Resistance to western flower thrips in greenhouse cucumber: effect of leaf position and plant age on thrips reproduction

Three greenhouse cucumber (Cucumis sativus L.) accessions, previously selected for low levels of damage after infestation with Frankliniella occidentalis (Pergande), were tested for resistance against F. occidentalis in a no-choice greenhouse experiment at the mature plant stage. The three accessions showed a strong reduction in thrips damage compared to the susceptible control. The effects of leaf position and plant age of the four cucumber accessions on the reproduction of F. occidentalis were determined in a leaf disc assay. Leaf position had a significant effect on thrips reproduction, whereas plant age, within the test range, had not. In general, reproduction was higher on young leaves. Reproduction as measured on leaf discs from certain leaf positions was strongly correlated with resistance of mature plants in the greenhouse, and can therefore be used as a quick test to screen cucumber accessions for resistance against thrips. This revised version was published online in July 2006 with corrections to the Cover Date.     

Seasonal variation in resistance of chrysanthemum cultivars to Frankliniella occidentalis (Thysanoptera: Thripidae)

Seasonal variation in the level of host plant resistance can have important consequences for the repeatability of tests to measure host plant resistance to insect pests. In the present study, the levels of resistance to Frankliniella occidentalis of a susceptible and a partially resistant cultivar of chrysanthemum, Dendranthema grandiflora, were determined throughout the year. Thrips damage, reproduction and adult female survival were determined on excised leaves in Petri dishes under uniform conditions. Strong seasonal fluctuations were observed in these three characteristics. On leaves from plants grown in winter, damage, reproduction, and survival were higher than on leaves from plants grown in summer. Clear differences in resistance were observed between the susceptible and the partially resistant cultivar on leaves from plants grown in winter, while differences disappeared in summer. Damage on both cultivars and survival on the susceptible cultivar were negatively correlated with mean daily solar radiation during plant growth, suggesting that the level of resistance depends on light intensity during plant growth. This was confirmed in an experiment carried out in summertime with shaded and unshaded plants. Leaves from control plants, grown under high light intensity had a higher level of resistance than leaves from shaded plants grown under reduced light intensity. There were clear differences in resistance between the cultivars under shaded conditions (low light intensity), but not under unshaded control conditions (high light intensity). This revised version was published online in July 2006 with corrections to the Cover Date.     

Life history studies of the leafminer Liriomyza trifolii on susceptible and resistant cultivars of Dendranthema grandiflora

Summary The feeding, fecundity, mortality and rate of development of Liriomyza trifolii (Burgess) on 12 cultivars of Dendranthema grandiflora (Tzvel.) (Syn. Chrysanthemum morifolium (Ramat.)) were determined in no choice experiments. Number of feeding punctures, number of eggs laid and total number of larvae varied between cultivars but these characters were not strongly associated with leafminer population increase. Good indicators of host plant resistance were larval mortality, number of pupae and duration of the larval period. Of these three, larval mortality which could be as high as 98% was most suitable.Based on life history data it was predicted that Liriomyza trifolii cannot survive on the resistant cultivar Penny Lane. This prediction was verified experimentally.     

Abortion of infection structures of wheat leaf rust in susceptible and partially resistant wheat genotypes

Summary Arrest of the growth of wheat leaf rust infection structures was studied with fluorescence microscopy in seedling leaves and flag leaves of the susceptible spring wheat genotypes Morocco and Kaspar and the partially resistant genotypes Westphal 12A and Akabozu. The percentages non-penetrants and substomatal vesicle abortion were low in all genotypes. In the partially resistant genotypes the percentage abortion of infection structures was higher than in the susceptible genotype Morocco. Aborted infection structures had formed one or two haustorial mother cells. In adult plants differences in the percentage aborted infection structures between susceptible and partially resistant genotypes were more pronounced than in seedlings. The so-called late abortion was not observed.     

Growth of wheat leaf rust colonies in susceptible and partially resistant spring wheats

Summary The average size of wheat leaf rust colonies, measured using epifluorescence microscopy was significantly larger in the highly susceptible genotype Morocco than in the susceptible genotype Kaspar and the partially resistant genotypes Westphal 12A, Akabozu and BH 1146. This was already so three days after inoculation. Colony growth in partially resistant genotypes was continuously retarded compared to colonies in the highly susceptible genotype Morocco. No evidence was found for an initial inhibition of the growth of colonies in partially resistant genotypes. In partially resistant genotypes formation of uredial beds and sporulating areas started at a smaller colony size than in susceptible genotypes. Wheat leaf rust colonies in primary leaves of all genotypes studied were much larger than colonies in flag leaves measured at the same number of days after inoculation. Growth and sporulation of not intertwined colonies was not influenced by either a high or a low number of neighbouring colonies.     

Phenotypic and genotypic analysis of a commercial cultivar and wild populations of Anemone coronaria

Seven wild populations of Anemonecoronaria were assessed for 11 phenotypic traits, most of them having economic value for the flower industry. The wild populations were sampled to represent the diversity in habitats, climates, rock and soil types, terrains, and elevations in Israel. AFLP analysis was carried out on 12 individuals from each of six out of the seven wild populations and for six individuals from the commercial cultivar ‘Mona-Lisa’. It was found that the Dorot population, which is located in the area bordering the semi-arid zone at the very end of the species distribution, exhibits extreme and different phenotypes with relatively low variability compared withthe other wild populations. The other six wild populations, that grow in more favorable geographic and climatic conditions exhibit phenotypes with larger plants, larger numbers of flowers and less dissected leaves. These populations were less uniform than that of Dorot. Genetic characterization by AFLP markers revealed a total of 165 bands. The wild populations exhibit wide variation within-population, with about 80% polymorphic bands and average gene diversity between pairs of about 30%. The Dorot population has the lowest genetic variation and the Megido population the highest. Thus, the phenotypic variation reflects the genetic variation. The cultivar ‘Mona-Lisa’, as expected, has much lower genetic variation. The Dorot population and the ‘Mona-Lisa’ cultivar were found to have the largest genetic distances from the other wild populations, and the highest genetic variation between themselves. Phenetic analysis yielded a dendrogram describing the genetic relatedness of these populations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Variation in inheritance of resistance to sorghum midge, Stenodiplosis sorghicola across locations in India and Kenya

Sorghum midge [Stenodiplosis sorghicola (Coquillett)] is an important pest of grain sorghum, and host plant resistance is one of the important components for the management of this pest. We studied the inheritance of resistance to this insect involving a diverse array of midge-resistant and midge-susceptible genotypes in India and Kenya. Testers IS 15107, TAM 2566, and DJ 6514, which were highly resistant to sorghum midge in India, showed a greater susceptibility to this insect in Kenya. The maintainer lines ICSB 88019 and ICSB 88020 were highly resistant to sorghum midge in India, but showed a susceptible reaction in Kenya; while ICSB 42 was susceptible at both the locations. General combining ability (GCA) effects for susceptibility to sorghum midge for ICSA 88019 and ICSA 88020 were significant and negative in India, but such effects were non-significant in Kenya. The GCA effects of ICSB 42 for susceptibility to sorghum midge were significant and positive at both the locations. The GCA effects were significant and positive for Swarna, and such effects for IS 15107 and TAM 2566 were negative at both the locations. GCA effect of DJ 6514 were significant and negative in India, but non-significant and positive in Kenya; while those of AF 28 were significant and positive during the 1994 season in India, but significant and negative in Kenya. Inheritance of resistance to sorghum midge is largely governed by additive type of gene action. Testers showing resistance to sorghum midge in India and/or Kenya did not combine with ICSA 88019 and ICSA 88020 to produce midge-resistant hybrids in Kenya. Therefore, it is essential to transfer location specific resistance into both parents to produce midge-resistant hybrids.     

Variation in Ethiopian barley landrace populations for resistance to barley leaf scald and netblotch

One-hundred and eighty landrace populations and six-hundred single-head plants selected from 60 promising populations were evaluated for resistance to scald and netblotch at three locations in Ethiopia. Each accession was tested with and without the application of 50% of the recommended rate of fertilizer at planting. Plants were rated for disease attack two to four times during the season. Both diseases were enhanced by the application of fertilizer and were more severe at the testing sites of Holetta and Bekoji than at Sheno. The difference in disease resistance among and within populations was considerable. Moreover, populations from Arsi and Bale tend to be more susceptible to scald but more resistant to netblotch than populations from other regions. Populations collected from higher altitudes were more resistant to scald, but susceptible to netblotch, than were populations from lower altitudes. The paper illustrates approaches to the identification of valuable genotypes from landrace populations that can be incorporated into a breeding programme for the development of improved varieties with resistance to the principal diseases of barley in Ethiopia.     

西花蓟马在月季上的空间分布和种群动态研究

摘要：通过田间调查,和应用聚集度指标检验和线形回归方程检验,研究探讨了西花蓟马的空间分布型和种群动态。结果表明,该害虫在月季上呈聚集分布, 其分布的基本成分是个体群,个体间相互吸引,这种聚集主要是由环境条件和西花蓟马本身聚集习性引起。运用Iwao的m*-m直线回归方程建立了理论抽样数模型,田间理论抽样数可用N=1/D2[6.7692/m+0.4799]进行估计。田间抽样调查以棋盘式为最佳。6月8日到7月4日之间西花蓟马在月季上种群动态为单峰型,6月19日为种群密度最高时期。     

Genetic variation in testcrosses of European maize inbreds for resistance to the European corn borer and relations to line per se performance

The European com borer (ECB) Ostrinia nubilalis H. is a major pest in World maize Zea mays L. production. Objectives of this study were to (1) investigate the genotypic variance and covariance in testcrosses of European flint and dent inbreds for ECB resistance and agronomic traits, and (2) estimate the correlation between line per se and testcross performance for ECB resistance traits. A total of 16 flint and 24 dent inbreds and their testcrosses with two testers from the opposite germplasm pool were evaluated in four and three German environments, respectively. Using artificial infestation with ECB larvae, resistance was assessed by damage rating of stalks, tunnel length in dissected stalks, and relative yield of infested plots compared with protected plots. Yield losses due to ECB damage in testcross hybrids amounted to 40%. Significant genotypic variances between flint and dent lines and high heritabilities were found for damage rating of stalks for both line per se and testcross performance. Heritabilities were low or intermediate for tunnel length and relative grain yield. Correlations between line per se and testcross performance were tight for the damage rating of stalks and moderate for tunnel length and relative yield in both flint and dent germplasm. For damage rating of stalks, per se performance of lines tested in a few environments can be used to predict their testcross performance. In contrast, assessment of testcross performance for tunnel length and relative yield requires evaluating testcrosses with several testers in multi-environment trials.     

Somaclonal variation for some morphological traits, herb yield, essential oil content and essential oil composition in an Indian cultivar of rose-scented geranium

Somaclonal variation for plant height, plant spread, leaf shape, leaf size, leaf form, herb yield, essential oil content and 10 important constituents of the essential oil was studied in an Indian cultivar, ‘Bourbon’ of rose‐scented geranium (Pelargonium graveolens). Significantly larger variance was observed among in vitro‐regenerated plants of the SC1 generation (first generation following an in vitro phase) than among parental plants raised from stem cuttings for herb yield, plant height, leaf size, essential oil content, and for the contents of cis‐rose oxide, trans‐rose oxide, isomenthone and 10‐epi‐γ‐eudesmol in the essential oil. Plants of the SC₁ generation showing values beyond the higher or lower limit (depending on the trait) of the range observed among parental plants for different traits were developed into clones by their multiplication through stem cuttings, and evaluated again in the SC₂ generation (second generation following the in vitro phase). Somaclones selected for plant spread, and for the contents of linalool and trans‐rose oxide in their essential oils did not breed true in the SC₂ generation. However, for the remaining traits studied, 13–100% of the selected clones retained their selected traits in the SC₂ generation, suggesting that the changes in these somaclones were due to genetic causes.     

Genetics of adult plant stripe rust resistance in four Australian wheats and the French cultivar 'Hybride-de-Bersée'

Long-term resistance to rust diseases depends on the identification and use of durable resistance sources or on the continuing use of new resistances and combinations of genes for specific resistance. These studies include four Australian wheats with intermediate, but inadequate levels of resistance and a French wheat ‘Hybride-de-Bersée’ (‘Bersee’), with reputed durable resistance to stripe rust. Studies of F₂ and F₃ populations from crosses with the susceptible ‘Avocet’ indicated that intermediate levels of adult plant stripe rust resistance in cultivars ‘Harrier’, ‘Flinders’ and ‘M2435’ were inherited monogenically, whereas King possessed two genes for resistance. Cultivars Harrier and M2435 possessed the same gene. Similarly, cvs. King and Flinders carried a gene in common. Like ‘Harrier’ and ‘M2435’, ‘King’ and ‘Flinders’ share common parents. The higher level of resistance in ‘Bersee’ was controlled by four genes. This conclusion was based on conventional genetic analysis, tests on F₂-derived F₇ single-seed descent lines and testcross progenies.     

Variation and covariation in Vicia faba L. populations of Mediterranean origins

Summary Variation and covariation in 15 Vicia faba L. ssp. major populations from Italy. Greece and Egypt were analyzed. Ten quantitative morphobiological characters of agronomical and nutritional interest were observed. Differences among countries of origin were highly significant for all characters except for lowest podded node. Phenotypic distances among populations, both within and among origins, estimated on canonical variates evidenced that the Egyptian populations from a distinct group and that a relevant degree of similarity exists among the Greek and the Italian meterial. The covariation structure within populations, which was studied by means of factor analysis, was comparatively simpler in the Egyptian material than in that form the other two Mediterranean countries. The differences evidenced can be attributed to different gene associations between characters and suggest the possibility of obtaining, through recombination, genotypes agronomically more favorable.Research work supported by C.N.R., Italy, special grant. Sub-Project 1, Paper No. 299.     

Effect of Mutagenic Treatments on Somaclonal Variation in Wheat (Triticum aestivum L.)

Different wheat genotypes were treated with gamma-rays, sodium azide (SA) and EMS before tissue culture and immature embryos from M₁ plants or plants shortly after exposure to gamma-rays were used to initiate callus culture. Thousands of plants were regenerated and used to investigate the effect of mutagenic treatments on the regenerated plants and somaclonal variation in the M₃R₂ and M₂R₂ generations. The results showed that mutagen-induced damage in terms of reduction in plant height, fertility and spike length were not outstanding in the regenerated plants as compared with the untreated control. In the M₃R₂ generation, only SA treatment had significantly higher frequencies of somaclonal variations than the control. Increases in the variation frequencies were observed when explant embryos were irradiated with 2.5 and 5 gy gamma-rays and the highest frequency appeared when embryos were exposed to 5 gy gamma-rays on the 5th day after anthesis. Increased variation spectra also resulted from mutagenic treatments and most of the variants recovered were unsuitable for plant improvement.     

野生玫瑰抗旱性地理变异的初步研究

以吉林珲春,山东牟平,山东荣成3个地理种源的野生玫瑰为材料进行盆栽试验,研究了干旱胁迫下玫瑰的生理生化变化与抗旱性强弱。结果表明,干旱胁迫条件下, 3个种源野生玫瑰的5个抗旱生理生化指标的变化趋势基本一致,但各指标的变化程度因种源不同而异。通过“坐标综合评定方法”对5个生理生化指标进行综合评定,得到3个种源野生玫瑰的抗旱性强弱等级依次为吉林珲春,山东牟平,山东荣成。     

Inheritance of temperature-sensitive leaf rust resistance and adult plant stripe rust resistance in common wheat cultivar PBW343

Genetic analysis of common wheat cultivar PBW343 confirmed temperature-sensitive leaf rust resistance and adult plant stripe rust resistance. At low temperatures, PBW343 was resistant to P. triticina (Ptr) pathotype (pt.) 121R63-1, and at high temperature it was resistant to Ptr pt. 121R127. The low temperature resistance to pt. 121R63-1 was attributed to interaction between dominant and recessive genes. The dominant gene involved in low-temperature resistance to pt. 121R63-1 also conferred resistance to pt. 45R35. The high-temperature resistance to Ptr pt. 121R127 was governed by a different single partially dominant gene. Agra Local (a commonly used susceptible check) and IWP94 (a leaf rust differential used in India) are also resistant to pt. 121R127 at high temperatures. An allelism test indicated that PBW343 and IWP94 possessed a common gene for high temperature resistance to this pathotype. The adult plant stripe rust resistance against P. striiformis (Pst) was possibly conferred by one gene in addition to Yr27.     

Studies on glucosinolates in clubroot resistant selections and susceptible commercial cultivars of cabbages

Summary Heads of 59 commercial cabbage cultivars, all susceptible to clubroot disease, and of 86 individual clubroot resistant cabbage plants of various breeding selections were analysed for their composition in glucosinolates, determined by quantifying their hydrolytic breakdown products, thiocyanate, goitrin, and volatile isothiocyanates. The mean thiocynate ion content was significantly lower in the breeding selections (120 g/g dry weight) than in the commercial cultivars (204 g/g). In contrast, the mean goitrin content was significantly higher in the breeding selections (193 g/g) than in the commercial cultivars (35 g/g). Similar to goitrin, the range of volatile isothiocyanates and total glucosinolate were higher in the breeding selections, but the mean contents of each were not statistically different between selections and cultivars. Fourteen cultivars and four selections were found to be free of goitrin; three cultivars, but no breeding selection were free of volatile isothiocyanates. The breeding selections will provide germplasm for breeding new clubroot resistant and low glucosinolate cultivars.Contribution No. J-965.     

Variation for aphid resistance and insecticidal acyl sugar expression among and within Lycopersicon pennellii-derived inbred backcross lines of tomato and their F1 progeny

Five inbred backcross lines (IBL) were selected for higher relative expression of insecticidal acyl sugars (rank average) from an inbred backcross population derived from the cross Lycopersicon esculentum cultivar ‘Peto 84’×Lycopersicon pennellii accession LA716. These five BC₂S₅ IBLs were crossed in a partial diallel design (Method II), and their self and F₁ progeny and three control cultivars were tested at two California field locations in 1996. Counts of potato aphids, Macrosiphum euphorbiae Thomas, on leaves, as a measure of plant infestation, revealed significant general combining ability (GCA) for lower aphid numbers with IBL44 and IBL59; the F₁ hybrid IBL44 × IBL59 had significantly fewer aphids per leaflet than the susceptible cultivar ‘Alta’. GCA for acyl sugars was associated with IBL59 only. Of all the IBL and IBL × IBL F₁ hybrids, only IBL59 produced significant levels of acyl sugars. Significant within IBL59 variation for acyl sugars was observed, but not for aphid resistance. Our results suggest that factors other than acyl sugars contributed to L. pennellii-derived aphid resistance in IBL × IBL F₁ hybrids and IBL that do not produce significant amounts of acyl sugars. IBL59 and IBL44 may be useful for breeding for aphid resistance in cultivated tomato.     

Increased frost tolerance and amino acid content in leaves,tubers and leaf callus of regenerated hydroxyproline resistant potato clones

Summary A number of previously selected hydroxyproline (hyp) resistant cell lines of a diploid potato (Solanum tuberosum L., clone H²578, 2n=2x=24) could be regenerated into plants which were further analysed. Hyp resistance, although lower than in the originally selected calli, was still present in regenerated shoots and in callus initiated from these shoots and it was not lost upon (mini)tuber propagation. Regenerated shoots showed a wide range of phenotypic variation. The chromosome number, analysed in 4 clones, appeared to be hypotetraploid (44 or 45). Tuber-propagated regenerants generally showed increased frost tolerance both at the plant and the cell level. In leaves this seemed to be associated with increased levels of both proline and total amino acid content. However, in callus only the total amino acid content but not proline was still elevated. In the wild type the frost tolerance of the tubers appeared to be lower than that of the leaves. Between tubers of wild type and the hyp resistant regenerants no differences in frost tolerance were found, although proline and total amino acid content tended to be higher in tubers from the regenerants.     

Partial resistance in lettuce to downy mildew (Bremia lactucae). 1. Search for partially resistant genotypes and the influence of certain plant characters and environments on the resistance level

Summary In three bicyclic inoculation experiments in the field 756 genotypes from the IVT Lactuca gene bank were screened for differences in partial resistance against Bremia lactucae. Significant differences between genotypes were found. No linkage was found between the presence or absence of R-genes and partial resistance nor was there a clear relationship between plant characters such as size, erectness and lettuce type and resistance level. Comparison of test results for genotypes which were tested twice and in different years and/or environments revealed a rather good relationship. So no clear genotype × environment interactions for resistance level were found. Results imply that the bicyclic inoculation experiments are useful to determine levels of partial resistance.