The combined effect of plant stature and maturity on the response of wheat and triticale accessions to Septoria tritici

Summary The relationships between percent pycnidia coverage on the four uppermost leaves (PCD), plant height (PHT) and days to heading (HED) were evaluated for 21,000 wheat and triticale accessions tested in artificially inoculated (with fixed combination of S. tritici isolates) field nurseries over 8 trial years. A general Linear Model procedure (GLM) estimated Septoria severity using two correlative models: model 133-1 Year and model II–PCD=b₁PHT+b₂HED+C. The regression coefficients for PHT and HED in the two models were –0.54 and –0.40, respectively, with a R²=0.80^** and R²=0.29^** for model I and model II, respectively. The predicted cultivar best fitted to the model would be characterized as a semidwarf (PHT=115 cm) with an early-moderate maturity (HED=95 days to heading). The estimated mean percent pycnidial coverage for the two models over the 8 trial years was 40.8%. The performance of a group of 38 cultivars replicated yearly during the 8 trial years was assessed relative to model I. The deviation of each cultivar from the model was calculated using two functions: a) Sum Relative Serial Deviation (SRSD) and b) Total Relative deviation (TRD), in addition to Standard errors (SE). The proposed analytical protocol enabled identification of cultivars which expressed consistent yearly deviation (from the model) in host response combined with low-moderate mean pycnidial coverage (±30%). Such cultivars may possess a more stable type of genetic protection against the adverse effects of septoria tritici blotch.     

The response of field-inoculated wheat cultivars to mixtures of Septoria tritici isolates

Summary Wheat cultivars of diverse genetical background and response to Septoria tritici were inoculated during 2 years in the field with single or mixtures of isolates. Significant reductions in pycnidial coverage were recorded for mixtures of 2 or 5 isolates relative to the virulent isolate ISR8036 under the moderate 1989/1990 epidemic. The interactions between cultivars and all possible combinations among ISR398A1, USR8036 and the 1:1. mixture of the 2 isolates were highly significant. Cultivars exposed to mixtures of isolates expressed differential response in pycnidial coverage compared to the single isolate response. The coverage in the mixtures was significantly less than that of the arithmetic mean between the two isolates. Under the severe 1990/1991 epidemic pycnidial coverage on cultivars inoculated with the mixture of the same 2 isolates did not differ statistically from that of ISR8036, yet, ISR398A1 differed from ISR8036 and the isolate mixture. Losses in 1000-kernel weight for 12 wheat cultivars which were repeated during the 2-trial-years were significantly lower in the isolate mixture relative to that of ISR8036. The suppression of symptoms in isolate mixture relative to the expected expression of the most virulent component may be indicative of differential aggressiveness of isolates regardless of their virulence. The phenomenon may affect screening and selection procedures in breeding for resistance.     

Inheritance of resistance to two Septoria tritici isolates in spring and winter bread wheat cultivars

Summary All possible crosses (including reciprocals) were made among four winter bread (Aurora, Bezostaya 1, Kavkaz, and Trakia) and two Israeli spring wheat cultivars (spring x winter diallel), and among two South American spring wheats (Colotana and Klein Titan) with the same Israeli cultivars (spring x spring diallel) to study the inheritance of resistance to septoria tritici blotch. Parents, F₁, F₂ and backcrosses were grown in two separated blocks in the field over two years. One block was inoculated with isolate ISR398A1 and another with ISR8036. Each plant was assessed for plant height (cm), days to heading (from emergence or transplanting), and percent pycnidia coverage on the four uppermost leaves. Plant height and maturity had insignificant effects on pycnidia coverage. No cytoplasmic effects could be detected. In the spring x winter diallel general combining ability (GCA) was the major component of variation. Significant specific combining ability (SCA) was present in all cases. Partial dominance was operative in populations inoculated with ISR398A1. Resistance in the winter wheats was controlled by a small number of genes (usually two). The four winter wheats derive their resistance to ISR398A1 from their common parent Bezostaya 1 which lacks the 1B/1R wheat-rye translocation. Their resistance is readily overcome by ISR8036. Inheritance of the South American wheats can be explained by additive effects, with a small number of genes of recessive mode affecting resistance to both isolates. Breeding strategies that favor additive, and additive x dominance gene action should be pursued.     

Components of resistance to Mycosphaerella graminicola and Phaeosphaeria nodorum in spring wheats

Summary Infection frequency (IF), latent period (LP) and sporulation rate (S) were assessed on 23 genotypes (cultivars, breeding lines and parents) in the field and 36 genotypes in the glasshouse (with 22 being in common) following inoculation with conidia of either Mycosphaerella graminicola or Phaeosphaeria nodorum. Significant variation was observed among genotypes for each resistance component. Genotypes resistant to Mycosphaerella graminicola had long LP and low S but variable IF. Genotypes resistant to Phaeosphaeria nodorum had low IF, long LP and low to moderate S. IF and S were independent while a negative correlation was observed between LP and S for Mycosphaerella graminicola only. LP was most consistently correlated with field response. Components measured in the field better discriminated resistant genotypes from others. Combinations of genotypes were sought for which one genotype may contribute to a reduced disease severity for S. nodorum and the other genotype may contribute to a reduced disease severity for S. tritici in mixtures. Such combinations of genotypes were rare.     

The role of selection on the genetic structure of pathogen populations: Evidence from field experiments with Mycosphaerella graminicola on wheat

Summary Coevolution refers to reciprocal genetic changes that occur in two or more ecologically interacting species. In agricultural ecosystems, we are especially concerned with the genetic response of pathogen populations to resistant cultivars produced by plant breeding programs. It would be useful to be able to predict whether disease resistance is likely to be durable or ephemeral before a cultivar is widely grown. Though it may not be possible to predict durability in advance, knowledge of the genetic structure of pathogen populations may prove useful for making predictions about the rate at which pathogens adapt to resistant varieties. Much has been learned about the genetic structure of populations of obligate fungal pathogens such as rusts and mildews, which have become paradigms for plant pathology. We have focused our effort on the population genetics of the less known, non-specialized, necrotrophic pathogens, such as the Septorias of small grains. Our approach has been to use DNA fingerprinting and RFLP analysis to conduct field experiments that elucidate how populations of fungal pathogens adapt in agroecosystems. Our results suggest that mating system may have a greater impact than natural selection on the genetic structure of populations of Mycosphaerella graminicola (anamorph Septoria tritici).     

Chromosomal location of resistance to Septoria tritici in seedlings of a synthetic hexaploid wheat, Triticum spelta and two cultivars of Triticum aestivum

Chromosomal location of resistance to two virulent Argentinean isolatesof Septoria tritici was studied in two wheat (Triticum aestivumL.) cultivars (Cappelle-Desprez & Cheyenne), a synthetic hexaploid(Synthetic 6x) and Triticum spelta in seedlings. Substitution lines of these(resistant or moderately resistant) genotypes into (susceptible) ChineseSpring were selected from a previous screening. For Synthetic 6x,resistance was clearly located in chromosome 7D. Chinese Spring with the7D chromosome substituted by Synthetic 6x showed almost completeresistance, similar to the level of Synthetic 6x. For the substitutions withCappelle-Desprez, Cheyenne, and T.spelta there were no lines with abehaviour similar to the resistant parent. However, some substitutions weremore resistant than the susceptible parent suggesting that severalchromosomes could be involved in the resistance of these genotypes toSeptoria leaf blotch.     

Molecular mapping of quantitative trait loci determining resistance to septoria tritici blotch caused by Mycosphaerella graminicola in wheat

A set of 65 recombinant inbred lines of the ‘International Triticeae Mapping Initiative’ mapping population (‘W7984’בOpata 85’) was analysed for resistance to septoria tritici blotch at the seedling and adult plant stages. The mapping population was inoculated with two Argentinean isolates (IPO 92067 and IPO 93014). At the seedling stage, three loci were discovered on the short arms of chromosomes 1D, 2D and 6B. All three loci were detected with both isolates. At the adult plant stage, two isolate-specific QTL were found. The loci specific for isolates IPO 92067 and IPO 93014 were mapped on the long arms of chromosomes 3D and 7B, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

The use of wheat/goatgrass introgression lines for the detection of gene(s) determining resistance to septoria tritici blotch (Mycosphaerella graminicola)

At the IPK Gatersleben a series of 85 bread wheat (T. aestivum)/goatgrass (Aegilops tauschii) introgression lines was developed recently. Based on the knowledge that chromosome 7D of this particular Ae. tauschii is a donor of resistance to septoria tritici blotch (Mycosphaerella graminicola), a sub-set of thirteen chromosome 7D introgression lines was investigated along with the susceptible recipient variety ‘Chinese Spring’ (CS) and the resistant donor line ‘CS (Syn 7D)’. The material was inoculated with two Argentinian isolates of the pathogen (IPO 92067 and IPO 93014) at both the seedlings (two leaf) and adult (tillering) stages at two locations over 2 years (2003, 2004). The resistance was effective against both isolates and at both developmental stages, and the resistance locus maps to the centromeric region of chromosome arm 7DS. On the basis of its relationship with the microsatellite marker Xgwm44, it is likely that the gene involved is Stb5. Stb5 is therefore apparently effective against M. graminicola isolates originating from both Europe and South America.     

The influence of disease complexes involving Leptosphaeria (Septoria) nodorum on detection of resistance to three leaf spot diseases in wheat

Summary In controlled inoculation studies with Septoria nodorum and Pyrenophora tritici-repentis, estimates of the relative proportion of each pathogen demonstrated differences in the responses of cultivars to pathogen mixtures that were not apparent from measurements of diseased leaf areas. Under field conditions estimates of the relative proportion of S. nodorum, P. tritici-repentis and S. tritici varied between field screening locations in Western Australian but also between lines within locations. Lines with known resistance to P. tritici-repentis and S. tritici, but susceptible to S. nodorum, could not be distinguished from susceptible lines on the basis of leaf area diseased or grain weight depression when S. nodorum was present in the disease complex. Such conditions, while suitable for the selection of combined resistance to these pathogens, were unsuitable for identifying resistance to individual pathogens. As symptoms were similar, the proportion of diseased leaf area sporulating with each pathogen provided a means of measuring the variation in disease development induced on lines varying in resistance. Knowledge of the components of disease and their relative importance were essential in understanding varietal response information under mixed infections of these leaf spot pathogens.     

Chromosome location of resistance to septoria leaf blotch and common bunt in wheat-barley addition lines

Septoria leaf blotch and common bunt are important diseases of wheat to which Hordeum vulgare is resistant. Addition lines of H. vulgare in wheat were utilized to determine which H. vulgare chromosomes carry resistance genes. Resistance to septoria leaf blotch was conferred by gene(s) present all over the barley genome, but more strongly by those located on chromosomes 7 and 4. Almost complete resistance to common bunt was conferred by gene(s) present in chromosomes 6 and a slight but significant level of resistance was conferred by chromosome 7. This revised version was published online in August 2006 with corrections to the Cover Date.     

Resistance to Septoria nodorum blotch in several Triticum species

Summary Resistance to septoria nodorum blotch in Triticum monococcum, T. tauschii, T. timopheevii, T. dicoccum and T. durum was evaluated on plants at the three-leaf stage in greenhouse tests. A high frequency of resistant genotypes was found in T. monococcum, T. tauschii and T. timopheevii, but not in T. dicoccum and T. durum. The resistance of F₁ plants of crosses of resistant T. monococcum (PI 289599) and T. timopheevii (PI 290518) accessions with susceptible common wheat cv. Park and durum wheat cv. Wakooma, respectively, was evaluated on the basis of percentage leaf necrosis, lesion number, lesion size and incubation period. No dominance was found for long incubation period, but various dominance relationships occurred for low percentage leaf necrosis, low lesion number and small lesion size, depending on the cross. Multiple regression analysis showed that lesion number contributed more to percentage leaf necrosis than lesion size or incubation period. Resistance to septoria nodorum blotch was transferred successfully from T. timopheevii to cultivated durum wheat. Resistant BC₁F₇ lines, recovered from the T. timopheevii (PI 290518) × Wakooma cross, showed normal chromosome behaviour at meiosis (14 bivalents) and were self-fertile. However, an effective level of resistance was not recovered in lines derived from the other interspecific crosses.     

Date of heading and plant height of wheat varieties,as related to septoria leaf blotch damage

Summary Septoria leaf blotch readings, date of heading and plant height appeared strongly correlated in six variety trials with 25 varieties each. Three trials were conducted in 1972 and three in 1976. The taller and later the cultivars, the lower its Septoria leaf blotch score tended to be. The yields also were less strongly reduced in taller and later cultivars, as calculated from another experiment.     

Components of partial resistance to Leptosphaeria nodorum among seven soft red winter wheats

Summary Seven soft red winter wheat cultivars were evaluated for partial resistance to Leptosphaeria nodorum under field conditions. The results demonstrate that resistance is available among cultivars that are adapted to the southeastern U.S. and that resistance is long lasting. Resistant cultivars had longer incubation and latent periods, slower rates of lesion development, and reduced the level of sporulation of L. nodorum. Seedlings of susceptible cultivars sustained severe disease with dew periods as short as 48 hr in greenhouse tests. One resistant cultivar sustained little damage with dew period as long as 144 hr.Latent period was shortest on the second leaf below the flag leaf (F-2 leaf) of all cultivars and longest on the flag leaf which reflected the effect of microclimate and leaf age. The range in length of latent period on the flag, F-1, and F-2 leaves of resistant cultivars was less than that for susceptible cultivars. Differences between cultivars were greatest (up to 6.8 days) for the F-2 leaf. A delay in production of inoculum on the F-2 and lower leaves of resistant cultivars should delay infection of the flag leaf and spike.The greatest differentiation among cultivars for sporulation of L. nodorum was on upper leaves at Feekes growth stage 11.2. Oasis consistently had less sporulation than other cultivars at all sampling dates and leaf positions. The rate of disease progress up the plant (disease severity) and area under the disease progress curve were also least on Oasis.There were significant correlations among components of resistance and associated components suggesting that a single or interrelated mechanisms control expression of resistance. Overall, Oasis was the most resistant cultivar followed by Coker 762 and Coker 747. There cultivars have remained resistant for ten or more years. Stacy was intermediate in resistance and was the most variable of the seven cultivars for the components tested. Holley, Omega 78, and Florida 301 were highly susceptible by all criteria tested. Plant height was not a factor in resistance. The resistant cultivars are mostly later in maturity than the susceptible cultivars. In this study, crop maturity was similar under existing environmental conditions during the two seasons when most data were collected.     

Diallel analysis of resistance to Septoria tritici isolates in durum wheat

Summary All crosses, except for reciprocals, were made among ten cultivars originating from crop improvement programs in North Africa and the Middle East. The entries varied widely in reaction to Septoria tritici. F₁ and F₂ progenies of the crosses were evaluated using eight S. tritici isolates from seven countries in the Mediterranean area. Thus, sixteen separate combining ability analyses were excecuted. General combining ability (GCA) was the major component of variation, although specific combining ability (SCA) was present in most cases. Additive variance thus appears to be of predominant importance. Nevertheless, non-additive variance may interfere when line selection in a breeding program is practiced. While differing greatly among cultivars, specific GCA effects for each cultivar separately were of similar magnitude for all isolates. Ranking statistics determined that cultivars were ranked in similar order for both means and specific GCA effects independent of the isolate used. Different isolates may therefore interact with similar or identical genetically controlled mechanisms in a particular cultivar. This could indicate the absence of differential gene-for-gene relationships and suggests that isolates vary in aggressiveness rather than in virulence.     

Generation mean analysis to identify and partition the components of genetic resistance to Septoria nodorum in wheat

Summary Foliar symptom severity of seedlings artificially inoculated with S. nodorum were used to idenify the type of gne action controlling resistance to this pathogen in the early generations of two wheat crosses. In both crosses a resistant spring wheat cultivar was crossed to a susceptible cultivar. Reciprocal crosses were included in the analysis to determine if the cytoplasm contributed in any significant degree to the level of resistance present.Results indicated that resistance was polygenic and that it could be explaned prinerpally by additive gene effects. Some differences in reciprocal crosses were evident, but a significant role for the eytoplasm in resistance is not indicated.Cooperative investigations of the Agricultural Research Service of the U. S. Department of Agriculture and the Montana Agricultural Experiment Station. Journal Paper No. 1210.     

Recent advances in alien gene transfer in wheat

Summary The recent advances in alien gene transfer from distantly-related species into wheat are reviewed in the present paper. The main achievements during the last ten years include the great expansion of the range of wide hybridization and development of new techniques for production and characterization of wheat-alien chromosome translocations. Updated results of wide hybridization since 1983 and comprehensive characterization of wheat-alien translocation lines in our laboratory are compiled. The future outlook for alien gene transfer in wheat is also discussed.     

Identification of Vigna spp. through specific seed storage polypeptides

Summary Seed globulins of ten Vigna species were separated by means of SDS electrophoresis. Both inter and intraspecific variation were observed.Groups of specific bands which do not vary in the species being present in all the accessions of the species were identified. These species-specific bands, allow the identification of the 10 Vigna spp. analyzed.     

Resistance in Lactuca spp. to Microdochium panattoniana (lettuce anthracnose)

Summary Four hundred and forty-nine lines of Lactuca spp. were screened for resistance to an isolate of Microdochium panattoniana. Eighty-seven lines were resistant. Forty-four lines were then screened for resistance to four isolates; twelve groups of lines were identified on the basis of their pattern of resistance. A differential set of lines was used to analyse nine further isolates; this revealed five races of M. panattoniana. Salad Bowl was the only cultivar found to be resistant to three races. A line of L. saligna, UC83US1, was the only line found to be resistant to all the isolates tested.     

Eighth supplementary list of wheat varieties classified according to their genotype for hybrid necrosis

Summary The eight supplement contains 901 varieties etc. viz. 163 (18.1%) Ne ₁-, 153 (17.0%) Ne ₂- and 585 (64.9%) non-carriers. The total number of varieties etc. tested is 1461 (26.4%) Ne ₁-, 1184 (21.4%) Ne ₂- and 2885 (52.2%) non-carriers, together 5530.Various aspects of hybrid necrosis like the geographical distribution of the Ne-genes and their alleles, linkage, Green Revolution, durum wheat and the cause have been discussed. Some information is given on some of the listed varieties etc.This is my last supplement.     

Chromosomal location of resistance to Septoria tritici in Hordeum chilense determined by the study of chromosomal addition and substitution lines in `Chinese Spring' wheat

Hordeum chilense exhibits resistance to Septoria tritici. Addition and substitution lines of H. chilensein wheat were utilized in growth chamber and field experiments to determine which H. chilense chromosomes carry resistance genes. Resistance is conferred by gene(s) on chromosome 4 and, to a minor extent, by genes on chromosomes 5, 6 and 7. This revised version was published online in July 2006 with corrections to the Cover Date.