A pest risk assessment for Copitarsia spp., Insects associated with importation of commodities into the United States

Summary Eggs and larvae of Copitarsia spp. (Lepidoptera: Noctuidae) are frequently intercepted on fresh commodities arriving in the United States from Mexico, Central America, and South America. Copitarsia spp. are not known to occur in the US and, thus, are considered actionable pests by the US Department of Agriculture, Animal and Plant Health Inspection Service (USDA, APHIS). Whenever the genus is detected in imported goods, shipments must be disinfested, destroyed, or returned to the country of origin. Inspections and interdictions might be unnecessary if Copitarsia spp. were unlikely to establish in the US or if consequences of Copitarsia establishment were trivial. Consequently, we prepared a qualitative pest risk assessment to characterize the degree of risk posed by the genus to US agricultural and natural ecosystems. Published literature was consulted to describe the biology and ecology of the genus. Trade statistics and interception records were summarized to identify pathways of introduction. With this information, experts assigned risk ratings to each of eleven elements identified by USDA, APHIS that pertained to the likelihood or consequence of exotic-pest establishment. The likelihood of Copitarsia spp. becoming established in the US was considered high, but confidence in this assessment was low. Similarly, consequences of Copitarsia establishment were rated high, but confidence in this assessment was moderate. Overall, the assessment revealed that Copitarsia pose a high degree of risk to the US and phytosanitary measures to exclude the pest seem warranted. However, additional research is needed to address critical data gaps and refine assessments of risk for individual species within the genus.     

Diversity in selected wild and cultivated species of pigeonpea using RFLP of mtDNA

Diversity in 28 accessions representing 12 species of the genus, Cajanus arranged in 6 sections including 5 accessions of the cultivated species, C. cajan, and 4 species of the genus Rhyncosia available in the germplasm collection at ICRISAT was assessed using RFLP with maize mtDNA probes. Cluster analysis of the Southern blot hybridization data with 3 restriction enzymes – 3 probe combinations placed the genus Rhyncosia in a major group well separated from all the species belonging to the genus Cajanus. Within the genus Cajanus, the 4 accessions of C. platycarpus belonging to section Rhynchosoides formed a separate group in contrast to those in other sections of pigeonpea. In the section, Cajanus all the 5 accessions of C. cajan were grouped together and C. cajanifolius belonging to the same section was in a subgroup by itself closer to the main group. The four accessions of C. scarabaeoides, were together and the other species belonging to section Cantharospermum were in different subgroups. The intra-specific variation was seen even within accessions of certain pigeonpea wild species such as C. scarabaeoides, C. platycarpus, C. acutifolius, and even the cultivated species of C. cajan. This study suggests that RFLP of mtDNA can be used for the diversity analysis of pigeonpea and it gives some indications on the maternal lineage among the species. The variations in the mitochondrial DNA hybridization patterns also suggest the extensive rearrangement of the organelle genome among the Cajanus species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Crossability relationships among Cajanus,atylosia and Rhynchosia species and detection of crossing barriers

Summary Crossability of two cultivars of Cajanus cajan, eight species of Atylosia and one of Rhynchosia was investigated. Of the 73 combinations attempted, success was achieved in 12 cases. C. cajan crossed successfully with A. albicans, A. cajanifolia, A. lineata, A. scarabaeoides, and A. trinervia. Within the genus Atylosia, A. lineata crossed with A. albicans and A. scarabaeoides, and A. scarabaeoides with A. sericea. Three species A. platycarpa, A. volubilis and R. rothii did not cross with any other one. In most of the unsuccessful combinations, although the pollen germinated on the receiving stigmas, the pollen tube growth was inhibited inside the stigma or in the stylar tissue.     

A review of the nomenclature of the genus Arachis L.

Summary Confusion has arisen with regard to the correct botanical nomenclature for the taxa within the genus Arachis L. This paper discusses the proper usage, as mandated by the International Code of Botanical Nomenclature, of the epithets within the genus. Adherence to the rules described in this paper should reduce the present confusion in the nomenclature of Arachis.Paper number 6080 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27650 (USA).     

Evaluation of Paspalum germplasm for variation in leaf wax and heat tolerance

Summary The genus Paspalum contains a number of important forage grasses, including P. dilatatum Poir. (dallisgrass) and P. notatum Flugge (bahiagrass). Even though many Paspalum species are adapted to moist, humid areas, they frequently are subjected to extended periods of drought stress which reduces forage productivity. This study was initiated to determine the range of variation for different indicators of drought tolerance in several Paspalum species. Fifteen species representing a broad cross section of germplasm were grown in a replicated field nursery and sampled for leaf epicuticular wax content on four dates over three years. Wax was extracted with chloroform and quantified by the dichromate oxidation technique. Heat tolerance (solute leakage technique) was also determined by calculating the ratio of the conductivity of the external bathing solution of leaves following a heat treatment to the conductivity of the bathing solution after leaves were boiled. Wax values of the entries ranged from 5.7 to 0.88 mg/dm². Both relative rankings and absolute wax values were very consistent across all sampling dates. The accessions of Paspalum nicorae Parodi and P. quandrifarum Lam. were consistently high in wax content, while the accessions of P. commune Lillo and P. unispicatum (Scribn. et Merr.) Nash were consistently low. The heat tolerance testing demonstrated that the accession of P. notatum var. saurae Parodi was the most heat tolerant of the entries. Results from this investigation demonstrate the wide range of diversity that exists for both epicuticular wax and heat tolerance within the genus Paspalum.     

Rust infections of some Allium species: An assessment of germplasm for utilizable rust resistance

Summary Isolates of three species of rust (Puccinia allii, P. mixta and Uromyces ambiguus) were each inoculated onto a range of potential host plants, selected to include the major European crop Allium species together with the commoner wild species in the section Allium. Measurements of incubation period, lesion type, latent period and pustule quantity were made in a single environment. Each isolate was able to sporulate on a range of Allium species. There was evidence of specialisation to particular sections of the genus; all the leek isolates performed well on the majority of hosts in section Allium, whilst the chive isolate grew poorly on most members of that section. Exceptions to this are exemplified by A. fistulosum being attacked by all three rust species and A. sativum being attacked by both leek and chive isolates. A continuum of reaction types was found which, for the leek isolates, ranged from the low levels of quantitative resistance in leek cultivars, through higher quantitative levels within the A. ampeloprasum complex, to qualitative resistance in several interactions in non-host sections of Allium, where the pathogen was able to infect and form colonies of some size without sporulating.     

The phenotypical responses of gladiolus germplasm with different degrees of resistance to Uromyces transversalis

Summary The evaluation of populations of breeding lines, cultivars and species of the genus Gladiolus resulted in the development of an evaluation schedule and a standardized artificial inoculation technique. The entire population of cultivars that was evaluated is susceptible to Uromyces transversalis. However, some breeding lines and species were almost immune to gladiolus rust.     

Pollen storage of Fragaria and Potentilla

Summary Low temperature and humidity were used for the storage of pollen of four species of Fragaria (2n=14, 42 and 56) and two species of Potentilla (2n=14). The stainability of Fragaria pollen was assessed over a number of years by use of aceto-carmine stain and its viability by cross-pollinations; stainability of Potentilla pollen was assessed by acetocarmine. Fragaria pollen so stored remained stainable for seven years and showed the ability to set seed for three years. over the latter period, aceto-carmine staining gave a reasonable prediction of seed set produced by the stored pollen of Fragaria and so is of value in estimating pollen viability in that genus. Potentilla pollen remained stainable for three years.     

Inter simple sequence repeat analysis of genetic relationships in the genus Vigna

The utility of inter simple sequence repeat (ISSR) DNA polymorphisms to distinguish taxa within the genus Vignawas investigated. Nineteen primers, most containing either aGA or CA repeat, generated amplification products that differed among the taxa examined. The ISSR polymorphisms produced by 15 of these primers were very effective for distinguishing taxa at the species level or below. The Vigna unguiculataaccessions analyzed formed a cohesive group and appeared to be most closely related to V. triphylla and V. reticulata.In contrast, ISSR analysis was not able to clearly differentiate subgeneric divisions within Vigna. We attribute this loss of resolution at the subgeneric level to the high rate of evolution of the sequences we examined. Several probable instances of misclassification or hybrid origin of an accession were identified.     

Vegetative and floral characteristics of interspecific Brassica chimeras produced by in vitro grafting

Summary Interspecific Brassica chimeras (Brassica campestris+B. oleracea) were synthesized according to an in vitro graftculture method, and propagated by tissue culture of axillary buds or chimeric explants. A total of 127 regenerants obtained were investigated. The mericlinal chimera type was more easily produced than the other periclinal and revertant types. No sectorial chimera was produced. The flowering habit and inflorescence type of the chimeras were found to be controlled by the constitution of three tissue layers, but the petal shape and color were controlled only by the two outer tissue layers. Pollen viability of the chimeras were generally lower and more variable in parts than those of the parental types.     

The potential of high-resolution BAC-FISH in banana breeding

The genetic complexity in the genus Musa has been subject of study in many breeding programs worldwide. Parthenocarpy, female sterility, polyploidy in different cultivars and limited amount of genetic and genomic information make the production of new banana cultivars difficult and time consuming. In addition, it is known that part of the cultivars and related wild species in the genus contain numerous chromosomal rearrangements. In order to produce new cultivars more effectively breeders must better understand the genetic differences of the potential crossing parents for introgression hybridization, but extensive genetic information is lacking. As an alternative to achieve information on genetic collinearity we make use of modern chromosome map technology known as high-resolution fluorescent in situ hybridization (FISH). This article presents the technical aspects and applications of such a technology in Musa species. The technique deals with BAC clone positioning on pachytene chromosomes of Calcutta 4 (Musa acuminata ssp. burmanicoides, A genome group, section Eumusa) and M. velutina (section Rodochlamys). Pollen mother cells digestion with pectolytic enzymes and maceration with acetic acid were optimized for making cell spread preparations appropriate for FISH. As an example of this approach we chose BAC clones that contain markers to known resistance genes and hybridize them for establishing their relative positions on the two species. Technical challenges for adapting existing protocols to the banana cells are presented. We also discuss how this technique can be instrumental for validating collinearity between potential crossing parents and how the method can be helpful in future mapping initiatives, and how this method allows identification of chromosomal rearrangements between related Musa species and cultivars.     

Inheritance of spineless leaves in Aechmea (Bromeliaceae)

Bromeliaceae are tropical ornamentals with a variety of colors and inflorescence shapes. Leaves with spined margins are characteristic for the genus Aechmea. Crosses between spineless and spined Aechmea cultivars were attempted in order to obtain a spineless offspring. Crossing spined and spineless genotypes resulted in a progeny with on average 50% spineless plants. The hybrids of two spineless plants had on average 75% spineless leaves. This indicated that the spineless character was dominant. Homozygous plants were selected; these plants are interesting for further breeding and propagation by seed. This revised version was published online in July 2006 with corrections to the Cover Date.     

2n Gamete formation in the genus Brachiaria (Poaceae: Paniceae)

Microsporogenesis of several Brachiaria species of the Brazilian collection at Embrapa Beef Cattle has been analyzed in detail. This paper reports abnormal cytokinesis in three accessions of three different species (Brachiaria humidicola, 2n = 4x = 36, Brachiaria decumbens, 2n = 4x = 36, and Brachiaria dura, 2n = 6x = 54). Chromosomes paired in bi-, tri-, and quadrivalents in these accessions, whereas chromosome segregation at meiosis I was characterized by exclusion of laggards as micronuclei. In a high number of meiocytes, the first sign of cytokinesis appeared only in metaphase II and did not divide the meiocyte into a dyad. Total absence of cytokinesis was also detected among meiocytes in the second division. Since in both cases the two metaphase plates were very close, they favored the rejoining of chromosome sets after anaphase II and formed a restitutional nucleus in telophase II. Second cytokinesis occurred after telophase II in most meiocytes. Monads, dyads, and triads with n or 2n nuclei were observed among meiotic products. The 2n gametes observed correspond to the first division restitution (FDR). The number of affected cells in each accession was variable, but the number of microspores with restitutional nucleus, including those scored in tetrads and the released ones, did not exceed 9%. Although polyploidy is common in the genus Brachiaria, its origin is still unclear. Current results suggest that 2n gametes may have contributed to the evolutionary history of the genus.     

Brassica coenospecies: a rich reservoir for genetic resistance to leaf spot caused by Alternaria brassicae

Development of leaf spot resistant mustard cultivars is a relevant objective in view of heavy crop losses caused by this pathogen. Thirty-eight species belonging to 9 genera, including cultivated and wild allies, of the genus Brassica were evaluated under epiphytotic conditions for two years. Inoculations were done on whole plants (in vivo) and on detached leaves (in vitro). Data on incubation period, number of lesions per leaf, lesion size and leaf area covered by lesions were recorded. Species which never produced disease symptoms throughout the growing period in pots and until 72 hours after inoculation in detached leaf assays during both years were treated as resistant, while those that produced symptoms were classified as moderately resistant, susceptible or highly susceptible depending upon incubation period, size of lesions and leaf area covered by disease symptoms. Eight species (Brassica desnottesii, Camelina sativa, Coincya pseuderucastrum, Diplotaxis berthautii, D. catholica, D. cretacea, D. erucoides, and Erucastrum gallicum) were found completely resistant, whereas others were classified as moderately resistant (12), susceptible (11) or highly susceptible (9). Since resistance is unavailable within the cultivated species, these 8 resistant wild species could be used as donor parents for introgressing resistance to leaf spot disease in Indian mustard. This revised version was published online in August 2006 with corrections to the Cover Date.     

Species relationships in the subgenus Ceratotropis (genus Vigna) as revealed by RAPD analysis

Summary The genetic variation among 23 accessions of 5 species in the subgenus Ceratotropis, genus Vigna, were investigated by random amplified polymorphic DNA (RAPD) analysis. A total of 404 fragments amplified with 24 primers were scored and analyzed by cluster analysis. The accessions used were separated into two main groups with an average of 70% differences. Within the main groups, five subgroups were recognized, which are in complete agreement with taxonomic species. Wild forms were always grouped with their most closely related cultivated forms and they showed variation in each species. The largest intraspecific variation was found in V. radiata (mungbean), in which wild forms (V. radiata var. sublobata) were highly different from each other and from cultivated forms. V. angularis (adzuki bean) showed the least variation and thus, was probably differentiated in relatively recent times.     

Fingerprinting of alfalfa meiotic mutants using RAPD markers

Summary A calendar of female sporogenesis and gametogenesis was made for both apomictic tetraploid (2n=4x=36) Brachiaria brizantha and Brachiaria decumbens and their apomictic F₁ hybrids with sexual tetraploid (2n=4x=36) Brachiaria ruziziensis. Microgametogenesis was used as a reference. Apospory was facultative in both species and hybrids. Environmental conditions had variable effects on the level of apomixis according to each genotype. Ratios of segregation into sexuals and apomicts in the interspecific hybrids suggest an oligogenic determinism with dominant apomixis in the genus Brachiaria. Highly apomictic and partially male fertile hybrids were identified and will be used in an improvement program to transfer genes for apomixis into the sexual species B. ruziziensis.     

Chromosome numbers of Tulipa species and the occurrence of hexaploidy

Summary Chromosome numbers of Tulipa species were determined. For the first time hexaploidy was found in the genus. It became clear that in many species or subspecies several ploidy levels may occur.     

Production and characterization of inter-sectional hybrids between <Emphasis Type="Italic">Kalanchoe spathulata</Emphasis> and <Emphasis Type="Italic">K. laxiflora</Emphasis> ( = <Emphasis Type="Italic">Bryophyllum crenatum</Emphasis>)

The genus Kalanchoe is currently divided into section Kalanchoe and section Bryophyllum, and there has been no successful report on the production of inter-sectional hybrids. Therefore, reciprocal crosses were made between Kalanchoe spathulata (sect. Kalanchoe) and K. laxiflora (sect. Bryophyllum) in order to obtain basic information on the reproductive barriers between these two sections. The seeds were aseptically germinated in vitro and the plants were grown in greenhouse till flowering. When K. spathulata was used as a maternal donor, 39 out of 80 plants showed intermediate characteristics between K. spathulata and K. laxiflora. In contrast, no plants were obtained in the reverse crosses. Hybridity of these plants was confirmed by flow cytometric analysis, chromosome numbers and RAPD analysis. Bulbil formation on the leaf margin as one of the conspicuous characteristics of K. laxiflora was not observed in the hybrids. Some of the hybrid lines showed some pollen fertility, but failed to yield viable seeds by self-pollination or backcross-pollination. Successful production of the inter-sectional hybrid between the two species suggests that they are not so distantly related as considered previously.     

Assessment of the degree of genetic variation in beet based on RFLP analysis and the taxonomy of Beta

Summary Clones derived from Beta vulgaris and Beta maritima were assayed for their ability to detect restriction fragment length polymorphisms (RFLPs) in different beet accessions. The clones able to detect polymorphism were used as genetic markers to assess the degree of genetic variation existing between and within different species of the genus Beta. The data support the current taxonomy of the Beta vulgaris section, while the great genetic similarity found between Beta webbiana and Beta procumbens indicates that they could belong to the same species.Enough variation was found between Beta vulgaris cultivars, allowing the isolation of a sufficient number of genetic markers for the construction of detailed genetic maps.     

The genomes of Arachis hypogaea 2. The implications in interspecific breeding

Summary The existence of structural differentiation between genomes in section Arachis of the genus Arachis has important implications in the utilization of diploid wild species in this section as a germplasm resource. Maximum expression of desirable characters may not be achieved unless tetrasomic dose levels can be achieved. Possible breeding strategies discussed include natural and induced gene exchange between genomes and chromosome substitution which could be brought about by manipulation of ploidy level and where appropriate the use of ionizing radiation. Such strategies could be tested in the improvement of resistance to the Cercospora leafspots.Paper number 5561 of the Journal Series of the North Carolina Agricultural Experimental Station, Raleigh, NC 27650.