The elimination of clover diseases by shoot tip culture

Shoot tip culture was used to eliminate white clover mosaic virus (WCMV) and red clover necrotic mosaic virus (RCNMV) from red clover, and clover phyllody disease (CP) and clover red leaf disease (CRL) from white clover. Shoot tips up to 2.4 mm (in some cases 3 mm) could regenerate plants free from the pathogens, but the efficiency of elimination, at least for WCMV and CRL, tended to decrease with increasing shoot tip size. The efficiency of plant regeneration from shoot tips generally improved with increasing tip size.     

Inheritance of resistance to potyviruses in Phaseolus vulgaris L. II. Linkage relations and utility of a dominant gene for lethal systemic necrosis to soybean mosaic virus

Summary A single dominant factor, Hss, that conditions a rapid lethal necrotic response to soybean mosaic virus (SMV) has been identified in Phaseolus vulgaris L. cv. Black Turtle Soup, line BT-1. Inoculated plants carrying this factor developed pinpoint necrotic lesions on inoculated tissue followed by systemic vascular necrosis and plant death within about 7 days, regardless of ambient temperature. BT-1 also carries dominant resistance to potyviruses attributed to the tightly linked or identical factors, I, Bcm, Cam, and Hsw, so linkage with Hss was evaluated. No recombinants were identified among 381 F₃ families segregating for potyvirus susceptibility, thus if Hss is a distinct factor, it is tightly linked to I, Bcm, Cam, and Hsw. BT-1 was also crossed reciprocally with the line Great Northern 1140 (GN 1140) in which the dominant gene, Smv, for systemic resistance to SMV was first identified. Smv and Hss segregated independently and are co-dominant. The (GN 1140 x BT-1) F₁ populations showed a seasonal shift of the codominant phenotype. Evaluation of the (GN 1140 x BT-1) F₂ population under conditions where Smv is partially dominant allowed additional phenotypic classes to be distinguished. Pathotype specificity has not been demonstrated for either Smv or Hss. Genotypes that are homozygous for both dominant alleles are systemically resistant to the virus and in addition show undetectable local viral replication or and no seed transmission. This work demonstrates that a gene which conditions a systemic lethal response to a pathogen may be combined with additional gene(s) to create an improved resistant phenotype.     

我国大麦和性花叶病毒（BaMMV）研究初报

本文根据F(ab′)2－ELISA和ISEM实验,结合病毒粒子长度测定,报道了江苏省如东县农科所大麦黄花病毒源（吕种盐辐矮早3）中除存在大麦花花叶病毒（BaYMV）外,还复合感染大麦和性花叶病毒（BaMMV）,这是我国BaMMV的第一次报道。     

N equals two (times five). Exploring the effects of horse rewilding on five congeneric adult butterflies

Rewilding incomplete ecosystems by using ungulate megaherbivores represents a significant potential for sustainable management of habitats of declining species. Two xeric grasslands patches in the Podyjí National Park, Czech Republic, were rewilded by a feral horse breed, the Exmoor pony, in 2018. Before this in 2017, demography, mobility, and adult habitat use of five congeneric Melitaea butterflies co-occurring at the grasslands were investigated (Vodickova et al., J. Nature Conserv. 2019). In 2021, four seasons after the rewilding, we replicated the survey to assess the effects of the horse on the butterflies. Here, we compare the results of the two surveys and investigate changes in spatial patterns of adult distribution using Ripley’s K-functions.Total numbers of captures, and estimated population sizes, were consistently lower in 2021, with the largest drop for spring-flying M. cinxia. We cannot discern whether this was due to the cold 2021 spring, or due to reduction of grasses by the horse, possibly contributing to desiccation of M. cinxia host plants. Demographic parameters such as residency/longevity and capture probability changed only little. Mobility ranking among species remained identical, but within species, some mobility characteristics changed among years. Among early summer species, M. britomartis, second most abundant in 2017, switched to the first position with M. aurelia, and these two species displayed the most notable shift in adult habitat use between the two seasons. Short thorny shrubs avoided by the horse protect M. britomartis host plants; this threatened butterfly thus did not suffer from horse presence. M. athalia, a species of woodland edges, profited from decay of conifers caused by a series of dry years; and M. didyma, forming multiple generations, from increase of its host plant. Contrary to expectations, spatial distribution of most butterflies became more aggregated within rewilded pastures, probably due to regularities in home ranges use by the horses, which restructured the vegetation in a zonal, rather than patchy, way. A considerably larger areas should be rewilded by the herbivores to fully achieve the desired beneficial effects.     

Contribution of Mutation and RNA Recombination to the Evolution of a Plant Pathogenic RNA

The nucleotide sequence of 17 variants of the satellite RNA of cucumber mosaic virus (CMV-satRNA) isolated from field-infected tomato plants in the springs of 1989, 1990, and 1991 was determined. The sequence of each of the 17 satRNAs was unique and was between 334 and 340 nucleotides in length; 57 positions were polymorphic. There was much genetic divergence, ranging from 0.006 to 0.141 nucleotide substitutions per site for pairwise comparisons, and averaging 0.074 for any pair. When the polymorphic positions were analyzed relative to a secondary structure model proposed for CMV-satRNAs, it was found that there were significantly different numbers of changes in base-paired and non–base-paired positions, and that mutations that did not disrupt base pairing were preferred at the putatively paired sites. This supports the concept that the need to maintain a functional structure may limit genetic divergence of CMV-satRNA. Phylogenetic analyses showed that the 17 CMV-satRNA variants clustered into two subgroups, I and II, and evolutionary lines proceeding by the sequential accumulation of mutations were apparent. Three satRNA variants were outliers for these two phylogenetic groups. They were shown to be recombinants of subgroup I and II satRNAs by calculating phylogenies for different molecular regions and by using Sawyer's test for gene conversion. At least two recombination events were required to produce these three recombinant satRNAs. Thus, recombinants were found to be frequent (∼17%) in natural populations of CMV-satRNA, and recombination may make an important contribution to the generation of new variants. To our knowledge this is the first report of data allowing the frequency of recombinant isolates in natural populations of an RNA replicon to be estimated. Received: 14 May 1996 / Accepted: 17 July 1996     

Molecular Evolution and Phylogeny of Satellite RNA Associated with Bamboo Mosaic Potexvirus

Satellite RNA of bamboo mosaic potexvirus (satBaMV) is a linear RNA molecule which encodes a 20-kDa nonstructural protein. Sequences of seven different satBaMV isolates from bamboo hosts in three genera showed 0.7% to 7.5% base variation which spanned the whole RNA molecule. However, the putative 20-kDa open reading frame was all preserved in these isolates. The phylogenetic relationship based on the nucleotide sequence did not show particular grouping of satBaMV from the host in one genus; neither was the grouping of satBaMV evident by location of sampling. Putative secondary structures of the 3′ untranslated regions showed a basic pattern with conserved hexanucleotides (ACCUAA) and polyadenylation signal (AAUAAA) located in the loop regions. Although the satBaMV-encoded 20-kDa protein is a nonstructural protein, its predicted secondary structure contains eight-stranded β-sheets which may form ``jelly-roll' structure similar to that found in capsid protein encoded by satellite virus of panicum mosaic virus. Received: 26 June 1996 / Accepted: 9 September 1996     

Identification of somaclonal variants of sugarcane (Saccharum spp.) resistant to sugarcane mosaic virus via RAPD markers

Somaclonal variants resistant to sugarcane mosaic virus (SCMV) were obtained from susceptible sugarcane cv PR62258 through somatic embryogenesis by increasing the number of subcultures of the embryogenic callus tissue in MS medium with 3 mg/L 2,4-dichlorophenoxyacetic acid. Transfers were made at 30-day intervals for 1, 2 or 3 subcultures. Two somaclones, namely AT626 and BT627, were selected by their resistance to SCMV. These subclones have maintained the resistance trait over seven years of testing in the field. In this report we identified the somaclonal SCMV resistant variants from the maternal line and the nonresistant somaclones, using the RAPD technique.     

Rapid production and field testing of homozygous transgenic tobacco lines with virus resistance conferred by expression of satellite RNA and coat protein of cucumber mosaic virus

A procedure for the fast production of homozygotic transgenic plants was developed. Leaf discs of haploid tobacco plants from anther cultures were transformed with a chimaeric vector containing coat protein (CP) and satellite RNA (Sat-RNA) genes from cucumber mosaic virus (CMV). One-hundred-and-twelve Kanamycin-resistant transformed haploid plants were subjected to selection based on the expression of both CP and Sat-RNA. Eighty-nine transgenic plants expressing both genes were selected and tested for their resistance to CMV by inoculation with high concentration of CMV (200 g ml^–1). Only five plants showed no symptoms of viral infection 30 days after inoculation. These plants were then diploidized by colchicine treatment. Three homozygous diploid lines with high levels of resistance to CMV were obtained after only one generation. The three transgenic lines were further tested under field conditions. The results showed that the progenies of these transgenic lines were homozygous and were highly resistant to CMV under natural field infection and manual inoculation conditions.     

Physical map of DNA from a new cauliflower mosaic virus strain

The restriction enzymes AluI, BamHI, BglII, EcoRI, HindIII, and SalI have been used to characterize and map a new cauliflower mosaic virus strain (Cabb-S). These fragments have been ordered by examining their overlapping regions after double enzymatic digestion. The single SalI cleavage site was chosen as the point of origin. We compare this strain with those already described.