A comparison of controlled environment and field trials for detection of resistance in cereal cultivars to root rot caused by Rhizoctonia solani

A screening test was developed to study the effect of different quantities of inoculum of Rhizoctonia solani on root rot and growth of cultivars of wheat, barley, oats, rye and triticale in a controlled environment and the field in two seasons. The ranking of relative susceptibility to disease of cultivars within a cereal differed between the controlled environment and field experiments, and between seasons in the field. The ranking of relative susceptibility between cereals also differed between experiments. In the controlled-environment experiment, wheat had the highest disease rating, followed by oats, barley, triticale and rye, but in the field barley had the highest rating followed by wheat and then oats. The overall differences between the cereals were small.     

Association of Rhizoctonia strains with bare patch disease of wheat in Western Australia

Rhizoctonia -like fungi were isolated from the roots of diseased wheat plants sampled from the centre and periphery of three bare patches, and from apparently healthy plants from outside the patches. Of the isolates recovered, 81% were multinucleate and belonged to R. solani anastomosis group 8, and pectic zymogram group 1-1; the remaining isolates were binucleate Rhizoctonia spp. The multinucleate isolates could be grouped into highly virulent, intermediately virulent, and weakly virulent types. The binucleate isolates were all non-pathogenic. The multinucleate isolates were obtained at a significantly higher frequency from plants within the patches compared with outside the patches, and with the exception of a single isolate, the highly virulent isolates were not found outside the patches. The weakly virulent isolates were present at much lower frequencies than the highly virulent and intermediately virulent forms within the patches. The frequency of occurrence of binucleate isolates did not vary significantly among the locations sampled. None of the multinucleate isolates contained plasmids. Some of the isolates contained a prominent single dsRNA species and one or more minor dsRNA species. The distribution of these dsRNAs was not correlated with pathogenicity.     

Wheat leaf rust severity as affected by plant density and species proportion in simple communities of wheat and wild oats

ABSTRACT While it is generally accepted that dense stands of plants exacerbate epidemics caused by foliar pathogens, there is little experimental evidence to support this view. We grew model plant communities consisting of wheat and wild oats at different densities and proportions and exposed these communities to Puccinia recondita to induce wheat leaf rust. Wild oats was included because it is a common competitor of wheat and may act as a barrier to the dispersal of P. recondita spores among wheat plants. Disease severity was estimated as percentage of wheat flag leaves covered by rust lesions. Seeding density rarely had a significant influence on rust severity, probably because of compensation due to increased tillering at low seeding densities. In contrast, increasing the proportion of wheat in mixtures with wild oats consistently increased wheat leaf rust severity. Regression parameters describing wheat leaf rust severity as a function of wheat seeding density did not differ significantly between pure wheat stands and wheat-wild oat mixtures and, thus, failed to support an effect of wild oats on wheat leaf rust other than through its competitive impact on wheat tiller density.     

COMPETITION OF WILD OATS (AVENA FATUA L.) IN WHEAT AND FLAX*

Summary. This project was designed to study various aspects of wild oat competition in spring wheat and flax. From ten to forty wild oat plants/yd² were sufficient to cause significant yield reductions in wheat when grown on summerfallow land or when ammonium phosphate fertilizer was added to stubble land. However, when wheat was grown on stubble land without the benefit of a fertilizer treatment, seventy to one hundred wild oat plants/yd² were needed to suppress wheat yields significantly. This would suggest that on stubble land, soil fertility was a more important factor than moderate densities of wild oats in determining eventual crop yields. In these experiments, wild oats reduced the number of tillers per plant, but did not significantly affect the protein content of the harvested grain. Only ten wild oat plants/yd² were sufficient to reduce flax yields significantly on both summerfallow and stubble land. The only exception was in 1966, when flax grown on summerfallow land was not significantly affected until the density of wild oats reached forty plants/yd2. This confirms the general observation that flax is a poor competitor with wild oats. The results suggest that wild oat competition had already commenced prior to emergence of wheat, particularly with the higher densities of wild oats. In general, competitive effects increased with time and with wild oat density. In flax, severe competition had already taken place prior to the 2–3-Ieaf stage of the weed in 1964, but did not become severe until after the 2–3-leaf stage of wild oat growth in 1965 and 1966. Again, competitive effects increased with time and with wild oat density. Results of a final series of experiments, suggested that the optimum seeding date for flax in Manitoba is the latter part of May or the first week of June. Yield reductions due to wild oat competition became very severe as seeding dates were delayed. La compétition de la folle avoine (A vena fatua L.) avec le blé et le lin     

野燕麦田间发生密度对小麦、青稞产量损失估测及防除策略的研究

杂草对农作物有很大危害是众所周知的,确切知道不同情况下的草害程度对防治对策有现实的指导意义。目前各地都在进行这方面的试验,方法和准确性也异。本文介绍了野燕麦对小麦、青稞在青海省条件下的危害,其方法可供各地参考。同时对试验中所应用的数理统计是否合宜,也可供讨论。1.田间野燕麦发生密度对小麦、青稞产量损失之间有着极显著的回归关系。野燕麦穗数即花序数每增加1万穗/亩,小麦产量损失5.39斤、穗粒数减少0.15粒、千粒重降低0.102克,青稞产量损失3.5斤、穗粒数减少0.17粒、千粒重降低0.02克。2.小麦三叶期以前田间出苗的野燕麦危害最大,在野燕麦10万株/亩左右密度下,减产35.5%;小麦开始拔节以后出苗的野燕麦危害较小,造成减产8%以下。3.田间野燕麦密度越大,后期复盖阴闭越严重。野燕麦株数每亩16万株以上,复盖度90%以上,并导致小麦倒伏。4.据野燕麦危害损失,结合当前生产水平,对野燕麦发生的轻度危害田、中等危害田、严重危害田、控制田的划分指标和防除策略进行了探讨。     

Interactions between barban and benzoylprop etbyl, flamprop metbyl or flamprop isopropyl applied at two growtb stages for wild oat control in cereals

Barban was combined with benzoylprop ethyl, flamprop methyl, or flamprop isopropyl, and the eflects of the combinations on wild oat control and crop yield were assessed, tn greenhouse experiments, the interaction in all three combinations was synergistic, following application at the 2- or 4-leaf stage of wild oats. Under field conditions, combinations of barban + benzoylprop ethyl applied at the 2- or 4-leaf stage of wild oats were as eflective for wild oat control and wheat yield response as barban at 028 kg/ha applied at the 2-leaf or benzoylprop ethyl at 14 kg/ha applied at the 4-leaf stage of wild oats. Mixtures of barban + flamprop methyl applied at the 2- or 4-leaf stage of wild oats provided excellent wild oat control and wheat yield increases. Mixtures of barban + flamprop isopropyl applied at the 2- or 4-leaf stage of wild oats provided comparable wild oat control and barley yield increases to barban (028 kg/ha) applied at the 2-leaf or flamprop isopropyl (14 kg/ha) applied at the 4-leaf stage of wild oats.     

小麦苗期抗纹枯病鉴定方法的改良及抗病品种筛选

<正>小麦纹枯病又称尖眼斑(点)病,是由禾谷丝核菌(Rhizoctonia cerealis)和立枯丝核菌(Rhizoctonia solani)引起的一种以土壤传播为主的小麦真菌病害~([1])。引起小麦纹枯病的病原菌主要是禾谷丝核菌的第一菌丝融合群(CAG-1)~([2～4])。在自然条件下,病原菌首先侵染寄主植株基部叶鞘,随着     

The classification of isolates of Gaeumannomyces graminis from wheat, rye and oats using restriction fragment length polymorphisms in families of repeated DNA sequences

Isolates of the take-all fungus, Gaeumannomyces graminis var. avenae , which affects oats, wheat and other grasses, and of G.g. var. tritici , which preferentially affects wheat, rye and barley, contain a high proportion of repeated sequences. Total DNA from 57 fungal isolates collected from many locations and different cereal hosts, and scored for virulence on wheat, rye and oats, revealed many restriction fragment length polymorphisms. These RFLP s were observed either by staining the DNA directly, by hybridization to radioactively labelled total fungal DNA , or by hybridization with labelled wheat ribosomal DNA . With only a few exceptions, the isolates with the same preferred cereal hosts showed more similar patterns of restriction fragments than isolates that had different pathogenicity properties on cereal hosts, irrespective of the geographical origins of the isolates. This was even the case for R isolates of G.g. var. tritici that were virulent on wheat and rye compared with N isolates that were virulent only on wheat. Isolates were identified by hybridizing DNA from infected root samples with ³²P-labelled total fungal DNA . The restriction fragment polymorphisms involving families of repeated sequence can therefore be used as a predictive assay for host preference of an isolate, and have probably arisen by host selection of fungal lineages. The variation between isolates in different pathogenicity groups suggests that there is little gene flow between isolates that can infect different hosts, even though they can coexist in the same field.     

小麦苗期抗纹枯病鉴定方法的改良及抗病品种筛选

Wheat sharp eyespot, caused by Rhizoctonia cerealis and R. solani, is a soil-borne fungal disease, which poses a great threat to wheat yield. In order to increase the identification efficiency of wheat sharp eyespot resistance, an improved method of rapidly identifying wheat sharp eyespot resistance was established by inoculating wheat seedlings with diseased wheat grains in greenhouse. To verify its reliability, four standard materials and 96 wheat varieties from Huanghuai wheat region were used for resistance assessment to sharp eyespot. Meanwhile, the resistance to Rhizoctonia solani of aforementioned materials in the field was identified by traditional methods. The results showed that the correlation coefficient between the four repetitions of the improved method ranged from 0.735 to 0.825, and the correlation coefficient between the average number of repetitions and the traditional method was 0.630. The results of wheat sharp eyespot resistance identification in Huanghuai wheat area showed that 66 wheat varieties were susceptible, accounting for 68.8% of tested materials. This indicated that the resistance of wheat varieties in Huanghuai wheat area to sharp eyespot was poor on the whole and needed to be improved urgently. At the same time, eleven wheat varieties which showed resistance to sharp eyespot at seedling and adult stages were screened, which include Zhengzhou 8998, Beijing 841, Handan 94-5316, Jimai 32, Jinmai 50, Jinmai 54, Longmai 157, Lumai 23, Shanhe 6, Shi 02-1 and Xinmai 18. Therefore, this study provides a method for identification of wheat sharp eyespot resistance at seedling stage, by which the resistance of wheat varieties to sharp eyespot can be quickly and efficiently identified. Furthermore, selected resistant materials provide important material resources for wheat sharp eyespot resistance breeding in Huanghuai wheat region and even in China.     

Infection of oats and other cereals by oat chlorotic stunt virus in the field and laboratory

During 1992/1993 and 1994/1995, field experiments were carried out to investigate the infection of several cultivars of oats, other cereals and grasses, with oat chlorotic stunt virus (OCSV), which is provisionally identified as a member of the Tombusviridae . Under field conditions a high percentage of oat plants became infected when sown in infested soil and there was little difference in susceptibility between the oat cultivars compared. Although plants of other Poaceae such as winter wheat, winter barley and annual meadow grass also became infected, the percentage was low and the virus titre reached was much lower than in oats. In most infected plants the virus was localized within the roots, and only in a few plants did it spread systemically. This suggests that the virus was acquired through the roots, indicating further similarities between OCSV and members of the Tombusviridae . Several cereals, including oats, wheat, barley and maize, were infected by mechanical inoculation using an embryo-wounding technique; in the majority of cases virus infection only reached a low titre.     

THE EFFECT OF COMPETITION FROM CEREAL CROPS ON THE GERMINATION AND GROWTH OF AVENA FATUA L. IN A NATURALLY-INFESTED FIELD

Summary. The effect of winter wheat, winter rye, winter barley, spring barley, and fallow cultivated as for a winter cereal, on germination and growth of wild oats ( A. fatua ) was investigated on a naturally-infested field. Treatments were continued for 2 years on the same plots and in the third year all plots were cropped with spring barley. Wild oats were not allowed to shed seeds.
A. fatua was controlled by a dense crop of an autumn-sown cereal. The crop genus was unimportant provided it grew well on the site; its effectiveness depended on its density when the wild oats germinated in spring. Winter wheat and winter rye were equally effective. Even in a light crop of barley, wild oats grew much less vigorously than on the fallow plots. Beyond a certain crop density dependent on soil fertility, further increase in crop did not decrease the size of wild oats. The heaviest crop did not completely suppress the wild oats.
The crop affected the wild oats mainly by decreasing growth of the seedlings, but under winter wheat and winter rye some wild oat seeds may have remained dormant, germinating in the spring barley in the third year, perhaps because the crops decreased the soil moisture content. Nitrogenous fertilizer increased the weight of both crops and wild oats. Barley was more severely affected by soil acidity than wild oats and on acid areas of barley plots the wild oats were larger than where the pH was higher. In wheat and rye which were scarcely affected by soil acidity the size of the wild oat plants was unaffected by soil pH.
L'effet du competition des céréales sur la germination et le développement d' Avena fatua dans un champ naturellement infesté .     

Rhizoctonia species and anastomosis groups isolated from barley and wheat in Erzurum, Turkey

Ninety-eight isolates of Rhizoctonia spp. were obtained from barley and wheat grown in Erzurum, Turkey. Of these, 78% were Rhizoctonia solani (AG-2 type 1, AG-3, AG-4, AG-5 and AG-11), 10% were binucleate Rhizoctonia (AG-I and AG-K) and the remainder were Waitea circinata var circinata ( Rhizoctonia sp.). Among the binucleate Rhizoctonia , AG-I was not recovered from barley. In pathogenicity tests on barley and wheat, the highest disease severity was caused by isolates of AG-4 and AG-11, whereas isolates of AG-2 type 1, AG-3, AG-5 and W. c . var  circinata were moderately virulent. Isolates of binucleate Rhizoctonia were all nonpathogenic. This is the first report of R. solani AG-11 and W. c . var  circinata from Turkey.     

Bacillus sp. L324-92 for Biological Control of Three Root Diseases of Wheat Grown with Reduced Tillage

ABSTRACT Strain L324-92 is a novel Bacillus sp. with biological activity against three root diseases of wheat, namely take-all caused by Gaeumannomyces graminis var. tritici, Rhizoctonia root rot caused by Rhizoctonia solani AG8, and Pythium root rot caused mainly by Pythium irregulare and P. ultimum, that exhibits broad-spectrum inhibitory activity and grows at temperatures from 4 to 40 degrees C. These three root diseases are major yieldlimiting factors for wheat in the U.S. Inland Pacific Northwest, especially wheat direct-drilled into the residue of a previous cereal crop. Strain L324-92 was selected from among approximately 2,000 rhizosphere/rhizoplane isolates of Bacillus species isolated from roots of wheat collected from two eastern Washington wheat fields that had long histories of wheat. Roots were washed, heat-treated (80 degrees C for 30 min), macerated, and dilution-plated on (1)/(10)-strength tryptic soy agar. Strain L324-92 inhibited all isolates of G. graminis var. tritici, Rhizoctonia species and anastomosis groups, and Pythium species tested on agar at 15 degrees C; provided significant suppression of all three root diseases at 15 degrees C in growth chamber assays; controlled either Rhizoctonia root rot, takeall, or both; and increased yields in field tests in which one or more of the three root diseases of wheats were yield-limiting factors. The ability of L324-92 to grow at 4 degrees C probably contributes to its biocontrol activity on direct-drilled winter and spring wheat because, under Inland Northwest conditions, leaving harvest residues of the previous crop on the soil surface keeps soils cooler compared with tilled soils. These results suggest that Bacillus species with desired traits for biological control of wheat root diseases are present within the community of wheat rhizosphere microorganisms and can be recovered by protocols developed earlier for isolation of fluorescent Pseudomonas species effective against take-all.     

Characterization of cereal bare patch isolates of Rhizoctonia solani by random amplified polymorphic DNA analysis

RAPD-PCR was used to characterize isolates of Rhizoctonia solani from bare patches in cereal and pasture crops at two locations in Western Australia, Newdegate and Esperance. All of the isolates belonged to anastomosis group 8, pectic zymogram group 1-1 or 2. The pectic zymogram assignment could be confirmed by RAPD-PCR. There was no difference in RAPD-PCR pattern between highly virulent and weakly virulent isolates at Newdegate, or between isolates from different patches at Newdegate. The Newdegate isolates were identical to isolates from Esperance, and to isolates from various locations in South Australia.     

SOME ASPECTS OF THE USE OF BARBAN FOR WILD OAT CONTROL IN WINTER WHEAT

Summary. A study of the emergence and development of Avena fatua in winter wheat showed that after the mild winter of 1960/61 autumn-germinated wild oats constituted a far more serious weed problem than spring-germinated plants. It was concluded that the application of barban should be timed in relation to these autumn-germinated plants. As an extension of their work on spring cereals, the authors investigated the effect of barban on the yield ratio of winter wheat and cultivated winter oats grown as a mixture. A reduction in the oats fraction as a result of barban treatment was accompanied by an increase in wheat giving a total yield which was almost the same as untreated. Experimental data are also presented on the occurrence, and significance of an interesting variation in crop tolerance during the winter. No obvious correlation was found between increased crop sensitivity and development stage or temperature. The capacity of the crop to recover was found to be high.
Quelques données sur l'utilisation du barbane dans la lutte contre la folle avoine dans le blé d'hiver     

Stratified distribution of Fusarium and Bipolaris on wheat and barley with dryland root rot in South Australia

Dryland root rot of wheat and barley in South Australia is a syndrome from which the associated fungi Fusarium equiseti, F. acuminatum, F. oxysporum and Bipolaris sorokiniana were isolated consistently. Fusarium infections were concentrated on the subcrown internodes, crown roots and culm bases, and occurred with equal frequency on wheat and barley. Bipolaris infections were more numerous on barley than on wheat, and were concentrated on culm bases and subcrown internodes. Recoveries of each of the four fungi showed a pattern of infection that was neither randomly nor evenly distributed. Each fungus had preferences for certain sites which resulted in a stratified distribution over the roots and crown. When two barley cultivars were compared, the patterns of infection were different; the subcrown internode was attacked more severely, and there was a substantial increase in the amount of infection by all four fungi on one of the cultivars. Pathogenicity tests on barley and oats showed that all four species of fungi were capable of causing damage to roots, but there were differences between isolates of each fungus and differences in their ability to damage barley and oats.     

Identification of oat-adapted isolates of cereal Septoria in the UK using a detached leaf technique

Isolates of Septoria spp. from cereals were tested for their relative pathogenicity to detached seedling leaves of three cereal species. Each of 23 isolates showed unequivocal adaptation to either oats, or wheat, or barley. Five oat-adapted isolates were from Prince Edward Island, Canada, where S. avenue is prevalent on oats; three were from the UK, where there are few oat crops and where adaptation to oats has not been reported.
Oat-adapted isolates tended to have pycnidiospores of above-average length and could be referred to S. avenae. Wheat-adapted and most barley-adapted isolates had shorter spores and could be referred to S. nodorum. UV-fluorescent pigment was produced on oxgall agar by all wheat-adapted isolates, but only by a minority of oat-adapted and barley-adapted isolates.
It is suggested that adaptation to cereal species is a more useful character than spore length for classifying isolates.     

Modelling crop:weed interactions in wheat with ALMANAC

ALMANAC is a dynamic model for plant growth, water balance and soil nitrogen dynamics that can simulate on a daily basis two or more competing species. The simulation of competition for light is based on Beer's law, allowing a different extinction coefficient ( k ) for each species. Light is partitioned between species based on k -values, leaf area index and plant heights. Total hiomass is simulated with radiation use efficiency and grain yield with a harvest index approach, sensitive to water stress. The model simulates competition for water and nutrients based on each species current rooting zone and demand by each species. The effect of crop management on the competition issue can he simulated. The model was evaluated in Dijon (France) using 4 years of experimental data on wheat:oat mixtures, differing in oat ( Avena sativa L.) densities, the period of oat emergence, the date of weed suppression by herbicides and the wheat ( Triticun aestivum L.) genotype. Additional data on oilseed rape ( Brassica nupus L.) and vetch ( Vilcia sauiva L.) competition in spring wheat were also used. The wheat grain yield was reasonably simulated with a root mean square error (RMSE) of 0.10-0.35 t ha^-1. Corresponding values for oats were 0.10-0.55 t ha^-1. The competitiveness of oats, oilseed rape and vetch was correctly simulated. The model appears as a reasonable tool for estimating damage thresholds in integrated weed control programmes.     

Effects of summer fallow management on take-all of winter wheat caused by <Emphasis Type="Italic">Gaeumannomyces graminis</Emphasis> var. <Emphasis Type="Italic">tritici</Emphasis>

Crop rotation is the oldest, and perhaps the best cultural practice for reducing the risk of take-all. The effects of crops sown before wheat in a rotation are known in detail, but we know little about the opportunities for reducing take-all risk by planting certain crops in the summer period between wheat harvest and the planting of a subsequent winter wheat crop. We investigated the effects on take-all of five summer fallow crops, two soil tillage treatments and a fungicide seed treatment, in a five site-year experiment. We tested the effects of oats, oilseed rape, mustard, ryegrass and volunteer wheat crops. Bare-soil plots were also included. Take-all epidemics varied with year and site. Summer fallow crops had a greater effect on tilled plots. The incidence and severity of take-all were significantly higher in the wheat volunteer plots, whereas maintaining bare soil provided the lowest level of disease. Oilseed rape had no significant effect on take-all incidence in our experiment. The best candidates for reducing take-all risk appeared to be oats, mustard and ryegrass. These summer fallow crops decreased disease levels only when associated with conventional tillage. Summer fallow crops did not alter take-all decline in the same way as a break crop after a wheat monoculture.     

Influence of field burning and soil treatments on growth of wheat after Kentucky bluegrass, and effect of Rhizoctonia cerealis on bluegrass emergence and growth

Studies were conducted to assess the importance of soil-borne pathogens as impediments to the production of direct-drilled wheat following Kentucky bluegrass in rotation. Bluegrass sods were collected as cores from commercial seed fields in October (after open-field burning) and in December and March (after exposure to normal freezing and thawing), treated with glyphosate after a 2- to 3-week period of green-up in the glasshouse, and then planted to wheat 21 days later. Wheat seedlings in the 3- to 4-leaf stage were stunted and spindly in either burned or nonburned sods collected in October, but grew significantly better in burned than nonburned sods collected in December and March. Fumigation (methyl bromide), simulated tillage, and application of metalaxyl as a drench, singly or as combined treatments, improved the growth of wheat in nonburned sods. Growth of wheat in nontreated burned sods collected after frost had penetrated the upper portions was equivalent to that in fumigated sods. Experimental freezing at −20°C for up to 96 h, of burned and nonburned sods collected in October, followed by thawing also improved the growth of wheat subsequently sown directly into these sods. The stunted and spindly seedlings had roots girdled and severed by lesions typical of Rhizoctonia root rot. Isolates of Rhizoctonia cerealis were recovered from these roots and caused poor seedling emergence and stunted root and shoot growth of both wheat and bluegrass. The results suggest that both R. cerealis and Pythium spp. are potentially important soil-borne pathogens of wheat when following Kentucky bluegrass in rotation and that burning done routinely to improve the yield of bluegrass seed can also reduce the potential for damage caused by Rhizoctonia and Pythium root rots of wheat seeded directly into bluegrass sod.