Search

Sida golden mosaic virus (SiGMV) was first detected from snap bean (Phaseolus vulgaris L.) in Florida in 2006 and recently in Georgia in 2018. Since 2018, it has caused significant economic losses to snap bean growers in Georgia. This study, using a SiGMV isolate field-collected from prickly sida (Sida spinosa L.), examined the putative host range, vector-mediated transmission, and SiGMV-modulated effects on host–vector interactions. In addition, this study analyzed the phylogenetic relationships of SiGMV with other begomoviruses reported from Sida spp. Host range studies confirmed that SiGMV can infect seasonal crops and perennial weed species such as snap bean, hollyhock (Alcea rosea L.), marsh mallow (Althaea officinalis L.), okra (Abelmoschus esculentus (L.) Moench), country mallow (Sida cordifolia L.), prickly sida (S. spinosa), and tobacco (Nicotiana tabacum L.). The incidence of infection ranged from 70 to 100%. SiGMV-induced symptoms and virus accumulation varied between hosts. The vector, Bemisia tabaci Gennadius, was able to complete its life cycle on all plant species, irrespective of SiGMV infection status. However, SiGMV infection in prickly sida and country mallow positively increased the fitness of whiteflies, whereas SiGMV infection in okra negatively influenced whitefly fitness. Whiteflies efficiently back-transmitted SiGMV from infected prickly sida, hollyhock, marsh mallow, and okra to snap bean, and the incidence of infection ranged from 27 to 80%. Complete DNA-A sequence from this study shared 97% identity with SiGMV sequences reported from Florida and it was determined to be closely related with sida viruses reported from the New World. These results suggest that SiGMV, a New World begomovirus, has a broad host range that would allow its establishment in the farmscapes/landscapes of the southeastern United States and is an emerging threat to snap bean and possibly other crops. [ABSTRACT FROM AUTHOR]

Tomato yellow leaf curl virus is a species in the genus Begomovirus and family Geminiviridae. Tomato yellow leaf curl virus (TYLCV) infection induces severe symptoms on tomato plants and causes serious yield losses worldwide. TYLCV is persistently transmitted by the sweetpotato whitefly, Bemisia tabaci (Gennadius). Cultivars and hybrids with a single or few genes conferring resistance against TYLCV are often planted to mitigate TYLCV-induced losses. These resistant genotypes (cultivars or hybrids) are not immune to TYLCV. They typically develop systemic infection, display mild symptoms, and produce more marketable tomatoes than susceptible genotypes under TYLCV pressure. In several pathosystems, extensive use of resistant cultivars with single dominant resistance-conferring gene has led to intense selection pressure on the virus, development of highly virulent strains, and resistance breakdown. This study assessed differences in TYLCV genomes isolated from susceptible and resistant genotypes in Florida and Georgia. Phylogenetic analyses indicated that Florida and Georgia isolates were distinct from each other. Population genetics analyses with genomes field-collected from resistant and susceptible genotypes from Florida and/or Georgia provided no evidence of a genetic structure between the resistant and susceptible genotypes. No codons in TYLCV genomes from TYLCV-resistant or susceptible genotypes were under positive selection, suggesting that highly virulent or resistance-breaking TYLCV strains might not be common in tomato farmscapes in Florida and Georgia. With TYLCV-resistant genotypes usage increasing recently and multiple tomato crops being planted during a calendar year, host resistance-induced selection pressure on the virus remains a critical issue. To address the same, a greenhouse selection experiment with one TYLCV-resistant and susceptible genotype was conducted. Each genotype was challenged with TYLCV through whitefly-mediated transmission serially 10 times (T1-T10). Population genetics parameters at the genome level were assessed at T1, T5, and T10. Results indicated that genomes from resistant and susceptible genotypes did not differentiate with increasing transmission number, no specific mutations were repeatedly observed, and no positive selection was detected. These results reiterate that resistance in tomato might not be exerting selection pressure against TYLCV to facilitate development of resistance-breaking strains. TYLCV populations rather seem to be shaped by purifying selection and/or population expansion. [ABSTRACT FROM AUTHOR]

Simple Summary: Snap bean (Phaseolus vulgaris) production and quality have been negatively impacted by two whitefly-transmitted begomoviruses: cucurbit leaf crumple virus (CuLCrV) and sida golden mosaic Florida virus (SiGMFV), which often appear as a mixed infection in Georgia. However, there is no information available in terms of resistance to these two viruses in commercial cultivars/genotypes. Hence, commercially available snap bean varieties/genotypes (n = 84 in 2018; n = 80 in 2019; most of the genotypes were common in both years (with a few exceptions) were screened in two field seasons of 2018 and 2019. We also included two commonly grown Lima bean (Phaseolus lunatus) varieties in our field screening. As a result of this screening, we identified twenty Phaseolus genotypes with high-to-moderate levels of resistance and twenty-one genotypes with high levels of susceptibility. While there were differences among the Phaseolus spp. in severity of viral symptoms, suggesting differential susceptibility to viruses (CuLCrV and SiGMFV) and potential field resistance, the resistance mechanism is yet to be characterized. However, based on the greenhouse evaluation with two genotypes-each (susceptible vs. resistant) exposed to viruliferous whiteflies infected with CuLCrV and SiGMFV, we observed that the susceptible genotypes accumulated higher copy numbers of both viruses and displayed severe crumple severity compared to the resistant genotypes, indicating that resistant might potentially be against the virus complex than against the whiteflies. Adult whitefly counts differed among the Phaseolus spp. in both the years, indicating variability in host preference. We further sequenced 82 genotypes (80 snap bean and two Lima bean) to unravel the variations within the genomes. Genome sequencing followed by bioinformatic analyses revealed a considerable number of sequence variants, single nucleotide polymorphisms (SNPs), and insertions and deletions (InDels) in the genomes. Considering the variations in disease response and the underlying variations in the sequenced genomes, it can be speculated that some of the phenotypic variations (against CuLCrV and SiGMFV) could be due to a high level of genomic variation in the host. Future genome-wide association studies with the identified genomic variants may shed some light on this. The production and quality of Phaseolusvulgaris (snap bean) have been negatively impacted by leaf crumple disease caused by two whitefly-transmitted begomoviruses: cucurbit leaf crumple virus (CuLCrV) and sida golden mosaic Florida virus (SiGMFV), which often appear as a mixed infection in Georgia. Host resistance is the most economical management strategy against whitefly-transmitted viruses. Currently, information is not available with respect to resistance to these two viruses in commercial cultivars. In two field seasons (2018 and 2019), we screened Phaseolus spp. genotypes (n = 84 in 2018; n = 80 in 2019; most of the genotypes were common in both years with a few exceptions) for resistance against CuLCrV and/or SiGMFV. We also included two commonly grown Lima bean (Phaseolus lunatus) varieties in our field screening. Twenty Phaseolus spp. genotypes with high to moderate-levels of resistance (disease severity ranging from 5%–50%) to CuLCrV and/or SiGMFV were identified. Twenty-one Phaseolus spp. genotypes were found to be highly susceptible with a disease severity of ≥66%. Furthermore, based on the greenhouse evaluation with two genotypes-each (two susceptible and two resistant; identified in field screen) exposed to viruliferous whiteflies infected with CuLCrV and SiGMFV, we observed that the susceptible genotypes accumulated higher copy numbers of both viruses and displayed severe crumple severity compared to the resistant genotypes, indicating that resistance might potentially be against the virus complex rather than against the whiteflies. Adult whitefly counts differed significantly among Phaseolus genotypes in both years. The whole genome of these Phaseolus spp. [snap bean (n = 82); Lima bean (n = 2)] genotypes was sequenced and genetic variability among them was identified. Over 900 giga-base (Gb) of filtered data were generated and >88% of the resulting data were mapped to the reference genome, and SNP and Indel variants in Phaseolus spp. genotypes were obtained. A total of 645,729 SNPs and 68,713 Indels, including 30,169 insertions and 38,543 deletions, were identified, which were distributed in 11 chromosomes with chromosome 02 harboring the maximum number of variants. This phenotypic and genotypic information will be helpful in genome-wide association studies that will aid in identifying the genetic basis of resistance to these begomoviruses in Phaseolus spp. [ABSTRACT FROM AUTHOR]