Direct Delivery of Inoculum to Shoot Tissue Interferes with Genotypic Resistance to Ralstonia solanacearum in Tomato Seedlings

Employing known susceptible and resistant genotypes and pure bacterial inoculum (0.1 OD; 10⁸ CFU/ml^?1), five different inoculation methods were tried to assess the response of tomato genotypes to Ralstonia solanacearum. This included seed‐soaking inoculation, seed‐sowing followed by inoculum drenching, or at 2‐week stage through petiole‐excision inoculation, soaking of planting medium with inoculum either directly or after imparting seedling root‐injury. Seed‐based inoculations or mere inoculum drenching at 2 weeks did not induce much disease in seedlings. Petiole inoculation induced 90–100% mortality in susceptible checks but also 50–60% mortality in normally resistant genotypes within 7–10 days. Root‐injury inoculation at 2‐week seedling stage appeared the best for early and clearer distinction between resistant and susceptible lines. The observations suggest a role played by the root system in governing genotypic resistance to the pathogen. Direct shoot inoculation is to be adopted only for selecting highly resistant lines or to thin down segregating populations during resistance breeding.     

Mapping of quantitative trait loci for partial resistance to<Emphasis Type="Italic"> Mycosphaerella pinodes</Emphasis> in pea (<Emphasis Type="Italic">Pisum sativum</Emphasis> L.), at the seedling and adult plant stages

The inheritance of resistance to Ascochyta blight, an economically important foliar disease of field pea (Pisum sativum L.) worldwide, was investigated. Breeding resistant pea varieties to this disease, caused by Mycosphaerella pinodes, is difficult due to the availability of only partial resistance. We mapped and characterized quantitative trait loci (QTLs) for resistance to M. pinodes in pea. A population of 135 recombinant inbred lines (RILs), derived from the cross between DP (partially resistant) and JI296 (susceptible), was genotyped with morphological, RAPD, SSR and STS markers. A genetic map was elaborated, comprising 206 markers distributed over eight linkage groups and covering 1,061 cM. The RILs were assessed under growth chamber and field conditions at the seedling and adult plant stages, respectively. Six QTLs were detected at the seedling stage, which together explained up to 74% of the variance. Ten QTLs were identified at the adult plant stage in the field, and together these explained 56.6–67.1% of the variance, depending on the resistance criteria and the organ considered. Four QTLs were detected under both growth chamber and field conditions, suggesting they were not plant-stage dependent. Three QTLs for flowering date and three QTLs for plant height were also identified in the RIL population, some of which co-located with QTLs for resistance. The relationship between QTLs for resistance to M. pinodes, plant height and flowering date is discussed.Communicated by H.C. Becker     

Quantitative resistance of some Elite wheat lines to Puccinia striiformis f. sp. tritici

Host resistance is the most economical way to manage wheat stripe rust caused by Puccinia striiformis f. sp. tritici. Slow rusting, a type of quantitative resistance, has been reported to last for a long time. Quantitative resistance, in terms of slow rusting parameters including final rust severity (FRS), apparent infection rate (r), relative area under disease progress curve (rAUDPC) and coefficient of infection (CI), was evaluated in a set of 29 wheat genotypes along with susceptible control during 2008–2009 and 2009–2010 cropping seasons. This study was conducted in field plots at Ardabil Agricultural Research Station (Iran) under natural infection conditions with two times artificial inoculation. Artificial inoculation was carried out by yellow rust inoculum having virulent genes against Yr2, Yr6, Yr7, Yr9, Yr22, Yr23, Yr24, Yr25, Yr26, Yr27, YrA and YrSU. Results of mean comparison for resistance parameters showed that lines C-86-1, C-86-2, C-87-1 and C-87-3 along with susceptible had the highest values of FRS, CI, r and rAUDPC, therefore were selected as susceptible lines. The lines C-86-3, C-86-9, C-87-2, C-87-6, C-87-8, C-87-11 and C-87-18 were susceptible at the seedling stage and had low level infection at adult plant stage. Consequently, these lines with low different parameters most probably have slow rusting resistance. The remaining lines had no infection or were at low level of infection. Thus, they were selected as resistant or moderately resistant lines. In this study, correlation coefficient between different parameters of slow rusting was significantly high (r = 0.92–0.99).     

Screening for Barley yellow dwarf virus-Resistant Barley Genotypes by Assessment of Virus Content in Inoculated Seedlings

The content of Barley yellow dwarf virus (BYDV) in roots and leaves of barley seedling plants differing in their level of resistance was assessed by quantitative ELISA 1–42 days after inoculation with the strain of BYDV (PAV). High virus accumulation in roots and low concentration in leaves was characteristic of the period 9–15 days after inoculation. In leaves, the differences in virus content between resistant and susceptible genotypes became significant after 15 days and resistance to virus accumulation was better expressed 30–39 days after inoculation. Roots of resistant materials exhibited evident retardation of virus accumulation and the greatest difference in virus content between resistant and susceptible plants was detected 9 days after inoculation. By these criteria, the selected winter and spring barley cultivars and lines (in total 44 materials) fell in to five groups according to field reactions and the presence or absence of the Yd2 resistance gene. There were highly significant and positive relations between ELISA values and 5‐year field data on symptomatic reactions and grain‐yield reductions due to infection. Using the described method, resistant and moderately resistant genotypes (both Yd2 and non‐Yd2) were significantly differentiated from susceptible genotypes. The possible use of this method in screening for BYDV resistance is discussed.     

Effects of Ozone Exposure on Resistance of Wheat Genotypes to Pyrenophora tritici-repentis

Three spring wheat genotypes, susceptible, moderately resistant or resistant to Pyrenophora tritici-repentis (tan spot fungus) were exposed to charcoal-filtered air and to approx. 80, 160, 240 (g m^?3 ozone for five consecutive days (7 h per day). Visible leaf injury on seedling plants (three-leaf stage) was only observed after fumigation with 160 or 240 (g m^?3 O₃. Amount of injury was four-fold and 10-fold on the susceptible genotype when compared to resistant or moderately resistant genotype at the two highest concentration of ozone, respectively. Genotypic differences to O₃ tolerance were detected at the seedling growth stage (three-leaf stage) and flowering stage but not at the stem elongation stage. A significant increase in tan spot lesion area was observed only on O₃ predisposed second top most leaves of the susceptible genotype at all the three levels of ozone. Predisposition did not enhance tan spot development in resistant and moderately resistant genotypes. In a test with 12 wheat genotypes, a highly significant positive correlation (r = 0· 986, p < 0· 0001) was observed between ozone sensitivity (percent leaf area damaged due to 240 (g m^?3 ozone exposure) and tan spot development (mm² lesion area) following inoculation with P. tritici-repentis. It indicates that wheat genotypes resistant to the tan spot fungus might be tolerant to ozone damage.     

A cotyledon double inoculation technique for evaluating resistance to anthracnose (Colletotrichum orbiculare) and scab (Cladosporium cucumerinum) in cucumber

A technique for simultaneous inoculation of cucumber cotyledons with Colletotrichum orbiculare race 1 and Cladosporium cucumerinum has been developed. The procedure permitted both resistant and susceptible plants to be recovered. Seedlings were grown at 20°C and inoculated 24 h after emergence with Colletotrichum orbiculare (200 spores in 2 μ1 of water) and Cladosporium cucumerinum (1000 spores in 5 μ1 of water) followed by 48 h of incubation in the dark at 20°C and 100% r.h., and 48 h in a 20°C lighted growth chamber. Seedlings were then moved to a growth chamber at 21°C at night and at 26°C during the day for 4 days and plants were rated as resistant or susceptible 8 days after inoculation. No interference in the expression of resistance or susceptibility of cultivars to either pathogen was detected in simultaneous inoculations.     

A greenhouse assay to screen sunflower for resistance to Alternaria helianthi

A greenhouse assay to screen sunflower for resistance to Alternaria helianthi is described. A comparison of conditions led to the following standard conditions being recommended. The first or second pair of leaves of seedling plants at the V8 growth stage are inoculated using inoculum grown on sunflower leaf extract agar for 5–10 days at an inoculum density of 1–2 spores cm² of leaf tissue. A 48 h dew period should be applied to plants covered by a plastic tent. A dew period temperature of 26/26°C night/day and a post-dew period temperature relative to that experienced under local growing conditions should be applied. Lesions are measured 7 days after inoculation, and mean lesion size per plant is calculated. Mean lesion size of lines being tested is expressed as a proportion of the mean lesion size of a susceptible standard included in each screening experiment.     

Evaluation of some Iranian wheat elite lines’ reaction to Septoria tritici leaf blotch

Septoria tritici blotch is an important wheat disease in many areas of the world including Iran’s warm, humid regions. In this study, reaction of 79 lines from elite regional wheat yield trials of the Cereal Research Department from four climate zones was evaluated to S. tritici leaf blotch in adult plant stage under an artificial field inoculation in Khuzestan province in the south of Iran for two years (2008–2009 and 2009–2010). Nurseries were artificially inoculated by spreading infected plant debris (from last growing season). Taking notes was performed with a modified Saari and Prescott method in 00–99 double-digit scale. Wheat lines were classified in groups of immune (00), highly resistant (11–14), resistant (15–34), moderately resistant (35–44), moderately susceptible (45–64), susceptible (65–84) and highly susceptible (85–99). Result showed that from 79 lines, 37 lines had susceptible reaction; 2 lines had moderately susceptible; and 40 lines showed immune.     

Modification of Resistance Expression of Phaseolus vulgaris to Meloidogyne incognita by Elevated Soil Temperatures

The effect of temperature on the reaction of susceptible (Canario Divex) and resistant (A 211) bean pure lines to Meloidogyne incognita was studied with soil temperature tanks housed in a growth chamber at 22 or 24 C. Soil temperature remained constant at 16, 22, 24, 26, 30, or 32 C in several trials. Bean line A 211 was resistant at 16 and 22 C but was susceptible at 24 C and above. Resistance to root-knot nematode reproduction was affected by a lower temperature (24 C) than was resistance to root galling (26 C) in A 211. Incubation of A 211 at 30 C for 3 and 16 days after inoculation with M. incognita resulted in a significant increase in nematode reproduction and root galling, respectively. The resistant reactions of A 211 to nematode reproduction and root galling were retained when inoculated plants were incubated at 21 C for a minimum of 16 and 23 days, respectively, prior to high temperature treatment.     

Further Investigation of the Specificity of Interactions Between Wild Lactuca spp. and Bremia lactucae Isolates from Lactuca serriola

Callus cultures derived from isogenic lines of the tomato cultivars Moneymaker and Craigella, resistant or susceptible to F. oxysporum f. sp. lycopersici, were inoculated with Fusarium oxysporum f. sp. lycopersici race 1. Fungal growth was restricted on callus derived from resistant plants, after inoculation with a conidial suspension, whereas callus derived from susceptible plants was totally overgrown by the fungus within 7 days. The concentration of the phytoalexin rishitin was significantly higher in the callus culture derived from a resistant tomato line compared with the callus culture from a susceptible line, 2 and 3 days after inoculation with mycelium. The results of the experiments were compared with experiments with whole plants. Rishitin production as well as growth of the fungus was comparable with responses in plant-fungus interaction. Therefore callus culture may be useful in studying the interaction between tomato plants and race 1 of F. oxysporum f. sp. lycopersici.     

Comparison of transcript profiles in different life stages of the nematode Globodera pallida under different host potato genotypes

The potato cyst nematodes (PCNs) Globodera pallida and Globodera rostochiensis are important parasites of potato. PCNs undergo complex biotrophic interactions with their hosts that involve gene expression changes in both the nematode and the host plant. The aim of this study was to determine key genes that are differentially expressed in Globodera pallida life cycle stages and during the initiation of the feeding site in susceptible and partially resistant potato genotypes. For this purpose, two microarray experiments were designed: (i) a comparison of eggs, infective second‐stage juveniles (J2s) and sedentary parasitic‐stage J2s (SJ2); (ii) a comparison of SJ2s at 8 days after inoculation (DAI) in the susceptible cultivar (Desirée) and two partially resistant lines. The results showed differential expression of G. pallida genes during the stages studied, including previously characterized effectors. In addition, a large number of genes changed their expression between SJ2s in the susceptible cultivar and those infecting partially resistant lines; the number of genes with modified expression was lower when the two partially resistant lines were compared. Moreover, a histopathological study was performed at several time points (7, 14 and 30 DAI) and showed the similarities between both partially resistant lines with a delay and degeneration in the formation of the syncytia in comparison with the susceptible cultivar. Females at 30 DAI in partially resistant lines showed a delay in their development in comparison with those in the susceptible cultivar.     

海南普通野生稻稻瘟病抗性资源调查和鉴定

为挖掘海南普通野生稻稻瘟病抗性资源,2010年诱发鉴定了41个居群410份材料苗期叶瘟,2011年接种稻瘟病菌（YC25）鉴定了37个居群121份材料穗颈瘟,2012年调查了80个居群2461份材料田间自然状态的抗病性。结果表明：苗期叶瘟抗性鉴定有21份高抗、117份抗病。苗期抗、高抗叶瘟性的138份材料中穗颈瘟鉴定4份高抗和3份抗病,14份表现为田间自然抗病。苗期叶瘟鉴定不抗病或未作此鉴定材料中,4份表现为抗穗颈瘟和田间自然抗病。这些抗性材料来自海口、文昌、万宁、三亚、澄迈、东方等地。本研究为海南普通野生稻资源进一步研究和抗稻瘟病育种利用提供参考     

A cotyledon screen for resistance to scab (Cladosporium cucumerinum) in cucumber (Cucumis sativus) seedlings

An efficient protocol for differentiating cucumber (Cucumis sativus) seedlings resistant and susceptible to scab (Cladosporium cucumerinum) has been developed by examining the interacting factors of spore density and cotyledon growth stage. The procedure permitted both resistant and susceptible plants to be recovered. Seedlings were grown at 20°C and inoculated 1 day after emergence by placing a 5 μl inoculum droplet (2 × 10⁶ spores/ml) on the newly expanded cotyledons. Seedlings were incubated in a darkened dew chamber for 48 h at 20°C and 100% r.h., and then grown for 6 days at 20°C. Plants could be rated as resistant or susceptible 8 days after inoculation.     

Dr. Heinz rogoll‐70 Jahre

The wheat crop remains vulnerable to all three rust diseases (leaf rust, stem rust and yellow rust) caused by Puccinia spp. according to the prevalence of the pathogen in different wheat-growing areas worldwide. Stripe rust or yellow rust caused by Puccinia striiformis f. sp. tritici is the most significant rust pathogen which prefers cool, moist areas and highlands. The pathogen is recognised as responsible for huge production losses in wheat. Genetic variation in pathogen makes its control difficult. Therefore, resistance against all the races of the pathogen known as durable or race-non-specific resistance is preferred. The present study was carried out to identify durable resistance against stripe rust in selected wheat cultivars from Pakistan through seedling testing, field evaluation at adult stage, morphological marker studies and marker-assisted selection. Results revealed that 4% of the cultivars were resistant at the seedling stage while the rest were susceptible or intermediate. To confirm their field resistance, the same cultivars were evaluated under field conditions at Cereal Crops Research Institute Pirsabak (located in Khyber Pakhtunkhwa, KP) a hot spot of stripe rust in Pakistan. Observations exhibited that at the adult stage 4% of the cultivars were resistant, 70% intermediate or moderately resistant while the others were highly susceptible. Leaf tip necrosis was observed in 30% of the cultivars. Wheat cultivars showing susceptibility at the seedling stage were highly to moderately resistant at adult stage showing durable resistance. For further validation, morphological markers were also observed in cultivars indicating the presence of Yr18/Lr34 gene. Eleven cultivars (C-518, Mexipak, Kohinoor-83, Faisalabad-83, Zardana-93, Shahkar-95, Moomal-2002, Wattan-94, Pasban-90, Kiran-95, and Haider-2000) were identified, having durable or race non-specific resistance against stripe rust. These cultivars can further be utilised in wheat breeding programmes for deploying durable resistance to attain long lasting control against stripe rust.     

The mechanism and inheritance of adult plant leaf rust resistance in 12 wheat lines.

Twelve lines of wheat (Triticum aestivum L.) were developed that had susceptible infection types to leaf rust (Puccinia recondita Rob. ex Desm. f.sp. tritici) race UN 15 in the seedling stage but were resistant in the adult plant stage in the field. The lines were developed from four crosses, each involving four parents (eight in total) that had originally been selected for adult plant or field resistance to stem rust (Puccinia graminis Pers. f.sp. tritici Eriks, and Henn.). The objectives of the present study were to determine the mechanism of resistance to leaf rust and its inheritance in the 12 lines. The 12 lines were grown in an artificially inoculated field nursery in Saskatoon, coefficients of infection (CI) were determined at four dates, and the areas under the disease progress curve (AUDPC) were calculated. Four representative lines were grown in a growth chamber to measure the latent period and pustule size at the two-leaf and flag-leaf stages. Eight lines were crossed and backcrossed to a susceptible check and the parents, F1, F2, F3, and BC1F2 generations were grown in a field nursery. The 12 lines showed wide ranges in CI and AUDPC but all were significantly more resistant than the susceptible check. The four lines studied in the growth chamber had longer latent periods and smaller pustules than the susceptible check at both stages. The differences tended to be greater at the flag-leaf stage. The inheritance studied showed that resistance was recessive or partially recessive and was controlled by two or more genes in each line of the eight lines. In three of the eight lines, Lr34 may be one of the genes and in the other five both Lr13 and Lr34 could be present. However, additional genes are clearly involved. A single gene by itself had only a small effect, but in two and three gene combinations the effects appeared to be greater. This type of resistance appears to occur frequently and may be durable because its complex inheritance may make it more difficult for the rust fungus to overcome. It should be used in breeding wheat for areas where leaf rust is a major problem.     

Leaf Disk Inoculation — a Useful Tool for Selecting Infections of Sunflower Downy Mildew at Low Inoculum Concentration, but Inappropriate to Pathotype Characterization

A modified technique for leaf disk inoculation of sunflower with zoosporangia of the downy mildew pathogen Plasmopara halstedii was developed. Infection with low concentrations of inoculum was obtained down to the level of single sporangia. No significant difference in the infection rate was seen between disks from cotyledons and true leaves. This makes leaf disk inoculation particularly suitable for infections at low sporangium density and for the investigation on plant tissue which cannot be infected with whole seedling inoculation. The technique seems, however, to be inappropriate for pathotype characterization using differential host lines.     

The determination of physiological race of Fusarium oxysporum f. sp. lycopersici of tomato in Zhejiang, China

A group of differential tomato lines was used to identify the races of Fusarium oxysporum f. sp. lycopersici in Zhejiang, China. Marmande verte carries no resistant genes and Marporum carries gene I-1. Both lines Motelle and Mogeor have Gene I-1 and I-2. Tomato seedlings of eighteen days after sowing were inoculated with an isolate of Fusarium oxysporum f. sp. lycopersici, No. 98-2 and kept in a growth chamber. The seedlings were evaluated at fourteen days after inoculation. Results showed that Marmande verte and Marporum were severely infected by the pathogen and established as susceptible. Motelle and Mogeor were not infected and established as resistant. These results indicated that the isolate No. 98-2 represented the race 2 of Fusarium oxysporum f. sp. lycopersici and gene I-2 is necessary for obtaining resistance to this pathogen in the Zhejiang region.     

番茄苗龄对晚疫病生理小种T1的抗性表现差异研究

对感病和抗病品系3、6、9叶苗龄番茄幼苗人工接种晚疫病菌T1小种,结果表明,感病品系随着苗龄的增加,对晚疫病的感病程度有所减轻,其中6叶期较3叶期、9叶期较6叶期幼苗的病级指数分别降低了28.8%和3.9%,但差异不显著;9叶期较3叶期降低了31.0%,差异达显著水平。抗病品系的6叶期和9叶期较3叶期幼苗病级指数均降低了50%左右,差异达极显著水平;6叶期和9叶期幼苗抗性基本相同。     

Competition for canopy cover between accessions of Phalaris minor that are susceptible and resistant to ACCase inhibiting herbicides

Herbicide resistance has the potential to impose fitness costs in plants. In Mexico, Phalaris minor Retz. has evolved resistance to acetyl‐coa carboxylase (ACCase) inhibiting herbicides. However, it is unknown whether these changes may involve other ecological costs for resistant individuals under non‐selective conditions. The aim of this study was to determine whether the evolution of resistance has reduced the ability of P. minor to compete for resources at the seedling stage. De Wit's replacement series experiments (susceptible:resistant 100:0, 50:50, 0:100) were performed under two initial conditions. In the first experiment, we examined the effect of differences in germination time between resistant and susceptible genotypes on canopy cover. In the second experiment, germination was synchronized, and all the replacement series began at the same time. Delayed germination of resistant accessions reduced their ability to compete for canopy space, competition intensity index, and relative productivity in relation to susceptible accessions. When germination was synchronized, the resistant accessions had the same canopy cover and productivity as susceptible accessions. The delayed germination may cause displacement of resistant individuals in the absence of the selective factor (herbicide).     

Local and systemic changes in glucosinolates in Chinese and European cultivars of oilseed rape (Brassica nap us L.) after inoculation with Sclerotinia sclerotiorum (stem rot)

Four Chinese Brassica napus lines, generated through a breeding programme to identify Sclerotinia sclerotiorum tolerant and susceptible lines, and three European varieties were analysed for changes in glucosinolates (qualitative and quantitative), and general host reactions, after localised inoculation with a UK S. sclerotiorum isolate. Plants at the fifth leaf stage were either singly inoculated (third leaf) or were inoculated once (third leaf) and then challenged a second time (seventh leaf) 7 days after the first inoculation. The results showed very distinct reactions in the different lines and cultivars to the fungus, both locally and systemically. Of the European lines B. napus cv. Bienvenu showed good resistance (small lesions and less host damage) both 3 and 7 days post-inoculation. Capricorn was the most susceptible followed by Cobra; the third leaves of these cultivars were showing strong chlorotic and necrotic reactions by day 3 and lesions were well developed. By day 7 the third leaves of Capricorn were completely rotten whilst Cobra still had a little healthy tissue. Inoculation of the four Chinese lines showed that two had moderate resistance (014 and 020 — slightly less resistant than Bienvenu) and two were very susceptible (016 and 024 — similar reactions to Capricorn and Cobra), based on lesion size and host tissue damage. Glucosinolate induction in line 014 was good both locally and systemically, with clear local and systemic induction of indolylglucosinolates and 2-phenylethylglucosinolate both 3 and 7 days post-inoculation. Line 020 did not show no particular increases in glucosinolates after inoculation either locally or systemically. In line 016 there was a small local increase and a large systemic reduction in total glucosinolates. Inoculation of line 024 caused no major local changes in glucosinolates and again a big reduction in glucosinolates systemically. The dual inoculation system, with lines 014 and 016, produced comparable results, with line 014 showing good local and systemic induction of glucosinolates (after the first inoculation) and a further local and systemic induction after the second inoculation. This induction in pre-inoculated line 014 plants was associated with a reduction in lesion size of the second inoculum. Line 016 responded poorly both locally and systemically, and there were no real decrease in the lesion size of the second inoculum. It appears that in line 014 glucosinolate induction may be an important part of resistance, whereas in line 020 there are clearly other non-glucosinolate factors involved. The poor local and systemic induction of glucosinolates in lines 016 and 024, and subsequent susceptibility, implies that glucosinolate induction may be an important marker of resistance to S. sclerotiorum in oilseed rape.