Breeding and selection of Buxus for resistance to Calonectria pseudonaviculata

Box blight is a widespread disease of Buxus caused by the pathogen Calonectria pseudonaviculata. It is responsible for significant losses in nurseries, gardens and wild boxwood populations. Our goal was to maximize the efficiency of a breeding programme towards increased disease resistance. The use of artificial inoculation of young F1 seedlings with C. pseudonaviculata spores under greenhouse conditions appeared to be a reliable tool for early selection of interesting prebreeding material. Overall, the four hybrid populations screened showed a segregating behaviour between their parents when determining the percentage of diseased leaves and lesion diameter. Genotypes were also found with an increased tolerance as compared to the parental species. Approximately 50% of the seedlings had the same score for both parameters after artificial inoculation in the greenhouse and in the field. Of the seedlings that showed severe symptoms in the greenhouse, <15% showed no disease symptoms in the field. Therefore, for larger breeding programmes, we propose a two‐step selection procedure: first artificial inoculation at seedling level to eliminate all genotypes with severe symptoms and then evaluation of the remaining seedlings in the field. Using this strategy, we were able to select several genotypes in our four hybrid populations with improved resistance to C. pseudonaviculata.     

Induction of resistance in tomato against cucumber mosaic cucumovirus by plant growth-promoting rhizobacteria

Studies were done to evaluate specific strains of plant growth promoting rhizobacteria (PGPR) for induced resistance against cucumber mosaic cucumovirus(CMV) in tomato. In greenhouse experiments where plants were challenged by mechanical inoculation of CMV, the percentage of symptomatic plants in the most effective PGPR treatments ranged from 32 to 58%,compared with 88 to 98% in the nonbacterized, challenged disease control treatment. Field experiments were conducted in 1996 and 1997 to evaluate 4 PGPR strain treatments based on superior performance in the greenhouse studies. In the 1996field experiment, tomato plants treated with 3 PGPR strains exhibited a significantly lower incidence of CMV infection and significantly higher yields, compared with nonbacterized, CMV-challenged controls. In 1997, the overall percentages of plants infected with CMV in the control and PGPR treatments was higher than in 1996. CMV symptom development was significantly reduced on PGPR-treated plants in 1997compared with the control, but the percentage of infected plants and tomato yields were not significantly different among treatments. These results suggest that PGPR-mediated induced resistance against CMV infection following mechanical inoculation onto tomato can be maintained under field conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

水稻稻瘟病和纹枯病抗性鉴定方法

水稻(Oryza sativa)是世界上最重要的粮食作物, 但稻瘟病和纹枯病等病害严重危害水稻的产量和品质, 给我国乃至全球粮食安全带来巨大威胁。鉴定水稻抗病资源、克隆抗病基因、揭示抗性机理并在育种中加以利用, 对抵御水稻病害和保障粮食安全具有十分重要的作用。准确评价水稻资源的抗病性, 是开展抗病机理研究和育种生产应用的关键环节。该文详述了水稻幼苗期人工喷雾接种、分蘖期和孕穗期田间注射接种与离体叶片戳伤接种的稻瘟病抗性鉴定方法, 以及水稻分蘖期田间接种、孕穗期温室接种和离体茎秆接种的纹枯病抗性鉴定方法, 以期为同行鉴定水稻资源、开展抗病理论和应用研究提供参考。     

Plant resistance to fungal diseases induced by the infection of cucumber mosaic virus attenuated by satellite RNA

Biological control agents (BCAs) composed of attenuated cucumber mosaic (CMV) and its satellite RNA for controlling CMV diseases were found to induce plant resistance to a number of fungal diseases. Tests conducted in both the field and greenhouse showed evident protective effects against fungal infections by the BCAs. Artificial inoculation with a fungal spore suspension using BCA-treated plants, satellite transgenic plants and plants infected with CMV alone indicated that the resistance to fungi was induced by the virus infection, not by the presence of satellite RNA.     

A glasshouse screening method to assess resistance in onions to damage by onion fly (Delia antiqua) larvae

Factors influencing the resistance of onion (Allium cepa) cultivars to onion fly (Delia antiqua) damage were investigated. These included different environments, methods of plant raising and egg inoculation, and plant size. A glasshouse compartment maintained at 14 to 37 °C was as satisfactory for assessing the resistance as a controlled environment. The basic test unit comprised 10 onion seedlings raised in a 400 × 50 × 50 mm deep plastic trough and inoculated with 50 onion fly eggs from a laboratory culture. Resistance was assessed by counting wilted plants every two or three days for 21 days after egg inoculation. The reciprocal of number of days for each plant to wilt (wilting rate) was an appropriate variate for statistical analysis, adjusted for the length of the longest leaf at the time of inoculation. The method enables cultivars or breeding lines of onion species to be reliably screened for resistance to larvae of this pest in a glasshouse so that only the most promising need be tested in the field.     

Evaluation of Cultivars,Experimental Lines and Plant Introduction Collection of Sainfoin for Resistance to Meloidogyne hapla Chitwood

Stands of several cultivars and experimental lines of sainfoin (Onobrychis viciifolia) were severely reduced (92% average loss) in a field naturally infested with Meloidogyne hapla. Stands of two alfalfa cultivars included in the test were unaffected. In studies conducted in the greenhouse with plants inoculated at the time of seeding, average mortality was 55% for sainfoin entries and 7% for Ladak alfalfa. Little mortality occurred when plants were inoculated after establishment. Three months after inoculation, all sainfoin entries were heavily galled (range of 3.3-3.7 on a scale of 1-4) while roots of Ladak were only slightly galled (rating of 1.6). Intermating of plants selected in the field plots for resistance to M. hapla showed a slight increase in resistance. Of the 147 plant introduction lines tested in the greenhouse, none were resistant to M. hapla.     

The influence of foliar applications of sugars on the susceptibility of sugar beet to downy mildew

Spraying sugar-beet seedlings in the glasshouse, with 1% or 10% solutions of sucrose, 24 h before inoculation with Peronospora farinosa, significantly reduced their susceptibility to downy mildew. The proportion of inoculated plants that became infected was reduced by spraying with sucrose but the main effect was the inhibition of sporulation. Applications of glucose or fructose also increased the resistance of beet seedlings to P. farinosa. Spraying with sucrose 1 or 2 days before inoculation was much more effective than was spraying shortly before inoculation, or 24 h afterwards, or adding sucrose to the inoculum. Washing sucrose-sprayed seedlings with distilled water 1–2 h before inoculation removed only part of the effect of sucrose on sporulation. Although the mechanism by which applications of sugars affected susceptibility to downy mildew is not understood, the results suggest that the main effects occurred inside the host plant rather than externally. The possible significance of these results, in breeding for resistance to downy mildew and in the control of this disease in the field, is discussed.     

Effects of Inoculation with a Mild Strain of Tomato Aspermy Virus on the Growth and Yield of Tomatoes and the Potential for Cross Protection

Mechanical inoculation of seedlings of 26 tomato cultivars with an attenuated strain of tomato aspermy virus (TAV-M, ATCC # PV361) resulted in development of only mild symptoms, which had largely disappeared by the time the infected plants had begun to set fruit. Yield trials revealed that plants inoculated with TAV-M when transplanted at the 6–8 leaf stage displayed no delay in fruit set and had yields only slightly less than uninoculated plants. Cross protection studies carried out in the greenhouse revealed that TAV-M has the potential to interfere with infection of tomato seedlings by a more severe TAV strain (ATCC # PV127). ‘Pik-Red’ seedlings inoculated with TAV-M showed a significant reduction in symptom expression when challenged with the Blencowe strain of TAV 21 days after the initial inoculation with TAV-M; interference was incomplete at 7 and 14 days.     

The relative contributions of sexual reproduction and clonal propagation in Opuntia rastrera from two habitats in the Chihuahuan Desert

1 The clonal cactus Opuntia rastrera shows predominantly sexual reproduction in grasslands (GH) and clonal propagation in nopaleras (NH). We assessed the effects of light, herbivory, water availability and the habitat an offspring came from on the survival and growth of sexual or clonal offspring (i.e. seedlings and cladodes), through 3- and 4-year common garden and short-term greenhouse experiments.
2 Shading by nurse plants increased seedling survival in the field by an order of magnitude, and a small additional advantage due to predator protection by grasses was observed. Strong herbivory transforms a facultative nurse–protégé relationship for seedlings into an obligatory one.
3 In the greenhouse seedlings grew better under shade, but in the field the production of the first cladode was delayed in seedlings in the more shaded GH. Competition for soil resources may be more intense under a dense grass tussock than under a open shrub, thus affecting the nurse–protégé relationship. Seedling survival under nurse plants was similar in GH and NH, but higher plant cover suggests that a larger number of seedlings will establish in GH in the long term.
4 Cladode survival was higher in NH. Cladodes were more successful than seedlings at establishing in intercanopy areas, possibly due to physiological differences as well as their ability to survive partial predation. Cladode survival in intercanopy areas may explain the enhanced clonal propagation in the more open NH scrubland, together with their susceptibility to the flooding which affects GH.
5 The high seedling and cladode survival in the greenhouse experiments contrasted with that observed in the field, indicating that survival is determined by the interaction between herbivores, plants and abiotic conditions rather than the physiological aptitude of the plants.     

Early season root production and zoospore infection of cultivars of flue-cured tobacco that differ in level of partial resistance to Phytophthora parasitica var. nicotianae

Root production of four cultivars of flue-cured tobacco was quantified in the field, greenhouse and phytotron. The cultivars ranged in level of partial resistance to the black shank pathogen, Phytophthora parasitica var. nicotianae, from susceptible to highly resistant. In the field, root-observation plates were installed approximately 10 cm from plants, and in greenhouse and phytotron studies, plants were grown in 4-liter containers with one sloping transparent side for root observation. Root growth was determined weekly for four weeks after transplanting in the field and daily up to 14 days after transplanting in the greenhouse and phytotron. Root tracings were made on acetate sheets placed against the sloping transparent side of the containers or against the transparent observation plates in the field following removal of soil from the outside of the observation plate. Root growth was quantified by retracing the root pattern on the acetate sheets over a digitizing tablet attached to a personal computer. Numbers of roots, root length, and mean and maximum rate of root growth were determined. Cultivars Hicks (susceptible) and K-326 (low level of resistance) had significantly larger root systems than moderately resistant G-28 or highly resistant NC 82. Differences in total root length were due to increased branching that resulted in development of significantly greater numbers of roots in Hicks and K-326. For example, between day 21 and 28, Hicks produced more than three times the number of new roots as NC 82 in the field. The mean rate of root extension observed (2.17 mm hr^–1) was similar in all four cultivars. Infection efficiency on the different cultivars was determined in the field by inoculating roots with zoospores of P. p. nicotianae. Lesions were visible as water soaked areas within 24 hr of inoculation. At 48 hr after inoculation, percentages of inoculations that resulted in lesion formation were 57, 46, 23, and 16% for Hicks, K-326, G-28 and NC 82, respectively. The possible role of rooting intensity as a mechanism of avoidance to P. p. nicotianae in tobacco cultivars is discussed.     

Genotypic responses of scab-resistant apple cultivars/selections to two strains of Erwinia amylovora and the inheritance of resistance to fire blight

Apple cultivars and selections were tested for resistance to two strains of Erwinia amylovora following shoot tip inoculation in the greenhouse. Cv. Liberty was resistant to strain Ea 273, and Priscilla, Delicious and Coop 17 were highly resistant to strain Apple # 1. A significant genotype x strain interaction was obtained suggesting a differential host × pathogen interaction. Segregation of seedlings derived from 16 controlled crosses after fire blight inoculation indicated that resistance to fire blight is quantitatively controlled with evidence for presence of dominant additive gene effects.     

Large scale inoculation of actinorhizal plants withFrankia

Summary From 1979 to 1984 more than seven million seedlings of actinorhizal plants were successfully inoculated on an industrial scale withFrankia inoculants. Nodulated seedlings were produced in greenhouses to be used for land reclamation in northern Québec by the Societe d'Energie de la Baie James (SEBJ) and also by the City of Montréal for a revegetation program. Crushed-nodule homogenates andFrankia pure culture formulations were compared for large scale inoculation of green alder. Pure culture inoculant was found to be superior than crushed-nodule homogenates yielding reproducible nodulation of seedlings. Two inoculation methods of theFrankia pure culture inocula were compared: soil injection and spraying with greenhouse watering devices. Both methods resulted in efficient nodulation ofAlnus crispa, A. glutinosa, A. rugosa, Elaeagnus angustifolia, E. commutata, Hippophaë rhamnoides, Myrica gale andShepherdia argentea.     

基因聚合改良杂交稻组合的稻飞虱田间抗性表现

褐飞虱Nilaparvata lugens(Stl)是杂交水稻的重要虫害,培育高抗褐飞虱的杂交水稻新组合被认为是目前防治飞虱最有效、经济的方法。本研究以分子标记辅助选择培育的抗褐飞虱杂交水稻为材料,通过苗期和成株期的全生育期田间抗性鉴定,对基因聚合改良杂交稻组合的褐飞虱抗性进行综合评价,结果表明,基因聚合改良杂交稻组合的苗期抗性介于抗和中抗水平,田间虫量在7次调查中均低于800头/百丛,远低于2000头/百丛的防治标准,而对照扬两优6号、两优培九和当地农家品种两优63在8月29日到9月10日飞虱发生高峰期的百丛虫量分别最高达到5400头、2030头和10700头,高于或远高于2000头/百丛的防治标准。改良组合川香29A/华恢1462的产量在通城比对照扬两优6号增产11.8%。上述结果表明抗褐飞虱改良杂交稻新组合能够有效抑制稻田褐飞虱种群数量,节约人工和农药成本,增加水稻产量。     

Isolate specificity of quantitative trait loci for partial resistance of barley to Puccinia hordei confirmed in mapping populations and near-isogenic lines

Partial resistance is considered race-nonspecific and durable, consistent with the concept of 'horizontal' resistance. However, detailed observations of partial resistance to leaf rust (Puccinia hordei) in barley (Hordeum vulgare) revealed small cultivar x isolate interactions, suggesting a minor-gene-for-minor-gene interaction model, similar to so-called 'vertical' resistance. Three consistent quantitative trait loci (QTLs), labelled Rphq2, Rphq3 and Rphq4, that were detected in the cross susceptible L94 x partially resistant Vada have been incorporated into the L94 background to obtain near-isogenic lines (NILs). Three isolates were used to map QTLs on seedlings of the L94 x Vada population and to evaluate the effect of each QTL on adult plants of the respective NILs under field conditions. Rphq2 had a strong effect in seedlings but almost no effect in adult plants, while Rphq3 was effective in seedlings and in adult plants against all three isolates. However, Rphq4 was effective in seedlings and in adult plants against two isolates but ineffective in both development stages against the third, demonstrating a clear and reproducible isolate-specific effect. The resistance governed by the three QTLs was not associated with a hypersensitive reaction. Those results confirm the minor-gene-for-minor-gene model suggesting specific interactions between QTLs for partial resistance and P. hordei isolates.     

Components of partial resistance of barley to Rhynchosporium secalis: use of seedling tests to predict field resistance

Components of partial resistance [disease incidence (DI), infection frequency (IF), latent period (LP), spores per lesion (SPL)] were assessed on glasshouse-grown barley seedlings following inoculation with spore suspensions of Rhynchosporium secalis at growth stage 12 (Zadoks, Chang & Konzak, 1974). Four experiments were carried out at different times during 1988. Three spring barley cultivars [two from Cyprus (cvs Kantara and Athenais) and one from the UK (cv. Triumph)] were used in the first three experiments. In the fourth experiment eight additional UK cultivars with NIAB resistance ratings ranging from 3 to 9 were used. Two races of R. secalis were used in the first three experiments and three in the fourth. The three cultivars, Kantara, Athenais and Triumph, were examined in all four experiments and significant differences detected for virtually all components of partial resistance in each. Differences, however, were often small and ranking of cultivars varied in different experiments. The greater susceptibility of cv. Kantara compared to cv. Athenais, observed under field conditions in Cyprus, would not be anticipated from the small differences in components of partial resistance observed in these experiments, but, for these cultivars, the possibility of a marked genotype x environment interaction cannot be discounted. Mean values for the components of partial resistance differed in the four experiments. LP was correlated with mean glasshouse temperature from inoculation to the onset of sporulation but differences in IF and SPL were not correlated with temperature. For these components, light quality and/or duration appeared to be more important. Overall, there were no differences between races but significant race X cultivar interactions were observed in two experiments. In the fourth experiment, examining 11 cultivars, there were significant differences between cultivars for all components of partial resistance. IF and LP were correlated but neither of these components was correlated with SPL indicating independent control of this latter component. Both IF and LP were correlated with field performance (NIAB ratings) but there was no correlation with SPL. However, combining IF with mean values of SPL restricted to the 5 days following the end of the LP, produced the best correlation (r= 0.92) with NIAB ratings. Problems of assessing components of partial resistance and possible means of improving assessments are discussed.     

Evaluation of mycelial inocula of edible Lactarius species for the production of Pinus pinaster and P. sylvestris mycorrhizal seedlings under greenhouse conditions

Different methods to inoculate seedlings of Pinus pinaster and P. sylvestris with edible Lactarius species under standard greenhouse conditions were evaluated. Fungal inoculations were performed both under pure culture synthesis in vitro, followed by transplantation of acclimatized seedlings, and directly in the greenhouse using different techniques for inocula production (mycelial slurries, vegetative inoculum grown in peat-vermiculite and alginate-entrapped mycelium). In vitro inoculations with L. deliciosus produced thoroughly colonized seedlings. However, a sharp decrease in mycorrhizal colonization was detected on transplanted seedlings after 4 month's growth in the greenhouse. On the other hand, all the inocula applied directly in the greenhouse, except the alginate-entrapped mycelium, produced a variable number of mycorrhizal seedlings and colonization rates after the first growing season, depending on the plant-fungal combination and the inoculation method. Inoculations with vegetative inocula of the strain 178 of L. deliciosus were the most effective in producing mycorrhizal seedlings. All the seedlings inoculated with this strain were colonized although the colonization rates were relatively low. The commercial feasibility of the different inoculation methods for the production of seedlings colonized with edible Lactarius species is discussed.     

Standardization of cage techniques to screen chickpeas for resistance to Helicoverpa armigera (Lepidoptera: Noctuidae) in greenhouse and field conditions

Because of variations in insect populations and staggered flowering of chickpea, Cicer arietinum L., genotypes, it is difficult to compare the genotypic performance across seasons and locations. We standardized a cage technique to screen chickpeas for resistance to Helicoverpa armigera (Hübner). Leaf feeding by the larvae was significantly lower on ICC 506 than on ICCC 37 when the seedlings were infested with 20 neonates per five plants at 15 d after seedling emergence or 10 neonates per three plants at the flowering stage. Maximum differences in pod damage were observed when the plants were infested with six third-instar larvae per three plants in the greenhouse, and with eight larvae per plant under field conditions. Larval weights were significantly lower on ICC 506 than on ICCC 37 across growth stages and infestation levels. At the podding stage, percentage of reduction in grain yield was significantly greater on ICCC 37 and Annigeri than on ICCV 2 and ICC 506. The no-choice test can be used to screen segregating breeding material and mapping populations for resistance to H. armigera. It also provides useful information on antibiosis mechanism of resistance to H. armigera.     

Plant Growth‐promoting Fungus Penicillium oxalicum Enhances Plant Growth and Induces Resistance in Pearl Millet Against Downy Mildew Disease

Plant Growth‐promoting Fungus (PGPF) Penicillium oxalicum was isolated from rhizosphere soil of pearl millet and was tested for its ability to promote growth and induce systemic resistance in pearl millet against downy mildew disease. The fungal isolate P. oxalicum UOM PGPF 16 was identified as P. oxalicum using ITS sequencing and morphological analysis and sequence was deposited at NCBI with accession number KF150220. Pearl millet susceptible seeds were treated with three different inducers (CS, CF and LCF) of PGPF P. oxalicum and all the inducers significantly reduced the downy mildew disease and enhanced plant growth. Among the inducers tested, CS treatment recorded highest seed germination of 91% and 1427 seedling vigour followed by LCF and CF treatments. The vegetative growth parameter and NPK uptake studies under greenhouse conditions revealed that the CS treatment of P. oxalicum remarkably enhanced the parameters tested when compared to control plants. A significant disease protection of 62% and 58% against downy mildew disease was observed in plants pretreated with CS of P. oxalicum under greenhouse and field conditions, respectively. The spatio‐temporal studies revealed that inducers P. oxalicum required a minimum of 3 days for developing maximum disease resistance which was maintained thereafter. The maximum Peroxidase (POX) activity (62.7 U) was observed at 24 h in seedlings treated with CS of PGPF P. oxalicum and the activity gradually reduced at later time points after pathogen inoculation. Chitinase (CHT) activity was significantly higher in inducer treated seedlings when compared to control seedlings inoculated with pathogen after 48 h and remained constant at all time points.     

Combined genetic analysis of partial blast resistance in an upland rice population and recurrent selection for line and hybrid values

The CNA-IRAT 5 upland rice population has been improved for 4 years by recurrent selection for blast resistance in Brazil. In order to predict the efficiency of recurrent selection in different test systems and to compare the relative advantage of hybrids versus pure line breeding, a combined genetic analysis of partial blast resistance in the CNA-IRAT 5 population was undertaken. A three-level hierarchical design in inbreeding and a factorial design were derived from the base population. Partial blast resistance of lines and hybrids was evaluated in the greenhouse and in the field by inoculation with one virulent blast isolate. The means and genetic variances of the hybrids and lines were estimated. Genetic advance by recurrent selection was predicted from estimates of variance components. The inheritance of partial blast resistance was mainly additive but non-additive effects were detected at both levels of means and variances. Mean heterosis ranged from 4%–8% for lesion size and lesion density to 10–12% for leaf and panicle resistance. High dominance or homozygous dominance variances relative to additive variance and negative covariance between additive and homozygous dominance effects were estimated. A low frequency of favourable alleles for partial resistance would explain the observed organisation of genetic variability in the base population. Recurrent selection will efficiently improve partial blast resistance of the CNA-IRAT 5 population. Genetic advance for line or hybrid values was expected to be higher testing doubled haploid lines than S1 lines, or than general combining ability. Two components of partial resistance assessed in the greenhouse, lesion size and lesion density, could be used as indirect selection criteria to improve field resistance. On the whole, hybrid breeding for partial blast resistance appeared to be slightly more advantageous than pure line breeding.