Assessing progenies of potato for resistance to early blight

Summary Progenies from crosses between cultivars varying widely in resistance to early blight (Alternaria solani Sor.), were assessed for resistance as true seedlings in a glasshouse in Scotland. The resistance of a representative sample of surviving genotypes from each progeny was compared with samples of the same progenies not previously exposed to the fungus, both in the glasshouse in Scotland and in the field in Israel. The exposed population was more resistant. Resistance was identified more effectively in adult plants from tubers in the glasshouse than in true seedlings and agreement between glasshouse and field assessment was better when progenies were compared rather than individual genotypes. The mid parent and progeny mean scores of the unexposed population were correlated at both sites, thus confirming that the resistance is heritable. Selecting resistant individuals at the seedling stage is suggested as a useful tool for resistance breeding, having first chosen the best parents for crossing.     

Inheritance of resistance toFusarium sulphureum in crosses betweenS. tuberosum potato cultivars measured on field and glasshouse grown tubers

Summary Solanum tuberosum potato cultivars with differing levels of resistance to dry rot caused byFusarium sulphureum were hybridised in a half diallel crossing programme. Glasshouse grown tubers from true seedlings and field-grown tubers of the resulting progenies were assessed for their resistance toF. sulphureum. Statistical analysis revealed differences between the progenies forF. sulphureum resistance on both field and glasshouse grown tubers. On the field grown tubers, differences between progenies were due to differences in the general combining ability (GCA) of the parents. Parental phenotypes and GCA values were highly correlated. Overall. GCA was consistent for resistance or susceptibility, and glasshouse grown progenies showed a good correlation for GCA between years (r=0.85^***), and with the results of the field grown progenies (r=0.61^* in 1998 and r=0.69^** in 1999). It appears that resistance toF. sulphureum is heritable, and that this heritability is better assessed on field grown rather than glasshouse grown tubers, although the two are largely in agreement.     

Assessing progenies of potato for resistance to skin spot (Polyscytalum pustulans) in the glasshouse

Summary Crosses were made between six parents differing in susceptibility to skin spot and glasshouse-grown tubers from true seedlings of the nine resulting progenies assessed for resistance to the disease. The assessment was evaluated by a two-year comparison with the behaviour of field-grown tubers of the progenies and their parents. The correlations between progenies in the glasshouse and field were r=0.911 and 0.753 and those between the mid-parental values and the progeny means were high (r>0.864), indicating that parental differences were heritable. It is concluded that correlations were sufficient for glasshouse-grown tubers to be used for assessing large numbers of progenies in genetical studies and for eliminating highly susceptible progenies at an early stage in a breeding programme. R.L. Wastie died 16.01.96.     

The expression of resistance to the white potato cyst nematode (Globodera pallida) by individual potato seedlings under different inoculation treatments

Summary The resistance toGlobodera pallida of individual potato seedlings from three progenies derived fromSolanum tuberosum ssp.andigena CPC 2802 was assessed using three inoculation treatments. Plants grown from tubers from the seedlings were used to reassess resistance. All the seedling test inoculation treatments over-estimated the proportion of clones classified as resistant compared to the results from tuber-grown plants. However, the mean relative resistance of progenies estimated by both tests showed good agreement, and it is suggested that seedlings are best used for assessing the resistance of progenies of crosses to identify promising combinations rather than individual clones.     

Frühselektion auf relative Krautfäuleresistenz an Sämlingen der Kartoffel und deren spätere Kraut- und Braunfäuleresistenz

Zusammenfassung Im Gew?chshaus wurden 838 hoch krautf?uleanf?llige bis hoch resistente Kartoffelidiotypen als S?mling auf relative Krautf?uleresistenz (KR_G), als Einzelstaude und A-Klon im Scheibentest auf relative Braunf?uleresistenz (B_S) und als A-Klon auf relative Krautf?uleresistenz im Feld (KR_F) untersucht. Durch rechtzeitiges Abschneiden am Stengelgrund überlebten auch stark befallene S?mlinge. Bei scharfer S?mlingsselektion (KR_G≥8 behalten) blieben 24% der Ausgangszahl erhalten, aber nur 52% der vorhandenen resistenten Idiotypen mit KR_F≥5 und B_S≥6,4. Wurden nur S?mlinge mit KR_G≥7 behalten, so gingen immer noch 8% der sp?ter erkennbaren Resistenztr?ger für Kraut- und Braunf?ule verloren, jedoch ergab sich eine Einschr?nkung des Zuchtmaterials durch die Frühselektion auf 57% der Ausgangszahl. Es kam starke ontogene Pr?disposition des Krautes sowohl in Richtung erh?hter Anf?lligkeit als auch erh?hter Resistenz vor. Neunundrei?ig Braunf?uleresistenztr?ger waren als S?mling hoch krautf?uleanf?llig. Scharfe Selektion der S?mling ist unangemessen. Für die Sortenauslese wird die Frühselektion auf Krautf?uleresistenz nicht empfohlen.

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Summary The reliability of blight resistance assessments made at the seedling stage and subsequent loss of tuber blight resistance were studied in 838 seedlings with different relative resistance to foliage blight. The criteria were assessed after Darsow (1989) in a field experiment in which the effect of maturity class was largely eliminated. Seedlings with 4–6 developed leaves were inoculated in the glasshouse with 3–3.5×10⁵ zoospores of a mixture of pathotypes. Multiple assessments (NB 9=high resistance, 1=greatest susceptibility) and immediate removal of shoots at the stem base allowed those forms most susceptible to foliage blight to be regenerated for testing in subsequent years (single plants, A-clone). Table 1 gives the crosses, scores for resistance of the parents and the numbers of seedlings tested per progeny. The percentage distribution of foliage blight resistance in the field (KR_F) related to that of the seedlings (KR_G) is given in Fig. 1. Potato plants which were very susceptible at the seedling stage could nevertheless grow in the field and exhibit good foliage blight resistance. The reverse was also observed. The distribution after weak selection for the development of blight on the seedling in the field is given in Table 2. There was an unavoidable loss of 10% and 14% in those rotted seedlings that possessed foliage and tuber blight resistance respectively (Table 3). High tuber blight resistance (B_S) occurred in all classes of seedlings with foliage blight resistance; likewise susceptibility to tuber blight occurred in seedlings with foliage blight resistance. From seedlings with KR_G≥7, 204 out of a total of 222 retained their genotypes with KR_F≥5 and B_S≥6.4. A reduction of 43% in the final number of seedlings was accompanied by a loss of 8% of those that possessed combined resistance. Of the seedlings which had been harvested and pre-tested, 277 out of 481 later had insufficient levels of resistance. Early selection will only be advantageous by careful selection of progenies with increased levels of resistance. The interaction of resistance with environment and developmental stage does not at present commend the application of this approach to varietal breeding.

     

A root inoculation technique to screen potato seedlings for resistance toPseudomonas solanacearum

A seedling inoculation technique for screening potato progenies for resistance toPseudomonas solanacearum was devised, and the effect of certain treatment variables on efficiency of the technique was determined. Concentration of inoculum and age of seedlings were critical factors; with very young seedlings (16 days old) or low concentration of inoculum (10⁵ cells/ml for isolate K-60) many seedlings escaped infection. With older seedlings (25 days old) and high concentrations of inoculum (10⁹ cells/ml), very few or none of the seedlings survived. Inocula containing mixtures of the most virulent isolates, such as S-207, S-213, and S-123, even at relatively low populations (ca. 10⁵ cells/ml), killed most of the susceptible seedlings. In the standard procedure, true seed was sown in rows 3.2 cm apart in 50 x 35 cm flats and seedlings were grown for 20 days in a growth room at 22 C and a 14-hr photoperiod. For inoculation, 5 liters of a cell suspension of two pathogenic isolates ofP. solanacearum (S-207 and S-213, or S-207 and S-123) were added to each flat, and roots were cut immediately with a knife run between and across the rows of seedlings. Inoculated seedlings were incubated in a growth room at 28 C for 2 weeks, and survivors then were moved to the greenhouse for propagation. Stem inoculation of 20 clones derived from plants that survived the standard procedures showed that 16 of them had clear-cut resistance to the bacterium. Tests with 39 hybrid families from crosses of resistant clones with susceptible Mexican and Colombian cultivars showed a relatively high survival rate in progeny from crosses involving three specific resistant parents.     

A glasshouse test for assessing resistance to early blight (Alternaria solani)

Summary Fourteen genotypes of potato were assessed for resistance toAlternaria solani Sor., both in the glasshouse at the Scottish Crop Research Institute in Scotland and in the field in the Negev, Israel. Glasshouse assessments agreed well with field results, identifying the most resistant and susceptible genotypes. The effects on the glasshouse test of plant age, inoculum concentration, and length of time plants were kept damp after inoculation, were examined. The best agreement with field results was shown by plants inoculated at flowering, and the best discrimination between genotypes was achieved by keeping the foliage damp for 24 h after inoculating with a spore suspension containing 2.5×10³ spores/ml.     

A method of assessing potato seedling progenies for resistance to the white potato cyst nematode

Summary The resistance expressed by progenies of potato seedlings to the white potato cyst nematode (Globodera pallida) has been assessed on bulk sowings of seedlings and on individual plants raised from tubers, and a positive correlation between the seedling and plant tests has been established. The use of such a seedling test as an addition to other methods of screening is discussed.     

Inheritance of tolerance ofGlobodera pallida and the relationship between tolerance and resistance toG. pallida in potatoes

Summary The tolerance of and resistance toGlobodera pallida of two potato progenies which segregated for these characteristics were assessed in pots in the glasshouse. The level of tolerance varied widely between genotypes within the progenies, with several genotypes being significantly more tolerant than the intolerant parent. The levels of resistance and tolerance in the progenies were not significantly correlated. No indications were obtained that the ranking of genotypes for tolerance is influenced by the density ofG. pallida in the soil. The results confirm that selection for tolerance in aG. pallida resistance breeding programme is useful and feasible.     

Assessing general combining ability for gangrene resistance by means of a glasshouse seedling test

Summary A seedling progeny test for resistance to gangrene (Phoma foveata) was used to evaluate progenies from a 15×15 half diallel set of crosses, including 14 selfs and 25 reciprocal crosses, which was originally made to investigate the inheritance of resistance to late blight and cyst nematodes. Nine out of the 14 selfs were more susceptible than the crosses involving their parents, so that overall the selfs were slightly more susceptible than the crosses, thus providing evidence of non-additive gene action in favour of resistance. However, when the selfs were omitted from the analysis, all of the variation between progenies could be attributed to differences in the General Combining Abilities (GCAs) of their parents. The four parents with the best GCAs for gangrene resistance all had sizeable contributions fromSolanum tuberosum subsp.andigena in their pedigrees.     

Genetic analysis of resistance to whitebacked planthopper, Sogatella furcifera (Horvath), in some rice varieties

For genetic analysis of resistance to the whitebacked planthopper, Sogatella furcifera (Horvath) (Homoptera: Delphacidae), in 13 rice varieties, seedlings at the one-leaf stage were artificially infested in the greenhouse with second; and third-instar nymphs of this planthopper. Reactions of the seedlings were recorded 7–10 days after infestation when the susceptible check (control variety) TN1 was completely killed. The reactions of the F₁, F₂, and F₃ populations from the crosses of resistant varieties with TN1 revealed that single dominant genes condition resistance in the varieties Sinnanayam, ARC 13349, MGL 1, Sukhwel 20, Bam 3, Hornamawee, Senawee, A1, T1432, W128, and Chuvanna Kumbolum. The resistance in NP130 and CI-5662-2 was conditioned by two independent dominant genes. The allelic relationships of the latter genes for resistance in the test varieties to resistance genes Wbph 1 and Wbph 2 were determined. Reactions of the F₂ and F₃ progenies from the crosses of test varieties with IR13475-7-3-2 which is homozygous for Wbph 1, and with IR30659-2-165, which is homozygous for Wbph 2, showed that the resistance genes in Sukhwel 20, Senawee, T1432, and W128 are allelic to Wbph 1. The resistance genes in Sinnanayam, ARC 13349, MGL 1, Bam 3, A1, and Chuvanna Kumbolum are allelic to Wbph 2. The two independent dominant genes for resistance in NP130 and CI-5662-2 are Wpbh 1 and Wbph 2. However, there is a single dominant gene for resistance in Hornamawee which is independent and non-allelic to Wbph 1 and Wpbh 2.     

小麦航天诱变后代的条锈病抗性变异及选择效果研究

为明确小麦航天诱变后代条锈病抗性的变异和选择效果,在甘肃陇南用系谱法对8个小麦品种的诱变后代进行了研究。结果表明,兰天10号、兰天14号、兰天17号在SP1(诱变一代)和SP2(诱变二代),PASCAL和85-173-4在SP2的群体病谱均较原品种对照发生了不显著的变异,但它们在SP1和SP2都没有出现显著的条锈病抗性突变体;郑麦9023、陇原031和DORICO在SP2均出现了显著的条锈病抗性突变系且有分离现象。8个品种的SP2和SP3(诱变三代)共获得9个显著的条锈病抗性突变系和12个显著的非条锈病抗性突变系,其中15个突变系的后代都出现了条锈病抗性的分离和变异。经过4代的选择,证明感病品种在SP2出现的抗性不显著提高株系具有一定的选择可靠性,从郑麦9023和陇原031中分别获得了抗条锈、大粒和兼抗条锈、白粉病的优良突变系。这些结果表明,航天诱变小麦种子能够引起后代条锈病抗性的丰富变异;变异可能出现在SP1、SP2或以后世代;对于感病品种在SP2出现的抗性不显著提高株系可以进行选择;不论哪一方面性状的显著突变系,一般会随世代进展出现条锈病抗性的分离和变异,都应作为抗性选择的目标对象而注意保留。     

The effect of the moisture level of potting compost on the susceptibility of glasshouse-grown tubers to late blight

Summary The effect of the moisture level of potting compost at harvest on the susceptibility of tubers of three cultivars to late blight was investigated in the glasshouse in three successive years. Three moisture regimes (dry, moist, wet) were imposed at flowering time, the tubers harvested 3 weeks later and immediately dipped in a zoospore suspension ofPhytophthora infestans. Tubers from dry compost were significantly more susceptible than those from wet or moist compost, which showed similar levels of susceptibility.     

Screening for resistance to early blight (Alternaria solani) in potato (Solanum tuberosum L.) using toxic metabolites produced by the fungus

Summary The phytotoxic components of the culture filtrate of the fungusAlternaria solani Sor, which causes early blight in potato, were used in this study to differentiate between resistant and susceptible genotypes selected to represent a range of reactions when screened in the field. Detached leaflet assays, using spores and toxic metabolites from the culture filtrate, were compared with field ratings and a whole-plant glasshouse test. Rank correlations between several detached leaflet tests were highly significant (P<0.01) but the correlations between these tests and the glasshouse and field tests were poor. The disease ratings obtained in the various tests were clustered into four groups and assigned to resistance classes. For many of the genotypes there was a good correspondence between resistance classes for all test methods. Divergent results between tests were associated with foliage maturity characteristics of the genotypes. Contribution no. 3879050 of the Lethbridge Research Station.     

Glasshouse and field evaluation of fungicides for the control of Septoria apiicola on celery

Propiconazole was more effective than either triadimenol or hexaconazole when applied after infection, for the control of Septoria apiicola on celery seedlings. In three out of four glasshouse experiments, 25 mg propiconazole I⁻¹ controlled S. apiicola completely when applied within 3 days after inoculation. Propiconazole and triadimenol at 5–15 mg l⁻¹ were also effective when applied 2 days after inoculation. Soil applications of a granular formulation of triadimenol (up to 20 mg per plant) controlled S. apiicola for 5 weeks on celery seedlings grown in pots and, in the field, granules at 100 mg per plant applied at planting were effective for 6 weeks. In two other field experiments the most effective treatments were foliar sprays of 25 mg propiconazole l⁻¹ applied every 7–10 days with or without the addition of anilazine or chlorothalonil.     

Additive genes in wheat for resistance to stripe (yellow) rust (Puccinia striiformis Westend.)

Forty-nine lines of wheat (F₆ generation) containing minor additive genes conditioning resistance to stripe (yellow) rust (Puccinia striiformis Westend.) were evaluated to several virulence types (physiologic races) of the pathogen obtained from the USA and Europe. All wheat lines showed some level of resistance to all virulence types of P. striiformis but there were differences in level of resistance between crosses and between lines within a particular cross. Generally, all lines expressed the most resistance at the seedling stage when grown at higher temperatures (15°C during the dark period; 25°C during the light period) than at 2°C (dark period) and 20°C (light period). Lines with more resistance genes showed the most resistance, and this resistance was least sensitive to temperature change. Mature plants in the field had levels of resistance equal to, or greater than, those of their seedling counterparts. One parent of each cross evaluated was either a commercial cultivar or an advanced wheat selection, and was rated as susceptible. In many cases, these susceptible parents contributed to resistance in the progeny and thus the progeny showed transgressive segregation for resistance. Some parent cultivars, which were completely susceptible as seedlings and moderately resistant as mature plants, also contributed to seedling resistance in the progeny when combined with parents known to contain minor additive genes for resistance to P. striiformis. The advantages of using minor additive genes are discussed in relation to the control of stripe rust of wheat and to crop protection generally.     

A glasshouse progeny test for resistance to gangrene (Phoma foveata)

Summary Tubers were obtained from 80 glasshouse-grown seedlings of each of twelve progenies, inoculated withPhoma foveata Foister, and the mean percentage of infected tubers recorded. There was a good correlation (r=0.798) between this assessment and that made previously on field-grown tubers of eleven of the progenies. A gangrene test on glasshouse-grown tubers is suggested as a more rapid means of identifying progenies with useful levels of resistance.     

Impact of shading and cutting on the demography and composition of Mimosa pudica L., a ligneous weed species of tropical grasslands

The aim of the study was to evaluate the potential impact of grazing on the control of Mimosa pudica, a ligneous weed species that invades grasslands in French Guiana. Three experiments were conducted in a glasshouse to test the potential impact of: (i) shading by testing different Photsynthetically Active Radiation (PAR) fluxes on seedlings and (ii) cutting of juveniles, at three stages of development, on their survival, flowering rate and nutritive value as measured by the mass:length ratio of stems and by branching processes. A significant mortality rate (0·20) was obtained only for seedlings at the cotyledon stage when the PAR flux was reduced proportionately by 0·83. Shading reduced both flowering rate and mass:length ratio of stems. For seedlings at the cotyledon stage, the flowering rate decreased from 0·85 for the control to zero for the low light treatment (0·13 of PAR flux of the control treatment). The mass:length ratio of stems of seedlings in the low light treatment was reduced to 0·20 of that of control seedlings, at the fifth‐leaf stage. Cutting treatment had no effect on mortality of juvenile plants whatever the size of the juvenile plant. The proportion of juvenile plants flowering was high for all cutting treatments. It is suggested that regular, but not continuous grazing, could maintain a dense sward to limit recruitment by seedling establishment and seed production, and maintain branched and juvenile plants with a high‐nutritive value at the seedling stage.     

THE GROWTH AND DEVELOPMENT OF SOME GRASS SPECIES UNDER COMPETITIVE STRESS

Three experiments were carried out in a semi-controlled glasshouse environment to determine the response of individual plants to competition; (i) between seedlings of different species, (ii) between seedlings derived from seeds of differing sizes within a species, and (iii) between seedlings and established plants.
Differences were detected in seedling competitive ability between species and between plants derived from differing seed sizes. In associations of species of very high and very low competitive ability the differences in competitive ability were accentuated by an increase in plant density.
Established plants of Phalaris coerulescens were less aggressive to seedlings growing in close proximity than were plants of Lolium rigidum and H1 ryegrass. Despite the early death of established swards of L. rigidum , and the consequent removal of competitive stress, there was no rapid increase in the growth and development of seedlings in these swards. Possible mechanisms causing this effect are discussed.
There was evidence of a specific relationship between the species of the established sward and the seedling species, in particular seedlings of HI ryegrass were particularly susceptible to competition from established plants of their own species.
Dry weight per plant, tiller production, rate of leaf appearance and leaf size were ail affected by competition between seedlings; however, tiller production was generally more severely affected than rate of leaf appearance and leaf size.
Dry weight per plant, tiller production, seedling height, number of leaves per tiller and number of seeds per seedling were all affected by competition from established plants.     

大豆对大豆花叶病毒SC18株系的抗性遗传和基因定位

大豆花叶病毒(soybean mosaic virus,SMV)病是我国大豆生产上的一种主要病毒病害,SMV株系SC18是我国东北和南方两大产区的优势株系,在黄淮大豆产区亦零星发生。本研究对5个抗×感杂交组合衍生后代分离群体接种SC18后,发现各组合F_1均抗病,F_2表现3∶1(抗∶感)分离比,F_(2∶3)表现1∶2∶1(抗∶分离∶感)的分离比,表明5个抗病亲本(中作00-683、滨豆95-20、东大2号、中品661和RN-9)对SC18的抗性由一对显性基因控制。抗×抗杂交组合"中作00-683×东大2号"衍生后代分离群体接种SC18,F_2出现15∶1(抗∶感)的分离比,表明中作00-683与东大2号可能各携带一对显性基因,控制对SC18的抗性,且独立遗传;抗×抗杂交组合"中作00-683×滨豆95-20"的F_1、F_2和F_(2∶3)在接种SC18后均未检测出感病株,表明中作00-683与滨豆95-20所携带的对SC18的抗性基因是等位的。利用RN-9×7605重组自交家系将RN-9对SC18的抗病基因Rsc18定位到大豆6号染色体(C2连锁群)SSR标记Satt286和Satt277之间,遗传距离为6.12和4.69 cM。