Due to its tropical origin and adaptation, rice is significantly impacted by cold stress, and consequently sustains large losses in growth and productivity. Currently, rice is the second most consumed cereal in the world and production losses caused by extreme temperature events in the context of "major climatic changes" can have major impacts on the world economy. We report here an analysis of rice genotypes in response to low-temperature stress, studied through physiological gas-exchange parameters, biochemical changes in photosynthetic pigments and antioxidants, and at the level of gene and protein expression, towards an understanding and identification of multiple low-temperature tolerance mechanisms. The first effects of cold stress were observed on photosynthesis among all genotypes. However, the tropical japonica genotypes Secano do Brazil and Cypress had a greater reduction in gas exchange parameters like photosynthesis and water use efficiency in comparison to the temperate japonica Nipponbare and M202 genotypes. The analysis of biochemical profiles showed that despite the impacts of low temperature on tolerant plants, they quickly adjusted to maintain their cellular homeostasis by an accumulation of antioxidants and osmolytes like phenolic compounds and proline. The cold tolerant and sensitive genotypes showed a clear difference in gene expression at the transcript level for OsGH3-2 , OsSRO1a , OsZFP245 , and OsTPP1 , as well as for expression at the protein level for LRR-RLKs, bHLH, GLYI, and LTP1 proteins. This study exemplifies the cold tolerant features of the temperate japonica Nipponbare and M202 genotypes, as observed through the analysis of physiological and biochemical responses and the associated changes in gene and protein expression patterns. The genes and proteins showing differential expression response are notable candidates towards understanding the biological pathways affected in rice and for engineering cold tolerance, to generate cultivars capable of maintaining growth, development, and reproduction under cold stress. We also propose that the mechanisms of action of the genes analyzed are associated with the tolerance response.

Hail adjusters, entomologists, and others frequently use defoliation percentages to estimate soybean [Glycine max (L.) Merr.] yield loss caused by hail, insects, or diseases. Little information is available on the percent yield loss from defoliation under drought stress and adequate moisture. Thus, the objective of this research was to measure yield response of a determinate soybean cultivar ‘Lee 74’ to different levels of defoliation under irrigated and non‐irrigated conditions. Field experiments were conducted on a Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualfs) at Stuttgart, Ark., during a 3‐year period to study effects of four levels of defoliation (0, 50, 75, and 100%) applied at three stages of development (V5, R2, and R4) in 1974 and 1975 and two stages (V3 and R5) in 1976 on yield of irrigated and nonirrigated soybeans. Irrigation significantly increased yield 7% in 1974, 38% in 1975, and 51% in 1976. Mean squares for levels of defoliation, stages of treatment, and the defoliation × stage interaction were highly significant each year. The least reduction in yield occurred when plants were defoliated at vegetative stages, V3 and V5, and the most at reproductive stages, R4 (full pod) and R5 (beginning seed). Average yield reductions for 50, 75, and 100% defoliation were 11, 17, and 37%, respectively. Percent yield reductions under irrigated and non‐irrigated conditions were similar because all interactions with irrigation treatments were non‐significant. This same pattern existed regardless of whether the season was extremely dry as hi 1975 and 1976 or moderately dry as in 1974. Reduction in number of pods appeared to be the yield component primarily responsible for yield losses from defoliation. Results from these experiments indicated that percent reduction in yield from defoliation is similar for soybeans grown with adequate moisture or under drought stress.

Background: Rice is the main staple food for the global population and drought is one of the limited factor in rice production. In this research, progeny of a cross between an adapted U.S. rice cultivars with a tropical japonica and an indica rice genotype, were screened for drought resistant (DR) traits to identify DR loci, that would be useful for breeding U.S. rice cultivars for a water saving agricultural system.Results: A recombinat inbred line (RIL) population, generated from selfed progeny of the cross between the drought resistant tropical japonica U.S. cultivar Kaybonnet and an indica drought sensitive cultivar ZHE733, was chosen for quantitative trait locus (QTLs) analysis of drought-resistance related traits. The DR traits were quantified by measuring different parameters of morphological traits, grain yield components and root architectural traits. K/Z RIL population of 198 lines were screened in the field at Fayetteville (AR), by giving controlled drought stress (DS) and well-watered (WW) treatment at the reproductive stage, consequently for three years and the effects of DS were quantify by measuring morphological traits and grain yield components. The effect of abscisic acid (ABA) sensitivity screen on parents and 198 lines at the V3 stage in culture media was quantified by measuring root architectural traits. QTL analysis was performed with a set of 4133 single nucleotide polymorphism (SNP) markers by using QTL IciMapping software version 4.2.53. A total of 41 QTLs and 184 candidate genes within the DR-QTL regions were identified for drought related traits. The potential candidate genes were validated by RT-qPCR of parental lines. The results of candidate DR genes revealed that the gene expression of 15 candidate DR genes with known annotations, and two candidate DR genes with unknown annotations within the DR-QTL regions were up-regulated in the drought resistant parent (Kaybonnet) compared to the drought sensitive parent (ZHE733) under DS conditions.Conclusions: In this study, we detected 41 QTLs and 184 candidate genes within the DR-QTL regions, and most of the candidate genes were up-regulated in Kaybonnet as the drought resistant parent. The findings of this research provide important information to develop drought-resistant rice varieties with greater productivity under DS conditions.

Rice (Oryza sativa L.) is the primary food for half of the global population. Recently, there has been increasing concern in the rice industry regarding the eating and milling quality of rice. This study was conducted to identify genetic information for grain characteristics using a recombinant inbred line (RIL) population from a japonica/indica cross based on high-throughput SNP markers and to provide a strategy for improving rice quality. The RIL population used was derived from a cross of “Kaybonnet (KBNT lpa)” and “ZHE733” named the K/Z RIL population, consisting of 198 lines. A total of 4133 SNP markers were used to identify quantitative trait loci (QTLs) with higher resolution and to identify more accurate candidate genes. The characteristics measured included grain length (GL), grain width (GW), grain length to width ratio (RGLW), hundred grain weight (HGW), and percent chalkiness (PC). QTL analysis was performed using QTL IciMapping software. Continuous distributions and transgressive segregations of all the traits were observed, suggesting that the traits were quantitatively inherited. A total of twenty-eight QTLs and ninety-two candidate genes related to rice grain characteristics were identified. This genetic information is important to develop rice varieties of high quality.

Rice growth and productivity is adversely affected by low-temperature stress. From a previous screen of diverse rice genotypes for cold tolerance parameters at the vegetative stage, we selected the tolerant Nipponbare and M202 genotypes and sensitive Cypress and Secano do Brazil genotypes for further analysis at the reproductive stage for physiological and yield parameters. Cold stress severely affected grain yield as estimated by the number of grain per panicle, panicle length, and 100 seed weight. Analysis of gene expression of 21 genes involved in physiological responses to low temperature tested, in the flag leaf and inflorescence tissue of these genotypes, showed an increased expression of the Lipid Transfer Protein genes LTP7 and LTP10 in flag leaf tissue of the tolerant Nipponbare and M202, along with a significant increase in the relative expression of stress-responsive transcription factors (TFs) and cold-inducible genes. In flag leaf tissue OsNAC9, OsNAC10 and OsNAP genes showed high correlation with photosynthesis, stomatal conductance, transpiration and Quantum Efficiency of PSII. In consequence of the foregoing results, we conclude that Nipponbare and M202 are cold tolerant genotypes and that LTP7, LTP10, OsNAC9, OsNAC10 and OsNAP genes can be used as markers in screening for cold tolerance at the reproductive stage. Furthermore based on the results we propose a model of lowtemperature tolerance mechanism of how stress is perceived, and how the signal cascade acts to promote tolerance at below-ideal temperatures. ARTICLE HISTORY KEYWORDS Abiotic stress; transcription factors; lipid transfer proteinsCONTACT Andy Pereira apereira@uark.edu Key message: Rice genotype Nipponbare is identified as cold tolerant on the basis of physiological and yield parameters; supported by gene expression responses that indicate LTP7, LTP10, OsNAC9, OsNAC10 and OsNAP as markers in screening for cold tolerance at the reproductive stage.