Impact of a QTL for plasticity of productive tiller number on yield and yield competitive ability of spring wheat
Nasseer, Afaf Mahdee.
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Heat and drought stress are important limitations on wheat growth and reproduction. Therefore, there is a need to understand mechanisms that enable wheat plant adapted to heat and drought stress, and maintain plant growth, development, and productivity during stress periods. One of the most important plasticity traits in wheat is productive tiller number (PTN). This thesis reports two studies. The goal of the first study was to test the impact of a previously identified allele for high productive tiller number on yield and yield components, agronomics, and seed quality traits, in a set of near isogenic lines developed in three genetic backgrounds, including the crosses Vida/McNeal, Reeder/Choteau, and Reeder/Hank. Results from nine field locations showed that high productive tiller allele on QTn.mst-6B enhanced early tiller (ETN) formation regardless of the locations. Under favorable conditions, the large number of early tillers transferred into a capacity for high productive tiller number, which may enhance grain yield. Seed number per head and seed weight was affected negatively by the high tiller allele at QTn.mst-6B over all locations, and thus more tillers did not always equate to higher yield. Moreover the high productive tiller allele on QTn.mst-6B associated with high dry weight of roots based on a greenhouse study. The goal for second study was to assess the impact of QTn.mst-6B under different competition levels and levels of available water. Five near-isogenic line (NIL) pairs for two genetic backgrounds (Reader/Choteau, Vida/McNeal) were selected randomly from the three populations of our first study. Three competition levels were imposed on the NIL pairs in replicated experiments. Competition levels were 1) bordered rows representing high competition and limited water, 2) non-bordered rows representing less competition and more available water, and 3) space-planted rows representing no competition and abundant water. The experiment was planted over three locations on 2012 and 2013. The ETN more often developed into PTN in conditions with less competition levels, while did not develop into PTN in conditions of high competition and low water. The high plasticity of PTN was associated with high plasticity in grain yield, and low plasticity of seed weight.