Near-isogenic Wheat Lines Research Articles

The effect of the 1B/1R translocation and endosperm texture on amino acid digestibility in near-isogenic lines of wheat for broilers

Four near-isogenic lines of wheat were employed to compare the effects of endosperm texture (hard v. soft) and the presence or absence of the 1B/1R translocation on amino acid digestion as determined with young broilers. Wheat samples were incorporated into diets at rates of inclusion of 250, 500 and 750 g/kg, with wheat as the only protein source. Diets included a mineral/vitamin mixture (50 g), oil (50 g) and were made up to 1000 g with a 50[ratio ]50 starch[ratio ]glucose mixture. Titanium dioxide was included at 5 g/kg as an inert marker. Each of the 12 diets was fed to 6 pairs of growing male (Ross) chickens for 3 days. Samples of ileal digesta were obtained from the birds following slaughter at 21 or 22 days of age and analysed for amino acid and titanium dioxide content. True and apparent digestibility coefficients were determined by regressing the amount of dietary apparently digestible amino acid in the diet against the rate of wheat inclusion and extrapolating the response to 1000 g and 0 g wheat/kg. The ordinate intercept was assumed to represent endogenous losses. Both the presence of the translocation and hard endosperm texture were associated with decreases in the apparent digestibility of amino acids, although the latter characteristic was not as important. As examples, for methionine the translocation was associated with a decrease in the coefficient of digestibility from 0·872 to 0·802 and a change in endosperm texture from soft to hard was associated with a decrease from 0·845 to 0·829.

Disease development and β-1,3-glucanase expression following leaf rust infection in resistant and susceptible near-isogenic wheat seedlings

To determine the association of pathogenesis-related (PR) proteins with resistance conferred by the genes Lr29 and Lr34 to leaf rust, three near-isogenic wheat lines [Palmiet (Pa), Pa/Lr29 (Pa*4/RL6080[Lr29]) and Pa/Lr34 (Pa*4/RL6058 [Lr34])] were infected with the fungus Puccinia recondita f. sp. tritici . Activity levels and an immunological profile of the PR protein, β-1,3-glucanase, were recorded in relation to fungal structure development. Compared with the susceptible control, Palmiet, infection and colonization of leaf tissue were inhibited in lines containing either Lr29 or Lr34 . Induction of β-1,3-glucanase activity was observed in all lines, including Palmiet, concurrent with the formation of substomatal vesicles and subsequent differentiation of the pathogen. Following leaf rust infection, four major β-1,3-glucanases were revealed with Western blot analysis. Higher levels of activity were detected in infected than in non-infected plants. The hypothesis that resistance in lines carrying Lr29 or Lr34 is related to higher levels of β-1,3-glucanase expression was not confirmed.

Physiologic Specialization of Puccinia triticina in Canada in 1997.

In 1997, leaf rust of wheat (Triticum aestivum), caused by Puccinia triticina, was widespread throughout the prairies of western Canada. Warm summer temperatures with frequent dew periods favored spread of the disease in wheat fields in Manitoba, Saskatchewan, and Alberta. The leaf rust epidemic of 1997 was the most widespread and severe in western Canada since 1991. The Canada Prairie Spring wheat cultivars (AC Vista, AC Foremost, AC Crystal) were susceptible to leaf rust, while the bread wheats (AC Domain, AC Barrie, AC Cora, AC Majestic) were more resistant. Forty-seven virulence phenotypes of leaf rust were described in 1997 using 16 near-isogenic differential lines of Thatcher wheat. Phenotypes with virulence to Lr16 comprised 16% of the isolates in Manitoba and Saskatchewan in 1997. Many recently released Canadian spring wheats have Lr16 in addition to adult plant resistance genes. Thirty-three isolates also were tested for virulence to plants with adult plant resistance genes Lr12, Lr13, Lr34, and Lr13,34. Most isolates were virulent to genes Lr12 and Lr13. All isolates had lower infection types on lines with Lr34 compared with the susceptible line Thatcher.

Rumen digestibility in dairy cows of starch in near-isogenic lines of wheat

Wheat is a good source of carbohydrates for ruminants, and recent low prices in the UK suggest that usage is likely to increase. However, there is a shortage of information on the digestibility of wheat in the rumen. Such information is vital for predicting the relative value of wheat as a source of fermentable metabolisable energy or by-pass starch. Digestibility is likely to be affected by growing conditions and genetics. Genetic differences are found between wheat varieties, but comparisons of named varieties yield limited information because many characteristics vary simultaneously. This problem can be overcome by using near-isogenic lines of wheat that vary only in a limited number of known characteristics. The objective of this study was to determine the rumen digestion characteristics of different near-isogenic wheat lines grown under the same agronomic conditions.

Production of near-isogenic lines of common wheat for glaucousness and genetic basis of this trait clarified by their use.

Duplication of the genes for both wax production (W loci) and inhibition (proposed symbol, Iw loci) on chromosomes 2B and 2D hindered clarification of the allelic and linkage relationships between these loci in wheat. The near-isogenic lines of three genotypes, w1w1 w2w2, W1W1 w2w2 and w1w1 W2W2, for wax production (all iw1iw1 iw2 iw2 for wax inhibition) and two genotypes, Iw1Iw1 iw2 iw2 and iw1 iw1 Iw2Iw2, for wax inhibition (both W1W1 W2W2 for wax production) therefore were produced by ten backcrosses with Triticum aestivum cv. S615 (genotype W1W1 W2W2 iw1iw1 iw2iw2), or its equivalent w-S615 (w1w1 w2w2 iw1iw1 iw2iw2), as the recurrent parent. Segregation ratios between glaucous and non-glaucous plants in successive backcross generations or after selfing the backcrossed offspring indicated that all the wax-producing (W) and inhibiting (Iw) alleles were transmitted at equal frequencies to their respective recessive alleles, w and iw. Linkage analyses of W1, Iw1 and Ne2 (a gene for hybrid necrosis) on chromosome 2B and W2, Iw2 and C (a gene for compact ear) on chromosome 2D showed that the W1 and W2 loci respectively are located at sites different from the Iw1 and Iw2 loci. The presently accepted concept of multiple allelism for w, W and WI (wax inhibition) therefore is invalid. Rather two allelic sets, w and W, and iw and Iw, both of which are duplicated on chromosomes 2B and 2D, must be postulated for the glaucousness of wheat. The first genetic maps showing their linkage relationships to the centromere and the Ne2 and C loci have been constructed.

Aluminium induces an increase in cytoplasmic calcium in intact wheat root apical cells

Disturbance of cytoplasmic Ca 2+ homeostasis, leading to breakdown in Ca 2+ -mediated signal transduction processes, has been suggested as a primary mechanism of aluminium (Al) rhizotoxicity in plants. To test this hypothesis, Al-related changes in cytoplasmic free activity of Ca 2+ ions ([Ca 2+ ] c ) in root apical cells of near-isogenic wheat (Triticum aestivum L.) lines differing in Al tolerance at a single locus were examined by visualising the Ca 2+ -sensitive probe Fluo-3 with confocal laser scanning microscopy. Exposure of roots to 50 µM AlCl 3 (pH 4.2) led to an increase in [Ca 2+ ] c of root apical cells in both Al-sensitive (ES8) and Al-tolerant (ET8) wheat lines. An increase in [Ca 2+ ] c was greater in ES8 than in ET8; after 1-h treatment with 50 µM AlCl 3 an increase in [Ca 2+ ] c was 48 and 27 % in ET8 and ES8, respectively. An increase in [Ca 2+ ] c of ES8 roots, but not ET8 roots, was observed upon treatment with 2.6 µM AlCl 3 (pH 4.5). Al-related increases in [Ca 2+ ] c were correlated with inhibition of root growth. The Al-induced increase in the [Ca 2+ ] c was reversible upon removing AlCl 3 . These findings provide direct evidence to support the hypothesis that Al interactions with cytoplasmic Ca 2+ are involved in the Al toxicity syndrome in plants.

Growth of Near-isogenic Wheat Lines Differing in Development—Plants in a Simulated Canopy

Abstract An understanding of the principal factors regulating the growth of temperate cereals will identify opportunities to manipulate crop growth. In an accompanying paper (Gomez-Macpherson, Richards and Masle, Annals of Botany 82 : 315–322, 1998), growth around the start of floral initiation was studied in isogenic wheat ( Triticum aestivum L.) lines grown as spaced plants. In this paper, two of the same near-isogenic wheat lines were grown as mini-canopies in a growth chamber. The objective was to determine whether results obtained using spaced plants also apply to plants grown in a simulated canopy as a first step to emulate field conditions. Biomass of plant organs, leaf area and leaf and tiller appearance were determined from sowing to ear emergence of the early developing line. Contrary to results obtained using spaced plants, lines differed in their above-ground biomass accumulation, although total plant biomass accumulation was similar. After the early line reached terminal spikelet stage (TS), biomass partitioning to the roots and leaves decreased, whereas partitioning to the stem and ear increased. This resulted in a lower root:shoot ratio in the early flowering line than in the late line which remained vegetative. Tiller senescence also began after TS in the early line whereas no tiller senescence was observed in the late line during the experiment. Furthermore, after TS, net assimilation rate was greater and leaf area ratio was lower in the early line. It is suggested that, after reaching TS, plants grown in a canopy become source limited compared to widely spaced plants, or compared to plants that have not reached TS, and this results in less root growth.

Growth of Near-isogenic Wheat Lines Differing in Development—Spaced Plants

Abstract The relationship between phenological development in wheat (Triticum aestivumL.) and growth was studied to determine if the switch from a vegetative to a reproductive apex increases plant growth rate. Plant partitioning and relative growth rates during vegetative and pre-flowering reproductive periods were determined in two sets of near-isogenic lines differing in phenological development. Spaced plants were grown in two photoperiods (15 and 10 h) to increase the range of development rates. Lines within each isogenic set and photoperiod treatment did not differ in whole plant growth rate despite large differences in developmental rate. In addition, the partitioning of biomass between roots and shoots was also similar. The transition of the apex from vegetative to reproductive mostly affected the partitioning of shoot biomass into leaf (blades) and stems (rest of the shoot). A longer time to reach floral initiation was associated with the production of more, and larger, leaves as well as more tillers. This resulted in large differences in leaf area between isolines. However, at the whole plant level, all lines accumulated biomass at the same rate with time. The early flowering lines compensated for their reduced leaf area by having a higher net assimilation rate and were thereby able to maintain the same relative growth rate as their later flowering counterparts.

Dwarfing genes and cell dimensions in different organs of wheat

A field experiment was conducted under non-limiting water and nutritional conditions with three near-isogenic lines of spring wheat (dwarf, DD; semi-dwarf, SD and standard height, SH) to study the impact of the GA-insensitive alleles Rhtl and Rht2, at the cellular level, on the growth of different vegetative organs and of the pericarp of grains. Cell length and width of blades of different leaves (3, 7 and flag leaf), the flagleaf sheath and the penultimate internode as well as the pericarp of basal grains from central spikelets of the spike were evaluated. With the exception of the flag leaf, dwarfing genes produced a significant reduction in cell length in all the different vegetative organs analysed. There was no effect on the number of cells nor their width. Therefore, in vegetative organs, the effects of these alleles appeared to be exclusively due to a reduction in cell length. It would appear that dwarfing genes act on cell elongation without affecting cell division. The Rht alleles did not modify cell length nor width in the pericarp. Grain weight was different between the lines and these differences were associated with grain volume at the beginning of linear grain growth. Thus, they reduced the size of individual grains by reducing the total number of cells in the pericarp. It appears that Rht alleles reduced the final sizes of vegetative organs (such as internodes and leaves) and of tissues (pericarp) associated with reproductive structures (grains), but the modes of action in these different organs were different.

Dwarfing genes and cell dimensions in different organs of wheat

A field experiment was conducted under non-limiting water and nutritional conditions with three nearisogenic lines of spring wheat (dwarf, DD; semi-dwarf, SD and standard height, SH) to study the impact of the GA-insensitive alleles Rht1 and Rht2, at the cellular level, on the growth of different vegetative organs and of the pericarp of grains. Cell length and width of blades of different leaves (3, 7 and flag leaf), the flagleaf sheath and the penultimate internode as well as the pericarp of basal grains from central spikelets of the spike were evaluated. With the exception of the flag leaf, dwarfing genes produced a significant reduction in cell length in all the different vegetative organs analysed. There was no effect on the number of cells nor their width. Therefore, in vegetative organs, the effects of these alleles appeared to be exclusively due to a reduction in cell length. It would appear that dwarfing genes act on cell elongation without affecting cell division. The Rht alleles did not modify cell length nor width in the pericarp. Grain weight was different between the lines and these differences were associated with grain volume at the beginning of linear grain growth. Thus, they reduced the size of individual grains by reducing the total number of cells in the pericarp. It appears that Rht1 alleles reduced the final sizes of vegetative organs (such as internodes and leaves) and of tissues (pericarp) associated with reproductive structures (grains), but the modes of action in these different organs were different.

Effect of the Vrn1‐Fr1 Interval on Cold Hardiness Levels in Near‐Isogenic Wheat Lines

We investigated the feasibility of cold hardiness manipulation in wheat, Triticum aestivum L., with the Vrn1-Fr1 interval on chromosome 5AL. The interval contains a gene(s) that has influenced vernalization requirements and cold hardiness levels. We conducted LT 50 tests (lethal temperature of 50% of plants) on wheat NILs (near-isogenic lines) that differed for alleles at the Vrn1-Fr1 interval, to determine the effects of the interval on cold hardiness levels between hardy and nonhardy wheat. The NILs were derived from five backcrosses between a spring wheat recurrent parent, 'Marfed', and two winter wheat donor parents, 'Suweon 185' and 'Chugoku 81', hardy and nonhardy, respectively. The developed populations were Suweon 185/6*Marfed and Chugoku 81/6*Marfed spring and winter NILs. Results showed that the winter NILs could tolerate a 4.3 °C colder LT 50 score than the spring NILs, and that the Suweon 185/6*Marfed winter NILs could tolerate a 0.5 °C colder LT 50 than Chugoku 81/ 6*Marfed winter NILs. Results indicate that the Vrn1-Fr1 interval explained between 71 and 91% of the variation for LT 50 scores between these genotypes. The NILs were analyzed with the probe Xwg644 to confirm linkage with the Vrn1-Fr1 interval and to determine its utility as a marker for vernalization requirement and cold hardiness. EcoRI-digested DNA of the winter and spring NIL wheat, probed with Xwg644, showed that a 9.7-kb band co-segregated with the winter growth habit. Results indicate that differences in cold hardiness levels between winter wheat cultivars may be explained by this interval and that the interval may be manipulated through plant breeding to improve the cold hardiness of cultivars.

Development of Early Infection Structures of Puccinia recondita f. sp. tritici in Non‐host Cereal Species

AbstractThe development of infection structures, derived from urediospores of Puccinia recondita f.sp. trilici in nearisogenic lines of susceptible and resistant wheat, and in non‐hosts (viz. maize, oat, sorghum and barley), was examined by fluorescence microscopy and scanning electron microscopy (SEM). The infection structure formation on and in five cereal species follows a similar pattern. In sorghum, fungal development is arrested at the stage of substomatal vesicle formation, while, in maize, most fungal structures collapse during the stage of primary hypha development. By contrast, in wheat, barley and oat, the fungus forms many branched infection hyphae and haustorial mother cells.

Direct Evaluation of the Ca2+-Displacement Hypothesis for Al Toxicity.

One explanation for Al toxicity in plants suggests that Al displaces Ca2+ from critical sites in the apoplasm. We evaluated the Ca2+-displacement hypothesis directly using near-isogenic lines of wheat (Triticum aestivum L.) that differ in Al tolerance at a single locus. We measured both the growth and total accumulation (apoplasmic plus symplasmic) of 45Ca and Al into roots that had been exposed to Al alone or to Al with other cations. Root growth in the Al-sensitive line was found to be severely inhibited by low activities of Al, even though Ca2+ accumulation was relatively unaffected. In solutions containing the same activity of the Al3+ and Ca2+ ions as above, but also including either 3.0 mM Mg2+, 3.0 mM Sr2+, or 30 mM Na+, growth improved, whereas 45Ca2+ accumulation was significantly decreased. Since most of the 45Ca2+ accumulated by roots during short-term treatments will reside in the apoplasm, these results indicate that displacement of Ca2+ from the apoplasm by Al cannot account for the Al-induced inhibition of root growth and, therefore, do not support the Ca2+-displacement hypothesis for Al toxicity. We also show that total accumulation of Al by root apices is greater in the Al-sensitive genotype than the Al-tolerant genotype and suggest that cation amelioration of Al toxicity is caused by the reduction in Al accumulation.

Virulence in Puccinia recondita f. sp. tritici Isolates from Canada to Genes for Adult-Plant Resistance to Wheat Leaf Rust.

Sixty-seven isolates of Puccinia recondita f. sp. tritici collected in Canada were tested for virulence to adult plants of Thatcher near-isogenic wheat lines with leaf rust resistance genes Lr13, Lr22a, Lr34, Lr35, and Lr13 and Lr34 combined. All of the isolates had low infection type to the Thatcher lines with Lr22a and Lr35. All isolates had lower infection type and lower rust severity on the Thatcher line with Lr34 compared with Thatcher. The isolates were polymorphic for virulence to the Thatcher line with Lr13; many isolates were completely virulent to this line, and other isolates produced very low or intermediate avirulent infection type. On the Thatcher line with Lr13 and Lr34 combined, many isolates had infection type and rust severity similar to the Thatcher line with Lr34, while other isolates had lower infection type and rust severity compared with the single-gene lines with Lr13 or Lr34. Fifteen isolates with low, intermediate, and high infection type to adult plants with Lr13 were tested for infection type on seedling plants of the Thatcher lines with resistance genes Lr13, Lr22a, Lr34, Lr35, and Lr37, and on Thatcher lines with Lr13 paired with seedling resistance genes. Most isolates were completely virulent to seedling plants with Lr13 and Lr22a. Plants with Lr37 expressed seedling resistance to all isolates tested. Seedling plants with Lr34 had lower infection types to all isolates compared with Thatcher. Seedlings with Lr35 had high infection types to most isolates, with varying amounts of chlorosis. The Thatcher lines with Lr13 plus seedling resistance genes were most resistant to the isolates that had very low infection types on adult plants with Lr13 and intermediate infection types on plants with seedling resistance genes. Genes Lr22a, Lr35, and Lr37 offer additional sources of highly effective leaf rust resistance in wheat.

Identification of RAPD markers for 11 Hessian fly resistance genes in wheat

The pyramiding of genes that confer race- or biotype-specific resistance has become increasingly attractive as a breeding strategy now that DNA-based marker-assisted selection is feasible. Our objective here was to identify DNA markers closely linked to genes in wheat (Triticum aestivum L.) that condition resistance to Hessian fly [Mayetiola destructor (Say)]. We used a set of near-isogenic wheat lines, each carrying a resistance gene at 1 of 11 loci (H3, H5, H6, H9, H10, H11, H12, H13, H14, H16 or H17) and developed by backcrossing to the Hessian fly-susceptible wheat cultivar ‘Newton’. Using genomic DNA of these 11 lines and ‘Newton’, we have identified 18 randomly amplified polymorphic DNA (RAPD) markers linked to the 11 resistance genes. Seven of these markers were identified by denaturing gradient gel electrophoresis and the others by agarose gel electrophoresis. We confirmed linkage to the Hessian fly resistance loci by cosegregation analysis in F2 populations of 50–120 plants for each different gene. Several of the DNA markers were used to determine the presence/absence of specific Hessian fly resistance genes in resistant wheat lines that have 1 or possibly multiple genes for resistance. The use of RAPD markers presents a valuable strategy for selection of single and combined Hessian fly resistance genes in wheat improvement.

Radiation interception and radiation use efficiency of near-isogenic wheat lines with different height

Three near isogenic lines of spring wheat grown to determine whether Rht dwarfing alleles alter radiation interception. A field study (involving two sowing dates in two growing seasons) with lines containing different allelic dosage of Rht1 and Rht2 (i.e. dwarf, DD; semi-dwarf, SD and tall SH), was conducted without water and nutritional deficiencies. Dwarfing genes did not modify the timing of occurrence of phenological events. Above-ground biomass at anthesis was reduced by 22% in the DD line in relation of the rest of the lines. However, at maturity accumulated biomass of the DD and SH lines were not significant different. Dwarfing genes increased the light attenuation coefficient (k, with values of 0.48, 0.62 and 0.78 for the SH, SD and the DD line respectively). A similar trend was followed to the leaf thickness (estimated by the specific leaf weight, SLW). Despite the differences observed among the lines, both in k and SLW values, they did not differ significantly in the proportion of incoming radiation intercepted by the canopy, nor in the cumulative intercepted radiation during the pre and post-anthesis periods. Radiation use efficiency (RUE) differed significantly among the lines. While RUE during pre-anthesis was the lowest in the DD line, from anthesis to maturity the lines with Rht alleles showed higher RUE values than the SH line. The low pre-anthesis RUE in the DD lines could be associated with (i) poor canopy architecture due to reductions in leaf sheath and internode lengths and/or (ii) reduced canopy CO2 exchange rate. Post-anthesis RUE was lower than that recorded pre-anthesis in all lines. But the magnitude of the reduction was inversely related to the doses of the Rht alleles. Post-anthesis RUE appeared to be closely and positively associated with the number of grains set per unit biomass at anthesis. This relationship suggests a regulatory effect of the sink size on the efficiency of the crop to convert radiation into biomass during this period.

High-resolution RFLP mapping of the fertility restoration (Rf3) gene against Triticum timopheevi cytoplasm located on chromosome 1BS of common wheat.

Near-isogenic lines of alloplasmic wheat for the Rf3 gene controlling fertility restoration against the cytoplasm of Triticum timopheevi were developed by successive backcrossing of Chinese Spring to the F1 plants between (timopheevi)-CS (male sterile) and T. spelta (carrying Rf3). The resultant three BC3F1 plants were self-pollinated so as to obtain 125 BC3F2 progenies. Using this population, we precisely mapped the Rf3 gene on the short arm of wheat chromosome 1B (1BS) of the RFLP linkage map. The Rf3 gene was localized at a position 1.2 cM and 2.6 cM distant from Xcdo388 and Xabc156, respectively. The genetic distances of Rf3 from Nor and Gli-B1 were calculated to be 22.3 cM and 18.6 cM, respectively, supporting previous data. Estimation of the physical distance of the region suggets that the Rf3 gene resides within 500 kbp from the adjacent RFLP markers. The marker order of the genetic map corresponded to that of the cytological map, except for the position of Xbcd98. Comparison between genetic and cytological maps clearly shows that RFLP markers are unevenly distributed throughout the chromosome arm, and recombinations took place unequally in the chromosome arm.

Rooting patterns in near-isogenic lines of spring wheat for dwarfism

The effects of Rht alleles on root growth and distribution in isogenic lines of spring wheat (Triticum aestivum L.) are described under different environmental conditions. Above-ground biomass, root length, root dry-weight and their distribution along the soil profile were measured by destructive sampling for growth of aerial biomass and extraction of soil cores containing roots. Field experiments were conducted under non-limiting water and nutritional conditions during two consecutive years, using an early and a late sowing date each year. Dwarfing genes significantly reduced plant height and above-ground biomass at anthesis. In addition, stem mass ratio also was reduced with increases in the allelic dosage. Conversely, total root length and root dry-weight per unit area at anthesis were increased with decreased plant height, therefore, root mass ratio tended to be negatively correlated with plant height. Differences in distribution of root length and root dry-weight through the soil profile among lines were largely confined to the upper soil layers (i.e. the top 30 cm). Differences in root dry-weight were more important than in root length, so that the dwarf line had the highest root mass per unit root length. Furthermore, a significant positive correlation between the root mass ratio and stem mass per unit stem length was found. It is suggested that increases in root mass per unit root length associated with Rht alleles are evidencing a surplus of photoassimilates during stem elongation which are used for thickening the roots due to the lack of alternative sinks. Agronomic implications of this effect are discussed.

Expression of beta-1,3-glucanase and chitinase in healthy, stem-rust-affected and elicitor-treated near-isogenic wheat lines showing Sr5-or Sr24-specified race-specific rust resistance.

Pathogenesis-related expression of the two antifungal hydrolases beta-1,3-glucanase (EC 3.2.1.39) and chitinase (EC 3.2.1.14) was studied in wheat (Triticum aestivum L.) as part of the defence response to stem rust (Puccinia graminis f.sp. tritici, Pgt), mediated by the semi-dominantly acting resistance genes Sr5 and Sr24. Complete resistance (infection type 0), mediated by the Sr5 gene in cultivar Pre-Sr5, closely correlates with the hypersensitive response of penetrated cells at early stage of the interaction, when the first haustorium is formed. In contrast, cultivar Pre-Sr24 shows intermediate resistance (infection type 2-3) which is not directly linked to cell death. In both cases, the plant response included a rapid increase in beta-1,3-glucanase activity between 24 and 48 h after inoculation. One main extracellular 30-kDa isform of beta-1,3-glucanase was present in both lines, as shown by polyacrylamide-gel electrophoresis. Two additional minor isoforms (32 and 23 kDa) were detected only in Pre-Sr24, and only at later time points. Increased enzme activity and the appearance of new isoforms in the resistance lines was preceded by accumulation of mRNAs encoding beta-1,3-glucanase and chitinases. However, there were no changes in chitinase activity or isoforms. A high constitutive level of chitinase activity was observed in all wheat genotypes. Serological studies indicated the presence of a class II chitinase of 26 kDa. Accumulation of beta-1,3-glucanase and chitinase transcripts was detected before the pathogen penetrated the leaves through stomata and approximately 16 h before the typical hypersensitive response was observed, indicating that signal(s) for defense gene activation were recognised by the host plant long before a tight contact between the pathogen and a host cell is established. A glycoprotein (Pgt elicitor) derived from hyphal walls, strongly induced beta-1,3-glucanase. We discuss the possible role of the elicitor in the early signalling mediating Sr5- and Sr24-specified resistance in wheat.

Leaf Rust Resistance Gene Lr9 and Winter Wheat Yield Reduction: I. Yield and Yield Components

Leaf rust (Puccinia recondita Rob. ex Desm. f. sp. tritici) resistant near isogenic lines (NIL) of wheat (Triticum aestivum L.) have generally lower yields than the susceptible recurrent parent under disease free conditions. Analysis of growth and yield should increase our understanding of the reduced yielding ability of NIL. In a 3‐yr field study, the yield components of the leaf rust susceptible cultivar Arina were compared with six resistant NIL carrying the resistance gene Lr9 introduced from Aegilops umbellulata. The NIL were derived from two independently developed backcross populations with Arina as the recurrent parent. The NIL were phenotypicaily very similar to Arina. At anthesis and at mediumilk stage, the total aboveground dry matter was similar for the NIL and Arina. Differences in the dry matter accumulation appeared only after the medium milk stage. At maturity, the NIL had a 12% lower grain yield than Arina (5.88 ha−1) with a range from 5 to 14%. The lower grain yield resulted from a 3 to 11% reduction in grain number per square meter and a 2 to 7% reduction in mean grain weight. The smaller grain number per square meter was the result of a 6% smaller tiller number per plant and a 2% smaller grain number per ear. Artificially reducing grain number per ear suggested that both a reduced supply of assimilates and a diminished capacity to incorporate assimilates in the grain caused the reduced grain yield of the NIL. Deleterious effects of alien genes linked with the Lr9 gene from Aegilops umbellulata cannot be ruled out. However, the small differences within and between the NIL of the two Lr9 populations for the parameters tested suggest a direct relation between the yield depression and the leaf rust resistance conferred by the Lr9 gene.