (1998) estimated heat tolerance in wheat
by the reduction of trait values at heat conditions
compared to a control condition. A more advanced approach
was pursued by Mason et al. (2010) and Paliwal et al.
(2012), who calculated heat susceptibility for wheat on
a one-trait basis for yield components, relating the trait
value of plants grown under heat conditions with their
trait value at control conditions, taking into account the
stress intensity at the heat conditions across all
genotypes. However, to the best of our knowledge, (...truncated)