Bacterial Speck Of Tomato Research Articles

Signal interactions in pathogen and insect attack: systemic plant-mediated interactions between pathogens and herbivores of the tomato,Lycopersicon esculentum

Plant-mediated interactions (i.e., induced resistance) between plant pathogens and insect herbivores were investigated using several pests of the cultivated tomato,Lycopersicon esculentum. Single leaflets of tomato leaves were injured by allowing a third-instarHelicoverpa zealarva to feed on the leaflets or by inoculating the leaflets withPseudomonas syringaepv.tomato(the causal agent of bacterial speck in tomato;Pst) or withPhytophthora infestans(the causal agent of late blight). Leaflets on separate plants were sprayed with benzothiadiazole, a chemical inducer of resistance toPst. The effects of these treatments on the resistance of uninoculated or undamaged leaflets to bothPstandH. zeawere then assessed after appropriate periods of time. The levels or activities of several defense-related proteins were determined in parallel. Infection of leaflets byPstdecreased the suitability of uninoculated leaflets of the same leaf for bothH. zeaand forPst. Similarly, feeding byH. zeacaused leaf-systemic increases in resistance to bothH. zeaandPst. Infection of leaflets byP. infestans, in contrast, had no effect on resistance of leaflets toH. zea. Treatment of leaves with benzothiadiazole induced resistance toPstbut improved suitability of leaflets forH. zea. Feeding byH. zeacaused the systemic accumulation of proteinase inhibitor mRNA and the systemic induction of polyphenol oxidase activity; in contrast, treatment with benzothiadiazole and inoculation withP. infestanscaused the systemic accumulation of pathogenesis-related protein mRNA and the systemic induction of peroxidase activity. Inoculation of leaflets withPstcaused the leaf-systemic accumulation of both pathogenesis-related protein and proteinase inhibitor mRNA and the systemic induction of both peroxidase and polyphenol oxidase activity. These results provide clear evidence for reciprocal induced resistance involving certain pathogens and arthropod herbivores of tomato. In addition, these results provide several insights into the integration and coordination of the induced defenses of tomato against multiple pests and suggest that the expression of resistance against some pests may compromise resistance to others.

The disease-resistance gene Pto and the fenthion-sensitivity gene fen encode closely related functional protein kinases.

Resistance to bacterial speck in tomato is governed by a gene-for-gene interaction in which a single resistance locus (Pto) in the plant responds to the expression of a specific avirulence gene (avrPto) in the pathogen. Disease susceptibility results if either Pto or avrPto are lacking from the corresponding organisms. Leaves of tomato cultivars that contain the Pto locus also exhibit a hypersensitive-like response upon exposure to an organophosphorous insecticide, fenthion. Recently, the Pto gene was isolated by a map-based cloning approach and was shown to be a member of a clustered multigene family with similarity to various protein-serine/threonine kinases. Another member of this family, termed Fen, was found to confer sensitivity to fenthion. The Pto protein shares 80% identity (87% similarity) with Fen. Here, Pto and Fen are shown to be functional protein kinases that probably participate in the same signal transduction pathway.

The HrpZ proteins of Pseudomonas syringae pvs. syringae, glycinea, and tomato are encoded by an operon containing Yersinia ysc homologs and elicit the hypersensitive response in tomato but not soybean.

The Pseudomonas syringae pathovars are composed of host-specific plant pathogens that characteristically elicit the defense-associated hypersensitive response (HR) in nonhost plants. P. s. pv. syringae 61 secretes an HR elicitor, harpinPss (HrpZPss), in a hrp-dependent manner. An internal fragment of the P. s. pv. syringae 61 hrpZ gene was used to clone the hrpZ locus from P. s. pv. glycinea race 4 (bacterial blight of soybean) and P. s. pv. tomato DC3000 (bacterial speck of tomato). DNA sequence analysis revealed that hrpZ is the second ORF in a polycistronic operon. The amino acid sequence identities of HrpZPss/HrpZPsg and HrpZPss/HrpZPst were 79 and 63%, respectively. Although none of the HrpZ proteins showed significant overall sequence similarity with other known proteins, HrpZPst contained a 24-amino acid sequence that is homologous with a region of the PopA1 elicitor protein of the tomato pathogen, Pseudomonas solanacearum GMI1000. hrpA, the upstream ORF, was highly divergent: The amino acid sequence identities of HrpAPss/HrpAPsg and HrpAPss/HrpAPst were 91 and 28%, respectively, and no HrpA sequence showed similarity to known proteins. In contrast, the predicted products of the downstream ORFs in P. s. pv. syringae and P. s. pv. tomato, hrpB, hrpC, hrpD, and hrpE showed varying levels of similarity to those of yscI, yscJ, yscK, and yscL. These are colinearly arranged genes in the virC locus of Yersinia spp., which are involved in the secretion of the Yop virulence proteins via the type III pathway. The similarity of the Ysc proteins was generally stronger in comparisons with the P. s. pv. tomato Hrp proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of Simulated Acidic Rain on Bacterial Speck of Tomato

AbstractAmbient rain in southern Ontario has a volume‐weighted average pH of approximately 4.2. Tomato (Lycopersicon esculentum Mill var. ‘Chico III’) seedlings were exposed to simulated acidic rain in specially designed chambers. The inoculum of Pseudomonas tomato (Okabe) Alstatt, causal agent of bacterial speck, was sprayed on plants before or after exposure to acidic rain of pH 2.5, 3.5, and 4.5, as well as on plants not exposed to the simulated acidic rain. Speck symptoms (small, dark, brown spots with yellow halos) were found on all inoculated plants. Exposure of plants to simulted acidic rain inhibited speck development, but the inhibition was greater on plants exposed to acidic rain after inoculation than on those exposed to acidic rain before inoculation. Spot necrosis, a typical response to acidic rain, occurred on up to 15 to 20% of the leaf area on all tomato plants treated with acidic rain at pH 2.5. Plants also showed a decrease in growth (height and fresh and dry weights) with an increase in rain acidity. Leaves injured by simulated acidic rain and examined histopathologically displayed cellular malformations including hyperplasia and hypertrophy. Pseudomonas tomato failed to grow on acidified King B medium or Difco nutrient broth adjusted to pH 3.5 or lower.

Prevention-the Key to Controlling Bacterial Spot and Bacterial Speck of Tomato

Prevention-the Key to Controlling Bacterial Spot and Bacterial Speck of Tomato

Two Sources of Resistance to Bacterial Speck of Tomato Caused byPseudomonas tomato

Two Sources of Resistance to Bacterial Speck of Tomato Caused by<i>Pseudomonas tomato</i>

Bacterial Speck of Tomato: Sources of Inoculum and Establishment of a Resident Population

Bacterial Speck of Tomato: Sources of Inoculum and Establishment of a Resident Population

Evaluation of tomato genotypes for tolerance to major diseases in Uganda

Tomato (Solanum lycopersicum L.) is a priority vegetable in Uganda, but due to its limited genetic base, its cultivated types are prone to a variety of diseases. The objective of this study was to evaluate new tomato genotypes for resistance to major tomato diseases under hotspot conditions in Uganda. Fourty-five tomato genotypes were evaluated for reactions to tomato bacterial wilt, tomato bacterial speck, early blight and late blight. The study was conducted for two rainy seasons in 2019, at the National Crops Resources Research Institute, Namulonge in Uganda. Data for severity and incidence were collected at two-week intervals after transplanting. Twelve genotypes (Nouvella F1, Rambo F1, Commando F1, AVTO1315, AVTO922, AVTO1701, AVTO1219, AVTO1464, MT56, ADV1287A, Pruna and Vega) exhibited high levels of tolerance to bacterial wilt; while bacterial speck presented mild symptoms majorly seen on Vega, Zodiac and AVTO9802. Rhino, AVTO1418, AVTO1314, Eureka, Roma VFN, MT56, Pinktop, Assila F1, Money-maker, AVTO0922 and AVTO1464 were the least affected by early blight; while AVTO1219, AVTO1701, ADV12021, ADV12076 and ADV1287A expressed low AUDPC values for late blight. Overall, AVTO1315 was the best yielder (30.8 metric tonnes ha-1), followed by AVTO0301 (29.0 t ha-1) and Nouvella F1 (26.1 t ha-1). Among the tomato genotypes evaluated, we recommend AVTO1701, AVTO0922, AVTO1464, AVTO0301 AVTO1315, AVTO1219, Pruna, Vega, ADV1287A and MT56 for the national performance trials.