Symptoms In Bean Research Articles

Variation in the response to ascochyta blight in common bean germplasm

Ascochyta blights are major diseases of many legumes and an emerging disease in many areas in which common bean (Phaseolus vulgaris L.) is grown. Ascochyta blight symptoms in bean can be caused by three fungus species. We investigated the species that caused ascochyta blight symptoms in bean crops from northern Spain using species-specific molecular markers and analysis of their nucleotide sequences. Results suggested that the two local isolates analyzed may correspond to the specie Phoma exigua var. diversispora. The variation in the reaction of common bean germplasm against a local isolate was also investigated in controlled conditions and was scored using a 1–9 severity scale. A total of 200 accessions from a core collection, 89 breeding lines and 11 accessions of Phaseolus coccineus L. were screened to identify potential sources of resistance. Most Phaseolus coccineus accessions showed higher levels of resistance (score 5). However, five breeding lines and 17 accessions exhibited moderate resistance after five resistance tests, with variation in the response of seedlings within accessions. Thus, five lines were obtained by self-pollination from each of the 17 selected accessions. Evaluation of these lines revealed significant variation within lines derived from two accessions and allowed verification of the high level of resistance in lines derived from three accessions. Finally, the lines with higher levels of resistance identified in previous evaluations were tested in three additional tests. The lines UI465, BGE04435–22 and BGE04453–4 revealed resistance levels not significantly different from the best Phaseolus coccineus accession included in this study (score < 3.5). The identified resistance sources could be used in the in the short term to increase the level of resistance to ascochyta blight in specific bean genotypes or for development of new resistant genotypes by pyramiding of genes.

Begomoviruses Associated with Bean Golden Mosaic Disease in Nicaragua.

Begomovirus spp. cause substantial losses in bean crops in tropical and subtropical regions of the Americas. The predominant Begomovirus sp. in Central America associated with golden mosaic symptoms in bean is Bean golden yellow mosaic virus (BGYMV). However, Calopogonium golden mosaic virus was previously found to infect bean crops in the northern region of Costa Rica. The objective of this research was to identify Begomovirus spp. that infect bean plants in different geographical regions of Nicaragua. In all, 126 samples of young bean leaves with symptoms of golden mosaic were collected from eight different regions of Nicaragua. Using DNA hybridization with specific probes, 120 samples tested positive for BGYMV, 14 samples tested positive for Squash yellow mild mottle virus, and 7 samples tested positive for Calopogonium golden mosaic virus. Sequence analysis of polymerase chain reaction-amplified products from three samples (MA-9 Managua, BE-8 Rivas, and SO-9 Granada) also indicated that the symptoms of golden mosaic in bean are associated with viral sequences from three different Begomovirus spp. Management of bean golden mosaic disease must take into account that BGYMV is the predominant virus (95% of the samples) and that 12% of the samples exhibited possible mixed infections or recombination events in the south and central geographical regions of Nicaragua.

Real-Time Quantitative RT-PCR of Defense-Associated Gene Transcripts of Rhizoctonia solani-Infected Bean Seedlings in Response to Inoculation with a Nonpathogenic Binucleate Rhizoctonia Isolate

ABSTRACT Certain isolates of nonpathogenic binucleate Rhizoctonia spp. (np-BNR) are effective biocontrol agents against seedling root rot and damping-off. Inoculation of bean seed with np-BNR strain 232-CG at sowing reduced disease symptoms in bean (Phaseolus vulgaris) seedlings caused by R. solani. Molecular analyses of the spatial expression of three defense-associated genes were carried out using real-time quantitative reverse transcription-polymerase chain reaction (QRT-PCR) assays. This method allowed accurate quantitative evaluation of transcript levels of pG101 encoding for 1,3-beta-D-glucanase, gPAL1 encoding for phenylalanine ammonia lyase, and CHS17 encoding for chalcone synthase in 1- and 2-week-old bean seedlings that were inoculated simultaneously with np-BNR and infected with R. solani, and in seedlings that were singly inoculated with either fungi or not inoculated. In the seedlings that were infected with R. solani only, results revealed that, following infection, activation of all defense-associated gene transcripts was achieved with significant increases ranging from 7- to 40-fold greater than the control, depending on the defense gene and tissue analyzed. Seedlings that were treated with np-BNR and infected with R. solani had expression similar to those that were treated with np-BNR only, but the levels were significantly down-regulated compared with those that were infected with R. solani only. These findings indicate that disease suppression by np-BNR isolate is not correlated to pG101, gPAL1, and CHS17 gene activation.

Two Newly Described Begomoviruses of Macroptilium lathyroides and Common Bean

ABSTRACT Macroptilium lathyroides, a perennial weed in the Caribbean region and Central America, is a host of Macroptilium yellow mosaic Florida virus (MaYMFV) and Macroptilium mosaic Puerto Rico virus (MaMPRV). The genomes of MaYMFV and MaMPRV were cloned from M. lathyroides and/or field-infected bean and the DNA sequences were determined. Cloned A and B components for both viruses were infectious when inoculated to M. lathyroides and common bean. Comparison of the DNA sequences for cloned A and B components with well-studied begomovirus indicated that MaMPRV (bean and M. lathyroides) and MaYMFV (M. lathyroides) are unique, previously undescribed begomo-viruses from the Western Hemisphere. Phylogenetic analysis of viral A components indicated that the closest relative of MaYMFV are members of the Bean golden yellow mosaic virus (BGYMV) group, at 76 to 78% nucleotide identity, whereas the closest relative for the A component of MaMPRV was Rhynchosia golden mosaic virus at 78% nucleotide identity. In contrast, BGYMV is the closest relative for the B component of both MaYMFV and MaMPRV, with which they share approximately 68.0 and approximately 72% identity, respectively. The incongruent taxonomic placement for the bipartite components for MaMPRV indicates that they did not evolve entirely along a common path. MaYMFV and MaMPRV caused distinctive symptoms in bean and M. lathyroides and were transmissible by the whitefly vector and by grafting; however, only MaYMFV was mechanically transmissible. The experimental host range for the two viruses was similar and included species within the families Fabaceae and Malvaceae, but only MaYMFV infected Malva parviflora and soybean. These results collectively indicate that MaMPRV and MaYMFV are new, previously undescribed species of the BGYMV group, a clade previously known to contain only strains and isolates of BGYMV from the Caribbean region that infect Phaseolus spp. Both MaYMFV and MaMPRV may pose an economic threat to bean production in the region.

Evidence for intrastrand complementation in cowpea mosaic virus infection

In supplementation tests both middle component (M)-RNA and bottom component (B)-RNA of cowpea mosaic virus mutant N142 were shown to carry mutations affecting local symptoms in bean and cowpea. The M- and B-RNA mutations were separately incorporated into the two reciprocal hybrids of N142 and wild-type Sb, designated as M 142B Sb and M SbV 142. Mixtures of the two hybrids induced normal local symptoms in bean and cowpea as a result of reassortment of components. This was also the case with a mixture of M SbV 142 and mutant N123. The latter mutant was earlier shown to contain a M-RNA mutation for defective symptom expression in bean and cowpea. Although both M 142B Sb and N123 carried M-RNA mutations, mixtures of these isolates induced normal local symptoms. Subculturing showed no wild-type virus to be present in the inoculated leaves. Thus, intrastrand complementation was assumed to result in restoration of normal symptom production. We conclude that the results of genetic mixing experiments with multicomponent plant viruses must be interpreted cautiously. Subculturing experiments should be performed to determine whether restoration of wild-type symptoms results from exchange of nonmutated components or from intrastrand complementation.

Comparative Growth of Xanthomonas phaseoli and Xanthomonas vesicatoria and Development of Symptoms in Bean and Tomato Leaves

Comparative Growth of Xanthomonas phaseoli and Xanthomonas vesicatoria and Development of Symptoms in Bean and Tomato Leaves

PROPERTIES OF A STRAIN OF CUCUMBER-MOSAIC VIRUS ISOLATED FROM PRUNUS HOSTS

Some of the stone-fruit viruses that are transmissible only to cucumber and other cucurbits have occasionally been accompanied by a second virus that can be isolated by transfer to tobacco. This virus, herein called CMVP, appears to be latent in Prunus hosts, but induces symptoms in bean, cowpea, cucumber, Datura stramonium, Nicotiana glutinosa, petunia, tobacco, spinach, sugar beet, Swiss chard, and zinnia. CMVP has a small thermal coefficient, a thermal inactivation point between 65° and 70 °C, and a dilution end point between 10−3 and 10−4. It remains infective in expressed sap up to 96 hours at room temperature and for more than 6 days under refrigeration. It can be transmitted between cucumber and tobacco by Aphis gossypii and Myzus persicae, in which it is nonpersistent. Spherical "virus particles" associated with CMVP are about 35 mμ in diameter. Tobacco plants infected with this virus are partially protected against cucumber mosaic virus but not against tobacco ring spot virus.In symptom expression and in some of its properties, CMVP resembles both alfalfa mosaic virus and cucumber mosaic virus. Its particle size and immunological reaction suggest that it is an atypical strain of the latter. It is considered not to be implicated in the etiology of cherry yellows and related stone-fruit viroses.