Root Rot Of Lettuce Research Articles

First Report of Collar and Root Rot of Lettuce Caused by Plectosphaerella cucumerina in Serbia.

In March 2021, unusual plant stuning, collar, and wet root rot of lettuce (Lactuca sativa L.) during the rosette stage was observed in two commercial fields in Serbia (44°58'N, 20°32'E; 44°45'N, 20°43'E). Disease incidence in the fields (≈ 0.9 ha each) was approximately 15 and 20%, respectively. Initial above-ground symptoms were yellowing and wilting of leaves, while below-ground symptoms were collar, wet root rot, and lesions becoming necrotic. Eventually, whole plants wilted, collapsed, and died. A total of 35 symptomatic plants were collected from the fields, and diseased tissues were cut into small pieces, surface sterilized, and plated on potato dextrose agar (PDA). Isolation resulted in 20 morphologically uniform monoconidial isolates. The isolates formed white to creamy colonies, gradually becoming salmon pink, slimy, or moist in appearance, with sparse aerial mycelia. Numerous hyphal coils with conidiophores and hyaline, smooth-surfaced, ellipsoid to ovoid, septate or aseptate conidia were formed (4.5 to 10.1×1.2 to 3.7 μm (n = 100)). To confirm the species identity, the internal transcribed spacer (ITS) region and the D1/D2 region of a selected representative isolate 13-3-c were amplified and sequenced by using primer pairs ITS1/ITS4 (White et al. 1990) and N1/N2 (O'Donnell and Gray 1995), respectively. The sequences were deposited in GenBank (ITS: OR880564 and D1/D2: OR880567). Sequence analysis revealed 100% nucleotide identity with P. cucumerina isolates from different countries deposited in the NCBI GenBank, including isolate MH860704 (Vu et al. 2019) (ITS region) and isolate KY662256 (Su et al. 2017) (D1/D2 region). Neighbor-joining analysis was conducted based on the combined ITS and D1/D2 regions, and the tree was constructed with the substitution models (1,000 bootstrap). The combined phylogeny confirmed that the sequences shared a common clade with P. cucumerina. Hence, morphological, microscopic, and molecular characterization confirmed the pathogen as P. cucumerina (Palm et al., 1995; Carlucci et al., 2012). In a pathogenicity assay, 10 isolates were tested. Five 30-day-old lettuce plants (cv. Majska Kraljica) per isolate were root-dipped in the conidial suspensions (1×105 conidia/ml). The 10 inoculated plants were transplanted into 1 L pots containing sterile substrate (Floragard, Germany). Plants treated with sterile distilled water were used as controls. Plants were maintained in a greenhouse at 25 to 28°C under a 12-hour photoperiod (Cai et al., 2021). Four weeks after inoculation, stunting, chlorosis, and wilting of plants were observed, while collars and roots exhibited typical decaying symptoms. No symptoms were observed on the control plants. The pathogen was reisolated from symptomatic tissue as previously described. Koch's postulates were completed by confirming the identity of reisolates based on morphological features. To our knowledge, this is the first report of P. cucumerina on lettuce or any other crop in Serbia. P. cucumerina is already known as a pathogen of lettuce and other hosts grown in many countries worldwide, as well as in some European countries (Belgium, England, Italy, the Netherlands, and Switzerland) (Zhang et al. 2019). This emerging pathogen may cause significant economic losses in lettuce production in Serbia and in the entire Balkan region. Our results may help to develop effective management strategies based on accurate and timely identification and regular pathogen monitoring.

First report of Pythium root rot of hydroponic lettuce (Lactuca sativa) in Greece, caused by Pythium Cluster B2a sp.

Pythium root rot has been reported in several countries, but in Greece this disease was first detected in 2021, causing severe yield losses in a hydroponic lettuce crop. Isolations, morphological and molecular characterization, as well as pathogenicity assays identified a Pythium Cluster B2a species causing the disease in hydroponically grown lettuce. This is the first report of Pythium Cluster B2a sp. causing lettuce root rot in Greece.

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 Black Root Rot of Lettuce in Shizuoka Prefecture, Japan

First Report of Black Root Rot of Lettuce in Shizuoka Prefecture, Japan

First report of black root rot of lettuce in Japan caused by Berkeleyomyces rouxiae

In August 2016, lettuce plants (Lactuca sativa) cultivated in Gunma Prefecture became stunted and often wilted. Dark brown to black lesions were observed on roots of diseased plants. Most small feeder roots were lost. Fungi isolated from lesions on roots were identified as Berkeleyomyces rouxiae based on their morphological and genetic characteristics. Pathogenicity of this fungus on lettuce was confirmed by inoculation and reisolation. This report is the first of black root rot caused by B. rouxiae on lettuce in Japan.

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.

Fusarium oxysporum (F221-B) as biocontrol agent against plant pathogenic fungi in vitro and in hydroponics

Efficacy of non-pathogenic Fusarium oxysporum (F221-B) was assessed as a possible biocontrol agent against fungal pathogens, namely Curvularia lunata (C11, C12), F. semitectum (F113), F. oxysporum f.sp. lactucae (F221-R, F442-G), Rhizoctonia solani (R11, R12), Rhizoctonia sp. (R111, R112, R113) in vitro, while F221-B showed a moderate ability to inhibit the mycelial growth of tested fungi about 36–56%. Then, F221-B was further evaluated for its ability of controlling lettuce root rot and wilt caused by F442-G in hydroponics. It was revealed that F221-B reduced disease incidence and severity about 60–80% compared to the inoculated control and significantly promoted the growth of 3 lettuce varieties. Interestingly, using only F221-B gave the significantly highest fresh weight (twice over the healthy control). Conclusively, this study provides an important suggestion for further development of F221-B since it showed the ability of biocontrol agent and plant growth promoting fungus.

Effect of organic matter removal treatments and addition of aluminum-containing substances on incidence of Fusarium wilt of lettuce

In order to determine the mechanism of lettuce root rot suppression in topsoil of andosols we investigated the effect of removing humus from a topsoil of andosol and adding aluminum substances to a disease-conducive subsoil of andosol on the incidence of lettuce root rot. Both topsoil of andosols heated at 250°C and treatment with hydrogen peroxide sustained disease suppressive effect, and exhibited similar levels of disease suppression as the untreated topsoil of andosol. The disease suppressive effect was lost by heating topsoil of andosol at 400°C. Next, both subsoil of andosol amendment with aluminum-containing humic acid (Al-humic acid) and aluminum hydroxide gel (Al(OH)3) added the disease suppressive effect, but not with humic acid or crystalline structure aluminum hydroxide [crystalline Al(OH)3]. The addition of Al-humic acid and Al(OH)3 to potato dextrose agar medium significantly inhibited growth of the causal agent of lettuce root rot, Fusarium oxysporum f. sp. lactucae, compared with the control. Based on the above results, we speculate that noncrystalline aluminum hydroxide, which forms complexes with humus, inhibits growth of pathogenic fungus and thereby suppresses incidence of lettuce root rot.

Effect of corn steep liquor on lettuce root rot (Fusarium oxysporum f.sp. lactucae) in hydroponic cultures.

Recent reports indicate that organic fertilisers have a suppressive effect on the pathogens of plants grown under hydroponic systems. Furthermore, microorganisms exhibiting antagonistic activity to diseases have been observed in organic hydroponic systems. This study evaluated the effect of corn steep liquor (CSL) on controlling lettuce root rot disease [Fusarium oxysporum f.sp. lactucae (FOL)] in a hydroponic system. The effect of CSL and Otsuka A (a chemical fertiliser) on the inhibition of FOL in terms of mycelial growth inhibition was tested in vivo. Addition of CSL suppressed FOL infection rates. CSL inhibited FOL infection by 26.3-42.5% from 2 days after starting incubation. In comparison, Otsuka A inhibited FOL growth by 5.5-19.4%. In addition, four of 10 bacteria isolated from the nutrient media containing CSL exhibited inhibition zones preventing FOL mycelial growth. We found that CSL suppressed FOL in lettuce via its antifungal and biostimulatory effects. We suggest that activation of beneficial microorganisms present in CSL may be used to decrease lettuce root rot disease and contribute to lettuce root growth.

Reductional Effect on Injury Caused by Root Rot of Lettuce by Combining Application of Converter Slag for Soil pH Amendment and Cultivar Tolerance

Reductional Effect on Injury Caused by Root Rot of Lettuce by Combining Application of Converter Slag for Soil pH Amendment and Cultivar Tolerance

Antimicrobial lipopeptide iturin for disease suppression on Fusarium root rot of lettuce(The Joint Meeting of Japanese Environmental Microbiology-related Associations 2014)

Antimicrobial lipopeptide iturin for disease suppression on Fusarium root rot of lettuce(The Joint Meeting of Japanese Environmental Microbiology-related Associations 2014)

Analysis of RAPD and AFLP markers linked to resistance to Fusarium oxysporum f. sp. lactucae race 2 in lettuce (Lactuca sativa L.)

Root rot of lettuce, which is caused by Fusarium oxysporum f. sp. lactucae (FOL), is a critical problem in the production of lettuce. FOL-resistant lettuce genetic resources have been identified and used in breeding programs to produce FOL-resistant cultivars. However, the genetic characteristics of resistance genes have not been studied in depth and, therefore, no DNA markers are presently available for these genes. In this study, we analyzed the RRD2 (resistance for root rot disease race 2) locus, which confers resistance to FOL race 2. Resistance loci were analyzed using two cultivars of crisphead lettuce: VP1013 (resistant) and Patriot (susceptible). The segregation patterns of resistant phenotypes in F2 indicated a single major locus. To define the positions of resistance loci, a linkage map was constructed using amplified fragment length polymorphism and random amplified polymorphic DNA (RAPD) markers. Quantitative trait loci analysis revealed the position of the major resistance locus. A high LOD score was observed for RAPD-marker WF25-42, and this marker showed good correspondence to the phenotype in different cultivars and lines. We successfully developed a sequence characterized amplified region marker from WF25-42.

Podridão de raízes causada por Pythium aphanidermatum, em cultivares de alface produzidas em sistema hidropônico

A podridão de raízes, causada por Pythium aphanidermatum e outras espécies de Pythium, é a principal doença da alface cultivada em sistemas hidropônicos no Brasil. O presente trabalho teve como objetivo avaliar quatro cultivares comerciais de alface em relação à sensibilidade a podridão de raízes, causada por P. aphanidermatum. Os estudos foram realizados em placas de Petri contendo ágar-água com plântulas de alface das cultivares crespa (Vera e Verônica) e lisa (Regina e Elisa), infestadas ou não com o patógeno. Com as mesmas cultivares foram realizados quatro experimentos em sistemas hidropônicos (Nutrient Film Technique), sendo dois em estufa coberta com plástico e sombrite e dois em estufa coberta apenas com plástico. As plântulas, infectadas ou não com P. aphanidermatum, foram transplantadas para os sistemas infestados ou não. Foi avaliada a severidade da doença e o desenvolvimento das plantas. Todas as cultivares foram suscetíveis à podridão de raízes nos experimentos realizados in vitro e in vivo. A presença do sombrite não reduziu a podridão de raízes em cultivares de alface produzidas no sistema hidropônico. A cultivar Regina apresentou maior massa de matéria seca da parte aérea e das raízes, na presença ou ausência do patógeno, sendo a mais indicada para o cultivo hidropônico na época mais quente do ano.

‘Chouya No. 37’, a Fusarium Root Rot (Race 2)-Resistant Lettuce

Fusarium root rot of lettuce (RRL) caused by Fusarium oxysporum f. sp. lactucae (FOL) race 2 occurrs only in Nagano Prefecture, Japan. The area affected by the disease reached 17 ha in 2003. ‘Chouya No. 37’ crisphead-type lettuce (crisp lettuce), which is adaptable to summer cultivation, was bred with resistance to FOL race 2. As a maternal line to breed a resistant cultivar, the selection line of ‘Kikugawa No. 102’ was used as a genetic resource with resistance to FOL race 2. The resistant line was crossed with the selection line of crisp lettuce with slow bolting. The progeny had been selected by various methods until F6, ‘Chouya No. 37’ was bred. ‘Chouya No. 37’ is as highly resistant to FOL race 2 as its maternal line. Its resistance is superior to that of other lettuce cultivars that are adaptable to mid-summer cultivation in Nagano. ‘Chouya No. 37’ is very vigorous, its leaf color is green to slightly dark green, and its leaf luster is relatively high. The leaf margins have relatively shallow incisions, indentations, and mild undulations. The quality of the head upon harvest is categorized as “relatively good” to “good”. It also has slow bolting in mid-summer.

Black Root Rot Caused by Thielaviopsis basicola on Lettuce in California.

In 2005 and 2006, field-grown iceberg lettuce (Lactuca sativa) in California's coastal Salinas Valley (Monterey County) was affected by a previously unreported disease. Symptoms were observed on iceberg lettuce at the post-thin rosette stage (8 to 12 leaves). Plants were stunted and slightly chlorotic. Fine feeder roots had numerous, small (4 to 8 mm long), elongated, dark brown-to-black lesions. Larger secondary roots and taproots lacked lesions. No vascular discoloration was present. Isolations from root lesions consistently resulted in gray fungal colonies that formed catenulate, cylindrical, thin-walled, hyaline endoconidia and catenulate, subrectangular, thick-walled, dark aleuriospores. The fungus was identified as Thielaviopsis basicola (2). Conidial suspensions (5.0 × 105) of eight isolates from iceberg lettuce were used for pathogenicity tests. Iceberg cv. Ponderosa and romaine cv. Winchester were grown for 3 weeks in soilless peat moss rooting mix. Roots of 20 plants per cultivar were washed free of the rooting mix and soaked in conidial suspensions for 5 min. Plants were repotted and grown in a greenhouse. Control plant roots were soaked in sterile distilled water (SDW). After 3 weeks, inoculated iceberg exhibited slight chlorosis in comparison with control plants. Feeder roots of all iceberg plants inoculated with the eight isolates exhibited numerous black lesions and T. basicola was reisolated from these roots. Romaine lettuce, however, did not show any foliar symptoms. Small segments of roots had tan-to-light brown discoloration and T. basicola was occasionally reisolated (approximately 40% recovery). Roots of control iceberg and romaine showed no symptoms. Results were similar when this experiment was repeated. To explore the host range of T. basicola recovered from lettuce, two isolates were prepared and inoculated as described above onto 12 plants each of the following: iceberg lettuce (cv. Ponderosa), bean (cv. Blue Lake), broccoli (cv. Patriot), carrot (cv. Long Imperator #58), celery (cv. Conquistador), cotton (cv. Phy-72 Acala), cucumber (cv. Marketmore 76), green bunching onion (cv. Evergreen Bunching), parsley (cv. Moss Curled), pepper (cv. California Wonder 300 TMR), radish (cv. Champion), spinach (cvs. Bolero and Bossanova), and tomato (cv. Beefsteak). Control plant roots of all cultivars were soaked in SDW. After 4 weeks, only lettuce and bean roots had extensive brown-to-black lesions, from which the pathogen was consistently resiolated. Roots of cotton, pepper, spinach, and tomato had sections of light brown-to-orange discoloration; the pathogen was not consistently recovered from these sections. All other species and the control plants were symptomless. This experiment was repeated with similar results except that inoculated peppers were distinctly stunted compared with control plants. To my knowledge, this is the first report of black root rot caused by T. basicola on lettuce in California. Disease was limited to patches along edges of iceberg lettuce fields; disease incidence in these discrete patches reached as high as 35%. Affected plants continued to grow but remained stunted in relation to unaffected plants and were not harvested. Black root rot of lettuce has been reported in Australia (1); that report also showed that lettuce cultivars vary in susceptibility to T. basicola and isolates from lettuce were highly aggressive on bean but not on many other reported hosts of this pathogen.

The Effect of UV-A Irradiation Treatment during Rising Seedling Period on Resistance against Lettuce Root Rot Desease

The Effect of UV-A Irradiation Treatment during Rising Seedling Period on Resistance against Lettuce Root Rot Desease

Phylogenetic relationships between the lettuce root rot pathogen Fusarium oxysporum f. sp. lactucae races 1, 2, and 3 based on the sequence of the intergenic spacer region of its ribosomal DNA

The genetic relationship between the vegetative compatibility groups (VCGs) and between physiological races of Fusarium oxysporum f. sp. lactucae (FOL), the causal pathogen of lettuce root rot, was determined by analyzing the intergenic spacer (IGS) region of its ribosomal DNA. A total of 29 isolates containing a type strain were tested: 24 Japanese isolates, 2 Californian isolates, and 3 Italian isolates. Three races (races 1, 2, and 3) were found in Japan, and race 1 was also distributed in California and Italy. Races 1, 2, and 3 each belonged to a distinct VCG: VCG-1, VCG-2, and VCG-3 (VCG-3-1, VCG-3-3), respectively. Phylogenetic (neighbor-joining) analysis of the IGS sequences revealed that races 1, 2, and 3 coincided with three phylogenetic groups (PG): PG-1, PG-2, and PG-3, respectively. These results indicate that the three races are genetically quite different and have a strong correlation with VCGs and phylogenetic groupings.

'Shinano Hope', a Fusarium Root Rot-Resistant Lettuce

The recent increase of root rot of lettuce (RRL) in Nagano, a major lettuce producing area in Japan, is becoming a serious problem because there are no suitable cultivars for summer cropping of crisphead-type lettuce (crisp-lettuce) resistant to RRL. We bred 'Shinano Hope' crisp-lettuce that is resistant to Fusarium oxysporum f. sp. lactucae (FOL) Race 1 that is adaptable for summer cultivation. 'Shinano Hope' is a hybrid between two crisp-lettuce lines: one is from a slow bolting selection line, whereas the other is from a breeding line resistant to FOL Race 1. 'Shinano Hope' is field-resistant to FOL Race 1, similar to its paternal plant. It's resistance is superior to those of other lettuce cultivars that can be grown in mid-summer in Nagano. The leaf color of 'Shinano Hope' is lustrous green. The leaf margins have relatively shallow incision, indentation, and mild undulation. The quality of the head in appearance upon harvest was categorized as good-superior; it matures similar to 'Patriot' and tends to bolt slowly in mid-summer.

Effect of Potassium Phosphonate on the Control of Phytophthora Root Rot of Lettuce in Hydroponics

The effect of potassium phosphonate (<TEX>$KH_2PO_3</TEX> or <TEX>$K_2 HPO_3$</TEX>) on the control of Phytophthora root rot of lettuce was evaluated in a liquid hydroponic culture. Phosphonate 100 ppm strongly inhibited mycelial growth of Phytophthora species in vitro but did not affect normal growth of lettuce in a greenhouse test. Application of the chemical before infection showed over 94% control value, while it was less than 35% when applied after infection. In a field trial, phosphonate 100 ppm, which was directly supplemented into the nutrient solution, satisfactorily controlled the disease as it did not develop until 28 days after transplanting and remained at less than 2% infection rate at the end of cultivation. Meanwhile, in the control plot, the disease initiated at 7 days after transplanting and developed rapidly reaching over 70% infection rate at 28 days. Population density of the causal pathogen, R drechsleri, in a heavily infested farm was 22.0-25.0 cfu/100 ml of nutrient solution. However, it decreased to 1.3-2.0 cfu/100 ml at 7 days after treatment with phosphonate 200 ppm.