Subcrown Internodes Research Articles

Quantification of common root rot symptoms in resistant and susceptible barley by image analysis

A series of tests were carried out to determine the effect of common root rot, caused by Cochliobolus sativus, on root growth and discolouration in the moderately resistant cv. Bonanza and the susceptible cv. Gateway of barley. An image analyser was used to quantify the growth and discolouration (mean intensity) of the roots and the subcrown internode (SCI) of individual plants. The plants were also visually rated for root rot severity and their root dry weight was determined. In the absence of disease, no differences in root discolouration or growth were observed between the two barley cultivars. In plants grown in naturally infested soil, visual root rot ratings and mean intensity values indicated that the SCls of Bonanza were less discoloured than those of cv. Gateway. In cv. Gateway, higher levels of disease were usually associated with a smaller root system than in cv. Bonanza, but the effect was significant (P < 0.01) only in the first experiment. The root system of cv. Gateway had lower (P > 0.05) mean intensity values (i.e., darker) than those of cv. Bonanza in the first experiment. Seedling emergence of cv. Gateway was lower in naturally infested soil than in fumigated soil, but this was not evident in cv. Bonanza. There was a strong inverse relationship between the mean intensity and visual rating of the SCI and a positive association between total root area as measured using image analysis and root weight. Image analysis also determined that in the severe root rot category, plants of cv. Gateway had SCIs that were more discoloured than those of cv. Bonanza. Discolouration of the SCI of root rot susceptible barley appeared to adversely influence the growth and discolouration of the root system, but this effect was not always significant.

The occurrence of barley root diseases in different agri-ecological zones of Syria

A survey was conducted to determine the occurrence of root diseases and the identity of causal agents on barley grown in northern agricultural areas of Syria in 1992 and 1993. In 1992, 20 plants with at least 1 cm long subcrown internodes were randomly selected from each of 53 fields when plants were between flowering and maturity. In 1993, 50 plants were selected from each of 72 fields. In addtion, four wheat fields were sampled in 1993. Plants were visually rated for disease severity on the subcrown internode. Fungal cultures were isolated from root tissues by plating on selective and general media. Isolates were tested for pathogenicity using a seedling bioassay, and representative pathogens were identified to the species level. Root rot was more severe in the drier agricultural zones and disease severity increased with crop maturity. There was a weak negative association between disease severity and the number of tillers per plant. The most prevalent pathogens in both years were Microdochium nivale (average of 43%), Cochliobolus sativus (35%), red-pigmented Fusaria (13%), and Microdochium bolleyi (8%). More than 80% of the C. sativus and M. nivale isolates, and less than 20% of the Fusarium spp. and M. bolleyi isolates, were pathogenic. Cochliobolus sativus was most common in the drier areas, whereas M. nivale was most common in the wetter areas, particularly from the northwest region. This paper is the first report of M. nivale and M. bolleyi on barley and Gaeumannomyces graminis var. tritici on wheat in Syria. Other root disorders (pests) found included cyst-forming nematodes and Porphyrophora tritici.

A rapid technique for determining common root rot reaction in barley

AbstractThe reaction of two barley cultivars (‘Thibaut’ and ‘Arizona’) and three lines (AECS 76,‘Tadmor’ and WI 2291) to infection by Cochliobolus sativus was evaluated by three methods. Deep seeding of inoculated seeds was performed in pots and field. Gibberellin (GA3) was applied to inoculated seeds in vitro. Susceptibility assessments were made in vitro at 2 weeks, and in pots at 7 weeks after inoculation, using a scale of 1 (very resistant) to 5 (very susceptible) according to the percentage infected area of the subcrown internodes. There were no differences between the results using the three methods.‘Arizona’ was the most susceptible, whereas ‘Thibaut’ and AECS 76 were partially resistant genotypes. The WI 2291 line and ‘Tadmor’ were moderately susceptible and moderately resistant, respectively. In vitro tests yielded the same order as tests from pot and field experiments.

PH-regulated leaf cell expansion in droughted plants is abscisic acid dependent

Elongation rates of barley (Hordeum vulgare L. cv Hanna) leaves decreased with decreasing soil water content, whereas the pH of xylem sap increased from 5.9 to 6.9 over 6 d as the soil dried. The reduction in leaf-elongation rate (LER) was correlated with the increase in sap pH. Artificial sap buffered to different pH values was fed via the subcrown internode to derooted seedlings. Although leaves elongated at in planta rates when fed artificial sap at a well-watered pH of 6.0, LER declined with increasing sap pH. This effect persisted in the light and in the dark. pH had no effect on the relative water content or the bulk abscisic acid (ABA) concentration of the growing zone of these leaves. LERs of the ABA-deficient mutant Az34 were uniformly high over the pH range tested, whereas those of its isogenic wild-type cultivar Steptoe were reduced as the artificial sap pH was increased from 6.0 to 7.0. However, supplying a well-watered concentration of ABA (3 x 10(-8) M) in the artificial xylem sap restored the pH response of the Az34 mutant. The results suggest that increased xylem sap pH acts as a drought signal to reduce LER via an ABA-dependent mechanism.

Effect of common root rot (Cochliobolus sativus) on yields of barley under experimental conditions in northern Syria

The impact of Cochliobolus sativus on grain yield of different barley cultivars was studied for 3 seasons in northern Syria by comparing plots with and without artificial inoculation. Distributing oat kernels infested with C. sativus next to barley seed and inoculating seed with C. sativus conidia in a peat carrier resulted in an increase in common root rot symptoms on the subcrown internode. Subcrown internodes were shorter in inoculated than uninoculated plots. The effect of inoculation differed greatly among cultivars and years. Highest losses from the common root rot occurred under dry growing conditions, whereas a significant yield increase was noted on 2 susceptible lines grown under adequate moisture. As common root rot can reduce barley yield in unfavourable environments, the disease should be considered by crop improvement programs aimed at low-rainfall zones in Mediterranean environments.

Effects of Two Triazole Seed Treatments, Triticonazole and Triadimenol, on Growth and Development of Wheat

The triazole fungicides, triadimenol and triticonazole, applied as seed treatments at various rates on spring wheat, affected plant growth, shoot development, and root axis production. The main growth regulatory effects were reductions in lengths of the coleoptile, the first leaf and the subcrown internode. A marked effect on tiller appearance occurred with high rates of triadimenol. Modification of root-system development included a reduction in the number of seminal roots, increased outgrowth of roots associated with the coleoptilar node, and a reduction of roots at the first foliar node (correlated with reduced production of Tiller 1). Seed treatment effects on both shoot and root development illustrated the close relationship between these plant structures. Both fungicides induced both beneficial and deleterious effects on wheat growth and development, but the magnitude of deleterious effects was less with triticonazole than with triadimenol.

Infection of Field-Grown Winter Wheat byCephalosporium gramineumand the Effect of Soil pH

Field experiments were conducted at the Plant Disease Research Farm, Pullman, WA, from 1989 to 1993 to determine when Cephalosporium gramineum infects winter wheat, which plant parts are infected, and the effect of soil pH on infection (1991 to 1993). C. gramineum was isolated from winter wheat plants beginning in October each year before soil freezing occurred, confirming that soil freezing was not necessary for infection of winter wheat by the pathogen. C. gramineum was isolated frequently from seminal roots, crown roots, and stems, but infrequently from subcrown internodes. Since C. gramineum was rarely found in subcrown internodes, crown roots appeared to be the primary infection court. Likewise, C. gramineum was rarely isolated from roots with intact root tips or from root tissue near intact root tips, suggesting that the pathogen may have infected plants by colonizing senescent root cortical tissue, followed by penetration of the vascular system. In 2 years, C. gramineum was isolated from fewer crown roots of plants grown in soil with pH 6.7 to 7.2 than pH 4.7 to 5.9, but not until February or March. Increased infection of roots at low pH may have contributed to increased disease incidence ; however, final disease incidence was greater for plants grown in the low pH soil in only 1 of the 2 years of this study.

Pathogenic Fungi Associated with Fusarium Foot Rot of Winter Wheat in the Semiarid &gt;Pacific Northwest

Winter wheat plants and soil were collected from 288 nonirrigated fields in the semiarid Pacific Northwest during 1993 and 1994. Fungi associated with 5,390 crown and subcrown internodes from 10 Oregon and nine Washington counties were identified. Fusarium graminearum Group 1 was most widespread and the dominant pathogen associated with a crown and root rot named Fusarium foot rot or dryland root rot. E culmorum was widely distributed in soil but was detected in plants in only half as many locations as F. graminearum. Other pathogens included Bipolaris sorokiniana, Microdochium nivale, and F. avenaceum. Highly variable isolation frequencies for all five pathogens were presumed related to a very dry and a very wet survey year. Each pathogen was considered dominant or co-dominant at one or more sites during one or more years. All five species and F acuminatum and F. oxysporum included isolates capable of killing wheat seedlings in the greenhouse.

Effects of Common Root Rot on Discoloration and Growth of the Spring Wheat Root System

Image analysis procedures were used to quantify the effect of common root rot on the growth and discoloration of the subcrown internode (SCI), crown roots, and seminal roots of spring wheat. Severe discoloration of the SCI was associated with diminished growth of the seminal and crown roots. The linkage of discoloration of the SCI to a reduction in root growth was most evident for the crown roots. Reduced growth of either the crown or seminal roots was not compensated for by increased growth of the other root system. The differences in root discoloration among different root rot categories were generally small. On average, the crown and seminal roots were whiter than the SCI in the healthy (nil) category. There was a weak negative relationship between discoloration of the SCI and the crown and seminal root systems. However, it was also observed that root discoloration usually increased with greater root length. Since plants with healthy SCIs usually had longer roots, they were more likely to be exposed to the pathogen and become discolored than were plants with severely diseased SCIs. The image analysis procedures developed in this study can be used to objectively and precisely measure damage caused by root diseases in other host species. This procedure validates the most commonly used field research method of rating plants for common root rot

Morphological Development and Anatomical Features of Wheat Seedlings as Influenced by Temperature and Seeding Depth

Temperature and seeding depth are two major factors influencing the early development of winter wheat (Triticum aestivum L.). The morphological and anatomical features were investigated for plants grown at seeding depths of 3, 6, and 9 cm and ambient temperatures of 10, 20, and 30 °C to determine the effects planting depth and temperature had on certain seedling properties important in seedling physiology. Planting at 6‐ and 9‐cm depths and at 10 °C significantly reduced seedling emergence rate, shoot and root dry weight, leaf area, and number of seminal and crown roots. Deep planting limited seminal root number to about three and increased subcrown internode length in all temperature regimes. Planting at 9‐cm depth and at 30 °C near surface temperature reduced effective xylem radius in the subcrown internode. It was concluded that the decreased seedling growth and xylem radius of the subcrown internode and associated hydraulic properties by deep planting depended strongly on the growing‐condition temperature, and was minimized at the optimal temperature (20 °C) for early development of wheat seedlings. Planting at a deeper depth and higher temperature has the potential of increasing hydraulic resistance of the subcrown internode for wheat seedlings.

Effect of sowing depth on seedling emergence, growth and development in barley and wheat

Crop prediction models often assume a ‘standard’ sowing depth but this may vary both between and within crops. This paper reports response of time of seedling emergence and plant development to sowing depth. Spring barley was sown at depths of 50, 100 or 200 mm in a glasshouse experiment and the growth of the coleoptile, elongating sub-crown internodes, leaves and roots were measured from germination until emergence of the fourth leaf. Winter wheat was sown in a continuous gradient of 0–150 mm in a sandy loam in the field. Seedling emergence and establishment were measured and emerged leaves were counted until flag leaf appearance. Lengths of the coleoptile, sub-crown internodes and leaves were measured and plant development was assessed. Time to wheat seedling emergence increased with increasing sowing depth and linear regression of thermal time to seedling emergence on depth of sowing accounted for 99% of the variation. Reported functions of response to sowing depth tended to underestimate time of seedling emergence. In both barley and wheat, length of elongating and primordial leaves was shorter when sown deeply. Final dry mass of the seminal root of barley, which was attained soon after emergence, was reduced by deep sowing. In barley, elongation of the sub-crown internodes was related to the elongation of the associated leaf, so that in deeply sown seedlings, adjustment of crown depth might continue until the third leaf is fully grown. Shoot apex stage and culm elongation of wheat were affected by depth of sowing. The depth at which seeds are sown, both between and within crops, may be a significant factor both in assessing crop development for crop management and for predicting crop stage.

Quantification by Image Analysis of Subcrown Internode Discoloration in Wheat Caused by Common Root Rot

Common root rot of wheat, caused by Cochliobolus sativus, produces a brown to black discoloration of the subcrown internodes (SCIs). The degree of discoloration is a measure of root rot severity and is directly related to yield losses. The rating system commonly used to assess the degree of discoloration is subjective, vulnerable to inconsistencies, and limited in quantification to only four categories. This study describes an image-analysis method that reliably quantifies discoloration of SCIs. Quantification is objective, highly precise, quick, and usable with any image analyzer. Image-analysis quantifications were compared with the four-category, subjective rating system for greenhouse collections of SCIs of wheat [...]

Incidence ofBipolarisandFusariumon Subcrown Internodes of Spring Barley and Wheat Grown in Continuous Conservation Tillage

Two cultivars each of barley and wheat were planted in three tillage systems (minimum till, chisel plow, and moldboard plow). Subcrown internodes were sampled twice each season (near heading and in the hard-dough to ripening stages) for common root rot and infection by Bipolaris sorokiniana and Fusarium spp. (F. acuminotum, F. avenaceum, F. culmorum. F. graminearum) in the fourth and fifth years of continuous cultivation. No significant interactions occurred between tillage and cultivar for the variables measured (...)

Natural Selection on Winter Barley Composite Cross XXVI Affects Winter Survival and Associated Traits

Winterhardiness of winter barley (Hordeum vulgare L.) has not been improved greatly during the last 40 yr. Explanations range from a presumed lack of genetic variance for hardiness to a lack of effective selection in winter barley improvement programs. Previous research in Montana utilized recurrent selection in composite crosses containing male sterility to increase genetic recombination and improve winterhardiness. Composite Cross XXVI (CCXXVI) was subjected to winter selection pressure at various Montana locations from 1966 to 1984. This research evaluated the effectiveness of natural selection on winter survival and various agronomic and morphological traits in CCXXVI. Field trials at 10 Montana locations from 1985 to 1987 were used to measure winter survival and agronomic traits. Changes in morphological traits were studied in field and controlled‐environment studies. Natural selection appeared to favor taller and later‐heading plants. No significant change in population grain yield over time was detected in CCXXVI. Natural selection improved winter survival in CCXXVI, but the selection was not uniform over generations and maximum population hardiness occurred midway through the experiment. The hardiest CCXXVI generation was lower in winter survival than a hardy winter wheat (Triticum aestivum L.) and the same as a nonhardy winter wheat and a hardy winter barley cultivar. No significant correlation was found between seedling leaf width, seedling leaf number, or subcrown internode and mean winter survival. Shorter seedling leaf length was associated with enhanced winter survival.

Assessment of yield loss caused by common root rot in wheat cultivars in Queensland

The effects of common root rot (CRR) caused by Bipolaris sorokiniana on grain yield, number of tillers, number of grains and grain weight of wheat plants were determined in four field experiments. Sites with different soil populations of B. sorokiniana were selected and inoculum of the fungus added to some plots. Disease and yield measurements were made on eight cultivars and lines differing in susceptibility to CRR. Timgalen, Songlen and Hartog were susceptible whereas Kite, 1008 C16, 141-4 and ISWYN 32 were partially resistant to CRR. Grain yield, tiller and grain number, but not grain weight decreased as disease severity increased. Diseased plants had lower tiller numbers than healthy ones and as a consequence a reduced number of grains and grain yield per plant. Five methods were compared for estimating yield loss caused by the disease. Polynomial regression equations for each cultivar between yield and disease rating of sub-crown internodes or multiple regression equations between yield and disease parameters of sub-crown internodes or tiller bases were established. A third method involved the projection of yield losses from one cultivar to other cultivars and in a fourth method yield losses were estimated from actual yields. In addition, an equation Yield loss (%) = 3 46 + 0.23 disease severity) (%) was established in one experiment and used as a fifth method in the other experiments. Yield losses estimated by methods 1 and 2 were similar and higher than those from the other methods. In areas where disease severity is high, methods 1 and 5 appear to be the most suitable for determining yield losses. Losses in a susceptible cultivar, Timgalen, varied between 13.9 and 23.9% whereas those in a partially resistant cultivar, 1008 C16, varied between 6.8 and 13.6%.

The Influence of Plant Water Stress on Infection and Colonization of Wheat Seedlings byFusarium graminearumGroup 1

The influence of seedling water potential on infection and colonization of wheat seedlings (Triticum aestivum) by Fusarium graminearum Group 1 was studied using wax partitioning of the soil so that the water potential of the seminal root zone was manipulated independently from the water potential of the infection zone in the subcrown internode region. Eleven days after seeds were sown, water was withheld from the root zone to induce water stress in seedlings, while nonstressed seedlings were watered every 48 h to a soil water content of 0.31 g g -1 , favorable for plant growth (...)

Wheat production in an arid environment. 2. Role of soil pathogens

In the Negev Desert agro-system, wheat ( Triticum aestivum L.) yields under fallow management practices have been shown to be 84% greater than those from continuous wheat. The higher yields for the fallow management were achieved without improved soil water storage, and soil nitrogen was not a limiting factor in either system. Yields were similarly increased after several years in continuous wheat, by chemical control of soil pathogens. The objective of this study was to identify the dominant soil pathogens in the different management systems and to assess their influence on grain production. A 19-month fallow period or a chemical soil treatment significantly reduced the population of two dominant nematodes, Pratylenchus mediterranea and Heterodera avenae. The nematicide aldicarb, which was used to differentiate between fungicidal and nematicidal effects of the broad-spectrum biocide metham-sodium, increased wheat yield significantly in one out of four years at Gilat, and in two out of four years at Magen. These results emphasize that, although the parasitic nematodes reduced yields in some years, no clear and consistent correlation between nematode population and grain-yield could be shown. The root-rot fungus Cochliobolus sativus was the dominant fungal pathogen in the soil, but frequency of recovery of the fungus from sub-crown internodes was not related to yield differences between management systems. Under irrigation, the pathogen Gaeumannomyces graminis var. tritici (the cause of take-all) became dominant, and greatly reduced grain-yields. When the disease was controlled either chemically or biologically, yields returned to the level prior to disease onset. No symptom of take-all was found in the same years and treatments under dryland conditions. It is concluded that the high yields achieved with the fallow wheat management are a result of improved soil sanitation, which justifies an effort in developing pest and disease-tolerant/resistant cereal varieties for continuous wheat cropping systems.

Agronomic practices and common root rot in spring wheat: Effect of tillage on disease and inoculum density ofCochliobolus sativusin soil

The effect of tillage, primarily zero tillage, on common root rot in spring wheat was studied at three locations in Saskatchewan. Generally, disease intensity was lower under zero than conventional tillage. It was significantly lower in 6 of 10 years at Scott and in 3 of 7 years at Swift Current. Differences occurred in wheat in oilseed - wheat - wheat, fallow - oilseed - wheat, and fallow - wheat rotations and in continuous wheat. On average, the disease intensity in minimum tillage plots at Swift Current was intermediate between that in zero and in conventional tillage. Effect of depth of seeding usually was significantly greater under conventional than zero tillage. Covariance analysis indicated that seeding depth influenced the disease intensity: shallow seeding was associated with the reduced disease under zero tillage. Isolations from subcrown internodes showed Cochliobolus sativus to be the dominant cause of common root rot at the three locations, with a positive association between the frequency of its isolation and disease intensity. C sativus was obtained more frequently from plants under conventional than zero tillage. The inoculum density of C sativus in the top 8 cm of soil usually was significantly less under zero tillage than under conventional tillage. However, there was no indication that the inoculum density of C sativus directly influenced the disease intensity. The former was nonsignificant as the covariance in covariance analysis of intensity. Possibly inoculum density always exceeded the threshold density required for maximum disease under the test environments.

Reaction of spring barley to common root rot under several moisture regimes: Effect on yield components, plant stand, and disease severity

The reaction of spring barley to common root rot and its effect on yield components, plant stand, and disease severity was studied under several moisture regimes. Infection of barley from natural soil inoculum, primarily Cochliobolus sativus, was augmented with inoculum of C. sativus or Fusarium culmorum to insure uniform disease pressure during plant development. In one study during the 1986 and 1987 growing seasons, a line-source sprinkler irrigation system was utilized to establish a soil moisture gradient from a high-moisture regime receiving both irrigation water and rainfall to a dryland regime receiving only rainfall. In 1986, a second study was carried out to examine the effect of soil moisture at three locations that differed in annual precipitation. Plant emergence and harvestable tillers were reduced by C. sativus in both studies as compared to the noninoculated controls. Grain yield loss was associated with C. sativus and low plant density under drought but not under moderate to high moisture conditions. In the irrigated moisture regimes, moderate and high rainfall locations, the inoculated plants compensated for reduced plant stand and harvestable tillers by producing heavier kernels. Disease severity, based on the subcrown internode lesion development during the soft dough growth stage, did not differ in the dryland and irrigated moisture regimes. However, disease severity was higher in the drought location than in the moderate and high rainfall locations. Prolonged drought and disease pressure during seedling development can result in grain yield reductions, whereas subsequent moisture will affect the crop's ability to compensate for common root rot. Key words: Hordeum vulgare, ranking and selection, canopy temperature

Chloride Fertilizer Effects on Winter Wheat Inoculated with Fusarium culmorum

AbstractStudies in the Northern Great Plains indicate that Cl fertilizers sometimes increase yield and reduce the severity of root diseases in small grains. Little information exists from this region on the relationship between Cl and common root rot incited by Fusarium culmorum (W.C. Sm.) Sacc., or the effect of Cl on winter wheat (Trificum aestivum L.) yield. The objectives of this study were to address these issues. Field experiments were conducted in south central Montana during 1988 and 1989 on a Fort Collins soil (fine‐loamy, mixed, mesic Ustollic Haplargids) that contained 57 and 39) kg Cl ha−1 (0−120 cm), respectively. The experiment consisted or two cultivars of winter wheat (Redwin and Cree), three seed treatments (heat sterilized F. culmorum, live F. culmorum plus chemical protectant, and live F. culmorum, and four CI fertilizer levels (0, 22.5, 45, and 90 kg Cl ha−1) in complete factorial arrangement. In. spection of lower stems and subcrown internodes at the soft dough stage indicated no effect from Cl on disease severity. Chloride fertilizer significantly increased grain yield in 1988 (P &lt; 0.001), but not in 1989. In 1988 grain yields at 22.5, 45, and 90 kg Cl ha−1 were not different and averaged 3306 kg ha−1, or 227 kg ha−1 more than plants not receiving Cl. Whole plant Cl concentrations at heading and indigenous soil Cl were not reliable predictors of yield response to C1 fertilizer. Seasonal factors may be important in defining the likelihood of a response to Cl fertilizer in addition to soil and plant Cl status.