Rot Of Lettuce Research Articles

First report of Phytophthora taxon × salinaslettuce (Subclade 8b hybrid) causing stem and basal rot in lettuce in North America.

More than 55% of U.S. lettuce (Lactuca sativa L.) production is in California, with Monterey Co. being the largest producer. Stunted mature romaine 'Valencia' and 'Stomper' and iceberg 'Frazier' lettuces with wilted outer leaves were collected from five commercial fields in Monterey Co. in spring 2023 and 2024. Brown internal stem and crown lesions progressed into sunken cavities and plant collapse. Incidence was approximately 5 to 75%. Margins of discolored stem and crown tissue were surface sterilized and plated on PARP-CMA (Jeffers and Martin 1986) and colonies resembling Phytophthora were recovered. Papillate sporangia ranged from 42 to 67.5 × 25 to 45 μm (avg. 56.1 × 37.0 μm, n = 30) and a length/breadth ratio of 1.4 to 1.7 (avg. 1.5). Globose, intercalary or terminal chlamydospores, 20 to 45 µm in diameter (avg. 32.6 µm, n = 30), and oospores, 17 to 29 μm in diameter (avg. 23.9 μm, n = 30) formed on 10 to 12-day-old cultures. Sequences from the two primary barcodes, ITS and COI (Robideau et al. 2011) were obtained from isolates collected from five different host cultivars and locations, finding identical multi-locus genotypes. ITS chromatograms contained six double-peaks, indicating interspecific hybridization. COI found the lettuce isolates forming a clade with the provisional P. taxon castitis, in Subclade 8b where hybrids are common (Bertier et al. 2013). If P. taxon castitis ITS is used as one parental ITS haplotype, the other haplotype is 1 bp different from P. lactucae and P. pseudolactucae ITS, suggesting one is the other parent of this hybrid taxon, provisionally introduced here as P. taxon ×salinaslettuce with accessions PQ427275-9 (ITS), and PQ424946-50 (COI). Pathogenicity assays were conducted on lettuce cultivars 'Bondi', 'El Guapo', and 'Valencia' (seven-week-old; 473-ml pots; 5 pots each for 'Bondi' and 'El Guapo', and 2 pots for 'Valencia'). Phytophthora inoculum of isolate 5411 was prepared as described in Hao et al. (2019) with oat seed replaced with long grain rice. Ten milliliter inoculum was added into two 6-cm-deep holes on opposite sides of the main stem. A non-colonized mixture was added to an equal number of control plants. All plants were maintained in a growth chamber with a 12-h photoperiod at 20°C/18°C. After one week, 'Bondi' and 'El Guapo' inoculated plants were stunted, and after two weeks, older leaves were chlorotic and wilted. After three weeks, 80% of the plants collapsed. Dark brown internal lesions were seen along the stem, crown, and tap roots of the collapsed plants after four weeks. 'Valencia' inoculated plants were stunted with no internal tissue discoloration observed over the same period. No symptoms were observed on any control plants; P. taxon ×salinaslettuce was reisolated and confirmed via ITS sequence from symptomatic stems, crowns, and tap roots of 'Bondi' and 'El Guapo', as well as non-symptomatic feeder roots of all three cultivars. No Phytophthora was recovered from the controls. This is the first report of P. taxon ×salinaslettuce detection on lettuce; P. taxon castitis has been isolated from strawberry and carrot in Sweden and Canada (Bertier et al. 2013), while P. lactucae and P. pseudolactucae have only been reported on lettuce in Greece and Japan (Elena et al. 2006; Rahman et al. 2015). Plans are underway to confirm the hybrid status and parentage of P. taxon ×salinaslettuce using genomics. This emerging pathogen may cause severe economic losses in CA lettuce production during the winter and spring growing seasons.

Selection of biofortified mini lettuce progenies resistant to Pectobacterium carotovorum subsp. carotovorum

Brazilian consumers are increasingly seeking unique vegetable products, such as mini lettuces. However, their production is hampered by a wide variety of pathogens, including Pectobacterium carotovorum subsp. carotovorum, which causes soft rot in lettuce. In this study, we aimed to select biofortified mini lettuce genotypes with good agronomic traits and resistance to P. carotovorum. A randomized block design consisting of 12 treatments, conducted in a field and greenhouse (Federal University of Uberlândia [UFU]), was used to select biofortified mini lettuce with good agronomic traits: SPAD index, stem and plant diameter, stem length, plant height, number of leaves, fresh weight, and bolt resistance. A completely randomized design consisting of 13 treatments was used for resistance or susceptibility testing. The bacterial suspension was inoculated and the following were assessed: disease severity, 16 days after inoculation; area under the disease progress curve, calculated separately at 4, 8, 12, and 16 days after inoculation as well as the sum of data calculated on all the assessment days; and the disease resistance class. The genotypes UFU 215#1 and UFU 215#2 had significantly high carotenoid concentrations. The genotypes UFU 66#4, UFU 215#1, and UFU 215#7 showed high bolt resistance. All genotypes were classified as resistant or moderately resistant to the P. carotovorum isolate, UFU A7.

Efficacy of essential oils in the management of soft rot caused by Pectobacterium aroidearum in lettuce

Lettuce is susceptible to several diseases, especially soft rot caused by bacteria of the genus Pectobacterium. Due to the adaptability of this pathogen and the lack of disease control registered for the crop, the objective of this work was to evaluate the effects of essential oils in the management of soft rot caused by P. aroidearum in lettuce. The study was developed at the Universidade do Estado da Bahia, Juazeiro, BA, Brazil, and the essential oils (EOs) of orange, bergamot, lemongrass, palmarosa, citronella, cloves, tea tree, rosemary, sage, and ginger were used in concentrations of 0.25; 0.5; 0.75 and 1.0% to assess the in vitro growth inhibition of the bacterium. Subsequently, the curative effects of the disease were evaluated by applying the EOs that obtained the best results in vitro in lettuce plants of the susceptible variety “Mônica”. The treatments were applied, via spraying, 12 hours after inoculation using the bite method with bacterial suspension. The best in vivo treatment was selected to assess its preventive and curative activity, as well as to find the ideal concentration for reducing epidemiological variables and chromatographic characterization. The EOs of palmarosa, sage, citronella, lemongrass, and cloves (0.25%), and that of sage (0.75%), inhibited bacterial growth in vitro. The EO of salvia showed the best results in vivo, inhibiting the growth of the disease in concentrations of 0.50 and 0.75%, so it was selected for the preventive and curative control tests alone. The preventive treatment was not efficient for the management of soft rot in lettuce, however, from the regression analysis, a concentration of 0.64% of the salvia EO was found as a potential for curative control of this bacteriosis, as it reduces the incidence and severity of the disease. Linalyl acetate and linalool were found in higher concentrations in the chromatographic analysis. These components, probably, conferred the bactericidal capacity of the EO of sage, being potential for the use in the control of P. aroidearum in lettuce.

PCR primers to identify and detect Berkeleyomyces rouxiae, a causal agent of black root rot of lettuce

Berkeleyomyces rouxiae, a causal agent of black root rot of lettuce, is morphologically and physiologically indistinguishable from the closely related species B. basicola. PCR primers specific for these species were designed based on the nucleotide sequence of genes specific to the species. The primer pair specific to B. rouxiae did not amplify DNA of other plant pathogens that invade root or stem base of lettuce and was useful for diagnosis and quantitating the pathogen from lettuce root tissue.

First Report of Pectobacterium aroidearum Causing Soft Rot in Lettuce and Chinese Cabbage in Brazil

Lettuce (Lactuca sativa L.) and Chinese cabbage (Brassica pekinensis Rupr.) are leafy vegetables of great socioeconomic value in Brazil. Bacterial diseases are among the factors that might limit their yield, particularly soft rot caused by bacteria of the genus Pectobacterium. In July 2014, vegetable gardens of approximately 1.0 and 0.18 ha in the cities of Juazeiro (09° 24′ 42″ S, 40° 29′ 55″ W), state of Bahia, and Petrolina (09° 23′ 55″ S, 40° 30′ 03″ W), state of Pernambuco, Brazil, showed 5% of lettuce plants variety Elba and 44.4% of Chinese cabbage cultivar Michihilli plants with wilt of leaves, foul-smelling soft rot, and inner medulla disintegration. Bacterial isolates were selectively isolated from stem and midribs of lettuce and Chinese cabbage by transferring rot tissue to a healthy pepper fruit using a sterilized toothpick (Takatsu et al. 1981). Pepper fruits were incubated at 26°C for 36 h in a moist chamber, and after incubation bacterial isolates were isolated in Petri dishes containing casamino acid–peptone–glucose (CPG) medium. Small white colonies with “broken glass” aspect (Kelman and Dickey 1995) were observed under a stereoscope, and after that, they were preserved in sterile distilled water (SDW). Twelve isolates were obtained from lettuce and Chinese cabbage plants with soft rot symptoms, which showed the same cultural characteristics in CPG medium. Pathogenicity testing was performed using seedlings of lettuce variety Elba (30 ± 2°C; 62 ± 2% relative humidity [RH]) and detached leaves of Chinese cabbage cultivar Michihilli (28 ± 2°C; 65 ± 2% RH), which are susceptible to bacterial soft rot. Ten microliters of bacterial suspension (10⁶ CFU/ml) were injected into the intermediary portion of the leaf midrib, followed by 48 h of incubation in a moist chamber. For the negative control, seedlings and detached leaves were treated similarly with SDW. The isolate CRMP1 of Pectobacterium aroidearum (Moraes et al. 2017) was used as a reference. Typical symptoms of soft rot were observed 12 to 24 h after inoculation, followed by pathogen reisolation onto CPG medium, fulfilling Koch’s postulates. Seedlings and detached leaves used as negative control remained symptomless, whereas seedlings and detached leaves inoculated with CRMP1 showed soft rot symptoms. Both isolates (UNEB 3 and CCRMPA35) presented gram-negative cells, grew at 37°C, were erythromycin resistant, and were positive for maceration in potato tubers. The Biolog Gen III System identified the isolates as Pectobacterium sp. with a level of 70% similarity. Two isolates were selected for molecular identification, one from lettuce (UNEB3) and one from Chinese cabbage (CCRMPA35). Fragments of the 16S rDNA region (Hauben et al. 1998) and icdA, proA, and mdH genes (Ma et al. 2007) of these isolates were sequenced, and BLASTn analysis of the 16S rRNA region (GenBank MH507334 and MH507330), icdA (GenBank MH500095 and MH500096), proA (GenBank MH507331 and MH507332), and mdH (GenBank MH507329 and MH507330) genes of the isolates UNEB 3 and CCRM35 showed similarity levels of 99, 99, 98, and 99% with sequences of the 16S rRNA region and icdA, proA, and mdH genes of the type isolate of P. aroidearum (isolate SCRI109ᵀ; GenBank JN600323, HM156915, HM157162, and HM156976). Phylogenetic analysis of concatenated sequences of the icdA, proA, and mdH genes using Bayesian inference between isolates UNEB 3 and CCRM35 and species and subspecies of Pectobacterium from GenBank grouped these two isolates with SCRI109ᵀ, with a posterior probability of 100%. To our knowledge, this is the first report of P. aroidearum causing soft rot in lettuce and Chinese cabbage in Brazilian territory. In addition, the present research helps to better know the host range of P. aroidearum in Brazil, which until now was only reported in zucchini (Moraes et al. 2017).

Biological control of root rot in lettuce caused by Exserohilum rostratum and Fusarium oxysporum via induction of the defense mechanism

Root rot diseases of plant are accountable for crop yield losses. Biological control of this disease is considered a feasible alternative and eco-friendly method. The root rot pathogens, Exserohilum rostratum HQ905473 and Fusarium oxysporum HQ905448, were isolated from lettuce plants. Biocontrol activity of Trichoderma harzianum JF419706 and Bacillus subtilis HQ656002 against lettuce root rot and their inducibility of the defense genes were evaluated. The results confirm the efficiency of T. harzianum and B. subtilis either singly or as a mixture in the control of the disease and alleviation of the negative effect of the pathogens on lettuce plants. The phytosanitary parameters of the plants, including plant height and weight, was greatly enhanced as a result of the application of bioagents. Content of photosynthetic pigments and primary metabolites (carbohydrates, proteins and proline) significantly increased in the treated plants. The Differential display PCR reaction (DD-PCR) revealed that 15 up- and down-regulated genes were detected in the treated plants. Among these genes, the encoded GTPase activating protein, that is an important gene in the plant defense mechanism, was identified. Gene expression was analyzed in inoculated plants after 25 and 50 days. The 50-day-old plants had a higher level of gene expression than the 25-day-old plants. The results confirmed the efficiency of the bioagents in enhancing the defense mechanism of plants against the disease and ensure the sustainability of this resistance throughout the life of the plant.

Suppression of soil-borne pathogens in container media amended with on-farm composted agro-bioenergy wastes and residues under glasshouse condition

The aim of this work was to assess the potential suppression of three on-farm green composts for controlling seven soil-borne pathogens in container media under greenhouse condition. Suppression of Pythium irregulare and Rhizoctonia solani damping-off of cucumber and bean, Phytophthora cinnamomi and Sclerotinia minor root rot of azalea and lettuce, and Fusarium oxysporum wilt of melon, tomato, and basil was studied on artificially inoculated seedlings. Three feedstocks of bioenergy wastes and agricultural residues were selected, on-farm composted, characterized, and tested for their suppressive properties by in vitro and in vivo experiments in comparison with one commercial compost from municipal solid biowaste. The composts showed differences in the suppressive properties when mixed with sterile peat at dosage of 35%. All green composts meanly suppressed P. irregulare damping-off of cucumber of 80%, R. solani damping-off of bean of 75%, P. cinnamomi root rot of azalea of 65%, and Fusarium wilt of up to 25%. The reference compost suppressed F. oxysporum wilt of melon, tomato, and basil from 60 to 70% and Pythium, Rhizoctonia, and Phytophthora diseases up to 30%. All composts suppressed S. minor root rot of lettuce of 35%. Suppression of Pythium damping-off and Phytophthora root rot was related to the sum of the bioactivities of the fungi and bacteria of compost. Suppression of Rhizoctonia damping-off and F. oxysporum wilt was associated with the specific bioactivity of a restricted number of fungi (Trichoderma, Aspergillus) and bacteria (Pseudomonas, actinomycetes) species. Suppression of Sclerotinia root rot was not related to any one variable of composts.

Wpływ nowych syntetycznych regulatorów wzrostu RW3, RW13 i RW14 na wzrost, plon i zdrowotność sałaty w szklami [Influence of new synthetic growth regulators RW3, RW13 and RW14 on the growth, yield and health of lettuce in the glasshouse

Influence of the preparations RW<sub>3</sub>, RW<sub>13</sub> and RW<sub>14</sub> synthesized in the Research Institute of Organic Chemistry in Warsaw on lettuce were investigated in the glasshouse. The preparation RW3 was a retardant and the RW<sub>13</sub> and RW<sub>14</sub> were growth sttandatons. The preparation RW<sub>3</sub> at 1000 ppm decreased markedly the diameter of plants and their weight. It also increased the resistance of plaints to dry tipbuirn, and wet rot of lettuce caused by <i>Botrytis</i> sp.

Óleos essenciais e extratos vegetais no controle da podridão mole em alface crespa

Avaliou-se o efeito de óleos essenciais e extratos vegetais no controle da podridão mole em alface, bem como, a influência desses produtos nas características físico-químicas desta hortaliça. Nos testes in vitro, discos de papel de filtro foram embebidos em 11 óleos essenciais e 20 extratos vegetais nas concentrações 0,0; 0,25; 0,50; 0,75 e 1% e 0,0; 10, 40, 70 e 100%, respectivamente, e depositados sobre meio de cultura contendo Pectobacterium carotovorum subsp. carotovorum (Pcc A1). Os halos de inibição foram mensurados após 24 e 48 h de incubação. Em casa de vegetação, plantas de alface cv. Veneranda foram tratadas com 11 óleos nas concentrações de 0,5 e 1%, 20 extratos na concentração de 10% e Mycoshield® (3 g L-1), sendo inoculadas com o isolado Pcc A1 após 72 h. A severidade da doença foi avaliada a intervalos de seis até 48 h, calculando-se a área abaixo da curva de progresso da doença (AACPD). Em experimento similar, plantas tratadas com óleo de Corymbia citriodora, sete extratos e Mycoshield® foram analisadas quanto aos teores de sólidos solúveis, vitamina C, acidez titulável e pH. Pcc A1 não foi inibido in vitro. Dois óleos (C. citriodora e Citrus sinensis) e sete extratos (Parkinsonia aculeata, Chamaecrista cytisoides, Sida galherensis, Polygala violaceae, Chamaecrista desvauxii e Pityrocarpa moniliformis) reduziram significativamente a severidade da doença em relação à testemunha, não diferindo do controle Mycoshield®. Já a AACPD foi reduzida por oito óleos e dez extratos. Destacaram-se com eficiência similar ao Mycoshield® e diferindo da testemunha (7,5 e 132,3) nas duas variáveis analisadas, o óleo de C. citriodora a 0,5% e o extrato de S. galherensis a 10% com severidades de 3,6 e 3,5 e AACPD de 83,35 e 88,25, respectivamente. Os teores de vitamina C, acidez titulável e pH não foram alterados em folhas de alface tratadas com óleo de C. citriodora e extratos de P. aculeata e C. cytisoides.

Plectosphaerella rot of lettuce, coriander, and chervil caused by Plectosphaerella pauciseptata

Rot diseases of hydroponically cultured leaf lettuce, coriander, and chervil were found in Chiba Prefecture, Japan. Stems and petioles of the three diseased plants became brown or black with a soft rot, and vascular parts of the stems became discolored. Seemingly similar fungi were isolated from the diseased plants. Pathogenicity of these fungal isolates to each plant was demonstrated by inoculation tests. The fungi were identified as Plectosphaerella pauciseptata based on morphological and cultural characters. This identification was supported by phylogenetic analysis with rDNA ITS1-5.8S-ITS2 regions. The diseases were named Plectosphaerella rot (Plectosphaerella huhai-byo in Japanese) of lettuce, coriander, and chervil.

Induction of reactive oxygen generation and functional changes in mitochondria and their involvement in the development of bacterial rot in lettuce caused by Pseudomonas cichorii

Pseudomonas cichorii is the major causal agent of bacterial rot disease in lettuce, and apoptosis-like programmed cell death is closely associated with disease development. Depletion of cellular ATP and expression of the alternative oxidase gene was observed in lettuce leaves inoculated with P. cichorii suggesting mitochondrial dysfunction. Cytochemical observation showed production of reactive oxygen species in mitochondria of P. cichorii-inoculated lettuce leaf cells. Release of cytochrome c into the cytosol was also induced by inoculation with the bacterium. Superoxide production was observed in the mitochondrial fraction isolated from P. cichorii-infected leaves much more intense than water-treated leaves. Loss of swelling ability was also observed in the mitochondrial fractions following inoculation with P. cichorii. Intriguingly, inhibitors of the mitochondrial respiratory complex III prevented loss of swelling ability, whereas superoxide generation was scarcely affected by inhibitors of mitochondrial permeability transition in the mitochondrial fractions. Inhibitors of the mitochondrial respiratory complex III and mitochondrial permeability transition delayed not only P. cichorii-induced cell death, but also disease development. In contrast, P. cichorii-induced DNA fragmentation was not inhibited in the presence of either type of inhibitor. The findings suggest that mitochondria may play a crucial role in DNA fragmentation-independent cell death pathway(s).

The hrp genes of Pseudomonas cichorii are essential for pathogenicity on eggplant but not on lettuce.

Pseudomonas cichorii causes necrotic lesions in eggplant and rot in lettuce. Through transposon insertion into P. cichorii strain SPC9018 we produced two mutants, 4-57 and 2-99, that lost virulence on eggplant but not lettuce. Analyses showed that a transposon was inserted into the hrpG gene in 4-57 and the hrcT gene in 2-99. Nucleotide sequences of the hrp genes of SPC9018 are homologous to those of Pseudomonas viridiflava BS group strains. The pathogenicity of 4-57 on eggplant was restored by transformation with an hrpF operon, originating from either SPC9018 or the BS group member P. viridiflava strain 9504 (Pv9504). These data suggested the involvement of hrp genes in the pathogenicity of SPC9018 on eggplant, and functional conservation of hrpF operons between SPC9018 and Pv9504. Both the hrpS mutant and the hrpL mutant were unable to cause necrotic lesions on eggplant leaves but retained their pathogenicity against lettuce. These results suggest that the pathogenicity of P. cichorii is hrp-dependent in eggplant, but not in lettuce.

Fungitoxicidade, atividade elicitora de fitoalexinas e proteção de alface em sistema de cultivo orgânico contra Sclerotinia sclerotiorum pelo extrato de gengibre

O patógeno Sclerotinia sclerotiorum é um fungo que sobrevive no solo e causa a doença conhecida como mofo branco ou podridão de esclerotínia na cultura da alface (Lactuca sativa) e outras culturas. A doença é considerada de difícil controle, uma vez que o fungo é muito agressivo e produzem estruturas de resistência, os escleródios. Na busca de novos métodos de controle de doenças, os extratos de plantas com propriedades terapêuticas surgem como opção. Neste trabalho avaliou-se o efeito do extrato bruto aquoso (EBA) de gengibre (Zingiber officinalis) nas concentrações de 1, 5, 10, 15, 20 e 25% sobre o crescimento micelial e produção de escleródios de S. sclerotiorum, in vitro. Também foi verificada a eficiência do gengibre na proteção de plantas de alface cultivadas organicamente e inoculadas com o patógeno. Além da incidência da doença, foi analisado o rendimento da cultura e a atividade de peroxidase nos tecidos da planta. Água e o indutor de resistência acibenzolar-S-metil foram utilizados como tratamentos controle. Adicionalmente, a capacidade elicitora do EBA de gengibre em proporcionar o acúmulo das fitoalexinas deoxiantocianidina e gliceolina foi avaliada em bioensaios com sorgo e soja, respectivamente. Os resultados indicaram a atividade antimicrobiana dos EBA de gengibre, com inibição do crescimento micelial e da produção de escleródios. Na cultura da alface, verificou-se que a aplicação de massa de gengibre na base da planta aumentou a atividade da enzima peroxidase e reduziu a incidência da doença. A presença de compostos elicitores no EBA de gengibre foi observada pela indução da produção de fitoalexinas em sorgo e soja, que ocorreu de maneira dose-dependente. Estes resultados indicam o potencial de Z. officinalis para o controle de S. sclerotiorum em alface, o qual pode ocorrer tanto por atividade antimicrobiana direta quanto pela ativação de mecanismos de defesa das plantas.

Black rot in lettuce: a new disease caused by Ceratocystis fimbriata in hydroponic culture in Brazil

Black rot in lettuce: a new disease caused by <i>Ceratocystis fimbriata</i> in hydroponic culture in Brazil

First Report of Rhizomonas Suberifaciens Causing Corky Rot of Lettuce in Australia.

Typical symptoms of corky root were observed on iceberg lettuce (Lactuca sativa) in Queensland, Australia. Slowgrowing bacteria with colonies similar to strains of Rhizomonas suberifaciens or other Rhizomonas species were isolated from lettuce seedlings which had been inoculated with an extract from soil adhering to lettuce roots with corky root symptoms. DNA from all strains was tested for DNA homology with DNA from strain CAI of R. suberifaciens and strain W14 of Rhizomonas sp. Twenty seven strains had moderate (29.2–57.7%) to high (59.9–80.9%) DNA homology with strain CAI and slight (4.8–10.8%) DNA homology with strain WI4. All of these strains induced typical symptoms of corky root on lettuce seedlings, cv. Salinas, and tested positive in an enzyme-linked immunosorbent assay with monoclonal antibody MAb-Rs1 specific for R. suberifaciens. This is the first report of R. suberifaciens causing corky root of lettuce in Australia.

Ultrastructural study of host–parasite interactions. II. Decay of lettuce caused by Botrytis cinerea and phyllosphere bacteria

Botrytis cinerea causes a fast-spreading soft rot in lettuce that, under favorable conditions, completely destroys the tissues in less than 72 h. Within the first 24 h, the fungus penetrates the cuticle into the foliar parenchyma, destroying the cell wall and cellular content. Dictyosomes and mitochondria are altered and disappear first. Chloroplasts resist longer but are deeply modified with inflating and stacking of thylakoids, an increase in number of osmiophilic globules, and the disintegration of the plastidial membrane. Lomasomes and microbodies appear. Cell walls are made visible by Thiéry's technique. Bacteria invade dead tissues and seem to participate in a more complete destruction of the host and the fungus.

Leaf spot and dry rot of lettuce caused by Xanthomonas vitians (Brown) Dowson

During the late winter and early spring of 1960, and again to a lesser extent in 1961 and 1962, many lettuce crops in the Murray Valley area of north-western Victoria were seriously affected by a disease characterized by blackening, dry rotting, and collapse of the affected leaves. The incidence of disease varied from about 10% up to practically complete destruction of some plantings. A yellow bacterium was consistently isolated from affected plants and proved to be pathogenic to lettuce. Laboratory studies have shown that the organism agrees closely with the recorded description of Xanthomonas vitians (Brown) Dowson, which has not, apparently, been previously studied in Australia.