Hybrid Seed Production Fields Research Articles

A new allele PEL9 GG identified by genome-wide association study increases panicle elongation length in rice (Oryza sativa L.).

Considering the male sterile line has the phenomenon of panicle enclosure, panicle elongation length (PEL) plays an important role in hybrid rice seed production. However, the molecular mechanism underlying this process is poorly understood. In this study, we investigated the PEL phenotypic values of 353 rice accessions across six environments, which shows abundant phenotypic variation. Combining the 1.3 million single-nucleotide polymorphisms, we performed a genome-wide association study on PEL. Three quantitative trait loci (QTL) qPEL4, qPEL6, and qPEL9 were identified as significantly associated with PEL, of which qPEL4 and qPEL6 were previously reported QTLs and qPEL9 was novel. One causal gene locus, PEL9, was identified and validated. The PEL of accessions carrying allele PEL9 GG was significantly longer than that of those carrying allele PEL9 TT. We also demonstrated that the outcrossing rate of female parents carrying allele PEL9 GG increased by 14.81% compared with that of the isogenic line carrying allele PEL9 TT in an F1 hybrid seed production field. The allele frequency of PEL9GG increased gradually with an increase in latitude in the Northern Hemisphere. Our results should facilitate the improvement of the PEL of the female parent of hybrid rice.

OsSYL2AA , an allele identified by gene-based association, increases style length in rice (Oryza sativa L.).

SUMMARYStigma characteristics are important factors affecting the seed yield of hybrid rice per unit area. Natural variation of stigma characteristics has been reported in rice, but the genetic basis for this variation is largely unknown. We performed a genome‐wide association study on three stigma characteristics in six environments using 1.3 million single‐nucleotide polymorphism (SNPs) characterized in 353 diverse accessions of Oryza sativa. An abundance of phenotypic variation was present in the three stigma characteristics of these collections. We identified four significant SNPs associated with stigma length, 20 SNPs with style length (SYL), and 17 SNPs with the sum of stigma and style length, which were detected repeatedly in more than four environments. Of these SNPs, 28 were novel. We identified two causal gene loci for SYL, OsSYL3 and OsSYL2; OsSYL3 was co‐localized with the grain size gene GS3. The SYL of accessions carrying allele OsSYL3AA was significantly longer than that of those carrying allele OsSYL3CC. We also demonstrated that the outcrossing rate of female parents carrying allele OsSYL2AA increased by 5.71% compared with that of the isogenic line carrying allele OsSYL2CC in an F1 hybrid seed production field. The allele frequencies of OsSYL3AA and OsSYL2AA decreased gradually with an increase in latitude in the Northern Hemisphere. Our results should facilitate the improvement in stigma characteristics of parents of hybrid rice.

Karakter Morfologi dan Kemampuan Silang Alami Tetua Padi Hibrida di Tiga Lokasi Berbeda

Adoption of the hybrid rice varieties by farmers is often impaired by the high price of hybrid seed, due to low yields in hybrid seed production fields. Female outcrossing ability and female hybrid seed production ability, defined as the rate of filled spikelets of the male sterile line and as its grain yield under outcrossing, respectively, determine plant traits for hybrid seed yield. We identified an morphological characters and outcrossing rate ability of 6 hybrid rice combination that affect grain yield of hybrid rice seed production. The experiment conducted in 3 locations i.e. Subang, Malang, and Ungaran districts during dry season of 2016. Subang is the best location to hybrid rice seed production with the highest average of grain yield. Hipa 19 was the hybrid varieties having > 1 ton/ha grain yield highest that others. The important agronomic characteristics that affected of F1 grain yield i.e. plant height, number productive tillers, number of filled grains, exerted panicle rate, dan outcrossing rate. Correlations between number of filled grains, outcrossing rate, and grain yield were tight and highly significant. High yield potential and cost-effective for hybrid seed production can be achieved using hybrid rice with high outcrossing rate and suitable condition of an environment.

Breeding for Outcrossing Ability in Rice, to Enhance Seed Production for Hybrid Rice Cropping

Background: Adoption of the hybrid rice varieties by farmers is often impaired by the high price of hybrid seed, due to low yields in hybrid seed production fields. Female outcrossing ability (FOA) and female hybrid seed production ability (FHSPA), defined as the rate of filled spikelets of the male sterile (MS) line and as its grain yield under outcrossing, respectively, determine plant traits for hybrid seed yield. Breeding for FOA and FHSPA in rice has suffered from the lack of a high throughput phenotyping method and the inbred breeding approach used for the development of MS lines. We developed an innovative hybrid rice breeding strategy that uses the monogenic recessive male-sterility gene ms-IR36 for the reciprocal recurrent improvement of maintainer and restorer populations.Results: High throughput screening for FOA and FHSPA can be achieved by scoring the grain weight of MS plants and the grain yield of fertile plants of progenies extracted from breeding populations segregating for the ms- IR36 gene. Using this phenotyping method in seven field trials, each involving several hundred entries, we reveal a very broad diversity for FOA (ranging from zero to 89%) and FHSPA, within the F3 progenies of bi-parental crosses and within S1 and S2 progenies extracted from different breeding populations. The seven experiments produced convergent results and heritabilities of 0.59-0.90 for FHSPA and 0.45-0.72 for FOA. Correlations between FHSPA and FOA were tight and highly significant. Correlations were looser between FHSPA and grain yield of the selfed fertile sibling (GW-MF). Correlations between FOA and GW-MF were not significant. Tight significant correlation was also observed between FHSPA of S1 lines and S2 lines extracted from the former.Conclusion: Population breeding through recurrent selection, using the ms-IR36 gene as a tool for both recombination and seed production for testcrossing, is a favorable framework for harnessing rice genetic diversity for FHSPA. Rapid and cost-effective genetic gain for hybrid seed production can be achieved using results of the ms- IR36 gene mediated test cross seed production process as FHSPA early screening.

Simulating Source‐Limited and Sink‐Limited Kernel Set with CERES‐Maize

CERES‐Maize simulates kernel set as a source‐limited process based on average plant growth rate during the lag phase after flowering. Yet the number of kernels formed by maize (Zea mays L.) also depends on timely interaction between male and female flowers, which can limit formation of reproductive sinks under some conditions. Failure to account for sink‐limited kernel set may contribute to simulation error observed under conditions that affect dynamics of pollen shed or silking, but do not alter crop growth rate. We developed algorithms for a Flowering Model to simulate sink‐limited kernel set from flowering dynamics. This model was calibrated against kernel production in hybrid seed production fields and then linked to CERES‐Maize. The Modified CERES‐Maize was calibrated against two years of field data involving three hybrids, eight population densities, and seven N levels. Integrating the capacity to simulate sink‐limited kernel set with source‐limited kernel set increased simulation accuracy dramatically, relative to original CERES‐Maize. For 13 commercial fields tested, Modified CERES‐Maize decreased simulation error for kernels per plant from 17.1 to 2.3%, improved r2 between measured and simulated values from 0.77 to 0.87, and decreased simulation error indicators mean error, root mean square error, and mean square deviation by 85, 40, and 64%, respectively. Modified CERES‐Maize accounts for a much greater range of variability in the biological processes controlling kernel set.

Influence of Plant Severing on Movement of <I>Ostrinia nubilalis</I> Larvae in <I>Zea mays</I> Hybrid Seed Production Fields

Genetically engineered corn hybrids that contain a cry gene from the bacterium Bacillus thuringiensis Berliner (Bt) are gaining popularity for controlling the corn pest Ostrinia nubilalis (Hübner). Continuous use of Bt corn, however, could select for O. nubilalis that are resistant to this corn. Monitoring for insect resistance is important, because it could help maintain the Bt technology. A possible monitoring method is to collect larval insects in commercial drying bins after harvest from Bt seed production fields. A drawback to this method is that these collections may be contaminated by insects that moved as later instars from severed non-Bt male rows into the adjacent Bt female rows. These larvae have little to no exposure to Bt toxin, resulting in possible "false positives." The objectives of this study were to first find which combination of planting and severing dates produces the least number of larvae that move from non-Bt male plants to Bt female plants and to assess O. nubilalis larval movement from severed non-Bt male rows to Bt female rows. Field studies in 2002 and 2003 were designed to simulate a hybrid seed production field. Results suggest that movement of O. nubilalis larvae from male corn is minimized when corn is planted early and male plants are severed by 2 wk post-anthesis. This reduces the likelihood of false positives by reducing the number of susceptible larvae moving between Bt and non-Bt plants. Also, larvae moved to all four female rows that were adjacent to the severed rows, but there were significantly more larvae found in the closest row compared with the other three. These results could be used to develop a monitoring program to find O. nubilalis larvae with resistance to Bt corn in field populations of O. nubilalis.

Weather Factors Associated with Development of Sorghum Ergot in the Texas Panhandle.

Since its first introduction in 1997, sorghum ergot, caused by Claviceps africana, has been observed yearly in the Texas Panhandle, where it has caused occasional epidemics in hybrid-seed production fields. To determine the effect of weather factors on ergot severity, inoculation experiments were conducted in 2003 and 2004 using sequentially planted sorghum plants. Sorghum flowers were inoculated with three inoculum concentrations (1 × 104, 1 × 105, or 1 × 106 spores/ml) prepared from infected sorghum panicles producing fresh honeydew. Each year, inoculations were conducted several times during sorghum flowering periods so that time of inoculations would coincide with different weather conditions. Weather variables (temperature, relative humidity, wind speed, precipitation, and radiation) were collected using an onsite weather station. Infected and uninfected florets were counted 8 to 13 days after inoculation, and the percentage of infected florets per sorghum panicle (severity) was determined. In both years, temperature and relative humidity were the predominant factors responsible for variations in sorghum ergot severity with all inoculum densities. Relationship between ergot severity and each of the two variables depended on inoculum density. Measurable infection occurred at a maximum temperature of 34°C with 1 × 106 spores/ml, while there was little or no infection at 30°C with 1 × 104 spore/ml. Cumulative departures from minimum relative humidity and maximum temperature infection thresholds 12, 18, 24, 36, 48, and 72 h after inoculation were calculated and regressed against ergot severity for each inoculum level. Cumulative departures of hourly temperature and relative humidity from maximum temperature and minimum relative humidity infection thresholds 18 and 24 h after inoculation were best related to sorghum ergot severity (R 2 = 89 and 91; P < 0001, respectively). Models based on these two time-durations then were used in predicting a regional site-specific ergot severity potential using radar-estimated rainfall.

Production of caffeine alkaloid by Claviceps sorghi

The ergot disease of sorghum (Sorghum bicolor), caused by the fungus Claviceps sorghi, restricted to the Indian sub-continent, is a disease in which the pathogen infects the florets, colonizing the unfertilized ovaries. Losses are higher in hybrid seed production fields due to a higher susceptibility of male sterile lines. The sclerotia of C. sorghi have never been found to contain alkaloids with a tetracyclic ergoline ring system, which is normal in most ergot pathogens. In this work, we show that sclerotia of C. sorghi contain caffeine alkaloid and the ability to produce it in vitro.

Evaluation of Relationships Between Weather Patterns and Prevalence of Sorghum Ergot in the Texas Panhandle

ABSTRACT Sorghum ergot caused by Claviceps africana was observed for the first time in the United States in Southern Texas in 1997. That year there was a widespread ergot epidemic in hybrid seed production fields in the Texas Panhandle. However, occurrence of the disease has been sparse during the past 3 years, easing fears that the hybrid seed industry in the region might be endangered. To determine whether climatic factors were associated with observed variations in prevalence of ergot, weather data (temperature, precipitation, and relative humidity) were collected from seven weather stations in the Texas Panhandle. Sorghum ergot prevalence data for the period 1997 to 2000 were collected from records of seed companies in the Panhandle and related to weather variables. Results showed that, in the southern section of the Panhandle, maximum temperature and precipitation between 1 and 15 August were associated (r(2) = 0.98, P = 0.001 and r(2) = 0.81, P = 0.0193, respectively) with variations in the prevalence of ergot during the 4-year period. In the northern section, only maximum temperature during 16 to 31 July was significantly associated (r(2) = 0.91, P = 0.0111) with disease prevalence. Over all, 1997 was wetter and cooler, during the 1 to 15 August period, than each of the subsequent 3 years. In addition to creating humid conditions for ergot development, precipitation was associated with suppression of maximum temperature, enhancing ergot-favorable temperature conditions. Examination of historic weather data for the region showed that there were many instances in the past where temperature depression was associated with a rise in cumulative precipitation, creating ergot-favorable conditions similar to those in 1997. Cross-spectral analysis was used to determine whether such association is periodic. Weather data from five of the seven locations in the region showed peaks of significant coherency ( alpha< 0.05) at 2 to 4 years and 7 to 10 years or greater, indicating the existence of a periodic cycle in the temperature-precipitation association. The results of the investigation suggested that association of precipitation with temperature depression is a primary factor in development of ergot in the Texas Panhandle, and such association has a periodic cycle.

Cytomorphological Characterization of a Nuclear Male Sterile Line of Chilli Pepper (Capsicum annuum L.).

Morphological and cytological characterization of a nuclear male sterile line (MS-12) of chilli revealed association of 3 morphological markers, viz., taller plant height, erect plant growth habit and dark purple anthers with the male sterile plants. A scheme has been proposed to identify and remove majority of male fertile plants from hybrid seed production field at early growth stage based on shorter plant height and intermediate growth habit (male fertile) followed by identification and removal of the remaining male fertile plants on the basis of light purple anthers at later stage. Meiotic analyses of male fertile and male sterile plants revealed that MS-12 was a sporogenous male sterile line, in which microspores degenerated immediately after formation of the tetrads.

Evaluation of sorghum ergot toxicity in broilers

Three experiments evaluated the performance of broilers fed sorghum ergot consisting of sphacelia/sclerotia of Claviceps africana present in tailings removed by conditioning of seed from grain sorghum hybrid seed production fields near Uvalde (Experiments 1 and 2) and Dumas (Experiment 3), Texas. Percentage sphacelia/sclerotia and total alkaloid content, respectively, in sorghum ergot tailings were 8% and 11.3 ppm for Uvalde and 75% and 235 ppm for Dumas. Sorghum ergot and control sorghum diets were based on the NRC (1994) requirements for starting broilers. In Experiment 1, neither growth nor feed efficiency were significantly reduced in male broilers fed sorghum ergot from hatch to 3 wk of age, but liver weights were significantly greater than those in the control. In Experiment 2, straight-run broilers were raised to 6 wk of age in floor pens using a three-phase feeding program. Sorghum ergot significantly reduced gain in 4-wk-old broilers and cumulative body weight at 5 wk. Feed conversion was significantly reduced during all three phases of feeding. In Experiment 3, control sorghum and the 75% ergot tailings were added to corn-soy basal diets at rates of 2.5, 5, and 10% by weight and fed to male broilers from hatch to 3 wk of age. Sorghum ergot did not significantly reduce growth, but, during Weeks 2 and 3, feed-to-gain ratios were higher. Neither type nor concentration of sorghum ergot significantly affected relative liver weights. We did not observe significant mortality or obvious symptoms of ergot toxicity, such as necrotic lesions of the feet or vesicular dermatitis of the comb, in any of the three experiments.

First Report of Sorghum Ergot Caused by Claviceps africana in the United States.

In March 1997, ergot was found on sorghum (Sorghum bicolor (L.) Moench) regrowth in several abandoned commercial grain sorghum fields in Cameron and Hidalgo counties in the Lower Rio Grande Valley (LRGV) of Texas. White sphacelia in florets produced honeydew containing macrospores (hyaline, oblong to oval, 10 to 25 μm × 5 to 7 μm) and microspores (hyaline, spherical, 3 μm in diameter). Macrospores germinated iteratively to form secondary conidia when placed on water agar and in situ following rain. Secondary conidia were hyaline, pyriform, with a protruding hilum, and measured 10 to 17 μm × 5 to 7 μm. High-pressure liquid chromatography analysis detected the alkaloid di-hydroergosine in sphacelia, which is unique to C. africana (1). The pathogen was also confirmed on adjacent johnsongrass (S. halepense). The spread of ergot across Texas was associated with the progressive maturation of the commercial sorghum crop as follows: LRGV (mid-May), Coastal Bend near Corpus Christi (June), Winter Garden area southwest of San Antonio (July), and the seed production region of the Texas Panhandle (mid-August). Ergot incidence ranged from a trace to 10% of the heads in (self-fertile) grain sorghum fields of the LRGV. Most heads had only a few infected florets, but a few heads had 35 to 50% of the florets infected. Only trace amounts were found in grain sorghum fields in other areas of the state. Incidence and severity of ergot were greatest in fields of male-sterile sorghums grown for forage. Ergot was generally low in primary heads of male-sterile sorghums in hybrid seed production fields but, in the absence of pollen, axillary tillers sometimes developed high levels of ergot. The major impact of sorghum ergot is expected to be in hybrid seed production fields in the High Plains of Texas. Reference: (1) D. E. Frederickson et al. Mycol. Res. 95:1101, 1991.

Intervarietal variations of floral characteristics with special reference to F1 seed production in Japonica rice (Oryza sativa L.)

自殖性作物であるイネで，F1種子の大量採種を可能とするには，種子親となる雄性不稔系統の自然交雑率を飛躍的に高める必要がある.そこで自然交雑率に関係する花器形質について温帯日本型の日本型育成品種，在来品種，ならびにOKA(1958)とOKA and CHANG(1962)の分類による熱帯日本型を対象に調査を行った.また，農林水産省生殖質保存管理室の種子保存目録の中の品種名のあとに(Majiri品種)と記載されている日本型在来品衝に着目した.種子親の花器形質として頴花あたり露出柱頭数(2本ある柱頭について開頴時の露出柱頭数)，花粉親の花器形質として穎花から抽出した直後の葯の花粉残存数を調査した，各花器形質について有意な品種間差が見られた.穎花あたり露出柱頭数は，熱帯日本型は平均0.52本で最も多く，1.0本以上の品種も見られた.一方，温帯日本型では値の小さい品種がほとんどであるが。(Majiri)の記載がある在来品種の平均値は(Majiri)の記載がない品種より大きく，さらに前者には水口濡(N0.72)のように0.5本以上の欠きた値を示す品種がいくつかあった.したがって，穎花あたり露出柱頭数が自然交雑率と深くかかわっていることが示唆された.また，葯抽出時の花粉残存数は，熱帯日本型のManggarsi I(No.129)が最高で葯あたり1，736粒であり，温帯日本型の日本在来品種でも1，000粒を越える品種が多数みられた.以上，温帯日本型でも形質に分離が生ずる雑駁な品種には自然交雑率を高め得る花器形質が存在するので，これらの品種を利用すれば花器形質の改良が可能である.自然交雑率をさらに高めるためには，交雑不稔を生じるなどの問題はあるが，熱帯日本型の有用花器特性を遺伝子給源として利用できると思われる.

A Single Dominant Gene for Rust Resistance in Pearl Millet1

Pearl millet rust (Puccinia penniseti Zimm = P. substriata var. indica) can reduce yields in hybrid seed production fields, quality in forage, and occasionally grain yields. Results are reported on the inheritance of a source of rust resistance discovered in crosses which involved one Sf progeny, #2696‐1‐4, selected from a pearl millet [Pennisetum americanum (L.) Leeke] germplasm accession originating from Chad. F1, F2, BC1, BC2 plants and the parents of crosses between the resistant source and two different susceptible male sterile lines were evaluated under severe rust pressure at three locations in India. Progeny of 2696‐1‐4 and the F1 hybrids between 2696‐1‐4 and male sterile lines were all resistant, while the male sterile lines were severely rusted at each location. In general, F2 populations from susceptible ✕ resistant crosses showed a good fit to a 3 resistant: 1 susceptible ratio and the backcrosses involving susceptible male‐sterile lines as recurrent parents showed a reasonably good fit to 1 resistant:! susceptible, indicating that rust resistance is conferred by a single dominant gene and susceptibility by its recessive allele. We propose the symbols Rpp1 and rpp1 for these genes.

Cross‐Pollination of Awned and Awnleted Isogenic Lines of Soft Red Winter Wheat1

Five pairs of lines of soft red winter wheat (Triticum aestivum L. em Thell.) nearly isogenic except for awns vs awnlets were compared to determine which type would serve as the best pollinator or best female in a hybrid seed production field. Pollen dispersal was measured in the field by pollen collected with adhesive coated slides mounted on wind vanes and by percent seed set on male‐sterile lines. Although the differences were small, awnleted pollinators produced greater pollen loads than the awned, 142 vs 121 pollen grains/10 mm2 in 1968 and 154 vs 120 in 1969; percent seed set from the two pollinator types was not significantly different, 42 vs 40 and 66 vs 63 in the two respective years.Pollen dispersal of awnleted and awned types was also studied in the laboratory by using individual excised spikes placed over pollen traps. Significantly more pollen was collected from the awnleted lines. The 55.2% anther extrusion for the awnleted lines was not significantly greater than the 52.6% for the awned lines. The correlation of percent anther extrusion with number of pollen grains collected gave a coefficient of 0.74 which with 248 degrees of freedom was highly significant.Male‐sterile lines which were segregating for awns vs awnlets were studied to determine which type would serve as the best female. The awned male‐steriles gave 4% higher seed sets.In all phases of this study the differences between the isogenic lines were small or nonsignificant. There seemed to be a tendency for the awnleted type to be the best pollinator and the awned type to be the best female. Cross‐pollination potential is likely to be affected more by other morphological features.

Inbred Maize Performance Following Tassel and Leaf Removal1

AbstractMechanical detasseling in hybrid seed production fields of corn (Zea mays L.) frequently is accompanied by loss of some leaf material. Little is known about the effect of this practice on seed production in those instances where the seed parent is an inbred line. We investigated the effects of tassel removal and tassel plus leaf removal on 5 short season inbred lines grown at Guelph, Ontario and 5 later maturing lines grown at Harrow, Ontario. Treatments at both locations consisted of a check, and the removal just prior to anthesis of the tassel, tassel plus one leaf, tassel plus two leaves, and tassel plus three leaves. When tassels alone were removed, there was an average increase “of 6.9%g rain yield. When 1, 2, and 3 leaves were removed with the tassel, yield reductions for the 10 inbreds averaged 1.5, 4.9, and 13.5% relative to the yield for tassel removal only. Yield differences were the result of a reduction in both kernel weight and number of kernels per row. However, yield responses to leaf removal varied greatly between inbreds, and therefore, it is impossible to generalize on the effects on grain yield of leaf removal during detasseling. For some inbreds, particularly shorter season ones, the reduction in yield due to removal of 2 and 3 leaves with the tassel is large enough to warrant consideration in seed production. On the other hand, yield of some of the later inbreds was reduced only slightly when 3 leaves were removed with the tassel. This probably reflects the higher percentages of leaf area removed in earlier inbreds as compared to the later inbreds.

Towards a more efficient utilization of genic male sterility in breeding hybrid barley and wheat

The author suggests that in nature cytoplasms may occur which can restore fertility in male sterile lines in which male sterility is based on one recessive gene ms. If indeed such a “fertilizing” cytoplasm should be found a male sterile (S) ms ms-line could be increased using the male fertile counterpart (F) ms ms as a male. Thus the female rows in hybrid seed production fields consist of male sterile plants only. A method is outlined to trace a fertility restoring cytoplasm and to introduce it into a male sterile line.