bluuebunny/crossref_metadata_2025 huggingface dataset:
Winter Survival in Switchgrass Populations Bred for High IVDMD
Authors: Vogel K. P. , Hopkins A. A. , Moore K. J. , Johnson K. D. , Carlson I. T.
Published: July 2010

In vitro dry matter digestibility (IVDMD) was improved by three cycles (C) of recurrent selection in a switchgrass (Panicum virgatum L.) population but significant winter kill occurred in the Cycle 4 (C4) mass selection nursery. Stand density losses in strains differing in IVDMD also were noted in pastures intensively grazed for 3 yr. Two studies were conducted to evaluate the effect of genetic changes in IVDMD on plant survival of switchgrass. Seed was harvested from the original high IVDMD C3 parent clones to produce half‐sib family seedlings that were planted into a replicated half‐sib progeny evaluation nursery in 1991 at Mead, NE. This nursery was harvested in 1993 and 1995 for biomass yield after plants had headed, forage was analyzed for IVDMD, and plant survival was determined. There were significant differences among the families for biomass yield, IVDMD, and plant survival. Among the half‐sib families, the correlations of 1993 and 1995 IVDMD with 1995 survival were not significant nor were the correlations between 1993 and 1995 yields and 1995 stands. In the C3 high IVDMD populations, some families had decreased winter survival but other families had high IVDMD and good survival. Randomly selected plants from pasture trials (PC or pasture clones) of ‘Trailblazer’ and ‘Pathfinder’ were polycrossed and the resulting bulk populations were evaluated with parent populations in replicated sward trials at three locations along with the High IVDMD C3 population and its derived winter survival (WS) population produced by harvesting bulk seed from surviving plants in the C4 selection nursery. Differences among populations for stand were not detected in the sward trials, likely because survival and IVDMD have low correlations within populations. It should be feasible to continue to breed for high IVDMD in switchgrass but survival will need to be an additional selection criterion.
Aflatoxin Accumulation of White and Yellow Maize Inbreds in Diallel Crosses
Authors: Betrán F. J. , Isakeit T. , Odvody G.
Published: July 2010

Preharvest aflatoxin (AF) contamination is one of the main limitations for corn (Zea mays L.) production in the southern USA causing enormous economic losses and posing a risk to animal and human health. The objectives of this study were (i) to evaluate and compare hybrids of new and selected potential sources of AF resistance for AF accumulation under field conditions, (ii) to identify the inbreds with the most consistent expression of resistance under different hybrid combinations and growing conditions; and (iii) to estimate combining abilities of white and yellow inbreds for aflatoxin accumulation and secondary traits. Two diallels among six local and exotic white and six yellow maize inbreds were evaluated at three locations in Texas. Inoculation with Aspergillus flavus Link:Fr. isolate NRRL 3357, either directly through the silk channel or as infested kernels on the soil surface, was effective in promoting AF accumulation in hybrids. White hybrids with low aflatoxin were CML269 × TxX24 and CML269 × CML176. CML269, CML176, and CML322 were the white inbreds with the lowest most consistent AF in hybrids and had the best GCA for aflatoxin resistance. Yellow hybrids with low AF were FR2128 × Mp715, Tx772 × Mp715, and Tx772 × CML326. Tx772 and FR2128 had the best GCA for reduced AF across locations or at specific locations. Inbreds CML326 and Tx772 had consistently low aflatoxin accumulation in hybrids across environments. AF content was correlated with husk cover, ear rot ratings, and insect damage. Exotic inbreds have genetic factors that can contribute to the reduction of aflatoxin contamination.
Pollen Production, Pollination Dynamics, and Kernel Set in Maize
Authors: Uribelarrea M. , Cárcova J. , Otegui M. E. , Westgate M. E.
Published: July 2010

Maize (Zea mays L.) pollen production has been found not to limit kernel set, but there is scarce information on pollen production of modern hybrids and the effect that breeding for reduced tassel size has had on this trait. Our objectives were to study genotypic differences in pollen production and flowering dynamics, and to estimate pollen availability per exposed silk. Four F1 hybrids were grown at different plant densities (between 2.5 and 12.5 plants m−2) in two distinct environments (cool Midwest USA and temperate Argentine Pampa). Pollen availability was also modified by delayed plantings and detasseling treatments. We measured the dates of anthesis and silking of individual plants, the anthesis‐silking interval (ASI), the number of exposed silks per apical ear, the number of pollen grains per square meter (PGM), and kernel number per ear. The number of pollen grains produced per tassel (PGT) and per exposed silk were estimated. Increased plant density promoted an increase in ASI, matched by an enhanced interplant variability in this parameter, and a reduction in PGT. The latter was reduced from 10.3 × 106 or 11 × 106 at 2.5 plants m−2 to about 3 × 106 at 12.5 plants m−2 (USA), and from 9.7 × 106 or 11.3 × 106 at 3 plants m−2 to 4 × 106 or 3.6 × 106 at 9 plants m−2 (Argentina). We estimated two thresholds beyond which kernel set could be affected: (i) 227 pollen grains cm−2 d−1 at the end of pollen shedding and (ii) two pollen grains per exposed silk. Some cropping conditions were closer to the second threshold than others.
Yield and Growth Response of Cuphea to Sowing Date
Authors: Gesch Russ W. , Forcella Frank , Barbour Nancy , Phillips Bliss , Voorheees Ward B.
Published: July 2010

Select germplasm of Cuphea, developed from an interspecific hybridization of C. viscosissima Jacq. and C. lanceolata f. Silenoides W.T. Aiton, shows good potential for commercial production in short‐season temperate climates. Cuphea seed oil could serve as a domestic source of medium‐chain fatty acids, which are in high demand by the chemical manufacturing industry. However, little is known about proper management practices for Cuphea agronomic production. A field study was conducted in west central Minnesota to determine optimum time of sowing in the northern Corn Belt region and describe influences of sowing date on growth and seed yield components of a semidomesticated germplasm line (PSR23). Seed was sown on 15 April, 1 May, 15 May, 1 June, and 15 June 1999 and 2000. Sowing in May resulted in greatest seed and seed‐oil yields, which were as high as 1.09 and 0.29 Mg ha−1, respectively. Seed yield declined as much as 31% when sown 15 April and 65% when sowing was delayed until 15 June. Plants developed from seed sown before June tended to form more branches and accumulated a greater amount of aboveground biomass. Typically, there was a distinct decrease in plant biomass accumulation and most seed yield components when sowing date was delayed until June. Cuphea PSR23 can be successfully grown in the northern Corn Belt, with early to mid May being the best time for sowing.
Embryo Drying Rates during the Acquisition of Desiccation Tolerance in Maize Seed
Authors: Cordova‐Tellez Leobigildo , Burris Joseph S.
Published: July 2010

Maize (Zea mays L.) seed quality is often reduced because of drying injury, although the causes and impairment mechanisms are poorly understood. In this study, we investigated changes in embryo drying rates and their effect on the acquisition of desiccation tolerance in maize seed. Ears of hybrid maize [B73 × (H99 × H95)] were harvested at about 550, 500, 400, and 320 g H2O kg−1 fresh weight (fw) and subjected to preconditioning (PC) (ear drying at 35°C and 0.47 m s−1 airflow rate) for 0, 12, 24, 36, and 48 h before fluidized bed (FB) drying (shelled seed, 35°C and 5.10 m s−1 airflow rate) treatments to decrease moisture content (MC) to about 130 g H2O kg−1 fw. Additionally, ears were entirely dried under PC (35C) and unheated‐air (NH) conditions. At the four harvests, different drying rate phases were evident in embryos of seed dried entirely at PC (35C) conditions. A slower drying phase coincided with the PC period, which increased with increasing maturation. Under FB drying, embryo MC declined at a faster rate down to about 400 g H2O kg−1 fw, followed by an intermediate drying rate down to about 200 g H2O kg−1 fw, and a slower drying rate below this point. As embryo MC declined to 400 g H2O kg−1 fw at slower drying rates, either with PC or field drying, the ability to withstand the faster drying rates of the FB progressively increased. This effect was illustrated by lower cell solute leakage and better performance in germination and vigor tests. We conclude that slow embryo drying rates to threshold levels may be crucial to acquire their ability to withstand higher drying rates without detrimental effect on seed germination and vigor.
Changes in Membrane Polar Lipid Fatty Acids of Seashore Paspalum in Response to Low Temperature Exposure
Authors: Cyril J. , Powell G. L. , Duncan R. R. , Baird W. V.
Published: July 2010

Seashore paspalum (Paspalum vaginatum Sw.) is a warm‐season turfgrass, best known for its superior salt tolerance. Plants are subject to injury during winter conditions along the northern boundary of their zone of adaptation. New cultivars that are more tolerant to low temperatures are needed for use in the transition zone. Cold tolerance has been correlated with the degree of unsaturation in membrane lipid fatty acids. Unsaturated fatty acids are thought to aid in maintaining membranes in a fluid state necessary for biological functioning (homeophasic adaptation). The primary objective was to characterize fatty acid composition of membrane lipids in three genotypes differing in cold tolerance. A second objective was to investigate changes in fatty acid content in these genotypes during exposure to low temperatures. Cold‐treated plants were exposed to a 10‐h photoperiod at 8°/4°C day/night temperatures and light intensity of 250 μmol m−2 s−1 photosynthetic photon flux density for 3 wk. Rhizomes and crowns were harvested at 7‐d intervals. Total lipids were extracted and the polar lipids separated by thin‐layer chromatography. Fatty acids were identified by gas chromatography (GC) and mass spectroscopy. In all three genotypes, the two saturated fatty acids, palmitic acid and stearic acid, did not change during cold treatment. The triunsaturated linolenic acid increased significantly during low temperature exposure. The magnitude of change was greater in the finer‐textured and more cold‐tolerant PI 509018‐1 (‘SeaIsle1’) than in the intermediately cold‐tolerant ‘Adalayd’ or in the cold‐susceptible, coarse‐textured PI 299042. These findings suggest that accumulation of linolenic acid partly explains the differential response in their cold tolerance.
Freezing Tolerance of Chicory and Narrow‐Leaf Plantain
Authors: Skinner R. Howard , Gustine David L.
Published: July 2010

‘Ceres Tonic’ and ‘Grasslands Lancelot’ narrow‐leaf plantain (Plantago lanceolata L.) and ‘Grasslands Puna’ chicory (Cichorium intybus L.) have received considerable interest as potential new forages for the northeastern USA because of their reported drought tolerance and high forage quality. However, all three cultivars were developed under New Zealand conditions and may not have sufficient winter hardiness to survive northeastern USA winters. Growth chamber and field studies were conducted to determine the freezing tolerance and winter survival of these new forages under well‐watered and drought conditions. Winter survival of chicory in the field ranged from 73% of marked plants in the wet treatment to 93% following summer drought. Likewise, winter survival of plantain in the field increased from 3% in the wet treatment to 41% in the dry treatment. Survival of Lancelot plantain in the growth chamber increased from 4% in the well‐watered to 16% in the drought treatment. However, survival of Tonic plantain and Puna chicory in the growth chamber was not affected by drought. Chicory survival was greater than survival of plantain in both controlled and field environments. Puna chicory appears to have sufficient winter hardiness to survive winters in the northeastern United States. Although Lancelot had slightly greater survival than Tonic, neither plantain cultivar had sufficient freezing tolerance to be recommended for use in the northeastern USA. Improved cultivars will need to be developed from populations that have evolved under more severe winter conditions before plantain can become a viable forage for most of this region.
Cultivar and Environment Effects on Annual Ryegrass Forage Yield, Yield Distribution, and Nutritive Value
Authors: Redfearn Daren D. , Venuto Brad C. , Pitman W. D. , Alison M. W. , Ward Jerry D.
Published: July 2010

Differences among annual ryegrass (Lolium multiflorum Lam.) cultivars for weight gain of grazing steers have been reported, even though plot experiments suggest that forage dry matter yield among cultivars should not be a limiting factor. Likewise, forage nutritive value differences among cultivars have not been assessed. The objectives of this research were to evaluate differences in cumulative forage yield, yield distribution, and nutritive value among ‘Gulf’, ‘Jackson’, ‘Marshall’, ‘Rio’, ‘Rustmaster’, and ‘Surrey’ annual ryegrass. Plots were harvested six times beginning in December at approximate 30‐d intervals during the 1997–1998 and 1998–1999 growing seasons. Nutritive value measurements included crude protein (CP), neutral detergent fiber (NDF), in vitro true digestibility (IVTD), and digestible NDF (DNDF). There were no differences among cultivars for cumulative forage yield (P = 0.99). However, for the January harvest, Surrey and Gulf averaged 1030 (±65) kg DM ha−1, whereas Marshall yielded only 672 (±79) kg DM ha−1 For the March harvest, yields of all varieties were similar and averaged 1350 (±95) kg DM ha−1 At the May harvest, Marshall and Jackson yielded 1232 (±123) kg DM ha−1, whereas Gulf yielded only 929 (±74) kg DM ha−1 Crude protein concentration differed significantly among harvests with a general decrease from 260 to 120 g CP kg−1 as the growing season progressed. Similar declines in nutritive value occurred for NDF, IVTD, and DNDF. Trends in yield distribution and forage quality may indicate a need for cultivar specific recommendations based on intended forage need and season of use.
QTL Mapping of Partial Resistance to Field Epidemics of Ascochyta Blight of Pea
Authors: Timmerman‐Vaughan Gail M. , Frew Tonya J. , Russell Adrian C. , Khan Tanveer , Butler Ruth , Gilpin Margy , Murray Sarah , Falloon Karla
Published: July 2010

Ascochyta blight of pea (Pisum sativum L.) is a fungal disease caused by Mycosphaerella pinodes (Berk. & Bloxham) Verstergren, Phoma medicaginis Malbr. & Roum. var. pinodella (L.K. Jones) Boerema, and Ascochyta pisi Lib. that can result in significant reductions to pea yield and quality. To characterize the genetics of resistance and to identify molecular markers for use in plant breeding, quantitative trait loci (QTLs) affecting Ascochyta blight resistance were mapped in F2:3 and F2:4 families produced from a cross between resistant breeding line 3148‐A88 and susceptible cultivar Rovar. A linkage map containing 96 loci on 11 linkage groups was constructed for 133 families from this cross. Resistance of progeny lines to natural Ascochyta blight epidemics was examined in field trials at Medina, Western Australia, in 1997, 1998, and 1999. Disease severity was assessed on stems, leaves, and pods by means of separate rating scales. Because pea shows increased susceptibility to Ascochyta blight as it matures, plant reproductive stage was assessed at the time of disease scoring in the 1998 and 1999 trials. Thirteen QTLs were detected for Ascochyta blight resistance on seven linkage groups. Eight of these QTLs were detected in multiple environments or by multiple trait scores. One QTL for plant developmental stage was detected. Linkage of Ascochyta blight resistance QTLs to candidate genes including disease response genes and resistance gene analogs and of the QTL for plant reproductive stage to a pea homolog of the Arabidopsis thaliana CONSTANS gene controlling flowering time in response to photoperiod is discussed.
Genetic Diversity among Forage Bermudagrass (Cynodon spp.)
Authors: Karaca Mehmet , Saha Sukumar , Zipf Allan , Jenkins Johnie N. , Lang David J.
Published: July 2010

Genetic analysis of forage bermudagrasses (Cynodon spp.) lags considerably behind other species, including the turf‐type bermudagrasses. This research was undertaken to identify and characterize genetic relationships within and between forage bermudagrass ecotypes and varieties. Genetic relationships within 31 forage bermudagrass genotypes were determined by means of 15 amplified fragment length polymorphism (AFLP), 10 chloroplast‐specific Simple sequence repeat length polymorphism (CpSSRLP), 10 random amplified polymorphic DNA (RAPD), and 10 directed amplification of minisatellite‐region DNA (DAMD) primers or primer pairs. The unweighted pair group method, using arithmetic averages (UPGMA) and the bootstrap analyses with 2000 replications, were used to calculate the relationships. Overall results indicated that forage bermudagrass genotypes have a narrow genetic base, with genetic similarity (GS) ranging from 0.608 to 0.977. The most genetically similar forage bermudagrass lines were ‘Tifton 78 WH’ and ‘Tifton 78’ (GS = 0.977), whereas ‘McDonald’ and ‘Alicia’ were the most genetically diverse bermudagrass lines (GS = 0.608). ‘Sumrall 007’, ‘Tanberg’, ‘Maddox’, McDonald, ‘Holly Springs’, ‘Murphy’, ‘Murphy II’, and ‘Stallings’ were distantly related to known varieties. The GS values of these genotypes were less than 0.85 compared with any other genotypes, indicating that these ecotypes were unique in their genome structure and provided genetic justification for their release as varieties. Close genetic relationships between some ecotypes and varieties were detected as follows: ‘Prairie I’, ‘Prairie II’, and ‘Prairie III’ to ‘Grazer’; ‘Lott I’, ‘Lott II’, and ‘Lancaster’ to ‘Callie’; and Tifton 78 WH to Tifton 78. Although DNA markers could differentiate these ecotypes, additional molecular, cytological, and phenological evidences are required to further confirm whether they could be considered as new varieties.
Development of Dominant Rice Blast Pi‐ta Resistance Gene Markers
Authors: Jia Yulin , Wang Zhonghua , Singh Pratibha
Published: July 2010

Incorporation of resistance genes into existing rice (Oryza sativa L.) cultivars is a powerful strategy and is commonly applied in breeding rice resistance to blast disease [caused by Pyricularia grisea Sacc. = P. oryzae Cavara (teleomorph: Magnaporthe grisea (Hebert) Barr)]. The rice blast resistance gene, Pi‐ta, originally introgressed into japonica from indica rice is important in breeding for rice blast resistance worldwide. In the southern USA, the rice cultivar Katy contains Pi‐ta and is resistant to the predominant blast M. grisea races IB‐49 and IC‐17 and has been used as the blast resistant breeding parent. Three pairs of DNA primers specific to the dominant indica Pi‐ta gene were designed to amplify the Pi‐ta DNA fragments by polymerase chain reaction (PCR). PCR products amplified by these Pi‐ta specific primers were cloned and sequenced. Sequence analysis confirmed the presence of the dominant indica Pi‐ta allele. These Pi‐ta primers were used to examine the presence of Pi‐ta alleles in advanced Arkansas rice breeding lines. The Pi‐ta containing rice lines, as determined by PCR analysis, were resistant to both IB‐49 and IC‐17 in standard pathogenicity assays. In contrast, lines lacking the Pi‐ta genes failed to protect rice plants against both races IB‐49 and IC‐17. The presence of Pi‐ta markers correlated with the Pi‐ta resistance spectrum. Thus, the Pi‐ta gene markers provide a basis for stacking other blast resistance genes into high yielding and good quality advanced breeding rice lines.
Variation among Accessions of Pisum fulvum for Resistance to Pea Weevil
Authors: Clement S. L. , Hardie D. C. , Elberson L. R.
Published: July 2010

The pea weevil, Bruchus pisorum (L.) (Coleoptera: Bruchidae), is one of the most intractable pest problems of cultivated pea, Pisum sativum L. The availability of resistant cultivars would give growers more pest management options. Searches for plant resistance to pea weevil were expanded to the Pisum secondary gene pool (P. fulvum Sm.) because seed resistance had not been located in P. sativum and subspecies. The objectives of this study were to determine the extent of pod and seed resistance to pea weevil in P. fulvum, and to use the life table format to characterize weevil stage‐specific mortality and survivorship on different P. fulvum accessions. Mortality of first instar larvae on pods, mortality of all weevil stages within seed, adult emergence from seed, and seed damage levels were quantified. In two greenhouse trials, more larvae died (14 to 50% averages) on pods of P. fulvum accessions than on pods of ‘Alaska 81’ (6% average), and mortality of first instar larvae entering seed of P. fulvum accessions averaged 83.7%. Seed damage ratings (1 = feeding scar on seed testa, 0‐1% cotyledon tissue eaten, dead first instar larva; 5 = extensive damage, live adult) averaged <3.0 for 26 P. fulvum accessions, compared with mean ratings of 4.9 for Alaska 81. Using weevil mortality and survivorship values in life tables and adult emergence rates, entries were classified as susceptible (two controls and five accessions), moderately resistant (14 accessions), and resistant (12 accessions). Antibiosis resistance was based on the death of weevil larvae on pods and seed testa and cotyledon tissues. The results identify sources of natural weevil resistance in the Pisum genome (26 moderately resistant and resistant accessions of P. fulvum) to endow pea cultivars with pod and/or seed resistance to B. pisorum.
Indirect versus Direct Selection of Winter Wheat for Low‐Input or High‐Input Levels
Authors: Brancourt-Hulmel M. , Heumez E. , Pluchard P. , Beghin D. , Depatureaux C. , Giraud A. , Le Gouis J.
Published: July 2010

Market prices and environmental concerns favor low‐input wheat (Triticum aestivum L.) production systems. This study assesses the efficiency of low‐input vs. high‐input selection environments to improve wheat for low‐input environments. Three standard cultivars, 11 parents, and 270 lines bred in INRA Mons‐Péronne were investigated for 2 yr (1998, 1999) in France at three INRA locations. Four agronomic treatments combining two levels of fungicides with two levels of nitrogen (N) were applied. Because of seed supply, only 10 year × treatment × location combinations were conducted. Broad‐sense heritabilities for grain yield (GY) ranged from 0.18 at low N without fungicide to 0.90 at high N without fungicide. Heritability estimates were higher at high N than at low N level. This was due to both an increase in error variance and a decrease in genetic variance at low nitrogen level. Heritabilities in treatments without fungicide were the same or higher than heritabilities measured in the corresponding controlled treatments. Broad‐sense heritabilities for grain N content (GNC) were similar between the controlled treatments with fungicide and the corresponding treatments without fungicide. They were lower at low N level and this was due to an increased error variance in both years. Genetic correlations between the 10 experiments were always positive for GY and N content: they ranged from 0.10 to 0.95 for yield and from 0.78 to 0.98 for GNC. The relative efficiency of indirect selection to direct selection for each pair of environments ranged from 0.15 to 0.99 indicating that indirect selection was never more efficient than direct selection. Therefore, breeding programs targeting low‐input environments should include low‐input selection environments to maximize selection gains.
Field Efficacy Assessment of Transgenic Roundup Ready Wheat
Authors: Zhou H. , Berg J. D. , Blank S. E. , Chay C. A. , Chen G. , Eskelsen S. R. , Fry J. E. , Hoi S. , Hu T. , Isakson P. J. , Lawton M. B. , Metz S. G. , Rempel C. B. , Ryerson D. K. , Sansone A. P. , Shook A. L. , Starke R. J. , Tichota J. M. , Valenti S. A.
Published: July 2010

Herbicide tolerant crops provide farmers access to a new weed control option of nonselective herbicide such as Roundup1 A wheat transgenic event 33391 was produced via Agrobacterium‐mediated transformation of a donor cultivar Bobwhite wheat (Triticum aestivum L.) and was identified as a commercial candidate to develop Roundup Ready wheat2 The objective of this study was to assess field efficacy of the transgenic event in spring wheat production regions in North America. Transgenic event 33391 was tested in field trials at 14 locations in 1999, 13 locations in 2000, and 14 locations in 2001. All trials were split‐plot designs with multiple rates of Roundup treatment. No vegetative or reproductive damage was observed with the application of 4 L ha−1 Roundup at the 3‐ to 5‐leaf stages. No yield reduction was observed with Roundup treatment. The transgenic event with or without Roundup application yielded as high as the nontransgenic Bobwhite. These results indicate that the wheat transgenic event 33391 has at least 2× tolerance to the nonselective herbicide Roundup.
Biogeography of WildArachis
Authors: Jarvis Andy , Ferguson Morag E. , Williams David E. , Guarino Luigi , Jones Peter G. , Stalker H. Tom , Valls Jose F. M. , Pittman Roy N. , Simpson Charles E. , Bramel Paula
Published: July 2010

The conservation status of wildArachisspp. is not well characterized for its maintenance and possible future exploitation for the improvement of cultivated peanut,Arachis hypogaeaL. Our objectives were to use 2175 georeferenced observations of wild peanut (Arachisspp.) to assess the conservation status of the genus and to prioritize biologically and geographically future conservation actions. Species distribution predictions were made on the basis of 36 climate variables, and these data were synthesized with land‐use data to map the potential distribution of each species, and hence the species richness of the whole genus, excludingA. hypogeahotspots of species richness were found in Mato Grosso around Cuiabá and Campo Grande in Brazil and around the Serra Geral de Goias, northeast of Brasilia. The current state of in situ conservation areas poorly represents wild peanut, with only 48 of the 2175 observations from National Parks. Several species were identified as being under threat of extinction. These includedA. archeriKrapov. & W.C. Gregory,A. setinervosaKrapov. & W.C. Gregory,A. marginataGardner,A. hatschbachiiKrapov. & W.C. Gregory,A. appressipilaKrapov. & W.C. Gregory,A. villosaBenth.,A. cryptopotamicaKrapov. & W.C. Gregory,A. helodesMartius ex Krapov. & Rigoni,A. magnaW.C. Gregory & C.E. Simpson, andA. gracilisKrapov. & W.C. Gregory (identification based on highly restricted ranges and land‐use pressures); andA. ipaënsisKrapov. & W.C. Gregory,A. cruzianaKrapov., W.C. Gregory & C.E. Simpson,A. williamsiiKrapov. & W.C. Gregory, A. martiiHandro,A. pietrarelliiKrapov. & W.C. Gregory, A. vallsiiKrapov. & W.C. Gregory, andA. monticolaKrapov. & Rigoni (identification based on insufficient observations and land‐use pressures). It is suggested that ex situ conservation efforts should focus on the area around Pedro Gomes (300 km southeast of Cuiabá), 170 km south along the planned road from Cuiabá to Corumbá, and around San José de Chiquitos in Bolivia, where some of the species adapted to lower temperatures may be found.
Improving Nitrogen‐Use Efficiency in European Maize
Authors: Presterl T. , Seitz G. , Landbeck M. , Thiemt E. M. , Schmidt W. , Geiger H. H.
Published: July 2010

Maize (Zea mays L.) cultivars with improved N‐use efficiency would be beneficial for low‐input production systems. Our objective was to estimate quantitative genetic parameters to optimize breeding programs for improving productivity under low N levels. Results of 21 field experiments with European breeding materials belonging to the flint and dent gene pool are presented. The study was performed during 1989 and 1999 at several locations in typical maize growing regions of Germany and France. All experiments were conducted at high (HN) and low (LN, no N fertilizer applied) N levels. Average grain yield was reduced by 37% at LN compared with HN. Coefficients of genotypic correlation between HN and LN were variable with an average of rG = 0.74 for grain yield and generally high for grain dry matter content. For grain yield, analyses of variance were computed from relative data, where plot values were expressed as percentage of the trial mean. Variances caused by genotype (G), G × location (L) interaction, and error effects were higher at LN compared with HN, with similar heritabilities at both N levels. For the untransformed data, components of variance were higher at HN than at LN. Genotype × N as well as G × L × N level interaction variances were significant in most experiments. Efficiency of improvement of grain yield at LN through indirect selection at HN was 70% compared with direct selection at LN. A trend toward increased efficiency of direct selection under LN conditions was evident with decreasing grain yield at LN.
Genetic Distance Based on Simple Sequence Repeats and Heterosis in Tropical Maize Populations
Authors: Reif J. C. , Melchinger A. E. , Xia X. C. , Warburton M. L. , Hoisington D. A. , Vasal S. K. , Srinivasan G. , Bohn M. , Frisch M.
Published: July 2010

Heterotic groups and patterns are of fundamental importance in hybrid breeding of maize (Zea mays L.). The major goal of this study was to investigate the relationship between heterosis and genetic distance determined with simple sequence repeat (SSR) markers. The objectives of our research were to (i) compare the genetic diversity within and between seven tropical maize populations, (ii) test alternative hypotheses on the relationship between panmictic midparent heterosis (PMPH) and genetic distances determined with SSR markers, and (iii) evaluate the use of SSR markers for grouping of germplasm and establishing heterotic patterns in hybrid breeding of tropical maize. Published data of a diallel of seven tropical maize populations evaluated for agronomic traits in seven environments were reanalyzed to calculate PMPH in population hybrids. In addition, 48 individuals from each population were sampled and assayed with 85 SSR markers covering the entire maize genome. A total of 532 alleles in the 7 × 48 genotypes assayed were detected. The analysis of molecular variance (AMOVA) revealed that 89.8% of the variation was found within populations and only 10.2% between populations. The correlation between PMPH and the squared modified Roger's distance (MRD) based on SSR markers was significantly positive (P < 0.05) only for grain yield (r = 0.63). With SSR analyses, it was possible to assign Population 29 (Pop29) to the established Heterotic Group A and propose new heterotic groups (Pop25, Pop43). We conclude that SSR markers provide a powerful tool for grouping of germplasm and are a valuable complementation to field trials for identifying groups with satisfactory heterotic response.
Autumn Defoliation Effects on Alfalfa Winter Survival, Root Physiology, and Gene Expression
Authors: Haagenson D. M. , Cunningham S. M. , Joern B. C. , Volenec J. J.
Published: July 2010

Harvesting alfalfa (Medicago sativa L.) after mid‐September in the North‐Central USA often reduces plant winter survival, but the physiological mechanisms associated with poor winter survival are not understood. Our objective was to determine how autumn harvesting affects alfalfa root physiology, gene expression, and plant winter survival. In Exp. 1, seven fall harvest dates were used to identify 1 to 15 October as a critical interval where significant changes in alfalfa winter survival and root physiology occur in Indiana. In Exp. 2, rows of six alfalfa cultivars possessing contrasting fall dormancy (FD) were established in May. Plants in one‐half of each row were defoliated in mid‐October, and roots were sampled at this defoliation and again in December. Winter injury was determined in mid‐April. Shoot removal in mid‐October increased winter injury and reduced plant vigor in spring. As expected, the October defoliation reduced root protein and starch concentrations in December, but unexpectedly increased root sugar concentrations. In addition, defoliation did not reduce the steady state transcript levels of several cold‐acclimation responsive (car) genes that are associated with genetic variation in winter survival. Although positively associated with genetic differences in winter hardiness, factors other than root sugar accumulation and expression of these car genes regulate defoliation‐induced changes in winter survival of these alfalfa cultivars.
Divergent Selection for Seedling Tiller Number in Big Bluestem and Switchgrass
Authors: Smart Alexander J. , Vogel Kenneth P. , Moser Lowell E. , Stroup Walter W.
Published: July 2010

Selection at the seedling stage in forage grass breeding would be extremely useful if seedling traits are highly heritable and correlated to desired agronomic traits. Objectives of this study were to determine the response to selection for high shoot weight and divergent selection for seedling tiller number in big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) seedlings and obtain estimates of realized heritability for these traits. Base populations were breeding populations of ‘Pawnee’ big bluestem and ‘Pathfinder’ switchgrass. Divergent selection for single or multiple (three or more) tiller(s) 6 to 8 wk after planting in a greenhouse produced four populations [big bluestem high seedling weight, multiple tiller (BBMT); big bluestem high seedling weight, single tiller (BBST); switchgrass high seedling weight, multiple tiller (SWMT); and switchgrass high seedling weight, single tiller (SWST)], which were planted in isolated polycross nurseries. Seed from polycross nurseries was used to conduct a second cycle of selection. Populations were evaluated in greenhouse studies for fresh weight and tiller number of seedlings. Seedling fresh weight was increased in BBST and SWST Cycle 2 populations, and divergent selection for tiller number resulted in populations significantly different from the base population. Realized heritability estimates for seedling tiller number in big bluestem and switchgrass were 0.26 and 0.23, respectively. The effect of genetic modification of seedling tiller number and shoot weight on establishment under field conditions and on mature plant phenotypes will need to be determined.
Genetic Analysis of Drought Resistance in Rice by Molecular Markers
Authors: Babu R. Chandra , Nguyen Bay D. , Chamarerk Varapong , Shanmugasundaram P. , Chezhian P. , Jeyaprakash P. , Ganesh S. K. , Palchamy A. , Sadasivam S. , Sarkarung S. , Wade L. J. , Nguyen Henry T.
Published: July 2010

Drought stress is the major constraint to rice (Oryza sativa L.) production and yield stability in rainfed ecosystems. Identifying genomic regions contributing to drought resistance will help develop rice cultivars suitable for rainfed regions through molecular marker assisted breeding. Quantitative trait loci (QTLs) linked to plant water stress indicators, phenology and production traits under irrigated and drought stress conditions were mapped by means of a doubled‐haploid (DH) population of 154 rice lines from the cross CT9993‐5‐10‐1‐M/IR62266‐42‐6‐2. The DH lines were subjected to water stress before anthesis in three field experiments at two locations. The DH lines showed significant variation for plant water stress indicators, phenology, plant biomass, yield and yield components under irrigated control and water stress. A total of 47 QTLs were identified for various plant water stress indicators, phenology, and production traits under control and water stress conditions in the field, which individually explained 5 to 59% of the phenotype variation. A region was identified on chromosome 4 that harbored major QTLs for plant height, grain yield, and number of grains per panicle under drought stress. By comparing the coincidence of QTLs with specific traits, we also genetically dissected the nature of association of root traits and capacity for osmotic adjustment with rice production under drought. Root traits had positive correlations with yield and yield components under drought stress. This study demonstrated that the region RG939‐RG476‐RG214 on chromosome 4 identified for root‐related drought resistance component QTLs also had pleiotropic effects on yield traits under stress. Consistent QTLs for drought resistance traits and yield under stress were detected and might be useful for marker‐assisted selection for rainfed rice improvement.
Development and Mapping of Markers Linked to the Rice Bacterial Blight Resistance Gene Xa7
Authors: Porter B. W. , Chittoor J. M. , Yano M. , Sasaki T. , White F. F.
Published: July 2010

Markers were generated that are linked to the rice bacterial blight resistance gene Xa7 Amplified restriction fragment length polymorphism (AFLP) analysis of a segregating, near‐isogenic F3 population of IR24 × IRBB7 revealed one polymorphic fragment, M1, which was mapped to position 107.3 centimorgans (cM) on the Rice Genome Research Program (RGP) map. Sequence comparisons of resistant and susceptible lines near M1 were used to develop additional markers. A sequence tagged site (STS) named M2 was mapped proximal to M1 and farther from Xa7, indicating that Xa7 lies distal to M1. On the distal side of M1, two simple sequence repeats (SSRs), M3 and M4, were mapped 0.5 and 1.8 cM, respectively, from Xa7. The pattern of recombinants was consistent with the order of M1–Xa7–M3–M4, and the map distances indicated that Xa7 is located in the region corresponding to the ends of the physically mapped Clemson University Genomics Institute (CUGI) bacterial artificial chromosome (BAC) contigs 96 and 143. A complex repeat was identified in the DNA sequence from rice (Oryza sativa L.) cultivars 93‐11 and Nipponbare that matched the end of contig 96 and a previously mapped expressed sequence tag (EST) marker (C52865S). Amplification of the repeat and flanking sequences revealed the presence and absence of the repeat in IR24 and IRBB7, respectively. No recombinants were identified between Xa7 and the polymorphic repeat, which was named M5, in 277 F3 susceptible progeny of the IR24 × IRBB7 cross. Comparison of the physical and genetic maps of rice in this region indicates that Xa7 could lie within 40 kilobases (kb) of M5, a distance suitable for gene pyramiding efforts and Xa7 cloning strategies.
Diallel Analysis of Fusarium Head Blight Resistance in Soft Red Winter Wheat
Authors: Hall M. D. , van Sanford D. A.
Published: July 2010

Fusarium graminearum Schwabe, the causative agent of Fusarium head blight (FHB), is an economically important pathogen of wheat (Triticum aestivum L.). Breeding FHB resistant wheat requires knowledge of the underlying genetic control of FHB resistance. While soft red winter (SRW) wheat breeders have begun to characterize germplasm for resistance, little information is available on the value of cultivars as parents in breeding for FHB resistance. Two diallel series of crosses, each involving nine SRW parents, were evaluated in both the greenhouse and field near Lexington, KY. The progeny and parents from the diallels were point inoculated with F. graminearum in both environments. FHB severity, deoxynivalenol (DON) level, and kernel damage were recorded. FHB severity ranged from 4.9 to 84.3% in the greenhouse and from 16.4 to 86.7% in the field. Significant general and specific combining ability effects were observed in both diallels in both environments. The nature of the resistance varied with diallel and with screening environment. On the basis of ratios of variance components, resistance in diallel 1 depended primarily on additive genetic effects, while in diallel 2 in the field dominance effects prevailed. Correlations between the greenhouse and field screening environments were low (0.36 in diallel 1 and 0.14 in diallel 2). Genotype × environment interactions were highly significant and due almost exclusively to rank change interactions. These results do not support indirect selection in a greenhouse environment for resistance expressed in the field.
Farmers' Seed Systems and Management Practices Determine Pearl Millet Genetic Diversity Patterns in Semiarid Regions of India
Authors: vom Brocke K. , Christinck A. , Weltzien R.E. , Presterl T. , Geiger H. H.
Published: July 2010

Pearl millet [Pennisetum glaucum (L.) R. Br.] landraces provide nutritional quality and security under the harsh environmental conditions of Rajasthan, India. Using amplified fragment length polymorphism (AFLP), this study investigated pearl millet genetic diversity patterns and related the results to farmers' local knowledge and seed systems. Thirty‐nine cultivars were assessed: 14 farmer landraces from western Rajasthan, 13 farmer landraces from eastern Rajasthan, and 12 control cultivars. Shannons' information index for western (H = 0.34) and eastern (H = 0.32) Rajasthan landraces was up to 14% higher than in composite‐based improved cultivars. Analysis of molecular variance (AMOVA) revealed that variation within landrace populations was much higher than between regional samples. In the west, intra‐village variation was higher than inter‐village variation. In the east, variation between landrace groups bearing a specific name was higher than intra‐group variation. Gene flow, inferred from genetic distances between populations, was used as an indicator for seed exchange between farmers. In western Rajasthan, seed exchange appears to be especially dynamic, as gene flow was greater than Nem = 25 among most of its populations. Farmers' knowledge of local cultivars and seed systems was, for the most part, supported by the AFLP analysis. These results are relevant for in situ maintenance and breeding strategies with a view to improving traditional cultivars, specifically performance and yielding stability.
Broad‐Sense Heritabilities, Genetic Correlations, and Selection Indices for Sugarcane Borer Resistance and Their Relation to Yield Loss
Authors: Milligan S. B. , Balzarini M. , White W. H.
Published: July 2010

The sugarcane borer [Diatraea saccharalis (Frabricius)] causes significant damage to sugarcane (Saccharum spp.), rendering cultivar resistance important. Researchers assess borer‐induced damage using up to five different measures: percentage bored internodes, percentage exited internodes, pupation success, moth production, and a damage rating. The inheritance of the different damage measures and the best approach to integrate the different variables into a simplified damage‐resistance assessment has not been well studied. Furthermore, the relationships of the damage traits to sugar production have not been comparatively assessed. We planted a replicated, two‐location test of 28 clones typical of the selection stage screened for borer resistance in the Louisiana sugarcane breeding programs. We recorded the five measures together with sucrose production and its components. Using appropriate variance components, the heritability, expected response to selection, and genetic correlations among the traits were used to construct selection indices of all combinations of the five damage traits studied. We used the regression coefficients of the damage traits on sucrose production as economic weights. The indices indicated that percentage bored internodes was the most effective single trait to reduce sugarcane borer damage. If data collection costs were considered, then the subjectively assessed damage rating was the most expeditious of the traits examined. High correlation values among several of the traits lead to the observation that inclusion of more than the bored internode, exited internodes, and the damage rating in an index were unnecessary.
The Effect of Grafting on the Flowering of Near‐Isogenic Lines of Soybean
Authors: Przepiorkowski Tomasz , Martin Steven K. St.
Published: July 2010

Grafting of soybean [Glycine max (L.) Merr.] genotypes differing in time to flower has been used to study translocation of flowering hormones and also as a tool to facilitate crossing. Our objective was to use Y‐shaped, grafted soybean plants to examine the mobility of the flowering stimulus. We grafted plants of ‘Harosoy’ (L58‐266, homozygous for the e1e2E3e5 genotype) and four isolines of Harosoy [L62‐667 (e1e2e3e5), L71‐802 (E1e2e3e5), L84‐307 (e1E2e3e5), and L84‐337 (e1e2e3E5)], differing by single maturity genes. The scion was reciprocally grafted on one of the branches, leaving the second branch as a stock. Ungrafted and self‐grafted controls were included, and plants were grown in growth chambers under short‐ (12‐h) and long‐day (20‐h) photoperiods. All treatments flowered at the same time under short‐day photoperiod. Under long‐day photoperiod, the greatest delay of flowering was observed in lines containing the E1 and E3 alleles. The stock and scion flowered independently of each other and no stock × scion interaction occurred. Hypothesizing that leaving full foliage on the plants could have been a reason for the lack of mutual effect of scion and stock, we performed a second experiment where one, two, four, eight, and all leaves were maintained on the scion. The scion and stock affected each other only slightly, and only when one or two leaves were present on a scion. The location of the first flowering node suggested the promotion of flowering in the isogenic line containing the late E3 allele.
A Cleaved Amplified Polymorphic Sequence (CAPS) Marker Associated with Root‐Knot Nematode Resistance in Sugarbeet
Authors: Weiland J. J. , Yu M. H.
Published: July 2010

Resistance to root‐knot nematode (Meloidogyne spp.) previously was introgressed into sugar beet (Beta vulgaris L.) from wild beet [B. vulgaris ssp. maritima (L.) Arcang] and was demonstrated to be dominant and simply inherited. Since resistance conferred by this gene was effective against six different Meloidogyne spp. tested, the locus was designated R6m‐1. An interpollinated progeny population of resistant heterozygotes segregating for R6m‐1, was exposed to nematodes in a greenhouse and rated for root knot disease symptoms. Resistance vs. susceptibility segregated at approximately a 4:1 ratio and 120 resistant roots and 48 susceptible roots were chosen for the generation of molecular markers linked to the resistance trait. Bulked DNA samples prepared from shoots sprouting from the selected plants were subjected to random amplified polymorphic DNA (RAPD) analysis and yielded a marker of 600 base pair (bp) that was highly associated with resistance. Sequence analysis of the 600‐bp product led to the design of DNA primers for specific amplification of a 580‐bp product, the generation by polymerase chain reaction (PCR) of which occurred in plants both susceptible and resistance to nematode. Comparison between the sequences generated from resistant plants and susceptible plants revealed numerous nucleotide substitutions. One base substitution associated in repulsion with resistance conditioned the existence of a recognition site for cleavage by the restriction endonuclease MseI. Amplification and cleavage of the product with MseI yielded a CAPS marker designated NEM06 that cosegregated with resistance to the root knot nematode. Computer‐assisted translation and comparison with sequences in public databases indicates that the marker DNA sequence encodes a protein with high sequence similarity to a plant transcription factor.