Spot Of Pepper Research Articles

Physio-pathological responses of cabbage stored under controlled atmospheres

Abstract The response of cabbage to controlled atmospheres (CA) of 1–3% O2 and 1–10% CO2; 3% O2 and 5% CO2 was studied in relation to the incidence of physiological and pathological disorders. Fungal infections, pepper spot, low oxygen injury, weight loss, colour, odour, flavour and ethanol were evaluated. The findings show that CA did not reduce Botrytis cinerea rot in comparison to low temperature storage in air. PVC film and CA, on the other hand, reduced pepper spot by over 50% with respect to the air control. In particular, pepper spot was eliminated by high CO2 (10%) levels. Low O2 (1% O2 and 1% CO2) atmospheres caused 33 and 50% injury respectively after 89 and 109 days of storage. CA and PVC film reduced weight loss to 1%, as compared with 11% in the heads in air, which had shrivelled. The combination of 3% O 2 5% CO 2 and PVC film delayed yellowing with respect to air control. Concentrations of 1–3% O2 and 10% CO2 resulted in off odours and flavours after 74 days of storage. This result was confirmed by a considerable increase in ethanol concentrations. The most effective concentration tested was 3%O 2 5%CO 2 although, in general, infection by B. cinerea limited the storage life.

Resistance in annual Medicago species to Phoma medicaginis and Leptosphaerulina trifolii under field conditions

Advanced breeding lines and potential new cultivars of annual Medicago species were screened for resistance to phoma leaf and stem disease (caused by Phoma medicaginis) and pepper spot (caused by Leptosphaerulina trifolii) in the field, and their performances were compared with appropriate control cultivars. Medicago murex had the best overall disease resistance of the Medicago species tested. There were large differences between varieties in the incidence of both diseases. Based on end-of-season scores, the most resistant to phoma leaf disease included M. murex cv. Zodiac and SAR 3490, M. tornata SA10012, and M. truncatula cv. Parabinga, with scores 52.8 on a 0-10 scale (0, nil disease; 10, >90% leaves affected). On the basis of area under disease progress curve (AUDPC), the most resistant to phoma leaf disease, with AUDPC values of <157, included all M. murex varieties except 87FB2.30, and M. truncatula cv. Caliph. Based on end-of-season scores, the most resistant to phoma stem disease, all with scores c4, included M. murex cv. Zodiac, SAR 3490, and 87F01.48; M. sphaerocarpos cv. Orion (SEP 29.1), SEP 29.2, and SEP 30.3; and M. tornata cv. Tornafield and SA10012. Resistance to phoma stem disease in these lines was confirmed by AUDPC values, especially for M. murex cv. Zodiac, SAR3490, and 87FO1.48, and for M. tornata SA10012, with values <154. Based on end-of-season scores, the most resistant to pepper spot leaf disease included M. polymorpha cvv. Serena and Circle Valley, with scores 52.8. On the basis of AUDPC, all M. murex varieties except SAR3490 and 87FO1.5 could be included among those most resistant to pepper spot leaf disease, with AUDPC values <275. Coumestrol levels in stems ranged from 117 to 1420 mg/kg DW, with lowest levels (5330 mg/kg) in M. murex cv. Zodiac, 87FO 1.48, and GRC 87; M. sphaerocarpos cv. Orion (SEP 29.1), SEP 29.2, and SEP 26.2.1; M. tornata cv. Tornafield; and M. truncatula Z601. There was positive correlation between the severity of phoma disease on stems and end-of-season (September-November) coumestrol concentrations.

Diversity of Plasmids inXanthomonas campestrispv.vesicatoria

Plasmid profiles were determined for 522 strains of Xanthomonas campestris pv. vesicatoria, the causal agent of bacterial spot of tomato (Lycopersicon esculentum) and pepper (Capsicum annuum). The numbers and sizes of plasmids in strains from culture collections, as well as in strains recently isolated from plants in commercial fields of pepper or tomato, were diverse. Each plasmid was placed into one of 13 classes based on size, as determined by electrophoretic mobility in agarose gels. Plasmid sizes ranged from about 3 to 300 kb. Ten strains had no detectable plasmid. Seventy-one different plasmid profiles were observed, with a maximum of five plasmid size classes in a profile. No plasmid or plasmid profile was characteristic for X. campestris pv. vesicatoria. Mobility of plasmids was demonstrated in field experiments after inoculation of pepper plants with donor strains containing plasmids in five classes and an antibiotic-resistant recipient strain that contained one unique plasmid. All strains recovered on an antibiotic-amended medium contained the unique plasmid present in the recipient strain. Twenty-nine percent of the 199 cultures recovered on the antibiotic-amended medium in one experiment contained one or more plasmids that were similar in size to those in the donor strains ; seven different plasmid profiles were observed. The diverse plasmid content of strains of X. campestris pv. vesicatoria in nature may be the result of frequent transfer of the plasmids between strains.

Two Genetically Diverse Groups of Strains Are Included in Xanthomonas campestris pv. vesicatoria

Two genetically diverse groups of strains were identified among cultures of Xanthomonas campestris pv. vesicatoria isolated from plants with bacterial spot of pepper and tomato. Group A strains do not pit pectate gels or hydrolyze starch, whereas group B strains are strongly positive for these reactions. Group A strains cause a hypersensitive reaction in plants of tomato breeding line Hawaii 7998, but group B strains do not. Other differences between the two groups of strains were discovered in tests for utilization of carbon compounds, serology, fatty acid profiles, silver-stained protein bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels, and DNA restriction enzyme digestion profiles. The levels of DNA homology between strains belonging to the same group were more than 74%, but the levels of DNA homology between strains belonging to different groups were less than 46%. The two groups of strains have different genetic backgrounds, but cause essentially the same disease of tomato and pepper.

Host – parasite relationships between the fungus Leptosphaerulina crassiasca and peanut

The mode of penetration and infection of the peanut leaf by Leptosphaerulina crassiasca were studied by means of light and electron microscopy. The attachment of the multicellular ascospores to the leaf surface was by a mucilagenous sheath that covered the ascospores at maturity. This sheath expanded rapidly in moisture and it extended along the germ tube as it elongated. Two types of germ tubes appeared to be formed, a short one and a relatively long one. Short germ tubes were not delimited by septa, and they penetrated the cuticle and host epidermal cell wall directly without appressorium formation. Penetration occurred 2–6 h after inoculation. The wall was breached by a relatively broad infection hypha that expanded in width inside the host cell wall. The lack of mechanical rupture at the infection site indicated that penetration may involve enzymatic activity. Intracellular hyphae were present in the epidermal cells, but only intercellular hyphae occurred in the palisade and spongy mesophyll tissues. The intercellular hyphae were frequently appressed to the outer surface of the host cell wall. Infected areas rarely exceeded 1 mm in diameter, and they were only sparsely colonized by hyphae of the pathogen. Host cells in the vicinity of hyphae underwent senescence and death. One to 2 months after inoculation, pseudothecia formed in the dead tissues of detached leaves. In some instances the presence of penetration hyphae by short germ tubes induced the formation of a papilla inside the host cell wall, which either restricted growth of the infection hypha or resulted in the death of the germ tube and the cell from which it arose. Long germ tubes were delimited by simple septa and they terminated in an appressorium; however, details of their behavior were not studied. Key words: Arachis hypogaea, Ascomycotina, Dothideales, leaf scorch, pepper spot.

Bacterial Spot of Pepper and Tomato in Barbados

Bacterial spot of pepper and tomato, caused by Xanthomonas campestris pv. vesicatoria, is widespread and severe in Barbados. The bacterium was isolated from infected plants and seeds of six of 24 commercial pepper and tomato cultivars. When the bacterial strains were tested for pathogenicity, races 1-3 were detected, with race 1 strains two to nine times more abundant than races 2 and 3. Strains from seeds were commonly race 1 or nonpathogenic, and some tomato strains were virulent on the tomato cultivar Hawaii 7998 (.)

A New Leaf Spot of Pepper Caused byCladosporium oxysporum

A previously undescribed leaf spot of pepper (Capsicum annuum) in the Sultanate of Oman was found to be caused by Cladosporium oxysporum. Symptoms included irregular, brown leaf spots, 1 -4 mm in diameter. The causal fungus was isolated and shown to be pathogenic by inoculation of attached and detached leaves of pepper under controlled conditions. Most cultivars tested were susceptible to the new leaf spot(.)

An Agar Medium for the Isolation and Identification ofXanthomonas campestrispv.vesicatoriafrom Seed

An agar medium was developed for the isolation and identification of Xanthomonas campestris pv. vesicatoria, the causal agent of bacterial spot of pepper and tomato. The new medium, designated as CKTM, contained soy peptone, Bacto tryptone, dextrose, L-glutamine, L-histidine, ammonium phosphate, potassium phosphate, magnesium sulfate, calcium chloride, Pourite, and agar (...)

Identification of a pathogenicity locus inXanthomonas campestris pv.vesicatoria

Mutants of a tomato strain of Xanthomonas campestris pv. vesicatoria (XCV), causal agent of bacterial spot of tomato and pepper, were produced using the transposon Tn5 carried in the suicide plasmid pGS9. One prototrophic mutant, M461, was isolated which caused no visible reaction on tomato or pepper, but maintained the wild-type ability to induce a hypersensitive reaction (HR) on tobacco. This mutant showed similar growth characteristics to the wild-type in culture, but growth in planta was reduced. A genomic library of wild-type XCV was constructed in the broad host range cosmid vector pLAFR3. Clone p6AD4 restored pathogenicity to M461 on tomato and the ability to induce a HR on pepper. This clone contained ca. 22 kb of XCV DNA. The insertion in M461 was in a site corresponding to a 1.1 kb EcoRI fragment of p6AD4.

Occurrence of frogeye leaf spot of sweet pepper in Ibaraki Prefecture (2)

Occurrence of frogeye leaf spot of sweet pepper in Ibaraki Prefecture (2)

Quantitatively Assessed Resistance to Bacterial Leaf Spot in Pepper That is Simply Inherited

Quantitatively Assessed Resistance to Bacterial Leaf Spot in Pepper That is Simply Inherited

Occurrence of frogeye leaf spot of sweet pepper in Ibaraki Prefecture

Occurrence of frogeye leaf spot of sweet pepper in Ibaraki Prefecture

ETUDE HISTOLOGIQUE DE LA BIGARRURE NERVALE, DE LA GRISELURE DU LIMBE ET DE LA MEDIANE NOIRE, TROIS DESORDRES DU CHOU EN ENTREPOT

The evolution in storage of three physiological disorders of cabbage (Brassica oleracea var. capitata) has been studied by means of histological tests done in situ or after fixation and staining. The tissues tested were sampled on necrotic and healthy parts from the three outer-head leaves of the susceptible cv. Safekeeper and of the resistant cv. Hitoma. The tissues affected by vein streaking, grey speck disease or black midrib showed a similar response to the many tests: the absence of lipids, lignin and suberin in the necrotic cells, but the presence of unidentified phenolic compounds, concomitantly with a modification of birefringence of the cell wall and an alteration of the cytoplasmic matrix. Vein streaking is associated with creases on the adaxial epidermis of the midrib, grey speck disease with abundant wax on the abaxial blade, and black midrib with large vesicles in the necrotic parenchyma cells of the midrib.Key words: Brassica oleracea var. capitata, chemical composition, cytology, pepper spot, physiological disorder, storage

Allelism Tests of Three Dominant Genes for Hypersensitive Resistance to Bacterial Spot of Pepper

Allelism Tests of Three Dominant Genes for Hypersensitive Resistance to Bacterial Spot of Pepper

The effects of soil-applied aluminium sulphate, soil pH and soil potassium on pepper spot development in two winter white cabbage cultivars

SummaryTwo winter white cabbage cultivars, one tolerant (Little Rock) and the other susceptible to pepper spot development during storage (Langedijk 3 Decema) were grown in 1978 and 1979 in an experiment in which soil pH was reduced by treatment with Al2(SO4)3 and the K status increased by the application of KCl. Neither treatment affected yield. Lowering pH greatly increased pepper spot only in the sensitive cultivar, whereas increasing the level of K fertilizer increased plant K concentrations and also slightly decreased pepper spot in both cultivars. Although the major element concentrations differed between cultivars the treatment effects on them were small and unrelated to symptom development; pH had a major influence on minor element composition in both cultivars. The degree to which pepper spot developed was positively related to the Ni concentration. A greater Mn concentration in the tolerant cultivar apparently suppressed any Ni-induced pepper spot and a regression model combining the Mn and Ni c...

Occurrence of bacterial leaf spot of pepper in Pakistan

Abstract Bacterial leaf spot of pepper, Capsicum annum L., characterized by small dark moist spots on the underside of the leaflets which eventually become brown or black and dry scabby, is reported for the first time from Pakistan. Isolations from diseased plants collected from Islamabad yielded two isolates: Xcv1 and Xcv2 of Xanthomonas campestris var. vesicatoria (Doidge) Dawson from bell pepper, C. annum var. grossum and ornamental pepper, C. annum var. minimum respectively. The cultures were pathogenic in cross inoculations to both hosts and gave hypersensitive reactions in tobacco plant. The isolate Xcv1 produced a copious yellow slime on yeast extract dextrose CaCO3 at 25°C and 48 h incubation. These cultures were biochemically and physiologically similar.

Damage to white clover foliage in grazed pastures caused by fungi and other organisms

Abstract Incidence and severity of damage to white clover (Trifolium repens L.) foliage, caused by Pseudopeziza trifolii (Biv.) Fckl. (pseudopeziza leafspot), Uromyces trifolii (Hedw. f: DC) Fckl. (rust), Mycosphaerella killianii Petr. (sooty blotch), Leptosphaerulina trifolii (Rost.) Petr. (pepper spot), necrosis induced by pathogens or abiotic agents, and invertebrates, were assessed in samples taken over 13 months from 7 lowland and hill country sites near Palmerston North. Leafspot diseases occurred in succession from winter (pseudopeziza leafspot) to summer (sooty blotch) to late autumn (pepper spot), with rust present throughout the year. More damage caused by pseudopeziza leafspot, rust, and invertebrates was recorded from cattle-grazed, grass-clover pastures than from those grazed by sheep. A sheep-grazed pasture at one location showed a more intense epidemic of pepper spot than a neighbouring cattle-grazed pasture. Pseudopeziza leafspot and sooty blotch were more common at lowland sites than in h...

Control of Bacterial Spot of Pepper Initiated by Strains ofXanthomonas campestrispv.vesicatoriaThat Differ in Sensitivity to Copper

Control of Bacterial Spot of Pepper Initiated by Strains of<i>Xanthomonas campestris</i>pv.<i>vesicatoria</i>That Differ in Sensitivity to Copper

Stemphylium sarciniforme . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Stemphylium sarciniforme . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Predominantly on the leaves of Trifolium . DISEASE: Target or pepper spot of clover ( Trifolium ) where it may infect 80% of the leaves (52, 3740). Also recorded as causing gram blight of Cicer arietinum (54, 1076; 53, 751). Reports of its occurrence on Lupinus luteus (57, 568) may be confusing this species with Stemphylium globuliferum or S. botryosum . GEOGRAPHICAL DISTRIBUTION: Widespread wherever clover is grown. Africa, Asia, Australia, Europe, North and South America (see CMI Map 139, ed. 3, 1977). TRANSMISSION: By air currents and seed (24, 42; 44, 471).

Cyanogenic potential of Trifolium repens L. in relation to pepper spot caused by Stemphylium sarciniforme

White clover (Trifolium repens L.) contains two cyanogenic β-glucosides (G), linamarin and lotaustralin. Upon injury to the tissues a β-glucosidase (E) effects the release of cyanide from the β-glucosides. Four selections of white clover differing in cyanogenic properties (G+E+, G+E−, G−E+, G−E−) were examined for differences in susceptibility to Stemphylium sarciniforme. Symptom development was determined at 24, 48, 72, 96, and 120 h after the leaves were inoculated. Symptoms for all four selections consisted initially of small brown flecks (1 mm in diameter), then dark spots (1–2 mm in diameter) with definite borders, and finally senescence and wilt of the interlesion tissue. Plants containing both β-glucosidase (EC 3.2.1.21)and cyanogenic glucosides (G+E+) and those with only glucosides (G+E−) developed symptoms 24 h earlier than did the G−E+ and G−E− selections. The earliest symptoms were observed at 48 h; by 96 h all four selections showed comparable degrees of senescence and wilt. Pathogen development in infected leaves prepared as whole mounts was examined microscopically. Through 72 h after inoculation, development of S. sarciniforme in the G+E+ and G+E− selections was slower than in the G−E+ selections. By 96 h, however, fungal development in all four selections was comparable; commencement of leaf senescence coincided with extensive fungal colonization of necrotic tissue. Accelerated rates of symptom expression and retarded pathogen development apparently were positively correlated with cyanogenic potential of each white clover selection. Necrosis of suscept tissue was not correlated with cyanogenic potential of each selection.