Speciation, Cytogenetics, and Utilization of Arachis Species

Utilization of wild species for improvement of cultivated forms has been investigated since Faircloth made the first interspecific hybrids in 1717. Many wild species have been of value in crop improvement for a large number of traits (Harlan, 1976; Hawkes, 1977; Stalker, 1980a; Hadley and Openshaw, 1980). However, in leguminous oilseeds, utilization of species germplasm has proven difficult, in large part because of barriers to interspecific hybridization between species (Smartt, 1979). Further, sterility often restricts introgression from wild to cultivated accessions even when initial hybridization is possible. Interspecific hybridization is also difficult among the peanut species in the genus Arachis, but breeding populations derived from crossing A . hypogaea L. with related species are currently being evaluated for farmer use (Moss, 1985b). Four species of Arachis have been cultivated, including two diploids (2n = 2x = 20: A . villosulicarpa Hoehne and A . repens Handro) and two tetraploids (2n = 4x = 40: A . glabrata Benth. and A . hypogaea). Arachis villosulicarpa has only been cultivated by Indians in the northwestern part of the Brazilian state of Mato Grosso (Gregory et al., 1973). Arachis repens and A . glabrata have been grown in different parts of South America as forages or as ground covers in urban areas. Arachis glabrata has also been selected for forage qualities in Florida, where recent cultivar releases have been made (Prine et al., 1981). However, A . hypogaea is the only species which is cultivated extensively for commercial production of seeds and oil

Embryo Rescue in Wide Crosses in Arachis. 3. In vitro Culture of Peg Tips of A. hypogaea Selfs and Interspecific Hybrids

Embryo rescue in wide crosses in Arachis has only been achieved from culturing ovules excised from well developed pods, or from immature pods derived from flowers treated with gibberellic acid (GA) and which had embryos large enough to dissect without injury. The objective of this study was to determine whether reproductive tissues could grow in vitro without the need to dissect them from the peg tip and to determine the effects of GA application on flowers at the time of pollination, age of peg when cultured, and the presence of the peg meristem on reproductive growth, callus production, and peg elongation in vitro. Pegs elongated in culture only when the peg meristem was not removed. Ovules enlarged and grew out of the surrounding peg tissue in 3.8 to 32.8% of the cultures. Significantly more ovules grew when the peg meristem was removed (p < 0.01) and when 10- and 20- day-old pegs were cultured (p < 0.05). Overall, the most successful treatment for growth of ovules was treating flowers with GA at pollination and culturing without the peg meristem 10 days after pollination when 25.0 and 32.8% of all hybrid and selfed ovules, respectively, grew. Embryo growth was observed in an average of 8.4 and 17.6% of embryo sacs in hybrid and self peg tips, respectively, with several embryos reaching the globular stage after 21 days in vitro. This illustrates the potential for culturing young reproductive tissues of Arachis to recover interspecific hybrid

Bounds on the mass-to-radius ratio for non-compact field configurations

It is well known that a spherically symmetric compact star whose energy density decreases monotonically possesses an upper bound on its mass-to-radius ratio, $2M/R\leq 8/9$. However, field configurations typically will not be compact. Here we investigate non-compact static configurations whose matter fields have a slow global spatial decay, bounded by a power law behavior. These matter distributions have no sharp boundaries. We derive an upper bound on the fundamental ratio max_r{2m(r)/r} which is valid throughout the bulk. In its simplest form, the bound implies that in any region of spacetime in which the radial pressure increases, or alternatively decreases not faster than some power law $r^{-(c+4)}$, one has $2m(r)/r \leq (2+2c)/(3+2c)$. [For $c \leq 0$ the bound degenerates to $2m(r)/r \leq 2/3$.] In its general version, the bound is expressed in terms of two physical parameters: the spatial decaying rate of the matter fields, and the highest occurring ratio of the trace of the pressure tensor to the local energy density.Comment: 4 page

Embryo Rescue in Wide Crosses in Arachis. 2. Embryo Development in Cultured Peg Tips of Arachis hypogaea

Embryo rescue techniques in Arachis are potentially important for recovering interspecific hybrids which have the propensity to abort. Pegs are commonly produced in interspecific crosses, but either they fail to reach the soil because growth is arrested, or pods are produced but embryo development is never re-initiated. Peg tips, with the ovule and embryo, of A. hypogaea L. cv. ‘NC 6’, were used to determine whether peg tips can be used as nurse tissue for in vitro culture of embryos. Tissues were collected 1, 2, 3 and 4 d after self-pollination, after which peg meristems were removed from half the pegs, and cultured on five media combinations. Continued reproductive development was observed for embryos cultured at all four collection days; however, the highest frequency of growth was observed in 1-d-old tissues. Evidence is presented that meristematic activity may restrict embryo growth in the 2- to 4-d-old embryos and, once the sequence of events is initiated to slow embryo growth, it is not easily reversed in vitro. Achievements of embryo growth to multicellular, globular stages (stages 1–1 or 1–2) encourage the development of methods to recover very young embryos through tissue-culture techniques

Evaluation of Leaf Spot Resistance in Wild \u3ci\u3eArachis\u3c/i\u3e Species of Section \u3ci\u3eArachis\u3c/i\u3e

Wild diploid Arachis species are potential sources of resistance to early (ELS) and late (LLS) leaf spot diseases caused by Passalora arachidicola (syn. Cercospora arachidicola Hori), and Nothopassalora personata (syn. Cercosporidium personatum (Berk. & Curt.) Deighton), respectively. Within section Arachis, limited information is available on the extent of genetic variation for resistance to these fungal pathogens. A collection of 78 accessions representing 15 wild species of Arachis section Arachis from the U.S peanut germplasm collection was evaluated for resistance to leaf spots. Screening was conducted under field (natural inoculum) conditions in Dawson, Georgia, during 2017 and 2018. Accessions differed significantly (P , 0.01) for all three disease variables evaluated, which included final defoliation rating, ELS lesion counts, and LLS lesion counts. Relatively high levels of resistance were identified for both diseases, with LLS being the predominant pathogen during the two years of evaluation. This research documents new sources of resistance to leaf spot diseases selected from an environment with high inoculum pressure. The presence of ELS and LLS enabled the selection of resistant germplasm for further introgression and pre-breeding

Corn residue stocking rate affects cattle performance but not subsequent grain yield

This study investigated effects of stocking rate on cattle performance, quality and quantity of corn residue, and impact of residue removal on grain yield for 5 yr at the University of Nebraska – Lincoln West Central Water Resources Field Laboratory near Brule, NE. Four removal treatments—1) no removal (control), 2) grazing at 2.5 animal unit month (AUM)/ ha, 3) grazing at 5.0 AUM/ha, and 4) baling—were applied to a center pivot–irrigated corn field (53 ha). The field was divided into eight 6.6-ha paddocks to which replicated treatments were assigned. Samples of residue were collected in October and March (before and after residue removal) using ten 0.5-m2 quadrats per treatment replication. Residue was separated into 5 plant parts—stem, cob, leaf, husk, and grain—and analyzed for nutrient content. Esophageally fistulated cattle were used to measure diet quality. Cattle assigned to the 2.5 AUM/ha stocking rate treatment gained more BW (P \u3c 0.01) and BCS (P \u3c 0.01) than cattle assigned to the 5.0 AUM/ha treatment. Leaf contained the most (P \u3c 0.01) CP and husk had the greatest (P \u3c 0.01) in vitro OM disappearance (IVOMD) but the CP and IVOMD of individual plant parts did not differ (P \u3e 0.69) between sampling dates. Amount of total residue was reduced (P \u3c 0.05) by baling and both grazing treatments between October and March but was not different (P \u3e 0.05) in control paddocks between sampling dates. As a proportion of the total residue, stem increased (P \u3c 0.01) and husk decreased (P \u3c 0.01) between October and March. Diet CP content was similar (P = 0.10) between sampling dates for the 2 grazing treatments but IVOMD was greater after grazing in the 2.5 AUM/ha grazing treatment (P = 0.04). Subsequent grain yields were not different (P = 0.16) across all 4 residue removal treatments. At the proper stocking rate, corn residue grazing results in acceptable animal performance without negatively impacting subsequent corn grain production

Corn residue stocking rate affects cattle performance but not subsequent grain yield

This study investigated effects of stocking rate on cattle performance, quality and quantity of corn residue, and impact of residue removal on grain yield for 5 yr at the University of Nebraska – Lincoln West Central Water Resources Field Laboratory near Brule, NE. Four removal treatments—1) no removal (control), 2) grazing at 2.5 animal unit month (AUM)/ ha, 3) grazing at 5.0 AUM/ha, and 4) baling—were applied to a center pivot–irrigated corn field (53 ha). The field was divided into eight 6.6-ha paddocks to which replicated treatments were assigned. Samples of residue were collected in October and March (before and after residue removal) using ten 0.5-m2 quadrats per treatment replication. Residue was separated into 5 plant parts—stem, cob, leaf, husk, and grain—and analyzed for nutrient content. Esophageally fistulated cattle were used to measure diet quality. Cattle assigned to the 2.5 AUM/ha stocking rate treatment gained more BW (P \u3c 0.01) and BCS (P \u3c 0.01) than cattle assigned to the 5.0 AUM/ha treatment. Leaf contained the most (P \u3c 0.01) CP and husk had the greatest (P \u3c 0.01) in vitro OM disappearance (IVOMD) but the CP and IVOMD of individual plant parts did not differ (P \u3e 0.69) between sampling dates. Amount of total residue was reduced (P \u3c 0.05) by baling and both grazing treatments between October and March but was not different (P \u3e 0.05) in control paddocks between sampling dates. As a proportion of the total residue, stem increased (P \u3c 0.01) and husk decreased (P \u3c 0.01) between October and March. Diet CP content was similar (P = 0.10) between sampling dates for the 2 grazing treatments but IVOMD was greater after grazing in the 2.5 AUM/ha grazing treatment (P = 0.04). Subsequent grain yields were not different (P = 0.16) across all 4 residue removal treatments. At the proper stocking rate, corn residue grazing results in acceptable animal performance without negatively impacting subsequent corn grain production

Corn residue stocking rate affects cattle performance but not subsequent grain yield

This study investigated effects of stocking rate on cattle performance, quality and quantity of corn residue, and impact of residue removal on grain yield for 5 yr at the University of Nebraska – Lincoln West Central Water Resources Field Laboratory near Brule, NE. Four removal treatments—1) no removal (control), 2) grazing at 2.5 animal unit month (AUM)/ ha, 3) grazing at 5.0 AUM/ha, and 4) baling—were applied to a center pivot–irrigated corn field (53 ha). The field was divided into eight 6.6-ha paddocks to which replicated treatments were assigned. Samples of residue were collected in October and March (before and after residue removal) using ten 0.5-m2 quadrats per treatment replication. Residue was separated into 5 plant parts—stem, cob, leaf, husk, and grain—and analyzed for nutrient content. Esophageally fistulated cattle were used to measure diet quality. Cattle assigned to the 2.5 AUM/ha stocking rate treatment gained more BW (P \u3c 0.01) and BCS (P \u3c 0.01) than cattle assigned to the 5.0 AUM/ha treatment. Leaf contained the most (P \u3c 0.01) CP and husk had the greatest (P \u3c 0.01) in vitro OM disappearance (IVOMD) but the CP and IVOMD of individual plant parts did not differ (P \u3e 0.69) between sampling dates. Amount of total residue was reduced (P \u3c 0.05) by baling and both grazing treatments between October and March but was not different (P \u3e 0.05) in control paddocks between sampling dates. As a proportion of the total residue, stem increased (P \u3c 0.01) and husk decreased (P \u3c 0.01) between October and March. Diet CP content was similar (P = 0.10) between sampling dates for the 2 grazing treatments but IVOMD was greater after grazing in the 2.5 AUM/ha grazing treatment (P = 0.04). Subsequent grain yields were not different (P = 0.16) across all 4 residue removal treatments. At the proper stocking rate, corn residue grazing results in acceptable animal performance without negatively impacting subsequent corn grain production

Biogeography of wild Arachis (Leguminosae): distribution and environmental characterisation.

Geographic Information System (GIS) tools are applied to a comprehensive database of 3514 records of wild Arachis species to assist in the conservation and utilisation of the species by: (a) determining the distributional range of species and their abundance; (b) characterising species environments; (c) determining the geographical distribution of species richness; and (d) determining the extent to which species are associated with river basins. Distributional ranges, climatic variables and indices of endemism for each species are tabulated. A. duranensis Krapov. & W.C. Gregory, the most probable donor of the A genome to the cultivated peanut, is distributed in close proximity to both the proposed donor of the B genome, A. ipaënsis, and the closest wild relative of the cultigen, A. monticola Krapov. & Rigoni. This region in the eastern foothills of the Andes and the adjoining chaco regions of Argentina, Bolivia and Paraguay, is a key area for further exploration for wild Arachis. An area of particularly high species richness occurs in the State of Mato Grosso, close to the Gran Pantanal in southwest Brazil. Seventy-one percent of the species were found to have some degree of association with water catchment areas, although in most cases it was difficult to determine whether this was due to climatic adaptation reasons, restricted dispersal due to geocarpic habit, or the role of watercourses as a principal dispersal agent. In only two cases could climatic adaptation be eliminated as the reason for species distribution

Enhancing Crop Gene Pools with Beneficial Traits Using Wild Relatives

This review covers genetic resources from wild relatives; barriers and approaches to interspecific gene transfer; beneficial traits from wild relatives that contribute to the gene pool; biotechnological approaches to increase the utilization of wild relatives in crop improvement; and some results of usage of wild relatives in plant breeding