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.     

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.     

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,heritability and breeding behaviour of three sources of resistance to Septoria tritici in wheat

Summary We examined the inheritance, heritability, and breeding behaviour of resistance to Septoria tritict in the spring wheat cultivars Seabreeze, Veranopolis, and IAS-20 in crosses to the susceptible Australian spring cultivar Gamenya. Resistance in Seabreeze was higher than that in Veranopolis and IAS-20. Inheritance of resistance in Seabreeze seems to be determined by at least three recessive genes. Resistance in Veranopolis and IAS-20 might be due to a single gene. Similarity of inheritance patterns and breeding behaviour of the resistance from Veranopolis and IAS-20 and the common ancestry of these two cultivars suggest that they may carry the same gene. Standard unit heritabilities of Septoria scores, as measured by correlation of F₂ plant with F₃ family mean data, were high (57–68%). Parent offspring genetic correlations confirmed previously reported associations between resistance and lateness and resistance and tall plant height, but correlations were not sufficiently high to be a major obstacle to selection. Resistance in Veranopolis and IAS-20 were easily recovered in first backcrosses while that in Sea breeze was more difficult to recover.Contribution from the Department of Agriculture Western Australia.     

Inheritance of cleistogamic flowering in durum wheat (Triticum durum)

Summary Generally durum wheat flowers are chasmogamous but very rarely, cleistogamy may be observed. Genetic studies based on six crosses and back crosses showed that chasmogamy was determined by a single dominant gene Cl, plants homozygous for the recessive allele, cl, were cleistogamous. The flowering behaviour phenotypes were unaffected by environmental conditions. Cleistogamy was attributed to poorly developed lodicules and stiff perianth.     

Phenotypic variation in boron-toxicity tolerance at seedling stage in durum wheat (Triticum durum)

Summary Nineteen durum wheat landraces, cultivars or advanced lines of different origins in West Asia and North Africa (WANA), and three barley and two bread wheat varieties were evaluated for their boron (B) toxicity tolerance. Seedlings were grown at five levels of soluble soil B in a plastic house under controlled temperatures. Significant differences existed between the durum wheat entries in days-to-symptom appearance and foliar symptom score. Under the highest soil B treatment, large differences existed between entries for dry weight per plant (P<0.05) but differences were non-significant for shoot B concentrations. Days-to-symptom appearance was highly correlated with symptom score, which was not correlated with shoot B concentrations. Boron toxicity symptom scores of the durum wheat entries ranged from the sensitive barley check to the moderately sensitive bread wheat check. As expected, days-to-symptom appearance decreased and symptom severity increased as the soil B concentrations increased.The result of this study supported the preliminary finding that small, though statistically significant, variation in B toxicity symptom scores exist in durum wheat. The higher CV of symptom scores found here was mainly due to one sensitive entry, Cakmak. If Cakmak was excluded from the analysis, the CV would be reduced by half, to 10%. Durum wheat genotypes which are more tolerant to B toxicity should be sought. Based on the results of this study, and of soil surveys and information collected in WANA, germplasm collected from Algeria, Iraq, Libya, Syria, and the Anatolian Plateau of Turkey should be screened first.Abbreviations B boron - WANA West Asia and North Africa     

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.     

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.     

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.     

Genetics of resistance to Puccinia graminis tritici and Puccinia recondita tritici in Kenya Plume wheat

Summary Seven genes, viz. Sr5, Sr6, Sr7a, Sr8a, Sr9b, Sr12 and Sr17 were associated with seedling resistance to Puccinia graminis tritici in Kenya Plume wheat. The predominant field cultures were avirulent on seedlings with Sr7a, but possessed virulence for the other six genes. However, Sr7a did not confer adult-plant resistance when present on its own. Adult-plant resistance was attributed to Sr2 and possibly also to the interaction of Sr7a and Sr12.Two genes, Lr13 and Lr14a, were identified in seedling tests with various cultures of Puccinia recondita tritici. Lr13 conferred adult-plant resistance to the predominant field strains. Genetic recombination between Lr13 and Sr9b was estimated at 17.6±3.1%.     

Genetic variation for tolerance or resistance to barley yellow dwarf virus in durum wheat

Summary One durum wheat line (Triticum durum), cv. 82PCD476, with useful BYDV tolerance or resistance, was singled out of 5 152 lines evaluated between 1979 and 1986. A few other lines such as cv. Boohai and cv. 12th IDSN 227, slightly inferior to cv. 82PCD476, also showed some value. With an hybrid of cv. 12th IDSN227 with the susceptible cv. 84PCY-S531, broad-sense heritability values of 0.37–0.41 were obtained for symptoms and a heritability value of 0.55 was obtained for the total weight of spikes. The weight of spikes was considered as a good indicator of wheat tolerance to BYDV. Although BYDV resistance or tolerance genes are not very common in durum wheat, sources of heritable resistance could be found. However, the resistance ofT. aestivum to BYDV was superior to the one found inT. durum.Cintribution no. 323     

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.     

Diallel analysis of resistance to head blight caused by Fusarium culmorum in winter wheat

Summary Ten homozygous winter wheat genotypes representing different levels of resistance to Fusarium head blight were crossed in all possible combinations excluding reciprocals. Parents, F₁ and F₂ were inoculated with one pathogenic strain of Fusarium culmorum. Data for head blight, observed 21 days after first inoculation (OBS-2), and for the area under the disease progress curve, based on observations 14, 21 and 28 days after first inoculation (AUDPC), were analyzed. The contrast between parents and F₁ crosses indicated dommance effects of the resistance genes. Diallel analysis according to Griffing's Method 4, Model 1 showed significant general combining ability (GCA) effects for both F₁ and F₂; specific combining ability effects were not significant. With the exception of one genotype for which general performance for Fusarium resistance was not in agreement with its GCA, the resistance to F. culmorum was uniformly transmitted to all offspring, and the parents can be described in terms of GCA. It is suggested that in the progenies with one of the awned lines as parent, one resistance gene was linked with the gene coding for presence of awns, located on chromosome 4B. A single observation date, taken at the right time, was as effective in assessing resistance as the AUDPC.     

Physiological responses of six bread wheat and durum wheat genotypes to water stress

Summary The responses of six wheat genotypes to water stress were analysed. Soil moisture (H), leaf water potential (_w), photosynthesis (P_N), stomatal resistance (r_s) and transpiration (T) were measured during a water stress. The genotypes investigated differed in their stress avoidance (_w-H relationship) and their stress tolerance (P_N-_w and r_s-_w relationships). The most important differences observed concern the mechanisms of tolerance at low leaf water potential: two varieties, Haurani 27 and Baalback, can then maintain a high photosynthetic activity. These observations are in agreement with the drought resistance characteristics already known for these genotypes. Possible applications to wheat breeding are considered     

Genotypic variation in durum wheat root systems at different stages of development in a Mediterranean environment

Summary Glasshouse and field experiments were carried out to compare root growth of eight durum wheat genotypes at different stages of development with different moisture levels and in different soils. Genotypic differences were found, particularly at the stem elongation and heading stages of development, but the ranking of genotypes varied in relation to soil moisture level and fertility. Differences under optimal moisture level were mainly due to differences in tillering and disappeared by considering the root number and weight per culm. Drought caused an increase in the root-to-total-plant weight ratio (18.5 vs 14.3% at heading) but also an increase in absolute root weight. Karel, the genotype with the largest root mass under drought and the greatest proportion of roots in the upper soil layers (more than 50% in the 0–20 cm layer from heading onwards), showed the lowest yield reduction under severe stress. A large root system with a high density of roots in the upper layers of the soil profile may be beneficial in Mediterranean climates.Research supported by a grant of Ministero della Pubblica Istruzione (40%).     

Sources of resistance to Mayetiola Destructor in breadwheat and durum wheat in Morocco

Summary Grain yield reductions of both breadwheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L. var. durum) caused by attacks of Hessian fly (Mayetiola destructor Say) are second perhaps only to those caused by inadequate soil moisture in Morocco. To identify effective sources of resistance, 817 entries of common wheat and durum wheat reported to be resistant to Hessian fly were evaluated under natural infestations in Morocco. A large number of genes conferring virulence are present in populations of Moroccan Mayetiola. The genes H₁, H₂, H₃, h₄, H₆, H₇, H₈, H₉, H₁₀, H₁₁, H₁₄, H₁₅, and H₁₆ as well as the Marquillo, Kawvale and PI 94587 resistance sources are not useful for cereal improvement in North Africa. Luso, which has the gene H₁₂, also appeared susceptible in limited testing. Genotypes having the genes H₅ and H₁₃ were identified as significantly reducing larval survial in natural populations of Mayetiola. Of 11 resistant breadwheats identified with unknown genes, seven were from Portugal and three were from the Soviet Union. Although none of the durums tested had high levels of reistance, the two most promising durums were from Portugal. It is proposed that initially H₅ be deployed in durum wheats and H₁₃ be used in common wheat improvement. Leaf pubescence appears of little use in reducing the larval survival of Mayetiola.     

Levels of phenotypic variation for developmental traits in landrace genotypes of durum wheat (Triticum turgidum ssp. Turgidum L. conv. durum (Desf.) MK.) from Jordan

Summary A germplasm collection comprising 132 landrace genotypes of durum wheat (Triticum turgidum) ssp. turgidum L. conv. durum (Desf.) MK., from 10 districts in Jordan was evaluated for days to booting (DB), days to heading (DH), days to anthesis (DA), days to maturity (DM), filling period (FP) and grain yield (GY). In spite of the relatively strong genetic (Gr) and phenotypic (Pr) correlation coefficients between the developmental traits, the variation among genotypes was significant. GY was only positively and significantly correlated with DA and FP, while it was negatively correlated with DH. Genotypes with different combinations of early, medium and late developmental traits have been identified. Different combinations of DH and FP may or may not lead to differences in DM and GY. However, genotypes with long FP and medium-late DH gave the highest grain yield. Multiple linear regression of the duration of maturity (M) stage on the duration of booting (B), heading (H) and anthesis (A) stages (M = –260.87 + 2.09 B + 1.23 H + 0.9 A, R ² = 0.92) indicates that it is possible to manipulate the duration of these developmental stages and develop genotypes with high yield potential and early maturity, a highly desirable in drought-prone environments.     

Performance of durum wheat landraces in a Mediterranean environment (eastern Sicily)

Summary The evaluation aimed at identifying landrace genotypes adapted to the rather unfavourable growing conditions of durum wheat in Sicily, to be used as parental material in a breeding programme. The trial was carried out in three seasons experiencing varying climatic conditions, and included 75 landraces, 25 of which were selected under severe drought in Syria. Wide differences were observed for most traits among genotypes and seasons of evaluation. Yields of the best performing entries identified in each season never significantly differed from that of the best check variety. The top-yielding landraces were consistently better than the remaining entries for the three yield components, viz. number of spikes per plant, number of kernels per spike and mean kernel weight. In the driest season they were also significantly earlier in heading, confirming the importance of earliness under drought. An analytical breeding approach relying on an array of morpho-physiological traits as selection criteria did not seem appropriate for the given environment, as the variable stress level enhanced the importance of specific traits under specific situations. The genotypic response was largely season-specific. Nonetheless, five landraces were in the best group in all seasons. The selection made in Syria also appeared somewhat effective in Sicily, particularly in the less favourable seasons.     

Photosynthesis,transpiration, resistance to CO2 transfer,and water efficiency of flag leaf of bread wheat,durum wheat and triticale

Summary Net photosynthesis, transpiration, and resistances to CO₂ and water vapour transfer of two cultivars of each of four types (Triticum durum, Triticum aestivum. hexaploid Triticale, octaploid Triticale) were analysed. Hexaploid triticales have the highest net photosynthesis and the best water efficiency. Water efficiency was defined by the CER/transpiration ratio measured under saturating irradiance corresponding to full stomatal opening. Cultivated bread and durum wheat cultivars (Capitole, Champlein, Bidi 17) are characterised by a low CER associated with a large flag leaf area and a high mesophyll resistance. There is a close correlation between CER., flag leaf area, mesophyll resistance and total chlorophyll content.     

Nitrogen uptake and nitrogen harvest index in durum wheat cultivars varying in their grain protein concentration

Summary In a field experiment, plant (excluding roots) and grain nitrogen at harvest were estimated in 15 durum wheat cultivars varying in their grain protein concentration. They showed significant variation in grain yield, grain protein concentration, biological yield, total plant nitrogen at harvest and residual nitrogen in straw. Harvest index and nitrogen harvest index were calculated from this primary data. Nitrogen harvest index varied from 57 to 83%. Plant nitrogen showed significant positive correlation with biological yield, grain yield and grain protein yield, but the correlations with grain protein concentration, harvest index and nitrogen harvest index were not significant. Nitrogen harvest index was positively correlated with harvest index indicating that the distribution of N between straw and grain to a large extent, but not entirely, depends upon the partitioning of dry matter between the two. Grain protein concentration was neither correlated significantly to plant nitrogen nor to nitrogen harvest index.