Combining UAV-RGB high-throughput field phenotyping and genome-wide association study to reveal genetic variation of rice germplasms in dynamic response to drought stress.

Accurate and high-throughput phenotyping of the dynamic response of a large rice population to drought stress in the field is a bottleneck for genetic dissection and breeding of drought resistance. Here, high-efficiency and high-frequent image acquisition by an unmanned aerial vehicle (UAV) was utilized to quantify the dynamic drought response of a rice population under field conditions. Deep convolutional neural networks (DCNNs) and canopy height models were applied to extract highly correlated phenotypic traits including UAV-based leaf-rolling score (LRS_uav), plant water content (PWC_uav) and a new composite trait, drought resistance index by UAV (DRI_uav). The DCNNs achieved high accuracy (correlation coefficient R = 0.84 for modeling set and R = 0.86 for test set) to replace manual leaf-rolling rating. PWC_uav values were precisely estimated (correlation coefficient R = 0.88) and DRI_uav was modeled to monitor the drought resistance of rice accessions dynamically and comprehensively. A total of 111 significantly associated loci were detected by genome-wide association study for the three dynamic traits, and 30.6% of them were not detected in previous mapping studies using nondynamic drought response traits. Unmanned aerial vehicle and deep learning are confirmed effective phenotyping techniques for more complete genetic dissection of rice dynamic responses to drought and exploration of valuable alleles for drought resistance improvement.

Common and specific genetic basis of metabolite-mediated drought responses in rice.

Plants orchestrate drought responses at metabolic level but the genetic basis remains elusive in rice. In this study, 233 drought-responsive metabolites (DRMs) were quantified in a large rice population comprised of 510 diverse accessions at the reproductive stage. Large metabolic variations in drought responses were detected, and little correlation of metabolic levels between drought and normal conditions were observed. Interestingly, most of these DRMs could predict drought resistance in high accuracy. Genome-wide association study revealed 2522 significant association signals for 233 DRMs, and 98% (2471/2522) of the signals were co-localized with the association loci for drought-related phenotypic traits in the same population or the linkage-mapped QTLs for drought resistance in other populations. Totally, 10 candidate genes were efficiently identified for nine DRMs, seven of which harbored cis-eQTLs under drought condition. Based on comparative GWAS of common DRMs in rice and maize, representing irrigated and upland crops, we have identified three pairs of homologous genes associated with three DRMs between the two crops. Among the homologous genes, a transferase gene responsible for metabolic variation of N-feruloylputrescine was confirmed to confer enhanced drought resistance in rice. Our study provides not only genetic architecture of metabolic responses to drought stress in rice but also metabolic data resources to reveal the common and specific metabolite-mediated drought responses in different crops.

[Growth characteristics of rock plant Pogonatherum paniceum].

The study on the growth characters, above and underground biomass, and root-shoot ratio of Pogonatherum paniceum grown on three types of substrates and five types of habitats in Chongqing showed that there were significant differences in plant growth characters, including stalk basal diameter, plant canopy and height, root system area and depth, and maximum root length among five habitats. For shoot growth, though the plants grown on purple soil had the maximum stalk basal diameter (15.18 cm), canopy (3 086.77 cm2) and height (6.58 cm) while those grown on purple sandy rock had the minimum values (stalk basal diameter 10.89 cm, canopy 1 868.79 cm2, and height 60.75 cm). There were no significant differences among three types of substrates. As for root system, there were significant differences between sandy rocks and purple soil, the plants grown on sandy rocks having higher means of root system area (1 389.14 cm2 and 1 487.14 cm2) and maximum root length (45.83 cm and 39.24 cm) than those grown on purple soil (root system area 717.09 cm2, maximum root length 21.42 cm). The plants grown on sandy rock allocated more biomass to root system, and had higher root-shoot ratio, which was helpful for its fixation on rock and its endurance on the desiccation and arid of rock substrate.