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The lack of quantitative methods independent of the conventional qualitative phenology, may be a vital limiting factor to evaluate the temporal trends in the crop growth cycle, particularly in the heterogeneous canopies of cultivar mixtures. A digital camera used to take ground-based nadir images during two years of a field experiment conducted at the College of Agriculture, Shiraz University, Iran; in 2014-15 and 2015-16. The experimental treatments consisted of 4 early-to middle-ripening wheat cultivars and their 10 mixtures, under post-anthesis well-and deficit-irrigation conditions, arranged in a randomized complete block design with 3 replicates. Then the images were processed and three image-derived indices including CC (canopy cover), GR [(G-R/G); RGB color system], and CCGR (CC×GR) were used as the quantifying criteria. The declining trends of these indices during ripening showed strong fits to binomial equations, based on which simple prediction models were suggested and validated. Furthermore, the split linear trends and their slopes were estimated to assess the short-term variations. Some agronomic aspects were also evidenced using the mixturesmonoculture diversions, and the relationship between CC and GR. The frameworks evaluated appears to provide the reliable and simple solutions for quantifying the crop temporal trends parallel to the conventional phenology.

The lack of quantitative methods independent of the conventional qualitative phenology, may be a vital limiting factor to evaluate the temporal trends in the crop growth cycle, particularly in the heterogeneous canopies of cultivar mixtures. A digital camera used to take ground-based nadir images during two years of a field experiment conducted at the College of Agriculture, Shiraz University, Iran; in 2014-15 and 2015-16. The experimental treatments consisted of 4 early-to middle-ripening wheat cultivars and their 10 mixtures, under post-anthesis well-and deficit-irrigation conditions, arranged in a randomized complete block design with 3 replicates. Then the images were processed and three image-derived indices including CC (canopy cover), GR [(G-R/G); RGB color system], and CCGR (CC×GR) were used as the quantifying criteria. The declining trends of these indices during ripening showed strong fits to binomial equations, based on which simple prediction models were suggested and validated. Furthermore, the split linear trends and their slopes were estimated to assess the short-term variations. Some agronomic aspects were also evidenced using the mixturesmonoculture diversions, and the relationship between CC and GR. The frameworks evaluated appears to provide the reliable and simple solutions for quantifying the crop temporal trends parallel to the conventional phenology.

Background Mean grain weight (MGW) is among the most frequently measured parameters in wheat breeding and physiology. Although in the recent decades, various wheat grain analyses (e.g. counting, and determining the size, color, or shape features) have been facilitated, thanks to the automated image processing systems, MGW estimations have been limited to using few number of image-derived indices; i.e. mainly the linear or power models developed based on the projected area (Area). Following a preliminary observation which indicated the potential of grain width in improving the predictions, the present study was conducted to explore more efficient indices for increasing the precision of image-based MGW estimations. For this purpose, an image archive of the grains was processed, which were harvested from a 2-year field experiment carried out with 3 replicates under two irrigation conditions and included 15 cultivar mixture treatments (so the archive was consisted of 180 images including more than 72,000 grains). Results It was observed that among the more than 30 evaluated indices of grain size and shape, indicators of grain width (i.e. Minor & MinFeret) along with 8 other empirical indices had a higher correlation with MGW, compared with Area. The most precise MGW predictions were obtained using the Area × Circularity, Perimeter × Circularity, and Area/Perimeter indices. Furthermore, it was found that (i) grain width and the Area/Perimeter ratio were the common factors in the structure of the superior predictive indices; and (ii) the superior indices had the highest correlation with grain width, rather than with their mathematical components. Moreover, comparative efficiency of the superior indices almost remained stable across the 4 environmental conditions. Eventually, using the selected indices, ten simple linear models were developed and validated for MGW prediction, which indicated a relatively higher precision than the current Area-based models. The considerable effect of enhancing image resolution on the precision of the models has been also evidenced. Conclusions It is expected that the findings of the present study, along with the simple predictive linear models developed and validated using new image-derived indices, could improve the precision of the image-based MGW estimations, and consequently facilitate wheat breeding and physiological assessments.

Mean grain weight (MGW) is among the most frequently measured parameters in wheat breeding and physiology. Although in the recent decades, various wheat grain analyses (e.g. counting, and determining the size, color, or shape features) have been facilitated thanks to the automated image processing systems, MGW estimations has been limited to using few number of image-derived indices; i.e. mainly the linear or power models developed based on the projected area (Area). Following a preliminary observation which indicated the potential of grain width in improving the predictions, the present study was conducted to explore potentially more efficient indices for increasing the precision of image-based MGW estimations. For this purpose, an image archive of the grains was processed, which was harvested from a two-year field experiment carried out with 3 replicates under two irrigation conditions and included 15 cultivar mixture treatments (so the archive was consisted of 180 images taken from an overall number of more than 72000 grains). It was observed that among the more than 30 evaluated indices of grain size and shape, indicators of grain width (i.e. Minor & MinFeret) along with 8 other empirical indices had a higher correlation with MGW, compared with Area. The most precise MGW predictions were obtained using the Area*Circularity, Perimeter*Circularity, and Area/Perimeter indices. In general, two main common factors were detected in the structure of the major indices, i.e. either grain width or the Area/Perimeter ratio. Moreover, comparative efficiency of the superior indices almost remained stable across the 4 environmental conditions. Eventually, using the selected indices, ten simple linear models were developed and validated for MGW prediction, which indicated a relatively higher precision than the current Area-based models. The considerable effect of enhancing image resolution on the precision of the models has been also evidenced. It is expected that the findings of the present study improve the precision of the image-based MGW estimations, and consequently facilitate wheat breeding and physiological assessments.

Light extinction is the most fundamental aspect of green canopies. The exponential form of light gradient is extensively evaluated or utilized by conventional approaches mainly in contribution to the vital concept of leaf area index (LAI), which reasonably characterizes canopies based on their theoretical capability for light attenuation i.e. having greater leaf surfaces. We analyzed the image archive of heterogeneous wheat canopies (cultivar mixtures), captured from experimental plots of a two-year field study conducted at College of Agriculture, Shiraz University, Iran, to evaluate the option of using commercial digital cameras for comparing the canopies based on their relative optics, and also providing new representation of light extinction within the canopy. Here, two novel distinct techniques including different imaging and calculation methods were employed. In the first one, or Green-based Segmentation Model (GSM), pixels of vegetation parts were categorized into "n" light-to-darkness groups based on their similar Green values (RGB color system). Then, mean red, mean green, and mean blue values of each group were calculated and their separate trends were plotted against the mentioned green light-to-dark steps. In the second method, a kind of in-situ spectroscopy of sun-exposed leaves (DLBE, Double-shot Light Balance Equations) was evaluated under the isotropic scattering assumption, with the aim of estimating the absorbed portion of light by sun-exposed leaves, using reflected and transmitted portions. Facing the sun, and then with the sun behind the camera, two images not peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission.The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/241786 doi: bioRxiv preprint first posted online Jan. 1, 2018; 2 were taken from each plot; in which "Transmission" and "Reflection" ROIs (ranges of interest) were extracted, respectively. Finally, normalized color values were calculated using mean RGBs of either type of ROI. Results of GSM showed that the green-scaled gradient of reflected red and blue lights had robust exponential trends which could be readily utilized for identifying canopies in the form of one or two image-derived equation (

Wheat cultivar mixtures with heterogeneous phenology has a less-explored potential to improve crop diversity, yield stability, and agronomic features particularly in response to the currently increased environmental stresses and uncertainties. To investigate the option of using wheat cultivar mixtures with different ripening patterns for mitigating the adverse effects of postanthesis water stress, a two-year field experiment was conducted during 2014-15 and 2015-16 growing seasons at the research field of School of Agriculture, Shiraz University, Iran. The factorial experiment was a Randomized Complete Block Design with 3 replicates, in which 15 mixture treatments including monocultures and every 11 possible mixtures of four early-to middle-ripening wheat cultivars were grown under two normal and post-anthesis deficitirrigation conditions. Measured traits and estimated indices included grain yield and its components, canopy temperature, soil water content, water productivity, susceptibility index, and water use efficiency. The results indicated that under the stressful condition of post-anthesis deficit-irrigation, heterogeneity in the ripening pattern of mixtures was declined. Consequently, dissimilarities in grain yields as well as various agronomic characters of mixture treatments were also lessened. This may be an evidence for the negative effect of water shortage stress on heterogeneity within agroecosystems. Although cultivar mixtures showed some casual advantages in some traits, such beneficial effects were not consistent across all conditions. Moreover, no cultivar mixture produced higher grain yield than the maximum monoculture. Despite the general expectation for beneficial ecological services from cultivar mixtures, in many cases disadvantageous blends were found which led to a considerable reduction in grain yield and water productivity. Therefore, it is suggested that unless the performance, and preferably the involved mechanisms, of cultivar mixtures are not fully understood, use of blends as an alternative for conventional high-input wheat cropping systems may lead to adverse results. a potential solution for water deficit conditions prevailed in semi-arid areas (Haghshenas et al., 2013;Fang et al., 2014;Adu-Gyamfi et al., 2015;Wang et al., 2016).One kind of dissimilarities among the mixture components considered for designing cultivar blends are phenological differences, which are physiologically vital enough to mainly determine the fate of interaction between the crop and environment. Accordingly, Haghshenas et al., (2013) evaluated the option of mitigating the intensified post-anthesis competition within the mixed canopy of two early-and middle-ripening wheat cultivars, and reported that the intra-specific competition under various seasons and irrigation conditions was several percent lower in mixtures, compared with monocultures; however, this relative advantage did not lead to significantly higher grain yield and post-anthesis water use efficiency. Besides, the equal mixing ratio (1:1) of th...

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