28Recent advancements in phenomics coupled with increased output from sequencing tech-29 nologies can create the platform needed to rapidly increase abiotic stress tolerance of crops, 30 which increasingly face productivity challenges due to climate change. In particular, the 31 high-throughput phenotyping (HTP) enables researchers to generate large-scale data with 32 temporal resolution. Recently, a random regression model (RRM) was used to model a 33 longitudinal rice projected shoot area (PSA) dataset in an optimal growth environment. 34 However, the utility of RRM is still unknown for phenotypic trajectories obtained from 35 stress environments. Here, we sought to apply RRM to forecast the rice PSA in control 36 and water-limited conditions under various longitudinal cross-validation scenarios. To this 37 end, genomic Legendre polynomials and B-spline basis functions were used to capture PSA 38 trajectories. Prediction accuracy declined slightly for the water-limited plants compared to 39 control plants. Overall, RRM delivered reasonable prediction performance and yielded better 40 prediction than the baseline multi-trait model. The difference between the results obtained 41 using Legendre polynomials and that using B-splines was small; however, the former yielded 42 a higher prediction accuracy. Prediction accuracy for forecasting the last five time points 43 was highest when the entire trajectory from earlier growth stages was used to train the basis 44 functions. Our results suggested that it was possible to decrease phenotyping frequency by 45 only phenotyping every other day in order to reduce costs while minimizing the loss of pre-46 diction accuracy. This is the first study showing that RRM could be used to model changes 47 in growth over time under abiotic stress conditions. 48 3 Background 49 Plant biology has become a large-scale, data-rich field with the development of high-throughput 50 technologies for genomics and phenomics. This has increased the feasibility of data driven ap-51 proaches to be applied to address the challenge of developing climate-resilient crops (Tester 52 and Langridge, 2010). Crop responses to environmental changes are highly dynamic and 53 have a strong temporal component. Such responses are also known as function-valued traits, 54 for which means and covariances along the trajectory change continuously. Single time 55 point measurements of phenotypes, however, only provide a snapshot, posing a series of 56 challenges for research efforts aimed at understanding the ability of the plant to mount a 57 tolerant response to an environmental constraint. Advancements in high-throughput phe-58 notyping (HTP) technologies have enabled the automated collection of measurements at 59high temporal resolution to produce high density image data that can capture a plethora of 60 morphological and physiological measurements (Furbank and Tester, 2011). In particular, 61 image-based phenotyping has been deemed a game changer because conventional phenotyp-62 ing is laborious an...