Semi-dwarf Varieties Research Articles

Validation of the QTL for grain length linked to the Rht-B1 locus in two genetic backgrounds of bread wheat (Triticum aestivum L.)

Grain size is an important agronomic trait that influences the yield and end-use quality of bread wheat (Triticum aestivum L.). We conducted quantitative trait loci (QTL) analysis using recombinant inbred lines derived from a cross of a semi-dwarf modern variety with large grains (Zenkoujikomugi: Zen) and a landrace with small grains (Chinese Spring: CS). Grain size was evaluated as grain length (GL), grain width (GW), grain thickness (GT), and thousand-grain weight (TGW) under two environmental conditions. A major QTL (QGl.obu-4B) associated with GL was detected in both environments near the Rht-B1 locus for the semi-dwarf trait on chromosome 4B, despite Zen and CS having the same Rht-B1a allele. No QTL for GW was found in the QGl.obu-4B region, and QTLs for GT and TGW was detected in only one environment. To validate the effect of QGl.obu-4B, we developed two backcrossed populations in the CS and Zen genetic backgrounds. The Zen-derived allele conferred larger GL, GW, and GT, resulting in greater TGW (13.7% increase compared to the CS-derived allele) in the CS background. In contrast, the QGl.obu-4B effect was smaller in the Zen background, and the Zen-derived allele increased TGW by only 7.0%. The QTL was located within the 168-Mbp region tightly linked to the Rht-B1 locus. Further characterization and fine-mapping of QGl.obu-4B will facilitate the use of this allele by marker-assisted selection in wheat breeding programs.

Changes in starch quality of mid-season indica rice varieties in the lower reaches of the Yangtze River in last 80 years

Rice (Oryza sativa L.) quality depends mainly on the characteristics of starch stored in kernels. Understanding the changes in starch characteristics in kernels during variety improvement would have great significance to improve rice quality. This study was designed to investigate the starch characteristics in the kernels and associated physiological traits of indica rice varieties in the lower reaches of the Yangtze River in China in last 80 years. Eight representative mid-season indica rice varieties were grown in the field. The results showed that the grain yield was significantly increased with the improvement of varieties and such an increase was mainly attributed to the increase in total number of spikelets. The tall varieties applied in the 1940s–1950s had higher protein content, relative crystallinity and infrared (IR) ratio of 1 045/1 022 cm−1. The semi-dwarf varieties applied in the 1980s–1990s had higher gel consistency, amylopectin content, IR ratio of 1 022/995 cm−1, and breakdown value. With the improvement of varieties, the amylose content, large-sized starch granule number and volume distribution, onset and peak of gelatinization temperature, gelatinization and retrogradation enthalpy, setback value, pasting temperature, viscosity of peak, hot and final, and 1-aminocycopropane-1-carboxylic acid (ACC) concentrations in panicles and root bleeding were gradually decreased, whereas the medium-sized starch granule number and volume distribution, activities of key enzymes in grains, and zeatin (Z)+zeatin riboside (ZR) contents in panicles and root bleeding at grain filling stage were gradually increased. Correlation analysis showed that starch thermodynamic characteristics were closely related to starch structure and components, key enzymes and hormones. The results suggest that starch quality was enhanced through the optimization of starch components, structure, thermodynamics, and the regulation of key enzymes in grains and hormones in panicles and root bleedings at grain filling stage during the improvement of mid-season indica rice.

Pyramiding seed dormancy genes to improve resistance of semi-dwarf varieties to pre-harvest sprouting in rice

The quantitative trait locus SD1-2 for seed dormancy (SD) is identical to the semi-dawrf1 (sd1) gene prevailing in high-yield varieties of rice. However, sd1 alone appeared not sufficient to overcome the preharvest sprouting (PHS) problem in crop (or hybrid seed) production. This research aimed to address some genetic issues that may impact pyramiding of SD genes to improve semi-dwarf varieties for the PHS resistance. The isolated SD1-2, SD8, and SD10 loci were also associated with plant height (PH), awn or flowering time (FT), with the dormancy-enhancing alleles reducing stem elongation, increasing awned seeds, and promoting flowering, respectively. Allelic variants at SD1-2 and SD8 or SD10 were assembled in the same background as two digenic systems, each consisting of all the nine digenic genotypes. The two systems of plants were evaluated for the four traits and phenotypic data used to model trait correlations and the component additive, dominance, and epistatic effects of the two loci. FT was correlated with PH and germinability, but the correlations were opposite in direction between the two systems. Both additive and non-additive effects contributed to the variation for SD. All the three loci had effects on FT and PH in the digenic system(s). The SD10 alleles altered directions for effect on SD, with the late-flowering allele reducing germinability in the SD1-2 and SD10 system. This research demonstrated that genetic improvement of semi-dwarf cultivars for the PHS resistance involves proper selections for dormancy genes, recipient’s genetic backgrounds, and agronomic traits.

Development of introgression lines in high yielding, semi-dwarf genetic backgrounds\xa0to enable improvement of modern rice varieties for tolerance to multiple abiotic stresses free from undesirable linkage drag

Occurrence of multiple abiotic stresses in a single crop season has become more frequent than before. Most of the traditional donors possessing tolerance to abiotic stresses are tall, low-yielding with poor grain quality. To facilitate efficient use of complex polygenic traits in rice molecular breeding research, we undertook development of introgression lines in background of high-yielding, semi-dwarf varieties with good grain quality. The study reports the development and evaluations of over 25,000 introgression lines in eleven elite rice genetic backgrounds for improvement of yield under multiple abiotic-stresses such as drought, flood, high/low temperature. The developed introgression lines within each genetic background are near isogenic/recombinant inbred lines to their recipient recurrent parent with 50 to 98% background recovery and additionally carry QTLs/genes for abiotic stresses. The multiple-stress tolerant pyramided breeding lines combining high yield under normal situation and good yield under moderate to severe reproductive-stage drought, semi-dwarf plant type with good grain quality traits have been developed. The introgression lines in dwarf backgrounds open new opportunity to improve other varieties without any linkage drag as well as facilitate cloning of QTLs, identification and functional characterization of candidate genes, mechanisms associated with targeted QTLs and the genetic networks underlying complex polygenic traits.

RELACIÓN ENTRE EL GEN Lr67 DE RESISTENCIA A ROYA DE LA HOJA Y EL GEN Rht-D1 DE ENANISMO DEL TRIGO

El gen Lr67, localizado en el cromosoma 4D, confiere resistencia a la roya de la hoja causada por Puccinia triticina E. Este gen fue común en las variedades de trigo (Triticum spp.) de porte alto liberadas en México hasta antes de 1960, no así en las variedades semienanas liberadas desde esa fecha hasta el presente. Las variedades semienanas de trigo liberadas en México poseen ya sea el gen de enanismo Rht-B1 localizado en el cromosoma 4B o el gen Rht-D1 localizado en el cromosoma 4D. Con el fin de investigar si existe algún impedimento genético para conjuntar los genes Lr67 y Rht-D1 en la misma variedad de trigo, se caracterizó genotípicamente la F3 de la cruza entre la variedad Nasma que posee el gen Rht-D1 con la variedad Marroqui 588 poseedora del gen Lr67. Mediante pruebas de ji-cuadrada y marcadores moleculares de diagnóstico, se encontró que la distancia genética entre ambos genes es de 23.6 cM con análisis de ligamiento y de 27.6 cM con análisis molecular. Estas distancias son suficientemente grandes para que exista recombinación genética, por lo que no hay ningún impedimento genético para obtener genotipos recombinantes que combinen el gen de resistencia a roya de la hoja (Lr67) con el gen de porte bajo de planta (Rht-D1), mismos que en los progenitores se encuentran en fase de repulsión.

The 21st Century Agriculture: When Rice Research Draws Attention to Climate Variability and How Weedy Rice and Underutilized Grains Come in Handy.

Rice, the first crop to be fully sequenced and annotated in the mid-2000s, is an excellent model species for crop research due mainly to its relatively small genome and rich genetic diversity. The 130-million-year-old cereal came into the limelight in the 1960s when the semi-dwarfing gene sd-1, better known as the “green revolution” gene, resulted in the establishment of a high-yielding semi-dwarf variety IR8. Deemed as the miracle rice, IR8 saved millions of lives and revolutionized irrigated rice farming particularly in the tropics. The technology, however, spurred some unintended negative consequences, especially in prompting ubiquitous monoculture systems that increase agricultural vulnerability to extreme weather events and climate variability. One feasible way to incorporate resilience in modern rice varieties with narrow genetic backgrounds is by introgressing alleles from the germplasm of its weedy and wild relatives, or perhaps from the suitable underutilized species that harbor novel genes responsive to various biotic and abiotic stresses. This review reminisces the fascinating half-century journey of rice research and highlights the potential utilization of weedy rice and underutilized grains in modern breeding programs. Other possible alternatives to improve the sustainability of crop production systems in a changing climate are also discussed.

Identification and mapping of a new recessive dwarfing gene dw9 on the 6RL rye chromosome and its phenotypic effects.

The introduction of high-yielding semi-dwarf varieties of wheat into cultivation has led to a "green revolution." This has required intensive research into various sources of dwarfism in wheat. However, there has been very little advancement in research on dwarfing genes in rye in comparison to wheat or barley. So far, three dominant dwarfing genes (Ddw1, Ddw3, and Ddw4) and three recessive genes (ct1, ct2, and np) have been characterized and precisely mapped in rye. There is no complete catalog of dwarfing genes available in rye. This paper presents an identification of the source of dwarfism and preliminary characterization of the new recessive gene dw9 from the BK-1 line. The gene was mapped on the long arm of the 6R chromosome and belongs to the GA-insensitive group. The initial characterization of the influence of this gene on morphological traits shows that it significantly affects the decrease of yielding trait parameters. A full evaluation can be performed after detailed breeding studies.

Changes in the Phenotype of Winter Wheat Varieties Released Between 1920 and 2016 in Response to In-Furrow Fertilizer: Biomass Allocation, Yield, and Grain Protein Concentration.

Plant breeding has increased the yield of winter wheat (Triticum aestivum L.) over decades, and the rate of genetic gain has been faster under high fertility in some countries. However, this response is not universal, and limited information exists on the physiological traits underlying the interaction between varieties and fertilization. Thus, our objectives were to identify the key shifts in crop phenotype in response to selection for yield and quality, and to determine whether historical and modern winter wheat varieties respond differently to in-furrow fertilizer. Factorial field experiments combined eight winter wheat varieties released between 1920 and 2016, and two fertilizer practices [control versus 112 kg ha-1 in-furrow 12 -40-0-10-1 (N-P-K-S-Zn)] in four Kansas environments. Grain yield and grain N-removal increased nonlinearly with year of release, with greater increases between 1966 and 2000. In-furrow fertilizer increased yield by ~300 kg ha-1 with no variety × fertility interaction. Grain protein concentration related negatively to yield, and the residuals of this relationship were unrelated to year of release. Yield increase was associated with changes in thermal time to critical growth stages, as modern varieties had shorter vegetative period and longer grain filling period. Yield gains also derived from more kernels m-2 resultant from more kernels head-1. Historical varieties were taller, had thinner stems, and allocated more biomass to the stem than semidwarf varieties. Yield gains resulted from increases in harvest index and not in biomass accumulation at grain filling and maturity, as shoot biomass was similar among varieties. The allometric exponent (i.e., the slope between log of organ biomass and log of shoot biomass) for grain increased with, and for leaves was unrelated to, year of release. The ability of modern varieties to allocate more biomass to the kernels coupled to an early maturity increased grain yield and grain N-removal over time. However, increases in grain yield were greater than increases in grain N-removal, reducing grain protein concentration in modern varieties.

Effects of plant population and row spacing on grain yield of aerial-sown and drill-sown rice

Objective guidelines about plant population are essential to ensure that yield potential of rice grain is not compromised. Drill-sowing of rice is increasing in popularity in many rice-growing regions of the world in response to a requirement for increased water productivity, but little information is available on row-spacing widths required to maximise grain yield potential. This research investigated the impacts of plant population on grain yield and yield components for aerial- and drill-sown rice, and the effects of row-spacing width for drill-sown rice grown in a temperate environment. Ten aerial-sown and five drill-sown experiments were conducted in south-eastern Australia over three seasons using four semi-dwarf rice varieties. Plant populations ranged from 7 to 396 plants m–2. Plant populations as low as 30 plants m–2 were able to achieve grain yields >12 t ha–1 but only when the plants were uniformly distributed. At a population of ~100 plants m–2, the impact of plant-stand distribution was negligible. Grain yield was maintained across a large range of plant populations, mainly through compensatory effects of more tillers per plant and more grains per panicle at lower plant populations. For aerial-sown rice, maximum grain yield (up to 14.9 t ha–1) was always achieved with a minimum plant population of 100 plants m–2, and likewise for drill-sown rice provided the row spacing was ≤27 cm. At equivalent plant populations, 36-cm row spacing produced lower grain yield than narrower row spacings. When large gaps existed between plants within the rows, neighbouring plants could not compensate for the gap at the wider 36-cm row spacing, and grain yield was reduced. A practical optimal plant population of 100–200 plants m–2 was found to be suitable for the semi-dwarf varieties used in this study for both aerial- and drill-sowing methods.

The Role of Dwarfing Traits in Historical and Modern Agriculture with a Focus on Rice.

Semidwarf stature is a valuable agronomic trait in grain crops that reduces lodging and increases harvest index. A fundamental advance during the 1960s Green Revolution was the introduction of semidwarf cultivars of rice and wheat. Essentially, all semidwarf varieties of rice under cultivation today owe their diminished stature to a specific null mutation in the gibberellic acid (GA) biosynthesis gene, SD1 However, it is now well-established that, in addition to GAs, brassinosteroids and strigolactones also control plant height. In this review, we describe the synthesis and signaling pathways of these three hormones as understood in rice and discuss the mutants and transgenics in these pathways that confer semidwarfism and other valuable architectural traits. We propose that such genes offer underexploited opportunities for broadening the genetic basis and germplasm in semidwarf rice breeding.

The Israeli-Palestinian wheat landraces collection: restoration and characterization of lost genetic diversity.

For over a century, genetic diversity of wheat worldwide was eroded by continual selection for high yields and industrial demands. Wheat landraces cultivated in Israel and Palestine demonstrate high genetic diversity and a potentially wide repertoire of adaptive alleles. While most Israeli-Palestinian wheat landraces were lost in the transition to 'Green Revolution' semi-dwarf varieties, some germplasm collections made at the beginning of the 20th century survived in gene banks and private collections worldwide. However, fragmentation and poor conservation place this unique genetic resource at a high risk of genetic erosion. Herein, we describe a long-term initiative to restore, conserve, and characterize a collection of Israeli and Palestinian wheat landraces (IPLR). We report on (i) the IPLR construction (n=932), (ii) the historical and agronomic context to this collection, (iii) the characterization and assessment of the IPLR's genetic diversity, and (iv) a data comparison from two distinct subcollections within IPLR: a collection made by N.Vavilov in 1926 (IPLR-VIR) and a later one (1979-1981) made by Y.Mattatia (IPLR-M). Though conducted in the same eco-geographic space, these two collections were subjected to considerably different conservation pathways. IPLR-M, which underwent only one propagation cycle, demonstrated marked genetic and phenotypic variability (within and between accessions) in comparison with IPLR-VIR, which had been regularly regenerated over ∼90 years. We postulate that long-term ex situ conservation involving human and genotype × environment selection may significantly reduce accession heterogeneity and allelic diversity. Results are further discussed in a broader context of pre-breeding and conservation. © 2019 Society of Chemical Industry.

Drought-Tolerant Barley: I. Field Observations of Growth and Development

An ever-growing challenge to agricultural production worldwide is the reduced availability of water and increased incidence of drought. The development of low-irrigation barley cultivars marks a significant achievement in breeding efforts for drought tolerance, but specific traits conferring adaptation to water stress remain unclear. Here, we report results from two years of replicated field trials comparing yield, phenology, water usage, and rooting characteristics of low-irrigation varieties “Solar” and “Solum” to high-input, semi-dwarf varieties “Kopious” and “Cochise”. The objective was to identify differential performance of varieties under high- and low-water conditions through comparison of growth and developmental traits. Rooting characteristics were analyzed by digging in-field root profile walls to a depth of 1.8 m. Varieties were compared under high (877 mm) and low (223 mm) water regimes including irrigation and precipitation. Observed traits associated with improved performance of the low-irrigation varieties under drought conditions included early vigor, early flowering, greater root growth at 40–80 cm depth, and more effective water use exhibited by greater water extraction post-anthesis. The deeper rooting pattern of the low-irrigation varieties may be related to their ability to use more water post-anthesis under water stress, and thus, to fill grain, compared to high input varieties.

Preliminary Exploration of the Source, Spread, and Distribution of Rht24 Reducing Height in Bread Wheat

Rht24 is a major dwarfing allele that not only reduces plant height but also increases grain weight. The objective of this study was to trace the source, spread, and distribution of Rht24 and determine its frequency in conjunction with other important dwarfing alleles for Rht1 (Rht‐B1b), Rht2 (Rht‐D1b), and Rht8. Allele‐specific cleaved amplified polymorphic sequence (CAPS) markers were developed for accurate and effective genotyping of Rht1 and Rht2, and closely linked flanking markers were used for genotyping of Rht8 and Rht24. Marker analysis showed that Rht24 occurs at a higher frequency (84.2%) than other important dwarfing alleles in elite wheat (Triticum aestivum L.) varieties and usually couples with Rht2 or Rht8. Genotyping of old varieties and landraces showed that Rht24 was widely used in wheat breeding before the Green Revolution (GR). ‘Akakomugi’ and ‘Norin 10’, the donors of Rht8 and GR genes Rht1 and Rht2, respectively, harbored Rht24, so Rht24 likely followed the transfer routes of GR genes and Rht8 to spread worldwide. Pedigree analysis showed that many Chinese elite lines and backbone parents were derived from Akakomugi, contributing to the high frequency of Rht24 in Chinese varieties. Additionally, Norin 10‐derived semidwarf varieties from the CIMMYT were widely used in Chinese wheat breeding. Finally, Rht24 was also detected in 30 old Chinese varieties and landraces. Overall, these findings show that the presence of Rht24 in modern Chinese elite varieties originated from Akakomugi, Norin 10, or Chinese landraces. Thus, Rht24 was introgressed early, spread widely, and became genetically fixed in a wide range of modern Chinese wheat germplasm.

Mechanistic understanding of lodging in spring wheat (Triticum aestivum): An Indian perspective

Lodging in modern spring wheat (Triticum aestivum L.) varieties is largely overlooked in India. There is scanty information available in literature for Indian condition regarding the extent, distribution, direct and indirect losses caused by the lodging. Little work has been done on this problem post green revolution period in India. Introduction of dwarfing genes and development of semi-dwarf varieties has resulted in quantum yield gains during 1970-80.After this period till recent years the progress in yield gains are slowed down mainly due to plant architecture of modern varieties not supporting heavier heads inducing lodging. Therefore, the higher potential of genotypes could not be realized to full extent at field level and varieties promising consistent yield level of six tonnes /ha or more are lacking. The complex phenotyping strategies and models designed by the workers working on the problem elsewhere are further impeding the progress as these are not much helpful at field level under Indian conditions. The current paper takes into the consideration the mechanistic approach to understand the problem and correlate the facts andfindings of universal nature to design the strategies to manage the lodging through different approaches much suited to Indian conditions.

Location-dependent impacts of liming and crop rotation on bacterial communities in acid soils of the Pacific Northwest

The cropping systems of northern Idaho and eastern Washington are dominated by a cereal-based (winter wheat) rotation that is exclusively rainfed. Following the green revolution, the productivity of wheat increased dramatically with semi-dwarf varieties and inexpensive synthetic fertilizers. However, long-term and frequent use of ammonium-based nitrogen fertilizers has resulted in the gradual acidification of fields in the region, with reduced productivity and symptoms of aluminum toxicity in some locations. A micronized liquid formulation of lime (calcium carbonate) was evaluated at three locations to mitigate soil acidification in comparison to a no-lime control. To examine how liming affects bacterial community structure, soil samples were taken in the spring in wheat and pea rotations 7 and 19 months after lime application, DNA was extracted and the V1-V3 portion of the 16S rRNA gene was amplified and sequenced with Illumina MiSeq. pH was only increased ∼0.2–0.3 units in most locations, and liming only had a significant effect on bacterial community composition at one location (Pullman). Liming had no consistent or significant effect on community richness or diversity. Location had a stronger effect on communities than liming or crop rotation, but some specific taxa increased in relative abundance in response to liming, including the families Cytophagaceae and Flavobacteriaceae (Phylum Bacteroidetes), A4b (Phylum Chloroflexi), and Opitutaceae (Phylum Verrucomicrobia). A number of operational taxonomic units (OTU) in Chitinophagaceae and Xanthomonadaceae were increased by liming at the Pullman location, which had 3–4 X more OTUs affected by liming than the other locations. Streptomycetaceae and Oxalobacteraceae were more abundant in root zone soil of wheat than pea. In conclusion, there was a strong interaction between liming and location in determining soil bacterial composition, but specific components of the bacterial community responded to even minimal increases in soil pH.

Analysis of Genome Sequence Variations Among Three U.S. Rice Varieties Showing Differential Quantitative Disease Resistance to Bacterial Panicle Blight and Sheath Blight

<span style=font-size:11.0pt;font-family: times= new= roman,serif;mso-fareast-font-family:times= roman=>1. Abstract Bacterial Panicle Blight (BPB) and Sheath Blight (SB) are major rice diseases in the southeastern United States, and only quantitative disease resistance is known for these diseases. We analyzed draft genome sequence data for three U.S. rice varieties showing differential disease resistance traits for BPB and SB; Trenasse (long-grain, susceptible to BPB and SB), Bengal (medium-grain, susceptible to BPB and SB), and Jupiter (medium-grain, partial resistance to BPB and SB). Comparative genome sequence analysis along with 50 rice accessions revealed that the three US varieties are genetically close and clustered together, separated from other 50 accessions. According to this analysis, the long-grain semi-dwarf variety Trenasse is a tropical japonica type carrying a fraction of indica genome, while the medium-grain varieties Bengal and Jupiter are admixtures of tropical and temperate japonica types. Consistent with the breeding history and the phenotypic trait in grain-shape (but not with the phenotype in disease resistance), more variations were found in the Jupiter/Trenasse and Bengal/Trenasse pairs compared to the Jupiter/Bengal pair. The whole genome sequence information of these US rice varieties will be a useful resource for genetic studies of disease resistance to BPB and SB as well as development of new disease-resistant lines.

QTL mapping uncovers a semi-dwarf 1 (sdw1) allele in the barley (Hordeum vulgare) ND23049 line.

In barley, semi-dwarf varieties are attractive for their superior harvest index and lodging resistance, but many semi-dwarf barley genotypes suffer from poor spike emergence. We performed a genetic characterization of a semi-dwarf line (ND23049) that combines short stature, strong stiff culms, and adequate spike emergence. We developed a doubled haploid (DH) population derived by crossing ND23049 and the cultivar CLE253. A subset of 88 DH lines and parents were characterized for plant height in 2013 and 2014 and genotyped. In total, 1984 SNPs (345 unique loci) were used to produce a linkage map of 1127.1 cM. Three QTLs for plant height were detected in this population and coincided with the HvGA20ox2/Sdw1, HvBRI1/Uzu1, and HvPRR95 gene loci. The phenotypic variation explained by each QTL was 75.8%, 7.7%, and 4.1%, respectively, and jointly explained 83.3% (2013) and 87.7% (2014) of plant height. Our results suggest that ND23049 contributed the "short" allele at the HvGA20ox2/sdw1 locus while CLE253 provided "short" alleles at the HvBRI1/uzu1 and HvPRR95 loci. We identified a large deletion (at least 92.7 Kb), including HvGA20ox2 (Sdw1), as the causal mutation in ND23049. A set of tightly flanked SNP markers will help breeders to develop improved semi-dwarf varieties.

The impact of domestication and crop improvement on arbuscular mycorrhizal symbiosis in cereals: insights from genetics and genomics.

Contents Summary 1135 I. Introduction 1135 II. Recruitment of plant metabolites and hormones as signals in AM symbiosis 1136 III. Phytohormones are regulators of AM symbiosis and targets of plant breeding 1137 IV. Variation in host response to AM symbiosis 1137 V. Outlook 1137 Acknowledgements 1139 References 1139 SUMMARY: Cereals (rice, maize, wheat, sorghum and the millets) provide over 50% of the world's caloric intake, a value that rises to >80% in developing countries. Since domestication, cereals have been under artificial selection, largely directed towards higher yield. Throughout this process, cereals have maintained their capacity to interact with arbuscular mycorrhizal (AM) fungi, beneficial symbionts that associate with the roots of most terrestrial plants. It has been hypothesized that the shift from the wild to cultivation, and above all the last c. 50years of intensive breeding for high-input farming systems, has reduced the capacity of the major cereal crops to gain full benefit from AM interactions. Recent studies have shed further light on the molecular basis of establishment and functioning of AM symbiosis in cereals, providing insight into where the breeding process might have had an impact. Classic phytohormones, targets of artificial selection during the generation of Green Revolution semi-dwarf varieties, have emerged as important regulators of AM symbiosis. Although there is still much to be learnt about the mechanistic basis of variation in symbiotic outcome, these advances are providing an insight into the role of arbuscular mycorrhiza in agronomic systems.

Shortened Basal Internodes Encodes a Gibberellin 2-Oxidase and Contributes to Lodging Resistance in Rice

Breeding semi-dwarf varieties to improve lodging resistance has been proven to be enormously successful in increasing grain yield since the advent of the “green revolution.” However, the breeding of the majority of semi-dwarf rice varieties in Asia has been dependent mainly on genetic introduction of the mutant alleles of SD1, which encodes a gibberellin (GA) 20-oxidase, OsGA20ox2, for catalyzing GA biosynthesis. Here, we report a new rice lodging-resistance gene, Shortened Basal Internodes (SBI), which encodes a gibberellin 2-oxidase and specifically controls the elongation of culm basal internodes through deactivating GA activity. SBI is predominantly expressed in culm basal internodes. Genetic analyses indicate that SBI is a semi-dominant gene affecting rice height and lodging resistance. SBI allelic variants display different activities and are associated with the height of rice varieties. Breeding with higher activity of the SBI allele generates new rice varieties with improved lodging resistance and increased yield. The discovery of the SBI provides a desirable gene resource for producing semi-dwarf rice phenotypes and offers an effective strategy for breeding rice varieties with enhanced lodging resistance and high yield.

Decline in soil organic carbon and nitrogen limits yield in wheat-fallow systems

This study evaluated long-term trends of soil organic carbon (SOC), soil total nitrogen (N), and wheat (Triticum aestivum L.) yield to glean information for improving the sustainability of dryland winter wheat-summer fallow (WW-SF) systems in the inland Pacific Northwest (IPNW). Effects of fall burn (FB), no burn (NB), manure application (MN), and pea vine incorporation (PV) treatments on SOC, N, and wheat grain yield from 1931 to 2010 were evaluated in an on-going Crop Residue Long-term experiment (CR-LTE). A medium tall wheat variety (Rex-M) was planted during 1931–1966 and several semi-dwarf varieties were planted since then. We observed a slight but gradual decrease in wheat yield in all treatments from 1931 to 1966 and in FB and NB from 1967 to 2010. Wheat yield in PV and MN increased until 1995 and decreased thereafter. The SOC and N content in 0–30 cm depth declined in FB, NB, and PV treatments with the highest rates of SOC and N loss under FB. The SOC content in 0–30 cm depth in MN was maintained. Growers should match organic matter and nitrogen (N) inputs to C and N loss to maintain SOC, N and crop yields, and improve the sustainability of dryland WW-SF systems.