Cytoplasmic male sterility (CMS) is a maternally transmitted trait, whereby a plant is unable to produce viable pollen. Studies have revealed that this trait is a tool for enabling efficient and reliable coexistence between genetically modified (GM) and non‐GM cultivation by biocontainment of GM maize (Zea mays L.) pollen. Maize has three types of male‐sterile cytoplasm (T, S, and C), the fertility of which can be restored by nuclear rf genes or by interactions with the environment. Twenty‐two CMS versions of modern European maize hybrids were evaluated in 17 environments in Switzerland, France, and Bulgaria, with two or three sowing dates, in 2005 and 2006. Stable and unstable male sterility occurred in all three CMS types. T‐cytoplasm hybrids were the most stable, while S‐cytoplasm hybrids often showed partial restoration of fertility. C‐cytoplasm was similar to T‐cytoplasm with regard to maintaining male sterility. Climatic factors, especially air temperature, evapotranspiration, and water vapor, during the 10 d before anthesis as well as during anthesis, were correlated positively or negatively with the partial reversion to male fertility of CMS hybrids, indicating an interaction between genetic and climatic factors. This study illustrates that T‐ and C‐cytoplasm in particular open up viable prospects for containing transgenic pollen, especially for Bt‐maize.
Early generation breeding nurseries with thousands of genotypes in single-row plots are well suited to capitalize on high throughput phenotyping. Nevertheless, methods to monitor the intrinsically hard-to-phenotype early development of wheat are yet rare. We aimed to develop proxy measures for the rate of plant emergence, the number of tillers, and the beginning of stem elongation using drone-based imagery. We used RGB images (ground sampling distance of 3 mm pixel-1) acquired by repeated flights (≥ 2 flights per week) to quantify temporal changes of visible leaf area. To exploit the information contained in the multitude of viewing angles within the RGB images, we processed them to multiview ground cover images showing plant pixel fractions. Based on these images, we trained a support vector machine for the beginning of stem elongation (GS30). Using the GS30 as key point, we subsequently extracted plant and tiller counts using a watershed algorithm and growth modeling, respectively. Our results show that determination coefficients of predictions are moderate for plant count (R2=0.52), but strong for tiller count (R2=0.86) and GS30 (R2=0.77). Heritabilities are superior to manual measurements for plant count and tiller count, but inferior for GS30 measurements. Increasing the selection intensity due to throughput may overcome this limitation. Multiview image traits can replace hand measurements with high efficiency (85–223%). We therefore conclude that multiview images have a high potential to become a standard tool in plant phenomics.
Leaf development of wheat largely determines the rate of plant growth in the early growth stages and is most sensitive to salinity. The objectives were to investigate the shoot growth, area of leaves, and kinetics of leaf elongation of wheat seedlings (Triticum aestivum L.) grown in illitic-chloritic silt loam with four salinity levels from 0 to 120 mM NaCl in growth chambers. Shoot fresh mass (FM) and leaf area were measured at days 12 and 18 after sowing. Instantaneous measurements of the leaf elongation rate (LER) of leaves 3, 4, and 5 of the main stem were carried out by using linear variable differential transducers (LVDT). Spatial distribution of relative elemental growth rate (REGR) and the length of the leaf elongation zone were determined by measuring displacement rates with a pricking method. Shoot FM per plant linearly decreased with increasing salinity levels. Leaf area under saline conditions was significantly correlated to the shoot FM during vegetative stages, indicating that leaf growth most sensitively responds to salinity. Salinity delayed leaf emergence and affected leaf growth longitudinally and laterally. Reduction in the final length of leaves 3, 4, and 5 was mainly a result of a decrease in their LER. The decreased LER under saline conditions was more pronounced during the steady growth phase and during the light period compared to later stages and to the dark period, respectively. Salinity affected the LER more severely with increasing leaf number, probably as a result of the longer exposure to salinity and longer elongation zones for higher leaf numbers. The reduction in LER resulted from decreasing the REGR but did not result from shortening the length of the leaf elongation zone during the linear phase of leaf growth.
Prolonged low temperature phases and shortterm cold spells often occur in spring during the crucial stages of early maize (Zea mays L.) development. The eVect of low temperature-induced growth retardation at the seedling stage on Wnal yield is poorly studied. Therefore, the aim was to identify genomic regions associated with morpho-physiological traits at Xowering and harvest stage and their relationship to previously identiWed quantitative trait loci (QTLs) for photosynthesis and morpho-physiological traits from the same plants at seedling stage. Flowering time, plant height and shoot biomass components at harvest were measured in a dent mapping population for cold tolerance studies, which was sown in the Swiss Midlands in early and late spring in two consecutive years. Early-sown plants exhibited chilling stress during seedling stage, whereas late-sown plants grew under favorable conditions. SigniWcant QTLs, which were stable across environments, were found for plant height and for the time of Xowering. The QTLs for Xowering were frequently co-localized with QTLs for plant height or ear dry weight. The comparison with QTLs detected at seedling stage revealed only few common QTLs. A pleiotropic eVect was found on chromosome 3 which revealed that a good photosynthetic performance of the seedling under warm conditions had a beneWcial eVect on plant height and partially on biomass at harvest. However, a high chilling tolerance of the seedling seemingly had an insigniWcant or small negative eVect on the yield.
Maize (Zea mays L.) Plus‐Hybrids are a blend of cytoplasmic male‐sterile (CMS) hybrids and unrelated male‐fertile hybrids ensuring pollination of the whole stand. Combining potential benefits of male sterility (CMS effect) and allo‐pollination (xenia effect), they often outperform the corresponding male‐fertile sib‐pollinated hybrids in terms of yield. The combining abilities of five CMS hybrids and eight pollinators were investigated in a factorial split‐plot design in 12 environments in four countries and two years. The plant material from different breeders represented the three types of male‐sterile cytoplasm. Plus‐Hybrids increased grain yield, on average, by 10% or more and by up to 20% in specific environments. Three highly responsive CMS hybrids and four generally good pollinators were identified. The Plus‐Hybrid effect affected both yield components, CMS leading mainly to a higher number of kernels (KN) and the xenia effect mainly to an increase in the thousand kernel weight (TKW). Despite some differences in the response of the three types of CMS, the effect of the cytoplasm was not significant. While the CMS effect depended strongly on environment, the xenia was consistent in all environments but its extent varied. As well as increasing yield, we can expect that Plus‐Hybrids can make a large contribution to the coexistence of transgenic and conventional maize by biocontainment, that is, eliminating or reducing the release of transgenic pollen in Bacillus thuringiensis (Bt) maize or herbicide‐tolerant (HT) maize.
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