Maria Esther Noronha Fonseca

Black root rot, caused by two Berkeleyomyces species ( B. basicola and B. rouxiae ), is a major disease of lettuce ( Lactuca sativa L.) in tropical areas. Nationwide surveys in Brazil indicated similar levels of incidence as well as an overlapping geographical distribution of B. basicola and B. rouxiae across major lettuce-producing areas. The most promising strategy for managing these polyphagous and aggressive pathogens is the deployment of genetic resistance. The heirloom cultivar ‘La Brillante’ displayed resistance to a broad range of isolates of both Berkeleyomyces species. However, to date, there is no information about the genetic control of B. basicola and B. rouxiae . Inheritance studies investigating the resistance of ‘La Brillante’ to isolates of both pathogens were conducted separately employing F ₂ populations derived from crosses with the highly susceptible cultivar ‘Elisa’. The hybrid origin of individual F ₁ plants was assessed via RAPD marker genotyping. Two bona-fide F ₁ plants were then selfed to obtain two independent F ₂ segregating populations. The contrasting parental cultivars and F ₂ seedlings were then separately inoculated with B. rouxiae (F ₂ population size = 247) and B. basicola (F ₂ population size = 166). Chi-square test was employed to assess the goodness of fit of the observed segregation patterns against each pathogen to the predicted Mendelian ratios. All ‘Elisa’ plants displayed highly susceptible reactions to both pathogens, whereas all ‘La Brillante’ plants were resistant even under harsh inoculation conditions, indicating high levels of penetrance of this trait. The F ₂ populations inoculated with either B. basicola or B. rouxiae displayed a good fit to 3:1 resistant/susceptible segregation ratios, indicating monogenic and dominant resistance to both pathogens. Additional experiments are necessary to verify whether the same gene/locus or distinct genes/loci are controlling the resistance to B. rouxiae and B. basicola . Nevertheless, this simple monogenic inheritance will facilitate the incorporation of these resistant traits into elite lettuce breeding lines and cultivars.

Beans (Phaseolus vulgaris and P. lunatus) are the major hosts of bean golden mosaic begomovirus (BGMV). Robust taxonomic criteria were established for Begomovirus species demarcation. However, DNA–A identities among BGMV isolates display a continuous variation (89–100%), which conflicts with the current concept of a single viral species. The diversity of 146 Brazilian isolates designated in the GenBank as BGMV was assessed by comparing their complete DNA–A sequences. The isolates were clustered into four groups, being discriminated mainly by their original Fabaceae hosts. Additional Sequence Demarcation Tool analyses indicated that BGMV-related viruses comprise two clear-cut groups: isolates reported infecting mainly P. vulgaris (identities of 96–97% to the reference NC_004042 isolate) and a group associated with P. lunatus (identities of 89–91%). Moreover, we recognized a distinct set of genomic features in the iterons and Rep-associated protein motifs across these two diversity groups. The host prevalence and genomic differences suggest that most P. lunatus isolates are currently misclassified as BGMV strains, being more likely samples of a closely related (but distinct) Begomovirus species. Hence, the implications of this BGMV diversity should be taken into consideration by classical and biotech breeding programs aiming for large-spectrum viral resistance in Phaseolus species.

Leandria momordicae Rangel is the etiological agent of net spot, which is a very important disease of cucumber (Cucumis sativus), chayote (Sicyos edule), and in other Cucurbitaceae species. Although this pathogen was described more than a century ago infecting Momordica charantia, its taxonomic positioning has not yet been clarified. Moreover, a standard isolate of this fungus is not available in any reference mycological collection. In this context, the aims of the present work were (i) to clarify the taxonomic position of the fungus via morphological and phylogenetic analyses; (ii) to deposit a neotype of L. momordicae in a public mycological collection; (iii) to provide the first DNA sequences of the pathogen in GenBank. The morphometrical characteristics of distinct L. momordicae isolates were similar to those originally described. The phylogenetic analyses were carried out using information of five genomic regions. Using the BLASTn algorithm, it was observed that the L. momordicae-derived sequences displayed higher identity levels to fungal sequences of the order Pleosporales, which were subsequently included in the analyses. All sequences from the nine isolates of L. momordicae grouped within a single phylogenetic clade distinct from the other taxa in Pleosporales. Therefore, it is suggested the establishment of a new family of Pleosporales to include L. momordicae to which the name Leandriaceae is proposed. In addition, an ex-neotype and a neotype were illustrated and deposited in the Herbarium of the Federal University of Viçosa (VIC4754) and in the culture collection "Octávio Almeida Drummond" (COAD3403). The present study reinforces the view that many "hidden" fungal taxa are yet to be discovery under Neotropical conditions.

One of the emerging biotic problems of the lettuce (Lactuca sativa) crop in Brazil is the black root rot caused by two Berkeleyomyces species, B. basicola and B. rouxiae. Although sources of resistance have already been reported for B. basicola, there is still no information about the response of distinct lettuce accessions to B. rouxiae. Herein, we evaluated a diversified germplasm collection, composed of accessions from different L. sativa morphotypes, searching for sources of genetic resistance effective against isolates of both causal agents of the black root rot disease complex. Sixty-eight L. sativa accessions were initially screened for resistance to one B. basicola isolate. Thirty-three accessions (with the highest levels of resistance) were inoculated again with two B. basicola and two B. rouxiae isolates. Similar levels of resistance were observed for the isolates of B. basicola and B. rouxiae. The lettuce morphotypes ‘Romaine’, ‘Batavian’, and ‘Crispy loose-leaf’ displayed higher frequency of accessions with resistance to both fungi. Broad-spectrum resistance against both pathogens detected in distinct lettuce morphotypes opens the opportunity for breeding programs to incorporate these genetic factors in a wide range of commercial cultivars.

Sida mottle virus (SiMoV) and Sida micrantha mosaic virus (SiMMV) are major Brazilian begomoviruses (Geminiviridae). However, the range of DNA–A identity of isolates of these viruses (81–100%) is not in agreement with the current criteria for Begomovirus species demarcation (n = 47) comprises a wide range of strains (with a continuum variation of 88.8–100% identity) infecting members of five botanical families (Malvaceae, Solanaceae, Fabaceae, Oxalidaceae, and Passifloraceae). The SiMoV group now comprises eight isolates (90–100% identity) restricted to Malvaceae hosts, including one former reference SiMMV isolate (gb|NC_077711) and SP77 (gb|FN557522; erroneously named as “true SiMMV”). Iteron analyses of metagenomics-derived information allowed for the discovery of the missing DNA–B cognate of SiMoV (93.5% intergenic region identity), confirming its bipartite nature. Henceforth, the correct identification of SiMoV and SiMMV isolates will be a crucial element for effective classical and biotech resistance breeding of the viral host species.

The diversity of Geminiviridae and Alphasatellitidae species in tomatoes was assessed via high-throughput sequencing of 154 symptomatic foliar samples collected from 2002 to 2017 across seven Brazilian biomes. The first pool (BP1) comprised 73 samples from the North (13), Northeast (36), and South (24) regions. Sixteen begomoviruses and one Topilevirus were detected in BP1. Four begomovirus-like contigs were identified as putative novel species (NS). NS#1 was reported in the semi-arid (Northeast) region and NS#2 and NS#4 in mild subtropical climates (South region), whereas NS#3 was detected in the warm and humid (North) region. The second pool (BP2) comprised 81 samples from Southeast (39) and Central–West (42) regions. Fourteen viruses and subviral agents were detected in BP2, including two topileviruses, a putative novel begomovirus (NS#5), and two alphasatellites occurring in continental highland areas. The five putative novel begomoviruses displayed strict endemic distributions. Conversely, tomato mottle leaf curl virus (a monopartite species) displayed the most widespread distribution occurring across the seven sampled biomes. The overall diversity and frequency of mixed infections were higher in susceptible (16 viruses + alphasatellites) in comparison to tolerant (carrying the Ty–1 or Ty–3 introgressions) samples, which displayed 9 viruses. This complex panorama reinforces the notion that the tomato-associated Geminiviridae diversity is yet underestimated in Neotropical regions.

Aim: An extensive survey was done to clarify the prevalent Stemphylium species on Solanaceae plants across Brazil, and their host ranges. Methods and Results: Eighty nine (89) Stemphylium isolates were obtained from naturally infected tomatoes as well as S. paniculatum, potato, eggplant, scarlet eggplant (Solanum aethiopicum var. gilo), Physalis angulata, and Capsicum species. Phylogenetic analyses encompassing the ITS-5.8S rDNA and glyceraldehyde-3-phosphate dehydrogenase genomic regions placed the isolates into two distinct groupings with either Stemphylium lycopersici or S. solani. Isolates of S. lycopersici (n = 81) were obtained infecting tomato, potato, eggplant, S. paniculatum, and P. angulata. Isolates of S. solani (n = 8) were detected in natural association with scarlet eggplant and tomato. Two isolates of S. lycopersici displayed a wide experimental host range in greenhouse bioassays, infecting accessions of 12 out of 18 species. Ocimum basilicum (Lamiaceae) was the only experimental host outside the Solanaceae family.