In vitro culture of immature seed for rapid generation advancement in tomato

The importance of fast-trackt generation advancement in developing superior germplasm has been recognized in breeding of many crop species. To address this issue in tomato, immature seeds were excised from fruit at different maturity stages and transferred to culture medium. The best culture medium was modified full strength Moorashige–Skoog (MS) salts supplemented with 0.1 mg l⁻¹ IAA, 0.5 mg l⁻¹ IBA, 0.5 mg l⁻¹ GA₃ and 2% sucrose. If the excised seeds were able to grow, most showed shoot formation after a week. Seeds extracted as early as 10 days after pollination were successfully cultured provided they were transferred aseptically and without injury. No morphological or physiological changes in regenerated plants and their fruit relative to the parent were detected. Germination from immature seeds of tomato is a simpler alternative to in vitro culture of immature embryos or callus, as it can be undertaken in comparatively less stringent laboratory conditions. Using this approach, five generations can be produced in a year in contrast to a maximum of three generations with conventional methods. This offers an opportunity for rapid generation advancement aimed towards population development when coupled with marker assisted selection in tomato breeding for biotic and abiotic stress tolerance.     

Identification of drought responsive QTLs during vegetative growth stage of rice using a saturated GBS-based SNP linkage map

Drought is a major abiotic constraint for rice production worldwide. The quantitative trait loci (QTLs) for drought tolerance traits identified in earlier studies have large confidence intervals due to low density linkage maps. Further, these studies largely focused on the above ground traits. Therefore, this study aims to identify QTLs for root and shoot traits at the vegetative growth stage using a genotyping by sequencing (GBS) based saturated SNP linkage map. A recombinant inbred line (RIL) population from a cross between Cocodrie and N-22 was evaluated for eight morphological traits under drought stress. Drought was imposed to plants grown in 75 cm long plastic pots at the vegetative growth stage. Using a saturated SNP linkage map, 14 additive QTLs were identified for root length, shoot length, fresh root mass, fresh shoot mass, number of tillers, dry root mass, dry shoot mass, and root-shoot ratio. Majority of the drought responsive QTLs were located on chromosome 1. The expression of QTLs varied under stress and irrigated condition. Shoot length QTLs qSL1.38 and qSL1.11 were congruent to dry shoot mass QTL qDSM1.38 and dry root mass QTL qDRM1.11, respectively. Analysis of genes present within QTL confidence intervals revealed many potential candidate genes such as laccase, Calvin cycle protein, serine threonine protein kinase, heat shock protein, and WRKY protein. Another important gene, Brevis radix, present in the root length QTL region, was known to modulate root growth through cell proliferation and elongation. The candidate genes and the QTL information will be helpful for marker-assisted pyramiding to improve drought tolerance in rice.     

Yield, water-use efficiencies and root distribution of soybean, chickpea and pumpkin under different subsurface drip irrigation depths and oxygation treatments in vertisols

Most trickle irrigation in the world is surface drip yet subsurface drip irrigation (SDI) can substantially improve irrigation water use efficiency (IWUE) by minimizing evaporative loss and maximizing capture of in-season rainfall by the soil profile. However, SDI emitters are placed at depths, and in many soil types sustained wetting fronts are created that lead to hypoxia of the rhizosphere, which is detrimental to effective plant functioning. Oxygation (aerated irrigation water) can ameliorate hypoxia of SDI crops and realize the full benefit of SDI systems. Oxygation effects on yield, WUE and rooting patterns of soybean, chickpeas, and pumpkin in glasshouse and field trials with SDI at different emitter depths (5, 15, 25, and 35 cm) were evaluated. The effect of oxygation was prominent with increasing emitter depths due to the alleviation of hypoxia. The effect of oxygation on yield in the shallow-rooted crop vegetable soybean was greatest (+43%), and moderate on medium (chickpea +11%) and deep-rooted crops (pumpkin +15%). Oxygation invariably increased season-long WUE (WUE_sl) for fruit and biomass yield and instantaneous leaf transpiration rate. In general, the beneficial effects of oxygation at greater SDI depth on a heavy clay soil were mediated through greater root activity, as observed by general increase in root weight, root length density, and soil respiration in the trialed species. Our data show increased moisture content at depth with a lower soil oxygen concentration causing hypoxia. Oxygation offsets to a degree the negative effect of deep emitter placement on yield and WUE of SDI crops.     

Effects of Soil Type and Cover Condition on Cryptosporidium parvum Transport in Overland Flow

Overland transport kinetics of pathogens is controlled, in large part, by soil and vegetation. With an increasing number of concentrated animal operations, there is becoming a greater need to dispose of a vast amount of manure in a single, localized area. Animal manure contains a substantial amount of microbial pathogens, including Cryptosporidium parvum that may pose a threat of contamination of water resources. This study examines the kinetics of C. parvum in overland transport and critical factors involved in the design of best management practices, especially vegetative filter strips, to prevent the transport of harmful pathogens to water bodies. Three soil types were tested (Catlin silt-loam, Alvin fine sandy-loam, Darwin silty-clay), spanning the entire spectrum of typical Illinois soils. A 20-min rainfall event was produced using a small-scale (1.07 m?×?0.66 m) laboratory rainfall simulator over a soil box measuring 0.67 m?×?0.33 m. Each soil type was tested for pathogen transport kinetics with bare surface conditions as well as with smooth brome and fescue vegetative covers. Surface runoff, soil cores, and near-surface runoff were each analyzed for infective C. parvum oocysts using cell culture infectivity assays. Results showed that vegetation greatly reduced the recovery of infective oocysts, in addition to delaying the time to the peak recovery. However, there was no clear evidence of any one vegetation type being advantageous over another. The bare soil experiments resulted in a higher recovery of C. parvum oocysts from the Darwin soil compared to other two soils. Analyses of soil cores show a slightly higher recovery of oocysts in the Catlin soil compared to Alvin or Darwin soils.     

The effect of different mixtures of NaCl and CaCl2 on the silver fir (Abies alba Miller)

Young potted silver firs were treated with six different mixtures of NaCl and CaCl². Growth was measured as well as the foliar contents of Cl, Na and Ca and the development of chlorosis and necrosis was recorded. At both concentration levels used, growth inhibition and needle necrosis were more pronounced in test conditions rich in CaCl², a fact which is probably due to Cl toxicity.     

Growth and yield responses of a Nepalese spring wheat cultivar to the inoculation with Nepalese Azospirillum spp at various levels of nitrogen fertilization

The Azospirillum 10SW used in our experiments was isolated from roots of wheat growing in nitrogen-poor soil of a hilly region of Nepal, where inorganic nitrogen fertilizers were never used. The main objectives of this work were to assess the effects of inorganic nitrogen fertilization in the yield responses of wheat grown in association with the bacteria. The in vitro experiments were done in laboratory, whereas the pot experiments were performed in a greenhouse. The nitrogenase activities of in vitro grown Azospirillum were repressed by nitrate. The magnitude of repression was lower when the bacteria were growing in association with wheat. The number of roots per plant was increased significantly in inoculated plants irrespective of the nitrate concentration of the medium. Inoculation with Azospirillum 10SW also increased the yield of wheat grown in pots with medium levels of nitrogen fertilization. These data show the possibility of inoculation of this Azospirillum spp. in combination with nitrogen fertilizer to improve the yield of wheat. Azospirillum inoculation enhanced the development of roots and shoots in the early growth stages of wheat. It may be one of the factors responsible for the yield increases. Received: 11 December 1996     

On-farm measurements of nitrogen fixation by winter and summer legumes in the Hill and Terai regions of Nepal

Results are reported from on-farm surveys of N₂ fixation in Nepal, conducted between 1994 and 1999, involving the summer legumes soybean, mashbean and groundnut, and the winter legumes lentil and chickpea, at various locations in the Hill and Terai regions of Nepal. Additional less-detailed data were also collected for pigeonpea, grasspea and fababean. There were a total of 107 crops in the major and minor surveys. Estimates of the proportion of legume nitrogen (N) derived from N₂ fixation (Pfix) were determined using the natural ¹⁵N abundance method. Mean estimates of Pfix for the various species were 62% (soybean), 47% (mashbean), 57% (groundnut), 78% (lentil), 79% (chickpea), 75% (pigeonpea), 87% (grasspea) and 85% (fababean). Estimates of total N fixed (including roots) were 59 kg N ha⁻¹ (soybean), 28 kg N ha⁻¹ (mashbean), 153 kg N ha⁻¹ (groundnut), 72 kg N ha⁻¹ (lentil), 84 kg N ha⁻¹ (chickpea), 412 N ha⁻¹ (pigeonpea) and 80 N ha⁻¹ (grasspea and fababean). The on-farm measurements of N₂ fixation were generally similar to those of experimental crops in the same areas of the country. Correlation matrices of soil fertility parameters, shoot dry matter and N, and N₂ fixation revealed that the total amounts of N fixed were influenced primarily by crop growth. Based on the above figures, it was estimated that approximately 30,000 t N were fixed annually in Nepal by legumes, valued at US$ 15 million.     

Temporal and spatial dimension of dissolved oxygen saturation with fluidic oscillator and Mazzei air injector in soil-less irrigation systems

The wider scale use of aerated water for irrigation has been limited by dis-uniformity of aeration in the field, limited longevity of oxygen in irrigation water and lack of knowledge of what oxygen concentration brings optimal growth. Two options are presented for increasing dissolved oxygen (DO) in irrigation water: Venturi (VT) and fluidic oscillator (FO) aeration systems. Sweet corn was grown in pots to evaluate the effect of aerated water. Compared to the control treatment (CK), VT and FO showed an increase in irrigated water DO in the irrigation tank and feeding pots after aeration. Incorporation of surfactant in the irrigation water significantly improved DO level for the VT and FO treatment. Typically the DO levels reached a peak when the pump is turned off and then decline to a minimum after 24 h. The VT and FO systems had a higher magnitude and duration of the DO level in the water in all treatments compared to the CK system. The FO aeration maintained the longest duration of elevated DO in the water by a factor of two compared to the VT aeration. Compared to the CK, the best result on longevity and DO concentration was achieved using 4 ppm of a non-ionic surfactant. The corn biomass was significantly greater for the VT compared to both the FO and CK treatments.     

气源及活性剂对曝气滴灌带水气单双向传输均匀性的影响

曝气滴灌过程中水、氧、气传输均匀性是评价曝气灌溉质量的重要指标。活性剂的添加和传输方式的优选对曝气滴灌传输过程中微气泡的存在和溶解氧的保持有重要意义。为提高水气耦合物在滴灌过程中传输的距离和均匀性,该文采用Mazzei 1078文丘里空气射流器进行曝气增氧,以空气和氧气为供试气源,研究活性剂BS1000浓度(0、1、2和4 mg/L)和传输方式(单向和双向)对曝气滴灌下水、氧、气传输特性的影响。结果表明:曝气导致单向传输下流量均匀性略有下降,但可显著提高灌溉水中溶解氧和掺气比例;随着活性剂浓度的增加,掺气比例显著增加(P0.05);活性剂的添加促进了氧气曝气下溶解氧的增加;溶氧均匀性和流量均匀性随着活性剂浓度的增加无显著性变化,但单向传输下4 mg/L BS1000的出气均匀性较未添加活性剂显著降低;双向传输的流量均匀性、溶氧均匀性和出气均匀性分别在95%、96%和67%以上,较单向传输分别平均提高14.00%、4.05%和30.64%(P0.05),是曝气滴灌长程管道传输推荐的布置方式。研究结果为曝气滴灌过程中灌溉技术参数优化和管道的科学布置提供理论依据。     

Phenotypic and Genetic Characterization of Western Prairie Clover Collections From the Western United States

Few North American legumes are available for rangeland revegetation in the semiarid western United States. Western prairie clover (Dalea ornata [Douglas ex Hook.] Eaton & J. Wright) is a perennial legume with desirable forage characteristics and is distributed in the northern Great Basin, Snake River Basin, and southern Columbia Plateau. Understanding the genetic and ecotypic variability of this species is a prerequisite for developing populations suitable for revegetation purposes. To address this need, we established two common-garden plots of western prairie clover from 22 sites in Idaho, Oregon, and Washington. Significant variation was detected among the collections for all traits measured. Among the measured traits, flowering date was correlated with collection-site temperature and elevation. Population structure estimates from 474 amplified-fragment length polymorphism markers resulted in two distinct, genetically differentiated groups and a third admixed group, and flowering date played a significant role in discriminating those genetic-based groupings of collections. Positive correlations were observed between phenotypic and genetic distance matrices (r = 0.33, P = 0.005), phenotypic and geographic distance matrices (r = 0.35, P = 0.002), and genetic and geographic distance matrices (r = 0.31, P = 0.009). Based on these results, we recommend that two germplasm sources of western prairie clover be developed for use across the collection area, one from the Deschutes River region and the other encompassing Idaho, Washington, and eastern Oregon collection sites.