Texas, USA 2010 - International Herbage Seed Group

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Stem rust in perennial ryegrass seed crops: epidemiological and geneticresearch at USDA-ARSW.F. PfenderUSDA-ARS NFSPRC3450 SW Campus WayCorvallis, Oregon 97331 USABill.Pfender@ars.usda.govAbstractIn production of perennial ryegrass seed in the Northwest USA, stem rust is the primary diseaseconstraint in terms of management cost and potential yield loss. The USDA-ARS researchprogram on this problem is focused on improved decision making for fungicide use, and tools forgenetic improvement. Data from 10 years of field and greenhouse research was used to constructan epidemiological model. This model is based on the effects of weather (temperature, leafwetness) on plant growth and pathogen activity, and includes the effects of two major fungicideclasses (triazoles and strobilurins) on disease development, particularly on the spread of diseasewithin a plant. The model is implemented as a decision aid on a publicly-accessible internet site.Users enter scouting data and select a location for weather data to be loaded into the model. Thewebsite displays the model results, including the relationship of modeled disease development toan action threshold. The decision aid has performed well in large-scale field demonstration plotsacross 10 location-years, providing an average economic advantage of $39 per acre (range: $0 to$140) compared to standard fungicide programs. In genetic research, a perennial ryegrassmapping population was constructed from a cross between resistant and susceptible parents. Theprogeny (193 individuals) were tested by inoculating with two different pathotypes of the stemrust fungus, in separate experiments. Using a genetic map of these parents constructed with SSRand RAD markers, QTL analyses were conducted. The goal of this genetic research is toproduce genetic markers for marker-assisted selection of stem rust resistance, as well as toprovide information about genomic organization of disease resistance in perennial ryegrass.Stem rust on perennial ryegrass and tall fescue in the Pacific Northwest USAIn perennial ryegrass (Lolium perenne) and tall fescue grown for seed, the economically mostimportant disease in major seed production areas of the United States is stem rust caused byPuccinia graminis subsp. graminicola (Welty & Azevedo, 1984) Perennial ryegrass seed yieldlosses up to 98% due to stem rust damage have been recorded (Pfender, 2009a). The disease isalso a significant production constraint in New Zealand, where yield losses of 35% weredocumented (Hampton, 1986). Since the 1980s, there has been a research program at the USDA-ARS Forage Seed Research Laboratory in Corvallis, OR, USA. Starting in the late 1990s theresearch focused on developing an epidemiological model that could be used in a decision113
support system to optimize fungicide use in disease management. Within the last few yearsanother component, stem rust resistance genetics in Lolium, has been added to the effort.Epidemiological research and fungicide decision support systemThe goal of the epidemiological work at USDA-ARS has been to quantify the effects ofenvironmental factors on disease development, and to summarize that knowledge in the form ofa mathematical model. The model is intended to depict the linked disease cycle components, andis driven by weather data that can be collected with automated weather stations in the field.Stem rust epidemic modelWe determined that the probability of infection, given the presence of stem rust inoculum, can becalculated from temperature and leaf wetness occurring during nighttime hours and in the fewhours after sunrise. If the leaves are wet and temperature is greater than 2C, the fungus sporescan germinate and grow. At cold temperatures, a long period of wetness is required for adequategrowth to cause infection, but the required wetness duration is shorter at warmer temperatures.The temperature X wetness duration must be adequate during both the dark period (for sporegermination) and the early morning period (for penetration into the plant). We derived anequation for calculating infection probability from overnight and morning weather data recordedin the field (Pfender, 2003). After the fungus has successfully penetrated the plant, some time isrequired for the infection to develop sufficiently to produce the next generation of spores. Theduration of this time period between infection and production of new spores (the latent period) isdetermined primarily by temperature. The latent period duration can be calculated byaccumulation of heat units (e.g. degree days) (Pfender, 2001). The processes of infection and thelatent period form the core of the stem rust epidemic model.An additional important aspect of stem rust development is the ability of the fungus to spreadfrom infections on the sheath to the stem or flower that is extending from within the infectedsheath (Pfender, 2004). This disease spread occurs because the pustule on the sheath isproducing spores on the inner sheath surface as well as the outer surface. The result is that asingle infection on the flag sheath, for example, can produce hundreds of infections on theinflorescence head and stem. Our observations indicate that up to 80% of the infections thatappear on ryegrass stem sections at the height of an epidemic are the result of this process. Theamount of disease due to this within-plant component is dependent not only on the frequency oflesions on sheaths, but also on the rate of extension of the internodes. Therefore the epidemicmodel includes a component for stem elongation (Pfender, 2006), which is driven by heat units.The full epidemic model includes infection probability, latent period and within-plant spread.The model works on a daily time step, and the amount of inoculum at the beginning of each dayis proportional to the amount of disease (sporulating pustules) at the end of the previous day.Although within-plant spread seems to be a general feature of stem rust in perennial ryegrass, wehave noted that varieties differ in the prominence of the sheath lesions that act as sources for the114
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Proceedings of the 7th Internationa
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Table of ContentsORAL PRESENTATIONS
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Seed yield components and yield per
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International Herbage Seed Conferen
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16:15 - 16:30 Reliability of salini
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Hotel expense is covered for night
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40,000 were slaves (McDonald, 2007)
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Fig. 1. Texas AgriLife Research and
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$7 billion for cattle, $3 billion f
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principle and encourages both AgriL
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eceived by growers, the above perce
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seed conditioning plants are locate
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Table 4.Hectares of open-field burn
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system, a seed crop is produced fro
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Fig. 1. Land resource areas of Texa
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y land owners. Seed yields are low
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The influence of planting density o
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Simple correlation and regression a
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Variation in seed shattering in a g
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Seed retention (SR) was calculated
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mm160120Precipitation8040020Km h -1
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Young, B. A. (1986). A Source of Re
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Several methods are commonly used f
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Table 3. Effect of the length of ha
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Alfalfa seed production in semi-hum
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Rather near the meteorological stat
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ReferencesBolaños-Aguilar E.D., Hu
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ased bioenergy conversion plants wa
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Table 1. Average distances required
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Figure 1. Optimized locations for 1
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Perennial ryegrass (Lolium perenne
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Relative Seed Yieldsingle composite
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Flowers, M.D.; Hart, J.M.; Young II
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Thus, similar to tissue tests, remo
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Conclusion:Perhaps our most importa
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Modelling critical NDVI curves in p
Page 73 and 74: The five spectral reflectance measu
Page 75 and 76: Harvest loss in ryegrass seed crops
Page 77 and 78: Larger than expected harvest losses
Page 79 and 80: Rolston, P.; Trethewey, J.; McCloy,
Page 81 and 82: Optical sensors have the potential
Page 83 and 84: Figure 2. Seed yield response to ap
Page 85 and 86: Flowers, M. D., Hart, J.M., Young I
Page 87 and 88: In 2010, France has launched the fo
Page 89 and 90: Yield (% maximum)ConclusionThe resu
Page 91 and 92: Plant N uptakeN unavailableSoil nit
Page 93 and 94: Stresses associated with germinatio
Page 95 and 96: correspond to electrical conductivi
Page 97 and 98: applied later in the fall was more
Page 99 and 100: Figure 2. Establishment of five ove
Page 101 and 102: The seed vigour testing was perform
Page 103 and 104: Table 1. Germination index (GI) for
Page 105 and 106: Reliability of salinity screening L
Page 107 and 108: AcknowledgmentThis research was sup
Page 109 and 110: Table 2. Greenhouse salinity screen
Page 111 and 112: The seeds were collected from the A
Page 113 and 114: increases germination to its potent
Page 115 and 116: Light, lodging and flag leaves-what
Page 117 and 118: Relative seed yieldSeed yield (kg/h
Page 119 and 120: Hampton, J.G.; Clemence, T.G.A.; He
Page 121 and 122: The seed set is of major importance
Page 123: In grass species with poor seed ret
Page 127 and 128: weather stations in grass seed fiel
Page 129 and 130: ust resistance loci in Lolium peren
Page 131 and 132: Seed yield variation in a red clove
Page 133 and 134: 100Seed yield plant -1 (g)806040200
Page 135 and 136: Marden, J. H. 1984. Remote percepti
Page 137 and 138: Crimson clover seed production in t
Page 139 and 140: Piper, C.V. 1935. Forage plants and
Page 141 and 142: deal of investigation into the caus
Page 143 and 144: genes and subsequent ability to pro
Page 145 and 146: Gatenby, W.A., S.C. Munday-Finch, A
Page 147 and 148: Control of Vulpia myuros in red fes
Page 149 and 150: The strip design provides an opport
Page 151 and 152: The pot experiments did not reveale
Page 153 and 154: CharacterWeed abundance1 A few plan
Page 155 and 156: Jensen, P. K. (2010) Longevity of s
Page 157 and 158: Effects of intraspecific competitio
Page 159 and 160: flowering, Gangi accumulated a high
Page 161 and 162: The seed yield of Gangi was, on ave
Page 163 and 164: Seed yield components and yield per
Page 165 and 166: ResultsVariation among populations
Page 167 and 168: Table 2. Means of total seeds per p
Page 169 and 170: Ryle, G. J. (1970). Partition of As
Page 171 and 172: Control of Apion trifolii in red cl
Page 173 and 174: Number of seeds /inflorescencesimil
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population. However, in spite of th
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Corvallis where they were debearded
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Table 1. Effect of Palisade growth
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Variations on potential and harvest
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Determination of optimum desiccatio
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Relative seed yield (%)Flowers/m225
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Harvesting too soon after peak flow
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Annual ryegrass seed production in
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seed yield, kg/haExtractable Al, mg
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ReferencesHaby, V.A. (1995). Soil m
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Kentucky bluegrass (Poa pratensis L
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urn residue management (Fig. 1 and
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Comparing herbicide selectivity in
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Development of new tetraploid Chlor
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Following 4 (or 5) cycles of select
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Loch, D.S., Rethman, N.F.G. & van N
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KBGcocksfootHykorLofatimothymeadowf
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Figure 2 Relative seed yield (%) se
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and GA 4 . In consequence this inac
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Table 1 The effect of trinexapac-et
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Silberstein, T.B., Young, W.C. III,
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inflorescece number and seed yield
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Germination of Lolium multiflorum g
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Effect of sowing density on seed yi
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y-products of this grass seed crop
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Table 2. Effect of PGR on seed yiel
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Further culm length measurements ga
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chlorophyllometer. Measurements wer
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Table 2. Photosynthesis rate of fla
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Organization of grass seed research
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Path Coefficient and Ridge Regressi
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through y4 (0.133). Increasing y 1
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Newell G.J., Lee B. (1981)Ridge reg
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Relative humidity, seed moisture co
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Ergovaline contents in grasses from
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11.8 % (Central East) to 40.0% (Nor
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ReferencesBony, S. & Delatour, P. (
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Long-term Evaluation of Annual Ryeg
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seed yield. All systems of establis
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Preliminary results after four year
Page 255 and 256:
Casals, Marie-LaureFNAMSImpasse du
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Mao, PeishengForage Seed LabChina A
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Vanasche, DavidVanasche Farm36130 N
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Texas, USA 2010 - International Herbage Seed Group

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