US Cultivars Research Articles

Cytological and molecular characterization of wheat lines carrying leaf rust and stem rust resistance genes Lr24 and Sr24

Previous studies showed that Australian wheat cultivars Janz and Sunco carry leaf rust and stem rust resistance genes Lr24 and Sr24 derived from Thinopyrum ponticum chromosome arm 3AgL. However, the size of the alien segments carrying Lr24 and Sr24 in the lines were not determined. In this study, we used non-denaturing fluorescence in situ hybridization (ND-FISH), genomic in situ hybridization (GISH), and PCR-based landmark unique gene (PLUG) markers to visualize the alien segments in Janz and Sunco, and further compared them with the segments in US cultivars Agent and Amigo. The fraction length (FL) of the alien translocation in Agent was 0.70–1.00, whereas those in Janz, Sunco, and Amigo were smaller, at FL 0.85–1.00. It was deduced that the alien gene RAg encoding for red grain color and rust resistance genes Lr24 and Sr24 on chromosome arm 3AgL were in bins of FL 0.70–0.85 and 0.85–1.00, respectively. We retrieved and extracted nucleotide-binding site-leucine-rich repeat (NBS-LRR) receptor genes corresponding to the region of Lr24 and Sr24 on chromosomes 3E, and 3J, 3Js and 3St from the reference genome sequences of Th. elongatum and Th. intermedium, respectively. A set of molecular markers developed for Lr24 and Sr24 from those extracted NBS-LRR genes will provide valuable information for fine mapping and cloning of these genes.

An evaluation based on the analytic hierarchy process and GGEbiplot on French fry potato genotypes in Yunnan, China.

A total of 33 potato (Solanum tuberosum L.) cultivars and breeding clones imported from the United States and two local cultivars (Yunshu 401 and Cooperation 88, CK) were planted and evaluated. To determine their suitability for processing into French fries at five locations (e1-e5) in Yunnan Province, China, we developed a comprehensive evaluation system using the analytical hierarchy process (AHP). Eleven evaluation indicators for French fry quality, yield, and agronomic characteristics with a relative importance (weight coefficients) of 0.483, 0.301 and 0.216, respectively, were used to analyze the 35 potato genotypes (designated g1-g35).The genotypes were ranked and the results revealed that (1) on the average, the 33 potato genotypes imported from the United States showed a lower performance compared to the local cultivars. Compared with the CK, they were classified as not vigorous (Mean 5.11 vs CK 7.75), matured earlier (Mean 5.79 vs CK 1.70), and had a low resistance to late blight (Mean 3735.59 vs CK 1418.55), requiring the use of fungicides to control the disease at the five trial locations. (2) The US cultivar 'Defender' (g3) ranked in the top six at all five test locations because it had higher yield (29.56t h m-2), better fry quality (4.64), higher dry matter content (20.41%), better tuber length/width ratio (1.99), longer tubers (13.57cm), stronger plant vigor (7.17) and higher resistance to late blight (AUDPC: 3134.2). (3) By using GGEbiplot analysis, superior genotypes with high and stable yields were g3 and 'Echo Russet' (g33). 'Yunshu 401' (g34) and 'Yukon Gem' (g4) had high but not stable yields. The ideal test environments and hence experimental locations were Luquan (LQ, e2) and Lijiang (LJ, e4) which resulted in the best discrimination between genotypes among the five experimental locations in Yunnan. Overall, the developed evaluation system based on AHP and GGEbiplot analysis including 11 evaluation indicators for French fry quality, yield and agricultural traits can be a model for evaluation and promotion of new French fry cultivars, and evaluating and selecting the test location.

Yield component QTLs identified by genome‐wide association mapping validated in a diverse tropical japonica × tropical japonica rice biparental mapping population

AbstractThe Rice Diversity Panel 1 (RDP1) is a resource for genome‐wide association (GWA) studies to explore the five major rice (Oryza sativa L.) subpopulations indica, aus, aromatic, temperate japonica, and tropical japonica (TRJ). Previously collected phenotype data for yield‐related traits in RDP1 were reanalyzed using a recently released 4.8 million single nucleotide polymorphism (SNP) dataset to enhance GWA mapping precision. GWA mapping revealed numerous GWA quantitative trait loci (QTLs) that were specific to one or more subpopulations. Most southern US cultivars are classified tropical japonica (TRJ) or TRJ admixtures, thus TRJ was the focus for validating Rice Diversity Panel 1 GWA QTLs. Two diverse TRJ accessions, L‐202 originating from California, USA, and Trembese from Indonesia, were selected for developing a recombinant inbred line (RIL) population. This RIL population was phenotyped for 20 yield component traits, 16 of which were measured in RDP1, including six agronomic, six panicle architecture, and four seed traits. Genotyping with 1439 polymorphic markers and QTL mapping revealed 43 RIL QTLs. Examination of the GWA QTLs identified 163 GWA QTLs for the same or related traits co‐located with 37 RIL QTLs. A significant overlap was on chromosome 7 (21.8–25.4; 26.8–29.6 Mb) where the well‐known yield related genes, GRAIN WEIGHT7 (GW7) and FRIZZY PANICLE (FZP), respectively, are located and specific to TRJ. In this region, 10 RIL QTLs were co‐located with 36 GWA QTLs for panicle architecture or seed traits, especially secondary branching to increase the number of seeds. RIL QTLs co‐located with GWA QTLs are targets for developing SNP markers that can be utilized in cultivar development.

Pedigree reconstruction for triploid apple cultivars using single nucleotide polymorphism array data

Societal Impact StatementMany economically, culturally, and historically important apple cultivars are triploids, which have three copies of each chromosome instead of the more typical two copies in diploids. Despite their prevalence and importance, there have been conflicting reports regarding their origin and their ability to beget diploids. New genetic analysis methodologies outlined in this study have clarified the genetic origin of triploid apple cultivars and suggest that triploidy has been a dead end in historic apple pedigrees. The specific results of this study have resolved the pedigrees of many cultivars, including the famous English cultivar Cox's Orange Pippin and the oldest known US cultivar Roxbury Russet.Summary In apple (Malus × domestica), most cultivars are diploid, though a sizeable number are triploids, which tend to be stronger growing, more robust, and bear larger fruit. However, triploidy is also associated with strongly reduced fertility. Some recorded pedigrees for historical apple cultivars include triploids as parents of diploids, despite this reputation of poor fertility. This information, coupled with some initiatives using triploids in breeding efforts, result in confusion about how possible or common it is for triploids to be parents of diploid offspring. To date, no studies have systematically evaluated and identified pedigrees of triploid apple cultivars to resolve these contradictions. Here, we describe a method to make triploid genotype calls using Illumina Infinium single nucleotide polymorphism (SNP) array data through a novel Python script: ploidyClassifier. SNP data for 219 unique triploids was compared alongside 2498 unique diploid apple accessions to conduct pedigree reconstruction. Unreduced gamete‐donating parents were identified for over half of the triploid accessions. From those, reduced gamete‐donating parents were identified for nearly half. Full or partial pedigrees for many classic triploids were uncovered, including that of the oldest known American cultivar, ‘Roxbury Russet’. All tested pedigrees from literature that listed triploids as parents of diploids were deemed false, including that of the well‐known ‘Cox's Orange Pippin’, whose previously unreported second parent was also identified here as ‘Rosemary Russet’. These results together suggest that historic triploids are mostly or solely the product of diploid parentage and that triploidy has been a dead end in historic apple pedigrees.

A strong negative trade-off between seed number and 100-seed weight stalls genetic yield gains in northern Japanese soybean cultivars in comparison with Midwestern US cultivars

US soybean yields have steadily increased, largely due to genetic factors. In contrast, Japanese yields remain low, partly due to a lack of genetic yield gain, but the yield potential and associated traits in Japanese cultivars have not been fully evaluated. The objectives of the present study were to estimate genetic gains in soybean yield and agronomic traits in Japan, and to determine whether Japanese cultivars are inferior to US cultivars in yield and agronomic traits; if so, which traits should be improved? We conducted a 4-year field trial to compare yield and agronomic traits of cultivars released between 1953 and 2014 in northern Japan and the Midwestern US. Japanese cultivars had lower yield. New US cultivars showed genetic yield gain of 9.86 kg ha –1 year –1 , with the highest contributions from seed number. The increased seed number decreased 100-seed weight, but the increased seed number outweighed that effect, resulting in consistent yield gain. Increased node number contributed most to the increased seed number. Old and new Japanese cultivars showed no significant yield difference. Their yield did not increase over time because 100-seed weight increased but seed number decreased (i.e., there was a strong trade-off). Only 100-seed weight increased in new Japanese cultivars, as this trait is important to Japanese breeders; it determines the processing quality for tofu and the esthetic quality for nimame (boiled beans). We could not confirm a genetic yield gain, but variations in 100-seed weight and seed number contributed similarly to yield in Japanese cultivars. Japanese breeders also focused on improving seed number, but it has been difficult to achieve high yield by simultaneously improving 100-seed weight and seed number. Innovation will be needed to resolve the trade-off between these factors. • Soybean cultivars in northern Japan had lower yield than in the Midwestern US. • Increased seed number contributed strongly to yield gain in recent US cultivars. • There was no evidence of genetic yield gain by recent breeding in Japan. • Recent breeding in Japan increased 100-seed weight but decreased seed number.

Genetic variation among the salinity tolerant breeding lines identified from two multi‐parent advanced generation introgression line populations in rice (Oryza sativa)

AbstractSalinity is a major environmental constraint affecting rice production in both irrigated and non‐irrigated areas and threatening global food security. Development of salt‐tolerant rice varieties with desirable agronomic traits is a logical approach to maintain high yield in saline areas. Here, we report development of two multi‐parent advanced generation introgression line (MAGIL) rice populations in two US cultivar backgrounds and their physiological and morphological evaluation under salinity stress at germination and seedling stages. From the initial screening of 180 MAGILs in sand culture, 36 tolerant‐to‐moderately salt‐tolerant lines were selected and further confirmed in hydroponics experiment. The selected MAGILs showed lower root and shoot Na+/K+ ratio compared with the recurrent parents. The principal component and cluster‐based analysis using 12 morphophysiological traits revealed grouping of the selected lines with tolerant donors. Genotyping results with 100 polymorphic SSR markers indicated a low level of genetic diversity among these lines. Clustering based on molecular marker data separated the MAGILs from the salt tolerance donors in both populations but were grouped with the recurrent parents, suggesting genetic similarity of MAGILs with recurrent parents. The salt‐tolerant MAGILs identified in this study are useful resource for investigating molecular and physiological bases of salt‐tolerant mechanisms as well as for evaluating their yield potential for release as salt‐tolerant rice varieties.

Variation of Macro- and Microelements, and Trace Metals in Spring Wheat Genetic Resources in Siberia.

Western Siberia is one of the major spring wheat regions of Russia, cultivating over 7 Mha. The objective of the study was to evaluate the variation of macro- and microelements, and of trace metals in four distinct groups of genetic resources: primary synthetics from CIMMYT (37 entries), primary synthetics from Japan (8), US hard red spring wheat cultivars (14), and material from the Kazakhstan–Siberian Network on Spring Wheat Improvement (KASIB) (74). The experiment was conducted at Omsk State Agrarian University, using a random complete block design with four replicates in 2017 and 2018. Concentrations of 15 elements were included in the analysis: macroelements, Ca, K, Mg, P, and S; microelements, Fe, Cu, Mn, and Zn; toxic trace elements, Cd, Co, Ni; and trace elements, Mo, Rb, and Sr. Protein content was found to be positively correlated with the concentrations of 11 of the elements in one or both years. Multiple regression was used to adjust the concentration of each element, based on significant correlations with agronomic traits and macroelements. All 15 elements were evaluated for their suitability for genetic enhancement, considering phenotypic variation, their share of the genetic component in this variation, as well as the dependence of the element concentration on other traits. Three trace elements (Sr, Mo, and Co) were identified as traits that were relatively easy to enhance through breeding. These were followed by Ca, Cd, Rb, and K. The important biofortification elements Mn and Zn were among the traits that were difficult to enhance genetically. The CIMMYT and Japanese synthetics had significantly higher concentrations of K and Sr, compared to the local check. The Japanese synthetics also had the highest concentrations of Ca, S, Cd, and Mo. The US cultivars had concentrations of Ca as high as the Japanese synthetics, and the highest concentrations of Mg and Fe. KASIB’s germplasm had near-average values for most elements. Superior germplasm, with high macro- and microelement concentrations and low trace-element concentrations, was found in all groups of material included.

Microsatellite Loci Reveal Genetic Diversity of Asian Callery Pear (Pyrus calleryana) in the Species Native Range and in the North American Cultivars.

Pyrus calleryana Decne. (Callery pear) includes cultivars that in the United States are popular ornamentals in commercial and residential landscapes. Last few decades, this species has increasingly naturalized across portions of the eastern and southern US. However, the mechanisms behind this plant’s spread are not well understood. The genetic relationship of present-day P. calleryana trees with their Asian P. calleryana forebears (native trees from China, Japan, and Korea) and the original specimens of US cultivars are unknown. We developed and used 18 microsatellite markers to analyze 147 Pyrus source samples and to articulate the status of genetic diversity within Asian P. calleryana and US cultivars. We hypothesized that Asian P. calleryana specimens and US cultivars would be genetically diverse and would show genetic relatedness. Our data revealed high genetic diversity, high gene flow, and presence of population structure in P. calleryana, potentially relating to the highly invasive capability of this species. Strong evidence for genetic relatedness between Asian P. calleryana specimens and US cultivars was also demonstrated. Our data suggest the source for P. calleryana that have become naturalized in US was China. These results will help understand the genetic complexity of invasive P. calleryana when developing management for escaped populations: In follow-up studies, we use the gSSRs developed here to analyze P. calleryana escape populations from across US.

Japanese Bulb Onion: Production, Consumption, and Cultivars

Abstract Bulb onion is an ancient vegetable crop that has been cultivated for at least 5,000 years. In Japan, this cultivation has only 150 years of history, but nowadays, it ranks fourth in total production, fourth in cropping acreage, and second in consumption among vegetables grown domestically. Until the 1970s, open-pollinated onion cultivars were predominantly cultivated throughout the country; they were selected mainly from old US cultivars. Over the past three decades, these open-pollinated cultivars have been replaced with F1 hybrid cultivars that offer higher yield, better disease resistance, uniformity at maturity, and high bulb quality. In this review, an attempt is made to characterize the commercial production and consumption of Japanese bulb onion as well as agronomic characteristics of representative cultivars.

Development of a reliable screening technique for determining tolerance to Macrophomina phaseolina in strawberry

Macrophomina phaseolina is a typical soilborne fungal pathogen causing crown and root rot in strawberry (Fragaria × ananassa Duch.) worldwide. M. phaseolina has become a major problem for strawberry growers parallel to the phase-out of methyl-bromide since 2004 and is considered the most destructive soilborne pathogen of strawberry since then. Global warming is characterized by extreme weather conditions, in the Mediterranean area, as reflected by long, hot, dry summers without rain and relatively short, cold rainy winters. This together with regulatory restrictions on toxic fumigants creates favorable conditions for M. phaseolina to thrive. Screening for resistant germplasm is currently the most effective and sustainable approach for managing the disease. In order to screen for susceptible/tolerant strawberry cultivars, various inoculation techniques were assessed on five strawberry cultivars. Artificial inoculation of growth medium with naturally infected plant material and the use of the ‘toothpick’ method resulted in no significant differences. However, the use of artificially produced sclerotia in a soil mix at concentrations of 2.5 × 103 sclerotia/g soil exhibited differential cultivar mortality rates. High variation was found among 32 tested strawberry varieties (Israeli and US) grown under outdoor conditions in a screenhouse. Cultivars ‘Pelican’ (US), ‘Orly’, ‘Tamir’ and ‘Rotmy’ were considered tolerant compared to cultivars ‘Florida 90’ (US) and ‘Peles’ that were the most susceptible. The overall results indicate that the choice of certain Israeli and US cultivars may provide future germplasm for resistance breeding against M. phaseolina.

Effects of maturity group and stem growth habit on the branching plasticity of soybean cultivars grown at various planting densities

ABSTRACT To elucidate the effects of maturity and the stem growth habit on the planting density-dependent branching plasticity of soybean cultivars, we studied the branch traits of 12 cultivars or lines planted at different densities (8.3, 16.7, and 22.2 plants m−2) in Sapporo (2012) and Ebetsu (2013). The 12 cultivars and lines consisted of three determinate cultivars from Hokkaido, three indeterminate cultivars from the northern US, and near-isogenic lines with the backgrounds of Canadian, US, and Japanese cultivars exhibiting diverse stem growth habits. We investigated the relationship between the maturity or stem growth habit and branching plasticity, which was calculated based on the ratios of different branch traits under sparse and dense planting conditions. The use of the ratios of the total branch length and the number of nodes per branch under sparse and dense planting conditions as a measure of branching plasticity revealed varietal differences across years. For the determinate and indeterminate cultivars in both years, branching plasticity was positively correlated with the number of days until stage R5 (onset of seed filling), which is when branches cease to elongate. Comparisons of Japanese and US cultivars and near-isogenic lines for the Dt1 gene (mediating the stem growth habit) indicated that the branching plasticity of indeterminate cultivars and lines is greater than that of determinate cultivars, with a large variation among backgrounds and cultivars. The results of this study imply that branching plasticity is greater in late-maturing soybean cultivars. Moreover, the indeterminate growth habit substantially enhances branching plasticity.

Threat of Brown Rot of Potato and Existing Resistance

Brown rot of potatoes caused by Ralstonia solanacearum is common in developing countries. Historically, brown rot losses in the United States have been restricted to southern states. This trend will most likely change with new Ralstonia introductions and temperature variability. A cold tolerant Ralstonia strain was used in this study to compare resistance between 18 wild accessions from eight species, nine accessions from the International Potato Center (CIP), and seven common US cultivars. Testing was done at both 18 °C and 30 °C. Of the wild potato species tested, S. commersonii and S. microdontum were the most resistant. CIP accessions varied from moderately resistant to very resistant. Four of the US cultivars were also moderately resistant. With certain accessions temperature played a role in resistance with high temperatures usually increasing severity of disease and cool temperatures promoting the occurrence of asymptomatic plants. The resistance observed appears to be partial, multigenic resistance.

Use of objective imaging systems to assess subjective grain appearance traits important to the US rice industry

AbstractBackground and objectivesMilled rice grain appearance traits, including chalk, determine its grade, price, and marketability. These appearance traits are evaluated visually (VI) in the United States by officially trained inspectors and at commercial mills. Digital imaging systems (IS) provide an alternative means to objectively and rapidly measure these traits. The goals of this study were to compare chalk values determined by VI and IS and to identify IS parameters that are associated with the five grain appearance traits commonly assessed by the US rice industry.FindingsMilled rice chalk determined by three VI methods used by commercial mills, a rice export company, and government inspectors, and three IS, WinSeedle, SeedCount, and S21, differed significantly. However, all six methods agreed on ranking of the best and worst of 20 US cultivars for chalkiness. Multiple linear regression analyses identified quality parameters from each IS that are associated with—bran streaks, chalk, kernel color, uniformity length, and appearance overall as determined by commercial mills.ConclusionsIS can rapidly quantify rice grain appearance traits but agree with subjective ratings for chalkiness only when differences are extreme. Subjective grain appearance traits as determined by commercial mills appear to be based on several parameters detected by IS.Significance and noveltyIS demonstrated that discolored kernels and grain chalkiness are the major factors explaining differences in overall appearance of US long‐grain varieties as subjectively assessed by commercial mills.

Hidden Rice Diversity in the Guianas.

Traditional crop varieties are an important source of genetic diversity for crop adaptation and modern breeding. Landraces of Asian (Oryza sativa) and African (Oryza glaberrima) rice have been well studied on the continents where they were domesticated. However, their history of cultivation in northern South America is poorly understood. Here, we reveal the rice diversity that is maintained by Maroons, descendants of enslaved Africans who fled to the interior forests of the Guianas ca. 300 years ago. We interviewed subsistence farmers who practice shifting cultivation along the Maroni and Lawa rivers that form the natural border between French Guiana and Suriname, and used ethnobotanical and morphological methods to identify around 50 varieties, of which 15 were previously undocumented. The genetic origin of these varieties was explored using the Angiosperms353 universal probe set. Despite the large distances between sites and relative inaccessibility of the area, phenotypic and genetic diversity did not display any geographic structure, which is consistent with knowledge of seed exchange among members of the same ethnolinguistic group. Although improved US cultivars were introduced in Maroon villages in the 1940s, these have not displaced the traditional landraces, which are cherished for their taste and nutritious qualities and for their importance in Maroon spiritual life. The unique agricultural and ritual practices of Maroons confirm their role as custodians of rice diversity, a role that is currently under threat from external pressures and encroaching globalization. We expect that the rice diversity uncovered in this study represents only a fraction of the total diversity in the Guianas and may constitute a large untapped resource that holds promise for future rice improvement. Further efforts to inventory and preserve these landraces will help to protect a precious cultural heritage and local food security.

Highly polymorphic novel simple sequence repeat markers from Class I repeats in walnut (Juglansregia L.)

Walnut (Juglans regia L.) is the most important species in the genus Juglans due to the high commercial value of its nuts and timber. Simple sequence repeats (SSRs) are considered as the markers of choice owing to their codominant nature. Since very few SSRs have been developed in walnut, this study aimed to develop numerous polymorphic SSRs from Class I repeats by using DNA sequences of the Chandler cultivar. In all, 800 SSRs were designed and tested in 8 Turkish, 3 French, and 5 US walnut cultivars, of which 88 (11%) did not produce bands, 161 (20.1%) were monomorphic, and 551 (68.9%) were polymorphic. In all, 2696 alleles were produced by the 551 polymorphic SSR loci in the 16 walnut cultivars, ranging from 2 to 14 alleles per locus with an average number of 4.9. Polymorphism information content ranged from 0.21 to 0.89 with an average of 0.62. Cluster analysis produced a very robust dendrogram. The walnut cultivars were separated into two main groups: all Turkish cultivars were included in one group, whereas the US and French cultivars were included in the other group. A set of 20 SSRs was selected for their high genetic diversity values to be used in further genetic studies in walnut. The novel SSR markers developed in this study could be used in future studies for constructing a genetic linkage map, analyzing population genetics, identifying parents, and conducting marker-assisted breeding, fingerprinting, and germplasm characterization in walnut.

Evaluation of the adaptability, productivity, and leaf powder quality of eight Moringa oleifera cultivars introduced to a dry-hot climate of Southwest China

Although Moringa oleifera is a globally recognized multipurpose plant, and its seed-oil has been identified as an industrial source for the manufacture of cosmetic emollient, there is however lack of conclusive data on its performance in China, which is the most northerly latitude of moringa distribution in the world today. The objectives of this study were to (i) determine the adaptability, and (ii) evaluate the yield potential of seed-oil and quality characteristics of leaf powder from eight M. oleifera cultivars (‘Mali’ [ML], ‘Kenya’ [KE], ‘USA’ [US], ‘Cuba’ [CU], ‘Bangalore’ [BL], ‘Calcutta’ [CT], ‘Taiwan’ [TW], and ‘Myanmar’ [PO]) in the dry-hot regions of southwest China from 2014 to 2015. Evaluated cultivars showed variations in the studied vegetative and reproductive growth traits i.e. tree height, canopy diameter, and the number of branches producing fruit (NBF), etc. The results showed that the PO cultivar had the highest total number of ripe fruit loads (NRF). Although the plants from the US cultivar had the maximum number of fruit settings (NTF), they produced the smallest NRF/NTF ratio, suggesting that plants from different geographical provenances differed in their adapting to varied environments and a severe physiological fruit drop in the US cultivar. Also, the evaluated cultivars showed differences in the studied fruiting traits and yield components i.e. the number of seeds per fruit pod (NSF), seed weight, seed yield, and seed oil content. Among the plants assessed, M. oleifera from the PO produced significantly higher (P < 0.05) seed and oil yields per hectare, with respective average values of 1025 kg·ha−1 and 321 kg·ha−1 throughout the two evaluation years. In addition, nutrient variability in leaf powder as a fodder resource was analyzed for crude lipid, crude protein, and fibre components contents. There were no significant differences (P < 0.05) between the eight cultivars in the crude fiber, crude lipid, ash or dry matter (DM) contents, but the CT and BL cultivars exhibited significantly (P < 0.05) higher crude protein levels and in vitro dry matter digestibility (IVDMD) concentrations. These findings suggested that the best varieties regarding seed oil yield and leaf powder quality may be the PO cultivar from Myanmar, and CT and BL cultivars from India, respectively.

Yield and dry matter dynamics of vegetative and reproductive organs in Japanese and US soybean cultivars

ABSTRACTRecently, US soybean cultivars have exhibited higher yields than Japanese soybean cultivars. To identify the determinants for this yield difference in reference to dry matter dynamics, recently developed US cultivars and Japanese commercial cultivars were cultivated in drained paddy fields in 2012 and 2013. The total dry matter (TDM) of each cultivar was measured at the initial seed-filling stage (R5), at 30 d after R5, and at maturity (R8). From R5 to R8, the DM of abscised leaves and petioles were measured. The actual HI (with abscised leaves and petioles) and apparent HI (without abscised leaves and petioles) were determined at R8. US soybean cultivars showed higher yields and apparent TDM (without abscised leaves and petioles) than did Japanese cultivars at R8. However, the difference in actual TDM (with abscised leaves and petioles) production was not significant between US and Japanese cultivars at R8. On the other hand, the actual HI was higher in US cultivars than in Japanese cultivars. US cultivars exhibited a higher TDM distribution to the pod before R5 and a higher pod growth rate from R5 to 30 d after R5. US cultivars tended to show greater crop growth rates (CGRs) from R5 to 30 d after R5. The higher yield in US cultivars was associated with the higher actual HI, which was considered attributable to a greater TDM productivity during the seed-filling period and higher DM distribution in the pod before R5.

Genetic diversity of day-neutral converted landrace Gossypium hirsutum L. accessions

Upland cotton, Gossypium hirsutum L., is an important fiber crop that is grown in warmer climates in over seventy-five countries through-out the world and accounts for over 90% of world production. In this study we assessed the genetic diversity and population structure of 1115 day-neutral conversions of G. hirsutum L. landrace accessions (DNCA). One-hundred-thirty-four genome wide simple sequence repeat markers were used for genotyping and 192 polymorphic loci were identified. A total of 1560 alleles were identified across the DNCAs and a set of 14 US cultivars with 64% being unique to DNCAs and only 6% were unique to the cultivars. Alleles ranged from 36 on chromosome 13 to 93 on chromosome 076. The relationship matrix indicated that, as a group, the DNCAs were not closely related, and the analysis resulted in seven distinct groupings, but these were not related to the country of origin. Analysis of molecular variance revealed that most of the variation (58.3%) was due to diversity within geographic origin groups and 41.7% due to diversity among groups. Within western hemisphere or eastern hemisphere origin of collection, there is a high degree of common allele sharing, but across hemispheres, DNCAs share fewer common alleles. Accessions originating in the eastern hemisphere share 56.8–65% of alleles in common with US cultivars; whereas, accessions originating in western hemisphere share between 38 and 41% of alleles in common with US cultivars. This study identified extensive genetic diversity among DNCAs within G. hirsutum.

Identification of QTLs for Salt Tolerance Traits and Prebreeding Lines with Enhanced Salt Tolerance in an Introgression Line Population of Rice

Salinity is a major abiotic stress that limits rice productivity worldwide. Due to involvement of multiple genes and multiple mechanisms in salinity tolerance, development of tolerant varieties has been challenging. The present study used 112 introgression lines (ILs) of a salt-tolerant donor ‘Nona Bokra’ in the genetic background of a US cultivar ‘Cheniere’ to elucidate the genetic basis of seedling stage salinity tolerance and develop salt-tolerant prebreeding lines for use in breeding program. The ILs were evaluated under salt stress and control conditions and were genotyped using 116 microsatellite markers. A total of 32 QTLs were identified for eight morpho-physiological traits whereas 18 QTLs were detected for salt tolerance indices. Comparison of the QTL results with an earlier study involving the same donor indicated that detection of few common QTLs could be due to genetic background effects. Both studies suggested shoot Na+/K+ homeostasis, Na+ exclusion, and compartmentation as possible salt tolerance mechanisms in ‘Nona Bokra’. Candidate gene identification and gene ontology analysis revealed that the genes involved in ion transport, ion homeostasis, and signaling may have important role in improving salinity tolerance. In addition to their utility in isolation of salt-tolerant determinants, the prebreeding lines with enhanced salt tolerance will accelerate development of salt-tolerant varieties by accumulating favorable alleles through marker-assisted selection.

Physiological activity and biomass production in crop canopy under a tropical environment in soybean cultivars with temperate and tropical origins

In order to explore the plant factors facilitating better adaptation of soybean to high temperatures, genotypic variability till the beginning of seed filling (R5) were examined with reference to biomass production, relative transpiration activity and relevant plant factors under a tropical environment. Twenty-nine (in 2014 and 2015) and 20 (in 2016) soybean cultivars of temperate (Japan and USA) and tropical (Indonesia-old, Indonesia-modern, and Others) origin were grown in Serang, Banten (2014 and 2015; Experiment 1) and in Bogor, West Java (2016; Experiment 2), Indonesia. In Experiment 1, aboveground biomass at R5 (TDWR5) of the temperate cultivars was one-third to one-fourth of that of the tropical cultivars. This was associated with less than half the amount of the cumulative intercepted radiation to R5 (CIRR5) due to their shorter growth duration and lower value of the mean fraction of canopy light interception till R5 (mean FVE-R5). In addition, the radiation use efficiency (RUE) at R5 of the temperate cultivars was also as low as 0.54gMJ−1, as compared to 0.87gMJ−1 in the tropical cultivars. The value of canopy temperature minus air temperature (CTd), as an indicator of relative transpiration activity, of temperate cultivars was markedly larger than that of the tropical cultivars, indicating lower transpiration activity in temperate cultivars, which was associated with the low RUE. In Experiment 2, greater activity of transpiration in tropical cultivars was attributed to their higher stomatal conductance (gs) and greater stomatal density (Nstoma) of upper leaves than that in those from the temperate regions. These results indicate that low biomass production in temperate cultivars occurs not only due to the cumulative intercepted radiation in the canopy but also due to low RUE and that the low RUE in temperate cultivars is associated with low gas exchange activity, in which leaf morphological traits are involved. Within temperate cultivars, US cultivars tended to perform better than the Japanese cultivars with respect to gas exchange activity.