Short Communication Resistance to common bunt in Hordeum chilense X Triticum spp. Amphiploids

The reaction of tritordeum and its Hordeum chilense and Triticum spp. parents to common bunt incited by Tilletia tritici were determined in field experiments. H. chilense accessions were very resistant, and durum wheats exhibited high to moderate levels of resistance. Conversely, bread wheats were highly susceptible. Resistance from H. chilense was expressed in the amphiploids, although the level of resistance was partially diluted at higher ploidy levels. Hexaploid tritordeums were immune to the disease; some infection was observed among the octo-ploids but at much lower levels than in their respective wheat parents.     

Single-gene resistance to Septoria tritici blotch in the spring wheat cultivar 'Tadinia'

Resistance to Mycosphaerella graminicola causal agent of Septoria tritici blotch, was identified in progenies of crosses with European winter wheat cultivars, Tadorna and Cleo. This resistance was used to develop the resistant spring wheat cultivar Tadinia, selected from ‘Tadorna’/‘Inia 66’ released in 1985. Evaluation of the progeny of intercrosses between ‘Tadorna’, ‘Cleo’, ‘Tadinia’, and two short-statured resistant lines derived from hybrids with ‘Tadinia’ as one parent indicate the resistance was inherited as a single gene showing partial to strong dominance. The gene in ‘Tadinia’ was designated Stb4. Crosses between another resistant cultivar, ‘Bulgaria 88’, and ‘Tadinia’ suggest that ‘Bulgaria 88’ does not have Stb4. Successful introgression of Stb4 into Rht1+Rht2 short-statured lines revealed that plant stature and resistance to M. graminicola segregated independently. The Stb4 gene has been effective since 1975 against M. graminicola extant in California. A high positive correlation between seedling and adult plant disease scores, based on scoring of lesions producing pycnidia, indicated that the Stb4 gene is expressed throughout the life cycle under both field and greenhouse conditions, confirming that disease screening can be carried out on seedling plants. Separate assessment of necrotic lesions with and without pycnidia indicated that leaf necrosis without pycnidia, observed, especially under greenhouse conditions, can confound disease evaluations and lead to inaccurate genotype classification.     

Diallel analysis of four resistance components to Septoria tritici in six crosses of wheat (Triticum aestivum)

Four resistance components, i.e. incubation period, latent period, maturation period and pycnidial coverage, were studied in a diallel cross of four wheat cultivars differing in susceptibility to Septoria tritici. Inoculations and evaluations were carried out at the fourth leaf stage for two years. A combined ANOVA for both years exhibited a significant interaction between crosses and years for maturation period. A separate ANOVA for each year was done for this trait. The combined ANOVA showed that crosses were significantly different for incubation, latent period and pycnidial coverage. Cross effects were also significant for maturation period in each year for the separate ANOVA. Year effects were significant for latent period and maturation period. General combining ability (GCA) was significant and preponderant for incubation period, latent period and pycnidial coverage. For maturation period, the separated ANOVA showed the significance of the GCA for both years. Specific combining ability (SCA) was significant for incubation and pycnidial coverage and for maturation in one year. The preponderance of the additive genetic variance for all traits indicates the possibility of selecting for them in order to obtain improved cultivars. Incubation period was inherited independently of maturation period and pycnidial coverage, indicating that combinations of some of those characters may lead to more effective and durable resistance.     

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.     

Heading date and resistance to septoria tritici blotch in wheat not genetically associated

Nineteen cultivars, with large differences in heading date, were evaluated for their response to septoria tritici blotch in two experimental setups in Njoro, Kenya. Due to the more or less constant temperatures during the growing season and the overhead irrigation applied the epidemic conditions were similar over the whole observation period for the early and late cultivars. In experiment 1 the cultivars were assessed for disease severity at the same moment irrespective of the developmental stage, while in experiment 2 the cultivars were assessed at the same developmental stage. Measured at the same time, the disease severity was highest in the early maturing cultivars and lowest in the late maturing cultivars (r = –0.78). When assessed at the same development stage the disease build up was independent of heading date (r = –0.10) but strongly dependent on resistance level. There were no indications that early heading cultivars were more susceptible than late heading cultivars. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Inheritance of Resistance to Septoria Glume Blotch III. The Wild Wheat Species Aegilops Jongissima

The genetics of resistance to Septoria glume blotch (caused by the pathogen Septoria nodorum Berk.) in the wild wheat species Ae. longissima was investigated. The resistance was characterized by two parameters measured on detached leaves — lesion size (LS) and length of latent period (LP), and by disease severity (DS) under field conditions. Generations F₁, F₂ and F₃, derived from a cross between two Ae. longissima accessions, were analyzed. The two parameters measured on detached leaves (LS and LP) were highly correlated, while DS was moderately correlated to both LS and LP. The mean LS and the mean LP of F₁ generation indicated considerable dominance for resistance in both parameters. The estimates of broad-sense and narrow-sense heritability were moderate for LS and LP (0.21—0.55). Narrow-sense heritability for DS was high (0.77). Estimates of the number of genes controlling each of the parameters (LS, LP, DS) were between 2.5—3.2. It is suggested that the resistance is controlled by three to four quantitative genes with a partial dominance of the alleles for resistance. Indications for genie interaction were found in LS and in LP. A model of inheritance containing complementation between dominant resistance-alleles is suggested. Highly resistant Ae. longissima accessions are recommended as sources of germplasm for improving the resistance of cultivated wheats to Septoria glume blotch. The possibility of using dominant alleles for resistance in hybrid cultivars is discussed.     

The Inheritance of Resistance to Septoria Glume Blotch:

The inheritance of resistance in common wheat (Triticum aestivum, L.) to Septoria glume blotch, caused by the pathogen Septoria nodorum Berk., was studied. Four quantitative parameters of resistance were measured: infection efficiency (IE) and disease severity (DS) on intact young plants together with legion size (LS) and length of latent period (LP) on detached leaves. The method of testing the disease reaction of wheat to S. nodorum on detached leaves was refined and standardised to minimize the non-pathological sources of variation. Four wheat cultivars were tested for their reaction to 11 Septoria nodorum isolates. Two of the cultivars were crossed for studies on the genetics for host resistance, using a single S. nodorum isolate for inoculation; parental, F₁, F₂ and F₃ populations were analysed. Interaction between wheat cultivars and S. nodorum isolates was significant, but its variance component was quite small compared with the main effects of cultivars and isolates, The inheritance of resistance was mainly additive, with low to moderate heritability, apparently controlled by 3 to 4 quantitative genes, with indications of gene interactions. LS and LP were highly correlated, suggesting pleiotrapy for these two parameters of resistance. IE and DS (on intact plants) were moderately correlated to LS and LP (on detached leaves), apparently due to a partial pleiotropy or linkage.     

Inheritance and chromosomal location of Septoria passerinii resistance introgressed from Hordeum bulbosum into Hordeum vulgare

Septoria speckled leaf blotch (SSLB), caused by Septoria passerinii, has become one of the most serious diseases of barley in the Upper Midwest region of the USA. The recombinant line 36L5 derived from a backcross of the susceptible barley cultivar ‘Emir’ and a resistant Hordeum bulbosum parent Cb2920/4/Colch was found to be resistant to S. passerinii. Two doubled haploids derived from 36L5 were backcrossed to cv.‘Emir’ to obtain two BCF₂ populations for determining the inheritance of resistance to S. passerinii. BCF₂ progeny and BCF_2:3 families were evaluated at the seedling stage in the greenhouse for reaction to S. passerinii. BCF₂ progeny and BCF_2:3 families from both crosses segregated 3 : 1 (resistant : susceptible), and 1:2:1 (resistant : segregating : susceptible), respectively, indicating that the H. bulbosum‐derived SSLB resistance is conferred by a single dominant gene. The H. bulbosum introgressions were positioned on chromosome 4HL by genomic and fluorescent in situ hybridizations (GISH and FISH, respectively) and by Southern hybridization with the rye repetitive sequence pSc119.2. These findings indicate that SSLB resistance in H. bulbosum has the potential to be transferred and utilized in barley breeding programs.     

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.     

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.     

The Amphiploid Hordeum chilense× Triticum aestivum ssp. sphacrocoecum. Variability in Octoploid Tritordeum

In order to increase variability in the octopioid tritordeum a new octoploid tritordeum has been synthesized after colchicine doubling of the chromosomes of the Hordeum chilense × Triticum aestivum ssp. sphaerococcum hybrid. The amphiploid showed full pairing in 30 % of the pollen mother cells, The fertility was higher than in previous tritordeums (1.65 grains per spikelet and 43.00 grains per spike). Hybrids between the octoploid tritorceums were sterile. However, hexaploid × octopiold trhordeum hybrids were fertile and secondary tritordeums were extracted with increased fertility.     

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.     

The Inheritance of Resistance to Septoria Glume Blotch II. The Wild Wheat Species Aegilops speltoides

The inheritance of resistance in the wild wheat species Ae. speltoides L. to Septoria glume blotch (Septoria nodorum Berk.) was investigated. It was characterized by two parameters measured on detached leaves, namely lesion size (LS) and length of latent period (LP), and by the severity of the disease under field conditions (DS). The genetic analysis was based on the F₁ and F₂ generations of a 4 × 4 diallel cross between four Ae. speltoides accessions showing differential resistance to the pathogen. The three parameters of resistance were highly correlated. Considerable heterosis for resistance was found for each of the parameters in most of the diallel combinations. The estimates of broad-sense heritability were moderately high (0.50 — LS, 0.60 — LP, 0.52 — DS), while the estimates of narrow-sense heritability were low (0.16 for LS, 0.20 for LP, 0.25 for DS). There were no indications for genie interaction. It is suggested that the resistance is controlled by at least two genes with over-dominance of the alleles for higher resistance. Highly resistant Ae. speltoides accessions are a potential source of germplasm for improving the resistance of cultivated wheats to Septoria glume blotch. The possibility of using dominant alleles for resistance in hybrid cultivars is discussed.     

The contribution of Hordeum chilense to partial resistance of tritordeum to wheat brown rust

Summary Hexaploid and octoploid tritordeum and their Triticum spp. parents were studied in the seedling stage to compare their components of partial resistance to Puccinia recondita f.sp. tritici. The components studied were infection frequency, latency period and size of uredia. The non-host Hordeum chilense parent does not confer any increase of partial resistance to wheat brown rust to its amphiploids with wheat.     

Resistance of Triticum dicoccoides to infection with Erysiphe graminis tritici

Summary The reactions of 233 Triticum dicoccoides acessions, collected at 10 sites in Israel and elsewhere, to infection with cultures of Erysiphe graminis tritici, were determined. The reactions indicated that the number of sources of resistance to E. graminis tritici which can be obtained from T. dicoccoides plants growing wild in Israel and elsewhere is almost unlimited. One hundred and fourteen or 49% of the accessions were resistant, and 137 or 59% of the accessions were resistant or moderately resistant to infection with four cultures of E. graminis tritici which possess the virulence genes corresponding to most of the identified resistance genes in wheat. Accessions collected at sites with marginal habitats where T. dicoccoides grows poorly and has lower grain weight, were more susceptible than were accessions collected at sites with an optimal habitat for growth of T. dicoccoides. The results agreed with those in a previous study with Hordeum spontaneum, and indicate that to obtain H. spontaneum or T. dicoccoides accessions with the highest level of resistance to the powdery mildew pathogens, plants should be collected at sites in ecological and geographic regions where those two species occupy optimum habitats and are exposed to the powdery mildew pathogens.     

The reaction of x Tritordeum and its Triticum spp. and Hordeum chilense parents to rust diseases

Summary Hexaploid and octoploid tritordeums and their parents Hordeum chilense and Triticum spp. were screened for resistance to isolates of wheat and barley yellow and brown rusts. All H. chilense lines were highly resistant to both wheat and barley brown rust, few lines were susceptible to wheat yellow rust while susceptibility to barley yellow rust was common. In general the resistance of tritordeum is predominantly contributed by the wheat parent and apparently the genes for resistance in H. chilense are inhibited in their expression by the presence of the wheat genome.Abbreviations WYR wheat yellow rust - WBR wheat brown rust - BYR barley yellow rust - BBR barley brown rust     

Resistance to Karnal bunt in Hordeum chilense and its amphiploids with Triticum species

Reactions of Hordeum chilense accessions H1 and H7 and their amphiploids, HT8, HT9 and HT28 (named as tritordeum) alongwith wheat lines, T22, T24 and T59 used in their synthesis, were studied for resistance to the Karnal bunt pathogen (Tilletia indica) of wheat. Both the accessions of H. chilense and one tritordeum line, HT8, were rated as highly resistant with zero co-efficient of infection, whereas the other two tritordeum lines HT28 and HT9 were rated as moderately susceptible and susceptible with 5.2 and 10.5 co-efficients of infection, respectively, compared to reaction of the wheat lines involved in their synthesis. Karnal bunt infection was maximum on the susceptible wheat cultivar WL-711 with 24.3 co-efficient of infection. All the wheat lines involved in the synthesis of amphiploids were susceptible to Karnal bunt except, T59 (Triticum sphaerococcum) (6X), which showed a moderate level of resistance. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Genotypic variation for resistance to Septoria nodorum in triticale

Septoria nodorum leaf and glume blotch is an important disease of triticale (×_Triticosecale Wittm.) and can cause severe losses of grain yield in some regions. Quantitative genetic parameters for resistance were estimated for 2 years in two locations in triticale genotypes artificially inoculated with S. nodorum. The effect of infection was assessed by a visual symptom rating of flag leaves and spikes and by grain yield traits relative to an uninoculated control. The mean ratings of flag leaves and spikes, calculated from two to four ratings, were 2.6 and 3.9, respectively, with a range of six ratings for spikes and over five for flag leaves. Infection caused an 11.5% mean reduction in kernel weight per spike, which was the result of 13.2% lower 1000‐kernel weight. The number of kernels per spike and 50‐ml weight were little affected. For all relative grain yield traits, genotypic variation was small with high genotype‐environment interaction effects and thus moderate to low heritabilities. In contrast, for visual ratings genotypic variation was high, with low interaction effects leading to high heritabilities. Phenotypic correlation between flag leaf and spike ratings was low, indicating independent disease resistance mechanisms. The best association, although still moderate, was obtained between flag leaf rating and relative 1000‐kernel weight. Therefore, visual disease ratings do not satisfactorily assess the effect of Septoria infection on grain yield traits. The reduction in 1000‐kernel and possibly 50‐ml weight are good indicators, provided that multi‐environment tests are conducted.     

A New Source of Resistance to Puccinia striiformis f. sp. tritici in Spring Wheats (Triticum aestivum)

The use of P. striiformis f. sp. tritici pathotypes virulent or avirulent with respect to both Yr6 and a previously undescribed source of resistance, designated YrA, allowed the recognition of the corresponding host resistance genes m a range of Australian and exotic spring wheats. The phenotypes conferred by the YrA resistance varied when exposed to contrasting light intensities in the post-inoculation phase. The implications of the results in international studies of host resistance to P. striiformis f. sp. tritici are discussed.