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Guar, [Cyamopsis tetragonoloba (L.) Taub] is an annual summer legume that is widely grown in arid and semi-arid regions. It is a diploid legume (2n = 2x = 14) with a genome size of approximately 560 Mb. Guar can fix atmospheric nitrogen via a symbiotic process with rhizobial bacteria, thus enhancing soil fertility and decreasing the need for the use of expensive nitrogen (N) fertilizers. Guar is a drought- and heat-tolerant crop and can be grown using minimal agricultural inputs. Guar can be used as vegetable, feed/fodder, or green manure. One of the primary driving factors for guar cultivation is galactomannan gum, known as guar gum, found in the seed endosperm. Guar gum has various industrial uses that range from cosmetic applications, food ingredients, to the oil industries. India is the lead guar production and accounts for more than 80% of the world production. The U.S. is the world largest guar market. This review discusses the status of genomic resources in guar, the progress made for germplasm evaluation of various agronomic traits, and the genetic engineering efforts in guar.

Guar (Cyamopsis tetragonolobus L. Taub.) is a leguminous crop plant that produces a seed containing galactomannan gum, which is used in many applications as a lubricant, binder, thickener, and emulsifier, among other functions. A recent spike in worldwide guar consumption has been driven largely by the industrial uses of the gum. As a legume, the primary ecosystem service agricultural producers expect from guar is nitrogen fixation, but the common perception is that guar does not nodulate effectively. The objective of this replicated and repeated greenhouse study was to test the effects of contrasting soils, representing typical alkaline soils in which guar is cultivated worldwide, and Rhizobia inoculants on nodulation and plant growth characteristics in two guar varieties. In the study, abundant nodulation was observed. The soils had contrasting effects on nodulation, with a high nodule number of low weight (497 mg/24.3 nodules) in the clay loam and low nodule number of high weight (583 mg/8.64 nodules) in the sandy loam, but no effect of the inoculants was observed. The difference in nodule characteristics between the soils may have resulted from differences in indigenous Rhizobium population sizes and/or species available to associate with guar roots. The lack of inoculant effects may have resulted from high indigenous levels of Rhizobium in the soil and/or low concentrations of Rhizobium or uncompetitive Rhizobium delivered through the seed-applied inoculants. Based on the results of this study, we expect that guar will nodulate and fix nitrogen effectively in field conditions, given that these processes are not inhibited by exogenous factors, such as water stress. Achieving increases in nodulation and nitrogen fixation above baseline levels may require a concerted effort to develop effective inoculants for guar, which may offer a unique opportunity to expand biological nitrogen fixation in agriculture in semi-arid regions.

Guar [Cyamopsis tetragonoloba (L.) Taub] is a legume grown worldwide, tolerant of hot, dry, and saline conditions. Phenotyping is a key bottleneck in guar improvement, with belowground root nodule phenes being largely overlooked. To address this bottleneck, a greenhouse study was conducted to evaluate phenotypic variability and associations in 14 nodule and plant growth parameters in 50 guar genotypes over 48 days. Nodule mass per plant differed among genotypes and had moderate heritability (P = 0.011, H2 = 0.40), while nodule number did not differ and had low heritability (P = 0.247, H2 = 0.14), and the parameters were not correlated. Nodule mass was correlated with total plant N (r = 0.56), plus most biomass parameters, indicating phenotypic links between plant capacity to support nodulation, N2 accumulation, and plant biomass production. Stem diameter may be useful as an indirect, high-throughput selection trait for increased nodulation in guar, as there was a positive association between stem diameter and nodule mass. Branch number and stem diameter, which have great agronomic significance, had wide phenotypic variability and were highly heritable. Reproductive development was delayed in branched genotypes, which may have implications in breeding guar for environments that differ in growing season length. Despite low heritability, there was a wide range in specific leaf area (SLA) that may be exploited by breeders to optimize drought tolerance and N use efficiency traits. These analyses give novel and confirmatory insights on the nature and associations of phenotypic character traits in guar, particularly nodule traits, providing added tools for breeders in developing desired and beneficial plant ideotypes.

Legume inoculants are products that introduce legume-specific rhizobia bacteria to the soil and promote the process of biological nitrogen fixation. Guar (Cyamopsis tetragonoloba L. Taub.), also known as clusterbean, is a legume produced in semi-arid regions around the world, primarily for industrial uses of guar gum, but there is only one known commercial inoculant products for the crop, which is not available worldwide. The USDA-ARS National Rhizobium Germplasm Collection has four Rhizobium strains listed as compatible with guar: USDA 3089, USDA 3385, USDA 3386, and USDA 3595. The objective of this research was to test the efficacy of four peat-based, seed-applied inoculants derived from these strains, as well as a mixture of all four strains, compared with un-inoculated plants in controlled greenhouse conditions. Among the tested strains, USDA 3089 and USDA 3386 had the greatest positive impacts, as they increased nodule weight, total assimilated nitrogen, biomass production, and protein production per plant relative to the un-inoculated control. USDA 3385 and the Mix likewise increased nodule weight. No inoculant affected other measured aboveground plant morphological and productivity parameters or nodule number. These Rhizobium strains, particularly USDA 3089 and 3386, were identified as beneficial and recommended for further testing in the field in development of an effective inoculant for guar.

Demand for galactomannan gum from guar, commonly known as guar gum, has exponentially increased in the last few decades due to increased use in oil and natural gas, food, cosmetics, paper and other industries. The United States of America is the major importer of the guar gum in the world, which is mainly grown in deserts of India and Pakistan. There is need to increase guar production in non-traditional areas to ensure steady supply and reduce market volatility. Expanding guar acreage into cooler regions of the southern High Plains or in similar agroclimatic regions of the world is an attractive option. Therefore, a study was conducted in incubators to assess genetic variations among currently available guar cultivars for germination and early growth under cooler temperature ranges. Six temperatures (13, 16, 19, 22, 25, and 28 °C) and six guar cultivars (Kinman, Lewis, Matador, Monument, Santa Cruz and Judd 69) were used. Guar cultivars exhibited significant variations for germination percentage, mean germination time and seed vigor index under lower temperatures, which narrowed as the temperature increased closer to optimum. Mean seed germination percentage of cultivars reached maximum at 22 °C. However, speed of germination and seed vigor indices, which are indicators of quick and uniform establishment of guar in the field, continued to increase till 28 °C. Kinman, which was the most promising guar cultivar under cooler temperature, reached maximum germination percent at 16 °C and had the lowest germination time and highest seed vigor index among cultivars below 16 °C. In contrast, Matador reached maximum germination at 26 °C. Germination and early seedling traits indicate that it is better to plant guar in warm soils and if needed to plant in cooler conditions, cultivars like Kinman should be used.

In the semi-arid Texas High Plains, declining irrigation water supply hinders the profitable corn (Zea mays L.) silage production, the principle feed ingredient of the beef and dairy industries. Drought-tolerant and deep-rooting crops like forage sorghum (Sorghum bicolor L.) and pearl millet (Pennisetum glaucum L.) could be an alternative to corn silage under limiting irrigation. A field study was conducted during 2018 and 2019 at New Deal, TX to assess soil water depletion patterns, water use efficiency (WUE), and silage yield of forage sorghum, pearl millet, and corn under limited irrigation. The experiment was conducted in split-plot design with three irrigation levels [I0 (55 and 29 mm), I1 (172 and 147 mm), and I2 (323 and 260 mm) in 2018 and 2019, respectively] as main-plots and five cultivars [P1498AM (corn), AF7401 and Silo700D (BMR sorghum), and Epic and Exceed (BMR pearl millet)] as sub-plots with three replications. The soil water depletion amount was greater in I0 (105 and 57 mm) followed by I1 (60 and 37 mm) and I2 (44 and 13 mm) in 2018 and 2019, respectively. Fresh biomass yield was the greatest in I2 followed by I1 and I0; however, the highest WUE was achieved in I0 and I2 in 2018 and 2019, respectively. Water depletion depth was greater for sorghum and pearl millet plots (0–1 m) than corn plots (0–0.6 m) which resulted in greater water depletion amount in sorghum (75 and 31 mm) and pearl millet (68 and 48 mm) plots than corn (67 and 28 mm) during 2018 and 2019, respectively. Average yield and WUE were the highest in sorghum cultivars, followed by pearl millet and corn. Results confirmed that the higher silage yield and WUE can be achieved by sorghum compared to pearl millet and corn under limited irrigation conditions.

Guar (Cyamopsis tetragonoloba (L.) Taub.), a grain legume grown in India, Pakistan and the United States, draws interest for irrigated environments in the Mediterranean areas. A limitation to widespread guar adaptation in this environment is its low capability to develop N-fixing Rhizobium nodulation. A study was conducted in South-Eastern Sicily, Italy in 2005 and 2006, to examine three levels of Rhizobium inoculation (non-inoculated, inoculated at sowing, inoculated at sowing plus at the third true leaf) and two levels of applied phosphorus fertilizer (0 and 40 kg ha−1 P). Plant height, pods per plant, seed yield, number of nodules per plant and seed galactomannan content were measured. No significant difference was found due to year of cultivation. Plant height was not significantly affected by Rhizobium or P fertilizer. Phosphorus fertilizer promoted the number of pods per plant, especially when bacteria inoculation was applied. Seed yield was significantly increased by inoculation and phosphorus levels. Inoculant caused a significant increase in seed yield (by 34%) from 2.2 t ha-1 (I0) to 3.4 t ha-1 (I2), whereas phosphorus application enhanced yields by 18% when P0 (2.7 t ha-1) were compared with P40 plots (3.3 t ha-1). Without inoculant there was no nodulation, whereas the number of nodules per plant increased to 14 in plots with the highest level of inoculation. Fertilizer P application did not affect Rhizobium nodulation. Galactomannan content was not influenced by inoculation and P fertilization, however increased seed yield resulting from inoculation and P fertilization led to increased galactomannan production per hectare.

U.S. castor production is limited in part due to only one labeled herbicide (trifluralin) for effective weed control. Field studies were conducted in south Texas and in the Texas High Plains in 2008, 2009, 2012, and 2013 to evaluate castor tolerance and weed efficacy following the application of preemergence (PRE) herbicides. During years of little or poor rainfall, no castor injury was noted following the application of PRE herbicides. However, when rainfall occurred soon after application of PRE herbicides, linuron doses of 1.12 kg/ha or greater resulted in stunting of castor plants and reduced stands when compared with the non-treated control. Acetochlor, clomazone, pendimethalin, and trifluralin consistently caused the least injury to castor plants. However, castor bean yield in many instances was not affected by herbicide injury. Diuron at doses of 1.12 kg/ha or greater and the combination of diuron plus linuron at 0.56 kg/ha or greater effectively controlled (> 80%) smellmelon ( Cucumis melo L. var. Dudaim Naud.) and Palmer amaranth ( Amaranthus palmeri S. Wats), but provided inconsistent control (0–99%) of Texas millet [ Urochloa texana (Buckl.) R.Webster]. Results of these studies indicated that castor tolerance to PRE applications of acetochlor, clomazone, and pendimethalin was excellent, thus providing the greatest opportunity for future use in castor production.

This study was to determine if diffusion of soil ammonium may explain why many sandy soils have greater nitrogen (N)–supplying capacity to rice than clay soils. A laboratory procedure using transient-state methods measured the linear movement of soil ammonium (NH4) in tubes packed with five field soils under aerobic conditions. Ammonium diffusion was measured by sectioning tubes after 48 h of equilibration and then measuring NH4 by steam distillation. Effective diffusion coefficients, De, and NH4 diffusion distance, d, per day ranged from De = 4.6 × 10−5 cm2 d−1 and 1.5 cm d−1 for Katy sandy loam to De = 2.9 × 10−7 cm2 d−1 and 0.11 cm d−1 for League clay. Ammonium diffusion distance d was strongly related to soil clay content and hence was predicted by d = Y × {[100/(% clay)] − 1}, where Y is set to 0.1. Predicted d and measured d were highly related (R2 = 0.99).

Development of alternative sources through wastewater reuse is important to meet water demands in arid regions. However, effects of wastewater irrigation on soil properties and crop performance must be evaluated before advocating its widespread use. Objectives of this study were to evaluate: (i) effects of prior evaporative disposal of saline-sodic blowdown water (BW) on soil (fine-loamy, mixed, and thermic Typic Calciorthods) properties in the disposal area, and (ii) effects of flood irrigation with three water qualities (control, BW 1X, and BW 2X) on soil salinity and alfalfa performance using a greenhouse soil column study (soil collected from same study area as objective (i)). Results indicated that although prior land disposal of BW had increased salinity and sodicity of soil, they were within the tolerance limits of the intended crop, alfalfa. Mass balance calculations indicated measured (15·6 Mg ha−1) and calculated (13·2 Mg ha−1) salt accumulation at the test site used for evaporative disposal were similar. Alfalfa grown using BW under greenhouse conditions produced prime quality hay and biomass yield similar to the control treatment (8·3 g column−1 vs. 10·5 g column−1 in control). Although 3·6 years equivalent of flood irrigation with BW 1X did not result in saline soil (BW 1X irrigated soils EC ranged from 2·2 to 3·5 dS m−1), BW 2X irrigation resulted in saline soils. Sodicities of irrigated soils were greater in fine textured deep soils than coarse textured surface soils (e.g., SAR of 6·1 at 0–5 cm vs. 19·5 mmol1/2 L−1/2 at 30–60 cm in BW 1X), indicating the need for high solubility Ca amendments for long-term irrigation with BW on fine texture soils within the soil profile. Copyright © 2010 John Wiley & Sons, Ltd.

Cyclophosphates are not adsorbed by soil constituents and can be mobile in the soil profile. Mobile phosphorus (P) sources are of interest in soil science and for agronomic practices. Cyclotri (Na3P3O9; C3P), and cyclotetraphosphate (Na4P4O10; C4P) were compared to linear, ortho‐, pyro‐, and tripolyphosphate in four soils with different chemical, physical, and biological properties to determine their mobility and availability to corn (Zea mays, L.) in laboratory and greenhouse experiments. Cyclophosphate (C3P and C4P) hydrolysis products were evaluated by ion chromatography after incubating for 6 to 192 h with 100 and 200 µg P g−1 soil. Phosphorus distribution and mobility, and plant availability and uptake with time, were determined in 45‐cm columns for four soils. Cyclophosphates sorbed less and moved deeper in all soils compared to the linear phosphates. The results showed that after 24 h a large proportion of cyclophosphates (34% of C3P and 37% of C4P) remained unhydrolyzed in Falba sandy aci...

Nitrogen and P fertilizer response for cotton (Gossypium hirsutum L.) and sorghum [Sorghum bicolor (L.) Moench] in a reduced tillage rotation system in the Southern High Plains has not been well studied. During 2000 to 2003, an irrigated study of cotton-sorghum rotation vs. continuous cotton evaluated the crop rotation effects on cotton lint yield and assessed N and P fertilizer and residual fertilizer response for the two systems. Preplant soil samples were collected each spring to determine fertilizer rates. Cotton lint yields and cottonseed N were not affected by rotation with sorghum compared with continuous cotton. Nitrogen fertilizer response was observed in lint yields from 2001 to 2003 in cotton following sorghum, but not in continuous cotton. No P fertilizer or soil residual P response in cotton lint yields was found, regardless of rotation. Grain sorghum yields responded to N fertilizer in 2 yr. No grain sorghum response was observed to P fertilizer, but in 1 yr a yield response to residual P fertilizer relative to zero-P plots was noted. Seed N uptake was greater in sorghum than in cotton. Nitrogen fertility level increased seed N in sorghum and in cotton following sorghum. Infrequent crop response to P fertilizer was not unexpected, especially when Mehlich-3 soil P in zero-P subplots was near the 95% sufficiency level of 20 mg P kg -1 . The main finding of this study is that N fertilizer response was more consistent for cotton following sorghum than in a continuous cotton system. In refining N fertilizer recommendations, N debits may be needed for N immobilization in sorghum residue. Nitrogen credit may be appropriate from leaf litter for crops following cotton and for NO 3 -N in irrigation water.

Fertilizer response studies for peanut (Arachis hypogaea L.) in the semi-arid, alkaline soil regions of the western United States have been few. Peanut in the Southern High Plains is a relatively new crop and soil test-fertilizer response information is needed. A three-year factorial study was conducted of irrigated peanut with one rate of nitrogen (N), phosphorus (P), and zinc (Zn) fertilizer. Nitrogen fertilizer response was observed in only one of three years, and may have been related to herbicide injury. No response to P or Zn fertilizer was observed, despite below critical soil test P in all three years, and below critical soil Zn in one year. Leaf N, P, and potassium (K) at mid bloom or mid pegging responded inconsistently to fertilizer additions. However, leaf P was correlated with peanut yields in two of three years. In-season multispectral reflectance responded occasionally to fertilizer applications. Chlorophyll meter readings were positively affected by N in 2000 and 2001, and by P in 2001. In these same instances, chlorophyll meter readings were correlated with leaf N and P. This study demonstrates that fertilizer response in peanut is hard to document in the Southern Plains, and that more research is needed with this crop.

Cydotriphosphate (Na 3 P 3 O 9 , C3P) and cydotetraphosphate (Na 4 P 4 O 12 , C4P) are not appreciably sorbed by soil constituents. This property combined with a reduced rate of hydrolysis of C4P and its hydrolysis products may maintain P availability for plant uptake. The primary objective of this study was to determine the residence times of C3P and C4P and their hydrolysis products in four soils. Hydrolysis of C3P and C4P was dependent on soil moisture, temperature, biological activity, and time. Cyclic P hydrolysis followed apparent first-order reaction. Recovery of hydrolysis products of C3P and C4P was higher in soils, such as Falba sandy loam (sl), which demonstrated limited sorption for mono-, di-, and triphosphate. The presence of hydrolysis products may explain the decreasing rate constants observed in soils incubated for longer than 48 h. Cyclotetraphosphate was more stable than C3P in all comparable treatments, often by three to six times. The energy of activation (E A ) for C3P and C4P was 45.8 and 61.1 kJ mol -1 , respectively, in a Falba sl, and 38.6 and 51.2 kJ mol -1 , respectively, in a Branyon day (c). Cyclotriphosphate was more readily hydrolyzed in soils compared with C4P. These results indicate a potential advantage of C4P over C3P because of its slower hydrolysis in soils, and over all linear phosphates, which are strongly sorbed by soil constituents.

Cyclotriphosphate (Na(3)P(3)O(9)) and cyclotetraphosphate (Na(4)P(4)O(12)) are not strongly sorbed by soil constituents. Potential movement and efficient plant utilization of P from these compounds are dependent on the hydrolysis of the cyclophosphate ring structure and their hydrolysis products. The objectives of this study were to prepare pure useable quantities of these cyclophosphates and their hydrolysis products and to extract, separate, and analyze these compounds after application to diverse soils. Cyclophosphates of high purity (>99.0%) were prepared, and improved methods of extraction and analysis by ion chromatography were developed. Cyclophosphates and their hydrolysis products were extracted from soil using a sequential water/0.5 M H(2)SO(4)/1.0 M NaOH extraction that maximized P recovery and minimized hydrolysis of cyclic and linear phosphates during the extraction procedure. Gradient elution chromatography separated cyclic phosphates and their hydrolysis products. Separation and direct quantitative analysis of the applied cyclophosphates and their hydrolysis products were accomplished in

Chelator-buffering methods with N-(2-hydroxyethyl)ethylenedinitrilotriacetic acid (HEDTA) are used to elucidate Poaceae growth response to micronutrient metal activities including (Zn 2+ ), but reliable hydroponic methods that maintain stable (Zn 2+ ) for evaluating Zn deficiency in rice (Oryza sativa L.) have not been reported. The objective was to develop a chelator-buffered method that gauges rice growth response to (Zn 2+ ) in an otherwise chemically stable environment. Using GEOCHEM-PC to estimate solution activities, an aerobic HEDTA-nitrilotriacetic acid (NTA) dual-chelator method was developed that imposed five (Zn 2+ ) levels on cv. IR-36 seedlings for 21 d after transplanting (DAT) in a growth chamber. Control of pH 5.50 ± 0.05 using 3.0 mM2-(4-morpholino)-ethanesulfonic acid (MES) combined with periodic adjustment was critical to preserving target (Zn 2+ ). Solution treatments ranged from Zn deficient, where (Zn 2+ ) = 10 -10.0 M (0.25 μM total chelated Zn), to fully Zn sufficient where (Zn 2+ ) = 10 -8.8 M (4.00 μM total chelated Zn). Using 200.0 μM total chelated Fe(III), adequate Fe was maintained at (Fe 3+ ) = 10 -14.3 M. Phosphorous supply was controlled to prevent toxic P accumulation at low (Zn 2+ ). With increasing (Zn 2+ ), total biomass at 21 d ranged from 0.94 to 1.90 g plant -1 . Shoot Zn responded to (Zn 2+ ), not total chelated Zn 2+ , and roots responded similarly. Critical (Zn 2+ ) for normal growth was 10 -9.1 M, and leaf Zn-deficiency symptoms were observed at (Zn 2+ ) ≤10 -9.4 M (≤28 mg Zn kg -1 shoot). The HEDTA-NTA method provides a rapid and reliable means for evaluating Zn deficiency tolerance in IR-36 via diagnostic visual and physical symptoms in response to a range of (Zn 2+ ) levels.

Salinity is a limiting factor in irrigated alfalfa (Medicago sativa L.) production in many regions of the world. Objectives of this project were to evaluate twelve alfalfa cultivar responsesto salinity using laboratory, greenhouse and field experiments. The laboratory experiment evaluated plant germination under increasing levels of salt concentration (0 to 2%) and statistical differences were observed at 1.0%, 1.5% and 2.0% concentrations (10 000 ppm to 20 000 ppm). The greenhouse experiment evaluated forage production of cultivars using Salt Control Ratio (SCR) values using 3840 ppm irrigation water and significant differences were found between cultivars. The field experiment evaluated forage production under saline field conditions west of Pecos, TX (soil salinity 2131 ppm, water salinity 2950 ppm) with significant differences between cultivar yields.Canonical Correspondence Analysis (CCA), a constrained ordination technique,revealed statistical significance of canonical axes in explaining variation between alfalfa cultivars and laboratory, greenhouse and field experiments.

Canola is grown mainly as an oil-seed crop, but recently the interest in canola has increased due to its potential as a biodiesel crop. The main objectives of this paper were to evaluate effects of abiotic factors and seed treatment on canola plant establishment and pest pressure in the Southern High Plains of Texas. Data was collected at two field locations during the first seven months of two field seasons. Based on multi-regression analysis, we demonstrated that precipitation was positively associated with ranked plant weight, daily minimum relative humidity and maximum temperature were negatively associated with plant weight, and that there may be specific optimal growth conditions regarding cumulative solar radiation and wind speed. The outlined multi-regression approach may be considered appropriate for ecological studies of canola establishment and pest communities elsewhere and therefore enable identification of suitable regions for successful canola production. We also demonstrated that aphids were about 35% more abundant on non-treated seeds than on treated seeds, but the sensitivity to seed treatment was only within four months after plant emergence. On the other hand, seed treatment had negligible effect on presence of thrips.

Potential US castor production is limited due to only one labeled herbicide (trifluralin). Field studies were conducted at two Texas locations during 2008 and 2009 to evaluate postemergence herbicides for castor tolerance and weed control efficacy. Clethodim and fluazifop-P-butyl caused no castor stunting while acifluorfen, bentazon, imazethapyr, and lactofen caused stunting which ranged from 5 to 46%. Imazapic and 2,4-DB caused the greatest stunting (44 to 99%) and resulted in castor yields of 0 to 45% of the untreated check. Acifluorfen, imazapic, imazethapyr, lactofen, and 2,4-DB controlled at least 80% smellmelon (Cucumis meloL. var. Dudaim Naud.) while clethodim and fluazifop-P-butyl controlled at least 98% Texas millet [Urochloa texana(Buckl.) R.Webster]. Imazapic and imazethapyr provided 57 to 75% Texas millet control. Results suggest that castor tolerance to the graminicides, clethodim, and fluazifop-P-butyl is high; however, castor injury and yield reductions with the postemergence applications of broadleaf herbicides suggest that these herbicides should not be used in castor production.