Moroyoqui Parra, Marcela Alejandra
(2022)
Identifying canopy architecture traits to optimize light and increase radiation-use efficiency and grain yield in wheat.
PhD thesis, University of Nottingham.
Abstract
Wheat is the most widely grown crop which produces ~766 million tonnes per year (FAOSTAT, 2019) supplying 20% of the calories and protein for the human population (Braun et al., 2010). Staple crops (wheat, maize, rice and soybean) must increase their yield by 2.4% per year to meet the food demand for a growing population (Ray et al., 2013). Climate change has been predicted to increase the global temperature by ~ 2-4°C by the end of the 21th century (IPCC, 2014), with more frequent flooding and drought decreasing the production of grain crops (IPCC, 2014; Asseng et al., 2015). Harvest index (grain dry matter as a proportion of above-ground dry matter; HI) is approaching its theoretical limit (Austin et al., 1980; Foulkes et al., 2011), so other alternatives must be explored to increase biomass and hence grain yield. Radiation-use efficiency (above-ground dry matter per unit radiation interception; RUE) has therefore become an important trait for raising biomass and grain yield potential in plant breeding (Foulkes and Murchie, 2011a). In recent decades, growers in the Northwest of Mexico have adopted a raised-bed planting system (Fahong et al., 2004). This planting system showed advantages compared to the traditional flat-basin planting system such as water savings and reduced weeds and diseases (Fahong et al., 2004). However, effects on grain yield are still inconsistent so further studies are needed to prove grain yield benefits.
The overall objective of this thesis was to quantify genetic variation in canopy architecture traits and associations with light interception, radiation-use efficiency and grain yield in twelve spring wheat CIMMYT cultivars evaluated under two planting systems (raised beds and flat basins). These cultivars were evaluated in three field experiments under irrigated, yield potential conditions in 2017-18, 2018-19 and 2019-20 in the NW of Mexico. In the field experiments, measurements were taken of phenology, light interception, RUE during different phenophases, canopy architecture traits including flag-leaf angle and curvature, leaf size, biomass and dry matter partitioning at key developmental stages and grain yield and yield components. Two more experiments were carried out in the glasshouse at Sutton Bonington, UK in 2018 and 2019 to examine the photosynthetic rate eight of the 12 cultivars and its relation with radiation-use efficiency and biomass in the field experiments.
Results in the field experiments across the three years showed a planting system (PS) difference in grain yield which was 10.6% higher in beds than flats and a PS × G interaction. A planting system effect was also shown for grains per m2 (GM2), HI, grains per spike (GPS) and above-ground biomass at physiological maturity (BMPM). The higher grain yield obtained in beds was mainly explained by the 7.6 % greater biomass at maturity in beds. Biomass was initially lower in raised beds compared to flat basins at initiation of booting. The higher radiation-use efficiency calculated from initiation of booting to anthesis + 7 days (RUE_InBA7) in raised beds contributed to this PS catching up the biomass accumulation in the flat basins at anthesis + 7 days. A wide genetic variation was found for RUE calculated at five different phenophases from initiation of booting to physiological maturity. However, only RUE from emergence + 40 days to initiation of booting (RUE_E40InB), from initiation of booting to anthesis + 7 days (RUE_InBA7) and from emergence + 40 days to physiological maturity (RUET) showed a PS effect. A PS × G interaction was found for all the RUE’s except for RUE_InBA7. In both, PS positive associations were found among cultivars between RUE_preGF and biomass at GS65 + 7 days and biomass at physiological maturity. In addition, positive correlations were found among cultivars between each of RUE_preGF and RUET and grain yield in beds and flats. Results showed that grain yield responses of cultivars to planting system were mainly explained through effects on final biomass. Biomass responses to planting system were, in turn, associated with responses of RUE to planting system in the pre-anthesis period. Additionally, taller cultivars showed greater biomass increases at physiological maturity in B compared to F than shorter cultivars.
The flag-leaf curvature (FLcv; cm) was measured as the distance from the point of inflexion to the tip of the leaf. Genetic variation was found among the cultivars in flag-leaf angle and flag-leaf curvature at initiation of booting and anthesis+7 days. In flats, a strong negative association was found between flag-leaf angle and RUE during grain filling (RUE_GF), i.e. more upright flag leaves had higher RUE_GF. Additionally, a positive correlation between flag-leaf curvature at initiation of booting and anthesis + 7 days was found with RUE_InBA7 and RUE_GF in flats. In, beds, flag-leaf curvature at booting was positively associated with greater pre-anthesis radiation interception.
The planting system also affected flag-leaf angle at GS65 + 7 days with leaf angle decreasing (more upright leaves) in flat basins compared to raised beds, but cultivars differed in the extent of the decrease. Plant height measured in the beds was associated with responses PS of grain yield, biomass at physiological maturity and fractional light interception at anthesis + 7 days.
Averaging across the three years, a strong positive correlation among cultivars between grain yield and HI was found in flats whereas no significant correlation was found in beds. A negative correlation was observed between spike partitioning measured at anthesis + 7 days (SPI) and each of stem partitioning index (StemPI) and stem-internode 2 and 3 length. No associations between SPI and peduncle length was found. The genetic variation in GM2 was strongly associated with fruiting efficiency (grains per unit spike dry matter at GS65+7 days; FE) in flats and a trend was found in beds. FE accounted for more genetic variation in GM2 than SPI. The results in the present study confirm that plant breeders should consider the planting system when selecting canopy architecture traits to enhance RUE, biomass and grain yield as well as selecting lines with high FE.
In the glasshouse experiments, genetic variation among the cultivars was found for flag-leaf light-saturated photosynthetic rate (Amax) at anthesis. Encouragingly, a positive correlation was found between Amax at initiation of booting and anthesis measured in the glasshouse and biomass at physiological maturity in raised beds and flat basins measured in the field experiments.
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