The Interaction of Either an Effective or a Defeated Major Gene with Non-specific Resistance on Mildew Infection (Erysiphe graminis f. sp. hordei) and Yield in Mixtures of Barley

Three-component mixtures of two barley cultivars expressing partial resistance to mildew ( Erysiphe graminis f. sp. hordei ) with the third component either expressing complete resistance or a defeated major gene gave more yield than the mean of their components in monoculture in a series of field trials. However, there was no reduction in mildew infection in the mixtures and even a significant increase in one trial. The potential for using partially resistant cultivars in mixtures is discussed.     

Genotypic diversity effects on biomass production in native perennial bioenergy cropping systems

The perennial grass species that are being developed as biomass feedstock crops harbor extensive genotypic diversity, but the effects of this diversity on biomass production are not well understood. We investigated the effects of genotypic diversity in switchgrass (Panicum virgatum) and big bluestem (Andropogon gerardii) on perennial biomass cropping systems in two experiments conducted over 2008–2014 at a 5.4‐ha fertile field site in northeastern Illinois, USA. We varied levels of switchgrass and big bluestem genotypic diversity using various local and nonlocal cultivars – under low or high species diversity, with or without nitrogen inputs – and quantified establishment, biomass yield, and biomass composition. In one experiment (‘agronomic trial’), we compared three switchgrass cultivars in monoculture to a switchgrass cultivar mixture and three different species mixtures, with or without N fertilization. In another experiment (‘diversity gradient’), we varied diversity levels in switchgrass and big bluestem (1, 2, 4, or 6 cultivars per plot), with one or two species per plot. In both experiments, cultivar mixtures produced yields equivalent to or greater than the best cultivars. In the agronomic trial, the three switchgrass mixture showed the highest production overall, though not significantly different than best cultivar monoculture. In the diversity gradient, genotypic mixtures had one‐third higher biomass production than the average monoculture, and none of the monocultures were significantly higher yielding than the average mixture. Year‐to‐year variation in yields was lowest in the three‐cultivar switchgrass mixtures and Cave‐In‐Rock (the southern Illinois cultivar) and also reduced in the mixture of switchgrass and big bluestem relative to the species monocultures. The effects of genotypic diversity on biomass composition were modest relative to the differences among species and genotypes. Our findings suggest that local genotypes can be included in biomass cropping systems without compromising yields and that genotypic mixtures could help provide high, stable yields of high‐quality biomass feedstocks.     

The effect of six systemic fungicides on halo spot disease of barley caused by Selenophoma donacis

Six systemic fungicides were applied at growth stage 10 in a spring-barley field trial, artificially inoculated with Selenophoma donacis at each of three growth stages. Barley cultivars used were Mazurka and Zephyr. The level of disease was significantly reduced by the application of chemicals, benomyl and thiophanate methyl giving the best control. Yield results did not reflect the control of disease although benomyl and thiophanate methyl applications gave slight increases in 1000 grain weight and mean yield per head. Three of the fungicides caused some phytotoxicity in cv. Zephyr and prevented grain formation.     

Effect of yellow rust on yield components of barley cultivars with race-specific and slow rusting resistance to yellow rust

Yellow rust caused by Puccinia striiformis f. sp. hordei is an important disease of barley (Hordeum vulgare L.) in some parts of the world. We compared the effectiveness of different types of resistance in field plots at Ardabil Agricultural Research Station (Iran) during 2010–2011. Yield components along with slow rusting parameters including final rust severity (FRS), apparent infection rate (r), relative area under disease progress curve (rAUDPC) and coefficient of infection (CI) were evaluated for 25 barley cultivars. In all, two barley cultivars with race-specific resistance, 19 cultivars with different levels of slow rusting resistance and four susceptible cultivars were included in two experiments with and without fungicide protection under high disease pressure. Barley cultivars with slow rusting resistance displayed a range of severity responses indicating phenotypic diversity. Mean thousand kernels weight (TKW) losses for susceptible, race-specific and slow rusting genotypes were 31, 3 and 12%, respectively, and mean kernels per spike (KPS) losses for susceptible, race-specific and slow rusting genotypes were 19, 0.2 and 8%, respectively. Correlation coefficient of mean TKW and KPS losses with epidemiological parameters; rAUDPC, r, CI and FRS were highly significant. Slow rusting cultivars with low values of different parameters as well as genotypes with low yield component losses despite moderate disease levels were identified. Such genotypes can be used for breeding barely genotypes with high levels of resistance and negligible yield losses.     

Components of partial resistance to Septoria nodorum in winter wheat

Components of partial resistance to Septoria nodorum were investigated in 10 cultivars of winter wheat having similar field resistances. The components measured were infection frequency, latent period, size, shape and rate of growth of lesions, spore production and its rate of increase. Latent period was found to be lognormally distributed. Some of the components of resistance were found to be significantly different between cultivars. Cluster analysis also showed that cultivars could be distinguished on the basis of their components of resistance. Principal components analysis indicated that resistance could be broken down into four underlying factors, three of which could be readily interpreted. The measurements of the components of resistance were combined in a model, the r-index, based on Van der Plank's r. The amount of variation between cultivars cast some doubt on the predictive value of the index but all the cultivar values were well within the range bounded by two ‘synthetic’ cultivars made up of combinations of either the most resistant or the most susceptible components. It is considered that the r-index has potential in screening for field resistance. The possibility of incorporating the most resistant-type components into one cultivar is discussed. The use of cultivar mixtures containing cultivars having similar field resistances is also discussed in the light of the variability found in this study.     

Tolerance to manganese toxicity among cultivars of lucerne (Medicago sativa L.)

Two sand culture experiments were carried out to identify commercial cultivars of lucerne or alfalfa (Medicago sativa L.) which contain elite, Mn-tolerant plants for use in a selection programme to increase the acid-soil tolerance of this perennial legume. Differences in Mn tolerance, both within and between cultivars, were observed when a range of cultivars were exposed to regular waterings with dilute nutrient solution containing 20 or 25 mg Mn L^–1. Under these moderately toxic regimes, the winter dormant cultivars Cimmaron and WL 318 were found to contain elite plants that had greater dry matter yields than their mean cultivar yield under non-toxic Mn conditions.Cultivars which contained elite, Mn-tolerant plants could not be identified by phenotypic characteristics such as their height or their toxicity symptom score, nor by their winter dormancy class. Possible reasons for the occurrence of elite plants in these cultivars are discussed. The elite, high yielding Mn-tolerant plants could not be identified from the other plants within their cultivar population by their Mn toxicity symptoms nor by their height.     

Pathogenicity of Some European Collections of Crown Rust (Puccinia coronata Corda) on Cultivars of Perennial Ryegrass

Three collections of crown rust (Puccinia coronata), from Czechoslovakia, West Germany and the U.K., were tested for their pathogenicity on sixteen cultivars of perennial ryegrass. The Czechoslovakian collection had the highest level of infection on twelve of the cultivars, although with most cultivars there were no significant differences in infection levels. Three cultivars, although with most cultivars there were no significant differences in infection levels. Three cultivars, Kerem, Loret, ta and Tando, contained qualitative resistance to crown rust which was overcome by the Czechoslovakian collection, although they retained a moderately high level of background resistance to this collection.     

Disease progress of non-specialised fungal pathogens in intraspecific mixed stands of cereal cultivars. I. Models

Two mathematical models are presented which describe progress of disease, caused by an unspecialised pathogen, in pure and mixed stands of cereal cultivars. One is a simple, discrete model utilising the parameters infection frequency (lesions/spore) and sporulation rate (spores/lesion/event) on each cultivar. The model predicts that, in most circumstances, the amount of disease in mixtures will be equal to or less than the arithmetic mean of the component pure stands. An increase in disease is only predicted in situations where the ranking of cultivars with respect to infection frequency and sporulation rate is opposed. In the other model differential equations are proposed. Solutions of these equations indicate that disease amelioration can usually be expected in such mixtures, confirming the conclusions of the discrete model and that disease levels will deviate around the geometric, rather than arithmetic, mean of the pure stands. However the advantages of this model lie in wider generality and conceptual, rather than practical, utility.     

Disease progress of non-specialised fungal pathogens in intraspecific mixed stands of cereal cultivars. II. Field experiments

Epidemic development of Septoria nodorum was examined in pure stands and mixtures of two spring wheat cultivars, Kolibri and Maris Butler. In mixtures, disease development was reduced almost to that of the more resistant pure stand (Maris Butler). Disease levels, however, were low and no significant differences in grain yield per head were demonstrated. Disease development was further investigated for the host-pathogen combinations winter wheat/S. nodorum and winter barley/Rhynchosporium secalis. With both combinations the mixed stands again reduced disease levels to almost that of the more resistant pure stands. In general, mixed stands were more effective against R. secalis, although, with S. nodorum, disease levels were low. The yield response in mixed stands differed for the host cultivars and was not significantly changed by the presence of disease. The complexity of analysing such situations and the implications of these findings for mixtures of cultivars differing in resistance to non-specialised pathogens are discussed.     

Components of partial resistance of barley to Rhynchosporium secalis: use of seedling tests to predict field resistance

Components of partial resistance [disease incidence (DI), infection frequency (IF), latent period (LP), spores per lesion (SPL)] were assessed on glasshouse-grown barley seedlings following inoculation with spore suspensions of Rhynchosporium secalis at growth stage 12 (Zadoks, Chang & Konzak, 1974). Four experiments were carried out at different times during 1988. Three spring barley cultivars [two from Cyprus (cvs Kantara and Athenais) and one from the UK (cv. Triumph)] were used in the first three experiments. In the fourth experiment eight additional UK cultivars with NIAB resistance ratings ranging from 3 to 9 were used. Two races of R. secalis were used in the first three experiments and three in the fourth. The three cultivars, Kantara, Athenais and Triumph, were examined in all four experiments and significant differences detected for virtually all components of partial resistance in each. Differences, however, were often small and ranking of cultivars varied in different experiments. The greater susceptibility of cv. Kantara compared to cv. Athenais, observed under field conditions in Cyprus, would not be anticipated from the small differences in components of partial resistance observed in these experiments, but, for these cultivars, the possibility of a marked genotype x environment interaction cannot be discounted. Mean values for the components of partial resistance differed in the four experiments. LP was correlated with mean glasshouse temperature from inoculation to the onset of sporulation but differences in IF and SPL were not correlated with temperature. For these components, light quality and/or duration appeared to be more important. Overall, there were no differences between races but significant race X cultivar interactions were observed in two experiments. In the fourth experiment, examining 11 cultivars, there were significant differences between cultivars for all components of partial resistance. IF and LP were correlated but neither of these components was correlated with SPL indicating independent control of this latter component. Both IF and LP were correlated with field performance (NIAB ratings) but there was no correlation with SPL. However, combining IF with mean values of SPL restricted to the 5 days following the end of the LP, produced the best correlation (r= 0.92) with NIAB ratings. Problems of assessing components of partial resistance and possible means of improving assessments are discussed.     

Stem canker (Rhizoctoniu solani) on three early and three maincrop potato cultivars: effects of seed tuber size on growth and yield

Large seed tubers (mean 134 g) and small seed tubers (50 g) of three early and three maincrop potato cultivars, spaced respectively 48 and 30 cm apart within rows, were inoculated with Rhizoctonia solani at planting in 1985 and 1986. All seed of early cultivars was sprouted and maincrop seed was either sprouted or not sprouted. In all cultivars, plant emergence was slower from small than large seed and with both was delayed by inoculation. From 11 wk after planting numbers of stems and tubers and weights of foliage and tubers/m² were usually similar from small and large seed when not inoculated, but inoculating delayed plant growth and decreased tuber numbers and yield more from small than large seed. Inoculating decreased mean yields from large and small seed of early cultivars at 11 wk by respectively 24% and 31% (Arran Comet), 12% and 18% (Estima) and by 10% and 28% (Wilja) and losses were greatest with saleable sized tubers (3–4 cm). When grown to maturity inoculating decreased yields by 7% (Arran Comet), 5% (Estima) and 14% (Wilja). With maincrop cultivars, yields in October from large and small seed were decreased by respectively 4% and 10% (DCsirke), 9% and 12% (Maris Piper) and by 14% and 22% (Pentland Squire). In all cultivars yields of tubers < 44 mm and 44–70 mm were decreased and, with Pentland Squire, tubers > 82 mm were increased. The incidence of stem canker and of black scurf on progeny tubers was not affected by seed size but in all cultivars the percentage of greened tubers was slightly increased by inoculation.     

Phosphorus allocation in P-efficient and inefficient barley cultivars as affected by mycorrhizal infection

A glasshouse experiment was undertaken to investigate the effect of mycorrhizal infection on the allocation of phosphorus (P) in agronomically P-efficient (i.e. high yields at low P supply) and inefficient barley (Hordeum vulgare L.) cultivars. Four barley cultivars differing in agronomic P-efficiency were inoculated or not inoculated with Glomus etunicatum. Cultivars did not differ in percentage of root length infected. The concentration of P in roots of the inefficient cultivars was higher than that of the efficient cultivars. However, because of changes in root to shoot dry weight ratio and below-ground productivity, mycorrhizal infection significantly reduced the percentage of total plant P in roots of the inefficient cultivars. The distribution of P between root and shoot of P-efficient cultivars was not affected by mycorrhizal infection. Root to shoot dry weight ratio of the P-efficient cultivars was lower than that of the inefficient cultivars, and the decrease in the ratio following infection was significant in inefficient but not in P-efficient cultivars. This study indicates that mycorrhizal infection alters the allocation of P in inefficient cultivars and effectively improves the efficiency of P utilization with respect to shoot growth.     

The Expression of Partial Resistance of Wheat to Puccinia recondita

A range of winter wheat cultivars, which appeared to show no race-specific resistance to Puccinia recondita f. sp. tritici, was studied at seedling and adult growth stages to determine the components of partial resistance which might contribute to slow-rusting in the field. Under controlled environmental conditions, adult plants of cvs Atou, Bouquet, Cappelle-Desprez and Maris Freeman produced less uredospores per unit area than the control cv. Armada, and uredosori were smaller on these cultivars. Fewer uredosori erupted on cv. Cappelle-Desprez than on the control, and both cv. Bouquet and cv. Cappelle-Desprez showed longer latent periods than other cultivars. Cultivar Holdfast had a shorter latent period, with larger and more numerous uredosori than even the highly susceptible cv. Armada. Cultivar Waggoner displayed a similar response to infection to that of the control. The components of partial resistance detected in adult plants were not displayed by seedling leaves.     

Metabolic profiling of mango cultivars to identify biomarkers for resistance against Fusarium infection

Infection of mango panicles and young leaf shoots by Fusarium results in significantly lower fruit yields. Some mango cultivars are known to be tolerant to blossom malformation, while others are highly susceptible. Previous researchers linked the ability of certain cultivars to confine Fusarium infection to the production of high levels of mangiferin. This study further elucidates the role of phenolic metabolites contributing to tolerance. Phenolic profiles of mature leaf extracts from cultivars with varying degrees of resistance to Fusarium infection were obtained by ultrahigh performance liquid chromatography–time-of-flight-mass detection. Chemometric models constructed from the data revealed a clear distinction between the profiles of tolerant and susceptible cultivars and permitted the identification of biomarkers associated with susceptibility to infection. The presence of elevated levels of mangiferin, maclurin and maclurin O-galloyl-glucoside in the leaves were associated with a higher degree of tolerance. In contrast, high levels of iriflophenone glucosides were linked to increased susceptibility of the cultivars to infection. These models can serve as an important tool to investigate appropriate cultivars, prior to their introduction to areas prone to the disease.     

Screening of oilseed rape cultivars relation to diamondback moth,Plutella xylostella (Lep.: Plutellidae) in fields of Tehran

The diamondback moth (DBM), Plutella xylostella (L.) (Lep., Plutellidae), is one of the most important pests of oilseed rape, Brassica napus L., in the world. In this study, resistance of oilseed rape cultivars to DBM was evaluated in fields of Tehran based on injury rate of the cultivars. To evaluate cultivar resistance, 19 cultivars of oilseed rape were planted in randomised complete-block design with three replications. Total experiments were conducted in experimental field of Shahed University. Results showed that DBM had activity on the plants during season and peak of the injury occurred on 27 May. Results indicated that the total of oilseed rape cultivar was spotty. Statistical analysis showed that there was significant difference among determined characteristics in all cultivars. The highest and lowest numbers of holes in the leaf were observed in Midas, Karaj3, Zarfam and Hyola420, Hyola308 cultivars, respectively, in sampling of the end growth. Opera and Midas cultivars have the highest percentage of leaf infestation and the lowest percentage of leaf infestation was observed in Hyola420 and Hyola308. Also, Karaj3 and Zarfam cultivars have the highest percentage of meristem infestation and the lowest percentage of meristem infestation was observed in Licard and Hyola420 cultivars. Based on peak of the injury rate and importance of meristem injury, Hyola420 and Hyola308 cultivars were relatively resistant to DBM, and Karaj3 and Zarfam were relatively sensitive to DBM.     

Stem canker (Rhizoctonia solani) on five early and seven maincrop potato cultivars. II Effects on growth and yield

In 1983 and 1984, potato seed tubers of five early and seven maincrop cultivars were inoculated with cultures of Rhizoctonia solani during planting in field experiments to simulate severe seed infection. The size of foliage was assessed during June-August and tuber yields recorded during growth and at harvest in October. Stem canker delayed shoot emergence, decreased the number and length of stems and caused increased variation in stem length; these effects were greatest with Maris Peer and Arran Comet (early cultivars) and King Edward and Pentland Squire (maincrop cultivars). Total weight of foliage was decreased, especially with earlies, dry matter of stems increased and the proportion of foliage on lateral stems increased. With the early cultivars, tuber yield from sprouted Maris Peer seed 11 wk after planting in 1983 was decreased by 24%, and 13 wk after planting in 1984 yields were decreased by 42% (Maris Peer), 40% (Ulster Sceptre), 34% (Estima), 30% (Arran Comet) and 17% (Ulster Prince) with sprouted seed and by 20, 29, 53, 39 and 28% respectively with non-sprouted seed. Decrease in total yield at harvest in October averaged 13% with sprouted seed and 10% with non-sprouted seed. In all cultivars the weight of small tubers was decreased and with Estima the weight of large tubers was increased. Tuber bulking was also delayed with all maincrop cultivars and at harvest yields from sprouted King Edward seed were decreased by 13% in 1983 and by 16% (sprouted seed) and 23% (non-sprouted seed) in 1984; yields of Pentland Squire were decreased by 5, 16 and 21% respectively. Yield losses with other cultivars ranged from 5–13% with sprouted seed and 0–16% with non-sprouted seed. The yields of small tubers were decreased with all cultivars and yields of large tubers were increased with Pentland Squire, Pentland Crown and Cara.     

Mixing ability analysis of wheat cultivar mixtures under diseased and nondiseased conditions

Summary Mixing ability analyses, adapted from combining ability analyses used in plant breeding, were performed on yield and stripe rust (Puccinia striiformis) severity data for two-way mixtures among either four or five club wheat (Triticum aesitivum) cultivars grown in five environments. Initially, two statistics were calculated for each trait: general mixing ability (GMA), the average performance of a cultivar over all of the mixtures, and specific mixing ability (SMA), the deviation of a mixture from the estimated performance of the pair based on its average performance in mixtures. General mixing ability was further divided into two components: genotype performing ability (GPA), the innate ability of a cultivar to yield and resist disease in pure stand, and true general mixing ability (TGMA), the average ability of a cultivar to influence yield and disease when mixed with other cultivars. Significant mean squares for genotypes, GMA, SMA, and TGMA were found for all of the traits in most environments. Examination of TGMA and SMA revealed cultivars and cultivar combinations that were statistically better mixers than the others. Some of the significant effects were probably due to the use of cultivars that differed in height and stripe rust resistance, but for other combinations there was no apparent explanation for enhanced mixing ability.Paper No. 9132 of the Oregon Agricultural Experiment Station. Supported in part by USDA Grants 88-34106-3631 and 88-37151-3662     

Development of Pseudocercosporella herpotrichoides (Fron) Deighton var. herpotrichoides and var. acuformis on Wheat Plants Measured by ELISA

Using the ELISA method, the development of Pseudocercosporella herpotrtchoides var. herpotrichoides and var. acuformis in a susceptible cultivar of winter wheat was compared under controlled and held conditions. In the greenhouse, var. acufornis grew less vigorously, was slower in penetrating the coleoptile and the successive leaf sheaths and in colonizing the stem tissue than var. herpotrichoides. In the field, these differences were confirmed on the last leaf sheaths and the stem. At ripening stage, however, identical ELISA values were measured for both varieties. Moreover, a significant variation was observed between the individual isolates of each variety. Comparison of the effect of both varieties of P. herpotrichoides on 20 wheat cultivars characterized by different resistance levels showed significant interactions. The cultivars carrying the Pch-1 gene always remained the less diseased genotypes. In general, var. acuformis developed less antigen in the cultivars than var. herpotrichoides. It is concluded, that in tests for resistance to P. herpotrichoides mixtures of many highly pathogenic isolates of both fungus varieties should be used. Less complex mixtures or single isolates may result in wrong estimates of resistance.     

Effects of alien cytoplasm substitution on the response of wheat cultivars to Septoria nodorum

The effects of alien cytoplasm substitution on the response of wheat to Septoria nodorum were studied, using alloplasmic series of two cultivars, Chris and Selkirk. In general, cytoplasmic substitution caused unidirectional effects on Septoria-response, alloplasmic lines of both cultivars expressing lower levels of partial resistance (in leaf and head tissue) but higher levels of yield tolerance than the corresponding euplasmic line. The reduced resistance in alloplasmics was closely associated with reduced incubation periods of Septoria infection in both leaf and head tissue. Cytoplasmic substitution resulted in increased yield tolerance to Septoria-infection in both the non-tolerant Selkirk and the relatively tolerant Chris. Unlike their effects on partial resistance, specific cytoplasms exerted similar effects on tolerance in the two parental cultivars, several cytoplasms of the D plasmatype being particularly effective in increasing Septoria-tolevance. The potential for the development of Septoria-toterant cultivars by the incorporation of alien cytoplasms is discussed, in view of the observed neutral effects of D plasmatype cytoplasms on other agronomic traits.