Systemically Induced Resistance in Potato Cultivars with Different Degree of Resistance to Late Blight caused by Phytophthora infestans (Mont.) de Bary

Systemically induced resistance in potato plants (Solanum tuberosum L.) against late blight Phytophthora infestans was studied macroscopically on three potato cultivars with different degrees of resistance to late blight. The cultivars, were Bintje(2), Elin(3) and Matilda(4). Figures within brackets represent resistance to leaf late blight on a scale from 1 to 5, where 5 denotes the highest level of resistance. In vitro propagated cuttings were used in the experiments, which were, performed under controlled environmental conditions. Disease resistance was induced by a local pre-infection with P. infestans or with the nonpathogen P. cryptogea. Induced resistance was observed on all cultivars. The protection causedby, induced resistance tended to be most intense on cv. Matilda, with 50–60% reduction in lesion formation 4 days after challenge inoculation.     

Screening for fire blight resistance in apple (Malus pumila) using excised leaf assays from in vitro and in vivo grown material

The apple cultivars Greensleeves and Novole and somaclones derived from Greensleeves were tested for resistance to fire blight (Erwinia amylovora) using excised leaf bioassays. Cv. Greensleeves was consistently susceptible to fire blight in in vitro, and in glasshouse and excised leaf bioassays whilst cv. Novole was resistant. Greensleeves somaclones, identified as having intermediate levels of fire blight resistance in glasshouse and in vitro screening tests, also showed intermediate levels of resistance in excised leaf bioassays. The length of leaves and the inoculum concentration employed affected the severity of symptoms observed. Excised leaf bioassays were unsuitable as tests for fire blight resistance using field grown material.     

Relationship between Feeding Damage by Beet armyworm,Spodoptera exigua (Lepidoptera: Noctuidae) and Leaf Trichome Density of Potato

The responses (infestation level and feeding preference) of 50 potato cultivars, including seven Korean recommended cultivars to Spodoptera exigua larvae were examined in the field and the laboratory. Based on the number of potato leaves damaged by S. exigua larvae in the field, seven cultivars (Anco, Denali, Bintje, Jidose, Sandra, Shimabara, and Spunta) were found tolerant to the insect attack, whereas Nicola and Dejima cultivars were highly susceptible. In feeding preference tests using leaflets of 10 selected cultivars (Anco, Denali, Bintje, and seven recommended cultivars), no significant differences were seen among the cultivars, indicating no involvement of chemical resistance. In trichome density per mm² leaf area, underside leaf surface contained higher trichome densities than the upper side, and the number of long trichome were distributed four times more than short trichome on average. Total leaf trichome density was the highest on cv. Dejima of 32.1, followed by cvs. Bintje and Denali, but the lowest on cv. Jopung of 6.9. From correlation analysis, infestation level in the field by S. exigua was correlated with the density of shorter trichome on upper side of leaf surface (r = 0.737^* in 1996 and 0.772^** in 1997). However, it was not correlated with the density of the longer trichome on underside.     

A Histological Evaluation of Induced Resistance to Phytophthora infestans (Mont.) de Bary in Potato Leaves

Systemically induced resistance against Phytophthora infestans in the potato cultivar ‘Bintje’ was studied histologically at the light microscopy level on the leaf surface, in the epidermis and in the mesophyll of challenged potato leaves. Systemic disease resistance was induced by a local pre-infection with the same fungus. On the leaf surface of induced plants, the germination of cysts was enhanced. In the epidermis of induced plants, papilla deposition increased and penetration decreased, whereas in the mesophyll of induced plants the spread of hyphae was reduced. It is suggested that the reduction of disease severity in induced plants is the result of the combined action of several successive defence reactions.     

Stability of Sweet Potato Cultivars to Alternaria Leaf and Stem Blight Disease

Alternaria leaf petiole and stem blight is an economically important disease of sweet potato ( Ipomoea batatus L.) in tropical and sub-tropical environments. Published research on cultivar resistance to the sweet potato disease is limited. To evaluate cultivar reaction and stability to the disease, multi-location and replicated experiments were established in 12 environments in Uganda. Disease severity (area under disease progress curves – AUDPC), and cultivar root yield were also assessed. Significant differences (P < 0.001) in AUDPC were detected among cultivars. Mean AUDPC ranged from 46.3 (Araka Red) to 78.4 (New Kawogo) across locations and seasons and the genotypes Araka Red and Tanzania had the lowest disease values. The location and season effects accounted for 67.1% and 7.5% of the total variance of AUDPC recorded among cultivars. The ranking of cultivars based on predicted AUDPC from Additive Main Effect and Multiplicative Interactive model (AMMI) showed that the NASPOT 1, the susceptible check, and New Kawogo were most susceptible to the disease in 11 of the 12 environments. Low and stable disease was consistently recorded and predicted on NASPOT 3 and the landrace cultivars Tanzania, Dimbuca, and Araka Red across environments. These results suggest that landrace cultivars had relative stability to the disease and wide adaptation across environments. These results suggest that AMMI statistical model and other multivariate techniques can be utilized for prediction of Alternaria disease stability in these locations.     

Revealing the importance of meristems and roots for the development of hypersensitive responses and full foliar resistance to Phytophthora infestans in the resistant potato cultivar Sarpo Mira

The defence responses of potato against Phytophthora infestans were studied using the highly resistant Sarpo Mira cultivar. The effects of plant integrity, meristems, and roots on the hypersensitive response (HR), plant resistance, and the regulation of PR genes were analysed. Sarpo Mira shoots and roots grafted with the susceptible Bintje cultivar as well as non-grafted different parts of Sarpo Mira plants were inoculated with P. infestans. The progress of the infection and the number of HR lesions were monitored, and the regulation of PR genes was compared in detached and attached leaves. Additionally, the antimicrobial activity of plant extracts was assessed. The presented data show that roots are needed to achieve full pathogen resistance, that the removal of meristems in detached leaves inhibits the formation of HR lesions, that PR genes are differentially regulated in detached leaves compared with leaves of whole plants, and that antimicrobial compounds accumulate in leaves and roots of Sarpo Mira plants challenged with P. infestans. While meristems are necessary for the formation of HR lesions, the roots of Sarpo Mira plants participate in the production of defence-associated compounds that increase systemic resistance. Based on the literature and on the presented results, a model is proposed for mechanisms involved in Sarpo Mira resistance that may apply to other resistant potato cultivars.     

Induction of a proteinase K inhibitor in a potato cultivar with a high degree of field resistance against Phytophthora infestans

A proteinase K inhibitor (PLPKI) was isolated from a potato cultivar with a high level of field resistance ( Solanum tuberosum L. cv. Pampeana INTA), after 24 h of infection with Phytophthora infestans , when inhibitory activity was markedly increased. Purification was performed by heat treatment, gel filtration chromatography and affinity chromatography. A size of 60 kDa was estimated by SDS-PAGE in partially denaturing conditions and by gel filtration. It is multimeric and the monomer has a molecular mass of 8.5–9.0 kDa. PLPKI is highly active against proteinase K (EC 3.4.21.14) but poorly inhibits two serine proteinases of animal origin, trypsin (EC 3.4.21.4) and chymotrypsin (EC 3.4.21.1). A differential expression (determined by activity and immunoblotting assays) of PLPKI was observed between two potato cultivars with different degrees of field resistance to P. infestans . In the resistant cultivar (cv. Pampeana INTA) PLPKI induction (19-fold with respect to healthy leaves) occurred 24 h after infection and remained over basal levels after 48 h infection. By contrast, in the susceptible cultivar (cv. Bintje), no induction was observed.     

Dorsoventral asymmetry of photosynthesis and photoinhibition in flag leaves of two rice cultivars that differ in nitrogen response and leaf angle

Rice is believed to show photosynthetic symmetry between adaxial and abaxial leaf sides. To verify this, we re‐examined dorsoventral asymmetry in photosynthesis, chlorophyll fluorescence and anatomical traits in flag leaves of two Oryza sativa cultivars that differ in nitrogen (N) response and in leaf angle: ‘Akenohoshi’, a cultivar that can adapt to low‐N (LN), with low leaf angle (more erect leaves), and ‘Shirobeniya’, a cultivar that is unable to adapt to LN, with higher leaf angle. Plants were grown under standard‐N (SN) and LN conditions. LN leaves of both cultivars became more erect than SN, but LN Akenohoshi still had more erect ones than Shirobeniya. Contrary to results of previous studies, leaves of both cultivars showed an asymmetry in photosynthetic rate between adaxial and abaxial sides (higher on the adaxial side) under SN. SN leaves of both cultivars showed lower susceptibility to photoinhibition on the adaxial side than on the abaxial side. However, leaves of Akenohoshi showed less asymmetry in these traits under LN than under SN, whereas leaves of Shirobeniya had similar degrees of asymmetry in these traits under both SN and LN. Both cultivars also showed dorsoventral asymmetry in anatomical traits of mesophyll tissue regardless of N level, but the degree of asymmetry was lower in LN Akenohoshi. These data reveal that rice leaves exhibit dorsoventral asymmetry in photosynthetic and anatomical features, and that the degree of asymmetry varies with cultivar and N level. It is suggested that lower leaf angles (particularly in Akenohoshi) in the presence of LN represent a light acclimation to prevent photoinhibition.     

Responses of potato cultivars (Solanum tuberosum) to infection with Cucumber mosaic virus isolated from different host species

Eight isolates of Cucumber mosaic virus (CMV) isolated from seven different host species were tested for their virulence on potato cv. Desirée. Three isolates caused a systemic infection, of which one isolate from Asiatic lily (CMV-P26) and one from cucumber (CMV-J) appeared to be highly virulent, in contrast to the third isolate (CMV-M) that originated from cucumber and caused mild symptoms only. These three isolates were transmitted to 26 additional potato cultivars by mechanical inoculation in a greenhouse. All cultivars were infected with at least one CMV isolate and developed local chlorotic symptoms, but only 17 cultivars (including Desiree) developed primary systemic symptoms including necrosis, mosaic and/or malformation of leaves. Furthermore, in only five cultivars (including Desiree) CMV was transmitted to tubers and was subsequently detected in plants of the first and second vegetative progeny, the secondary symptoms of these plants being severe. The observed phenotypic responses of potatoes to CMV were not associated with the maturity type (early or late) or resistance to other viruses. Results of this study indicate a high level of biological variability among CMV isolates and that infection in potato depends on CMV isolate and potato cultivar.     

Relationship between Symptom Development and Actual Sites of Infection in Leaves of Anthurium Inoculated with a Bioluminescent Strain of Xanthomonas campestris pv. dieffenbachiae

The infection process of bacterial blight of anthurium was monitored with a bioluminescent strain of Xanthomonas campestris pv. dieffenbachiae. The relationship between symptom expression on infected leaves (assessed visually) and the extent of bacterial movement within tissues (evaluated by bioluminescence emission) varied among anthurium cultivars. In several cultivars previously considered susceptible on the basis of symptom development alone, bacterial invasion of leaves extended far beyond the visually affected areas. In other cultivars previously considered resistant, bacterial invasion was restricted to areas with visible symptoms. In three cultivars previously considered resistant, leaves were extensively invaded by the bacterium, and yet few or no symptoms were seen on infected leaves. The pathogen was consistently recovered from leaf sections emitting bioluminescence but not from sections emitting no light. At an early stage of infection, no significant differences in the percentages of infected areas as determined by visual assessment were observed in any of the cultivars. However, differences among cultivars were detected by bioluminescence as the disease progressed, because bacterial invasion was not always accompanied by symptom expression. In susceptible cultivars, the advancing border of infection was 5 to 10 cm inward from the margins of the visible symptoms and often reached to the leaf petiole even when symptoms were visible in <10% of the total leaf area. Comparisons of anthurium cultivars in which a nondestructive method was used to quantify the severity of leaf infection by a bioluminescent pathogen have enabled us to evaluate susceptibility and resistance to bacterial blight accurately. Such evaluations will be of importance in breeding resistant cultivars for disease control.     

Genetic diversity among late blight resistant and susceptible potato genotypes

RAPD polymerase chain reaction analysis was used to study the genetic diversity among a wild potato variety Solanum demissum (very resistant to late blight) and six potato cultivars (Hanna, Lady-Olympia, Lady-Rosetta, Spunta, Diamant and Cara) varied in their resistance to Phytophthora infestans. Cluster analysis of six potato genotypes showed that, all tested genotypes were separated into two clusters (1 and 2). Cluster 1, included only the wild potato variety (S. demissum), whereas cluster 2 divided into two groups (G1 and G2). Late blight high resistant cultivars Hanna and Cara were grouped in G1. Group 2 included the moderate resistant cultivar Spunta and the susceptible cultivars Diamant, Lady-Rosetta and Lady-Olympia. The potato cultivars that showed highest genetic similarity to the wild potato variety were the resistant cultivars Hanna and Cara. Lowest genetic similarity was obtained with the susceptible cultivars Lady-Rosetta, Diamant and Lady-Olympia. RAPD primer K17 yielded a band with molecular weight of 936 bp found in all susceptible potato cultivars (Lady-Rosetta, Lady-Olympia and Diamant). On the other hand, band with molecular weight of 765 bp were detected in the wild potato and the resistant cultivars Hanna and Cara. Results of this study suggested that, the RAPD marker technique could be beneficial for revealing the genetic variability of different genotypes of potato varied in their resistibility to late blight.     

Observations on blight (Phytophthora infestans) and resistant potatoes at Toluca, Mexico

A late blight epidemic studied at Toluca, Mexico, in 1962 may have started from stems infected at soil level by soil-borne Phytophthora infestans. Its severity was demonstrated by the large differences in the rate foliage was destroyed and in yield of tubers between fungicide-sprayed and unsprayed susceptible and resistant cultivars. The foliage resistances of some Mexican and European cultivars were compared using conventional blight keys and recording the destruction of marked leaves. Cultivars reacted in four ways: (1) Up-to-Date and Alpha leaves were infected and killed soon after plants emerged; (2) Bertita, Conchita and Florita abscissed many infected lower-canopy leaves, and many infections on upper leaves aborted; (3) Elenita leaves had a few lesions in which the fungus grew slowly but remained alive; (4) Greta showed no infection until the potato plants met between rows but then infections developed rapidly and the foliage soon died. Mexican cultivars, except for Elenita, had few blighted tubers; susceptible European cultivars were killed before many tubers formed. Most spores were released during the morning, as in Europe, and leaf infection seemed associated with days with rain when much of the night remained humid. Cool nights lengthened incubation and generation times.     

Transformation of potato (Solanum tuberosum) cv. Mantiqueira using Agrobacterium tumefaciens and evaluation of herbicide resistance

Summary In search of establishing a system for genetic transformation of Brazilian potato cultivars, Agrobacterium tumefaciens carrying the plasmid pGV1040, was used to transform leaf discs of three cultivars of local importance, i.e., Aracy, Baronesa and Mantiqueira. This plasmid contains marker genes for resistance to kanamycin and phosphinothricin plus the gene for the enzyme -glucuronidase. A two step regeneration/selection procedure produced shoots of potato cultivar Mantiqueira with in vitro resistance to kanamycin and to phosphinothricin. After transfer to the greenhouse, the potentially transgenic plants, sprayed with the herbicide Finale^® (20% a.i.; Hoechst^®) remained green as compared to control clones that died immediately afterwards. Southern blot analysis and histochemical and fluorimetric assay for -glucuronidase indicated that the gene coding for the enzyme was integrated in the potato genome and could be expressed in potato tissues. No success was obtained for transformation of cultivars Aracy and Baronesa using this procedure.Abbreviations NAA Naphthalene Acetic Acid - BAP Benzyl-aminopurine - GA₃ Gibberellic Acid - PPT Phosphinothricin - PAT Phosphinothricin Acetyl Transferase     

Resistance of Three Bean Cultivars to Uromyces phaseoli Expressed Through Sporulation of the Fungus

Sporulation of the rust fungus Uromyees phaseoli was checked on three different Brasilian bean cultivars on the upper and lower leaf surface of primary leaves in a growth chamber at 21°C. Although the sporulating area of the pustules was greater on the upper leaf surface, the pustules on the lower leaf surface produced nearly two times more spores on all three cultivars. The total number of spores produced per pustule was 41,600/81,000 spores (upper/ lower leaf surface) for the susceptible cultivar Rosinha G-2/C-21 and for the cultivars which possess horizontal resistance: Carioca/C-224 29,600/49,500 spores (upper/lower leaf surface), Roxo/C-743 32,964/50,700 spores (upper/lower leaf surface). The two cultivars with horizontal resistance produced nearly a third less spores than the susceptible cultivar.     

马铃薯不同品种感染早疫病菌后防御酶活性变化

通过测定抗性不同的马铃薯品种接种和未接种情况下叶片内防御酶活性,研究马铃薯品种对早疫病的抗性机制。结果表明,在接种处理后,各品种植株体内苯丙氨酸解氨酶（PAL）、过氧化物酶（POD）、多酚氧化酶（PPO）和过氧化氢酶（CAT）活性均提高,抗病品种酶活性增幅高于感病品种,说明上述4种酶与品种抗性有一定的关联。     

Alternaria Brassicae Induced Changes in the Activity of Cell Wall Degrading Enzymes in Leaves of Brassica Juncea

After inoculation of Brassica juncea leaves with Alternaria brassicae, activities of the cell wall degrading enzymes, polygalacturonase (EC 3.2.1.15) and cellulase (EC 3.2.1.4) decreased in leaf blight resistant cultivar RC-781 and increased in the susceptible cultivar Varuna upto 3 d. In the leaves of both the cultivars 11 poly-peptides were observed in the absence of A. brassicae inoculation. After inoculation in the resistant cultivar RC-781 there was no change in the polypeptide pattern, while in the susceptible cultivar Varuna, four polypeptides (43.7 to 58.8 kDa) disappeared only at 3^rd day after inoculation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Comparative analysis of Phytophthora infestans induced gene expression in potato cultivars with different levels of resistance

Differential gene expression was analyzed after infection with Phytophthora infestans in six potato cultivars with different levels of resistance to late blight. To verify the infection of the potato leaflets, the amount of phytopathogen mRNA within the plant material was quantified by real-time quantitative PCR. The expression of 182 genes selected from two subtracted cDNA libraries was studied with cDNA array hybridization using RNA from non-infected and infected potato leaflets. Gene up- and down-regulation were clearly detectable in all cultivars 72 h post inoculation. Gene expression patterns in susceptible cultivars differed from those in potato varieties with a higher level of resistance. In general, a stronger gene induction was observed in the susceptible cultivars compared to the moderately to highly resistant potato varieties. Five genes with the highest homology to stress and/or defence-related genes were induced specifically in the susceptible cultivars. Four genes responded to pathogen attack independently of the level of resistance of the cultivar used, and three genes were repressed in infected tissue of most cultivars. Even in the absence of P. infestans infection, six genes showed higher expression levels in the somewhat resistant cultivars Bettina and Matilda. Possible reasons for the different levels of gene expression are discussed.     

Screening landraces for additional sources of field resistance to cassava mosaic disease and green mite for integration into the cassava improvement program

Twelve cassava landraces were evaluated for sources of resistance genes to diseases and pests of major economic importance in Africa. The objective was to assess their levels of field resistance to mosaic disease （ACMD）, bacterial blight （CBB）, anthracnose （CAD）, and green mite （CGM）, compared to TMS30572, an elite cultivar widely adopted in Africa. Considerable genotypic variation was observed among cultivars for resistance to ACMD and CGM but not for CBB and CAD. The lowest mean incidence of 12% and severity of 1.8 on a scale of 1-5 for ACMD was recorded for Atu, a landrace with farmer acceptable qualities. In comparison, the improved cultivar, TMS 30572, had a mean disease incidence of 72% and a severity score of 2.8. Another landrace, MS-20 had the lowest CGM damage score （2.1） while TMS 30572 emerged as one of the susceptible cultivars with a damage score of 3. Additional sources of resistance to ACMD and CGM that may possibly be better than the popular improved cultivar, TMS 30572, were identified in this study. These could serve as novel sources of additional genes to complement existing resources for elite cassava breeding in Africa.