Research Service, U.S. Department of Agriculture, St. Paul MN 55108, USA, ... University of Minnesota and 4Department of Horticultural Science, University of ...
Plantand Soil 171: 235-244, 1995. © 1995KluwerAcademicPublishers. PrintedintheNetherlands.
Oat residue and soil compaction influences on common root rot (Aphanomyes euteiches) of peas in a fine-textured soil V. A. Fritz 1, R.R. Allmaras 2, E L. P f l e g e r 3 and D. W. D a v i s 4 1Southern Experiment Station, University of Minnesota, 35838 120th St., Waseca, MN 56093, USA, 2Agricultural Research Service, U.S. Department of Agriculture, St. Paul MN 55108, USA, 3Department of Plant Pathology, University of Minnesota and 4Department of Horticultural Science, University of Minnesota, St. Paul, MN 55108, USA Received28 April 1994.Acceptedin revisedform 14 September1994
Key words: bulk density, cultural control, green pea yield, root disease rating, soil hydraulic properties, traffic patterns, vine growth
Abstract Management of common root rot (Aphanomyces euteiches Drechs.) in peas (Pisum sativum L.) is sought primarily by host crop avoidance for several years. Soil compaction is known to aggravate A. euteiches disease in peas but effects on infection and subsequent symptom development are not sufficiently known to assist in cultural control. Several isolated observations have noted that oat crop residues may suppress A. euteiches infection and disease in pea roots. The individual and combined influence (a factorial combination of two factors each at two levels) of a prior oat crop and soil compaction were studied for their effects on common root rot severity in processing peas grown in an A. euteiches disease nursery on a fine-textured soil in the northern Corn Belt of the USA. A previous crop of summer oats relative to prior-year peas significantly suppressed common root rot and increased pea fresh vine weight 210% at peak bloom stage. Both fresh vine weight and green pea yield were reduced as much as 63% by soil compaction and increased as much as 48% by a prior oat crop. Greater soil bulk density at the 10 to 25-cm depth identified wheel traffic compaction patterns in each year. A 10-fold reduction of saturated hydraulic conductivity in the 10 to 25-cm compacted zone and high soil-water potentials within the upper 60 cm both confirmed an impaired water drainage, especially during infiltration events. These observations support the use of a previous full season or summer oat crop jointly with chisel plowing, plus the prevention of excessive traffic during secondary tillage and planting, to reduce common root rot in a field infested with A. euteiches. Shallow incorporation of oat shoot and root residue by chiseling could be a crucial component of the cultural control of the disease.
Introduction Common root rot in peas (Pisum sativum L.), caused by Aphanomyces euteiches Drechs., has been recognized as a serious soilborne disease since 1925 (Papavizas and Ayers, 1974). The disease is widespread not only in fine-textured/poorly drained soils in subhumid to humid climates (Papavizas and Ayers, 1974), but has also been observed in irrigated, coarse-textured soils (Kraft et al., 1990; Pfender and Hagedorn, 1983). Management of common root rot is sought primarily by avoidance of the host crop for six years or longer, yet crop loss remains unpredictable. Soil compaction
aggravates common root rot and often results in greater disease severity (Burke et al., 1969a, 1970; Tu and Findlay, 1986; Vigier et al., 1983). Preliminary work suggested that reduced soil compaction and a prior oats crop are two cultural practices that could help to sustain pea production on infested soils (Papavizas and Ayers, 1974; Tu and Findlay, 1986). A. euteiches also can be one component in a complex of fungi which individually can cause pea root disease and which are aggravated by soil compaction. Thus compaction also contributes to chick pea (Cicer arietinum L.) and pea root diseases caused by Fusarium solani (Mart.) Sacc. f. sp. pisi (ER. Jones) W.C. Snyder and H. N. Hanson
236 (Bhatti and Kraft, 1992; Burke et al., 1969a, 1970; Kraft and Allmaras, 1985). Furthermore, root disease caused by Pythium ultimum Trow is aggravated by compaction because the pathogen is often associated in a root-disease complex with either A. euteiches (Tu, 1987) or E solani f. sp. pisi (Kraft and Allmaras, 1985; Tu, 1987). Effects of soil compaction on root disease development depend on the soil ecology imposed and the requirements of the pathogen. Soil compaction may be produced within a tilled layer or at the base of a tilled layer and usually has a spatial pattern that is related to traffic/tillage patterns (Allmaras et al., 1988a, b). Spatial patterns of compaction can be characterized by bulk density or penetrometer measurements, but associated hydrothermal, aeration, and mechanical resistance in the root zone are the factors that impact infection and disease development (Allmaras et al., 1988a). A. euteiches and F. solani f. sp. pisi inoculum predominance in the plow layer of pea fields in Wisconsin (Burke et al., 1969a, b, 1970) was related to the extent of pea rooting, as well as to tillage mixing of soil and organic debris above a plow pan. Burke et al. (1972a, b) demonstrated a similar influence of moldboard-plow and disk pans on the rooting of field beans (Phaseolus vulgaris L.) and on the incidence of Fusarium solani (Mart.) Sacc. f. sp. phaseoli (E R. Jones) W. C. Snyder and H.N. Hanson above zones of bulk density sufficient to impede rooting. Inoculum of A. euteiches and F. solani f. sp. pisi occasionally has been found below the Ap layer (Burke et al., 1970; Kraft and Allmaras, 1985; Kraft et al., 1990). Burke et al. (1969a, b) showed that infection of A. euteiches on pea roots was not influenced by temperature but was hastened by brief soil saturation. Brief localized saturation is likely to occur in compacted soil located in plow pans or even in traffic lanes in the Ap layer (Allmaras et al., 1988b). However, the expression of symptoms in peas is influenced by temperature. Soil moisture conditions for P ultimum and A. euteiches infection are not greatly different, but P. ultimum symptoms usually occur at lower temperatures (Alconero and Hagedorn, 1967) than those of A. euteiches. Damping-off of sugar beet (Beta vulgaris L.) seedlings shows a similar time development pattern for the disease complex of A. cochlioides Drechs. and Pythium ultimum (Payne and Asher, 1989). Burke et al. (1969) demonstrated a rapid spread of A. euteiches infection from pea roots that had grown from noninfested into infested soil. They contrasted this rapid spread ofA. euteiches with a much slower spread of E
solani f. sp. pisi infection along the root from zones of infested to noninfested soil. Oat (Avena sativa L.) residues have reduced common root rot severity and increased seed yield of peas in the greenhouse (Davey and Papavizas, 1961), and in the field (Tu and Findlay, 1986). A saponin found in oat roots and their extracts may lyse zoospores of Aphanomyces spp and P ultimum oospores (Deacon and Mitchell, 1985). In the quest for effective cultural management of A. euteiches, we field tested the individual and combined influence of a prior oat crop, and an induced soil compaction (produced during secondary tillage and planting operations) on a fine-textured soil in a long-term pea-disease nursery in the northern Corn Belt of the USA. The test of oats as a cultural control measure was suggested by observations in the nursery as early as 1986 (D.W. Davis and F.L. Pfleger), that this crop could be used to reduce A. euteiches severity at a level suitable for evaluating germplasm susceptibility.
Methods and materials
The field experiment was conducted in an approximate area of 50 × 10 m (Fig. 1) within a long-established, heavily infested nursery for evaluating pea response to common root rot caused by A. euteiches. The experimental site, a moderately to poorly drained Webster clay loam (fine loamy, mixed, mesic Typic Haplaquoll), has about 2% slope. It is located at the University of Minnesota, Southern Experiment Station, Waseca. The Ap layer consists of 348, 326, and 326 g kg-x respectively of sand, silt, and clay; the organic matter content is 47.4 g kg- i. The respective composition of the adjacent subsoil is 320, 342,338, and 33.0 kg- 1. The site had been fall moldboard plowed annually for more than 10 yr, including the fall of 1986. The sequence of treatments and measurements was initiated at pea (vat. Bolero) planting (12 May) and oat (vat. Steele) planting (1 May) in 1987 and terminated at pea harvest in 1989 (Table 1). One half of the experimental area was selected randomly to be planted to oats in 1987 and the other one-half to peas. This treatment assignment began the crop history to be tested in 1988. About 2 of the pea vines were deposited back onto respective plots after pea harvest in July 1987; oats were harvested on 4 August and straw removed within several days. (Current tillage practices for pea production in the Midwest are almost
237 Q o p p l r ~ Sequence N
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I
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.
.
.
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4
Host Crop
I
oats
peas
oats
peas
2
OOtS
pegs
none
peos
Plot NO,'
n/n
.
1987 Test Crop 2
. .
21:
1988 Test CrOp ~
1989 Host Crop
3
oats
peas
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peas
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IX:Its
peas
oots
peos
5
peas
peas
oots
peas
6
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peas
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peas
7
peas
peas
none
peas
8
peas
peas
oats
peas
i C/C: c o m p a c t e d rn 1988 and 1989 before
n/n
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21 m
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primary tillage in fall of 1987 and 1988 -
c~sel plow
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Fig. 1. Sequence of treatments and tests for period from planting 1987 to harvest 1989.
Table 1. Pea growth and disease development (1989) as influenced by soil compaction and prior crop treatments
Date
Stage of growth
1 June 7 June
2-3 node 3-5 node
15 June
6-7 node
29 June
Bloom
Main-effect response Compaction vs no compaction 10% hrb 20% hr with some diseased/dead plants 30% hr with more diseased/dead plants 50% hr with diseased/dead plants
Oats vs peas in 1988a No response No hiC; necrosis of lower leaves after peas 25% hi and no disease symptoms after oats; increased necrosis of lower leaves after pea More wilting, yellowing, necrotic leaf margins after peas than oats
a Peas with fallow after harvest in 1988 vs peas followed by a summer crop of oats in 1988 (see Fig. 1). b hr = height reduction due to compaction. c hi = height increase due to prior oats crop.
solely c o m p r i s e d o f planting into a p r e v i o u s l y chisel p l o w e d field h a v i n g m i n i m a l crop residue as f r o m soybean; t w o or three secondary tillages are used with a disk or spring tooth cultivator prior to planting.) The w h o l e e x p e r i m e n t a l area was chisel p l o w e d in autumn. In spring o f 1988 t w o levels o f c o m p a c t i o n (c/c and n/n) w e r e r a n d o m l y assigned within each o f the 1987
crop histories. The c o m p a c t e d plots w e r e each unif o r m l y packed using a m e d i u m - s i z e d tractor ( 5 0 0 0 - k g axle load, 200 kPa tire pressure), and the w h o l e area tilled with a spring-tooth cultivator. Peas w e r e planted across the entire site on 6 M a y in 2 5 - c m r o w s using a drill with a double-disk o p e n e r to a c h i e v e about 123
238 plants m -2. Seed was treated with Captan I Postemerge weed control consisted of two applications of a mix of bentazon (Basagran 1 at 0.8 kg a.i. ha - l ) and sethoxydim (Poast 1 at 1.1 kg a.i. ha-l). Irrigations of 2.5 cm each were applied over a 4 hr period on 24 May and 1, 6, 18 June. Peas were harvested on 5 July 1988. After pea harvest, two treatments were randomly assigned within each of the rectangular areas (i.e., previous test crop of oats in 1987 and compaction in 1988 in upper left rectangle in Fig. 1). These were bare fallow and summer oats (var. Steele) planted 29 August and supplementally irrigated when necessary to sustain growth. At killing frost on 5 October, the oats were about 50 cm tall and had not reached anthesis. The whole experimental area was chisel plowed on 17 October 1988. In spring of 1989, wheel compaction was imposed on the same plots and in the same manner as 1988; the whole experimental site was then tilled as in 1988 and planted to (Captanl-treated) peas on 16 May. Weeds were controlled with a pre-emerge application of propachlor (Ramrod 1 at 4.5 kg a.i. ha -1) and prometryn (Caparol 1 at 1.1 kg a.i. ha-l). Irrigations of 2.5 cm each were applied on 8 and 19 June, and 5 and 11 July. Peas were harvested on 11 July 1989. In 1988 field notes were recorded on pea plant growth and disease symptoms. Plant heights and disease symptoms were made on 10 randomly selected plants within each of the four treatments at various stages of growth. Soil related measurements were also made. Tensiometers were installed on 16 May and read three mornings per week until 10 July, using the procedure of Marthaler et al. (1983). There were three tensiometers at each of two depths (25 and 40 cm) within each of the compacted and noncompacted treatments (Fig. 1). The bulk density profile (2-cm increments to 50-cm depth) was measured in the compacted and noncompacted treatments during May and June, using a system of composited cores each 18 mm in diameter (Allmaras et al., 1988c). Precipitation and mean air temperature were recorded from a central weather station located less than 1 km from the nursery. More detailed plant data were obtained in 1989 by repeated observation of symptoms and growth of randomly selected plants. Disease symptoms and growth
of peas were observed over the period from two nodes to peak bloom. Root disease severity data was obtained from three samples of 10 randomly dug plants within each of the eight plots (Fig. 1) when the plants were at peak bloom on 29 June. Roots were washed and rated visually to assess the severity of common root rot using a scale of 1 to 5. The five-point scale was based on an estimate of the percent roots infected (1 = 0-10%, 2 = 11-25%, 3 = 26-50%, 4 = 51-75%, 5 = 76-100% ). Fresh vine weight and yield of green peas were obtained from the same plants sampled on 29 June for determining root disease severity. Variation among the three samples within each of the eight plots in Figure 1 was used to compute a standard error to compare the four treatments. Fresh vine weight and yield of green peas were obtained on 11 July from a harvest area of 3 m 2 selected randomly within each of the eight plots (Fig. 1). Vine height/length was measured on three sets of five plants, and the total number of plants was observed in each of three separate row lengths within each plot (Fig. 1) outside the harvested area. An error term for comparing the four treatments was generated from eight sets of yield versus vine length/height. Soil bulk density was measured on 16 June using the same procedure as in 1988. Triplicate cores (5 cm diam. and 5 cm long) for saturated hydraulic conductivity(Ksat were taken on 10 August at 10, 25, and 40 cm at each of two sites within the compacted and noncompacted treatments. The four sites (Fig. 1) were at the south end of plots 3 and 4 and north end of plots 5 and 6; all sites were within a 12-m 2 area. Ksat was measured in these cores using a falling head technique (Klute and Dirksen, 1986). In 1989 soilwater-potential sensors (Watermark 1) were installed at 10, 25, 40, and 60 cm at each of two locations within the compacted and noncompacted treatments. Their signal was automatically recorded hourly from 1 June until pea harvest. These sensors become erratic near saturation and have a + 10% accuracy in the range of -2 to -150 kPa water potential (McCann et al., 1992; Spaans and Baker, 1992). Their accuracy is improved when rewetted to saturation after a soil drying excursion.
Results l Mentionof a trademarkor proprietaryproductdoes not constitute a guaranteeor warranty of the productby USDA/Universityof Minnesota and does not implyits approvalto the exclusionof other productsthat may also be suitable. This article reportsthe results of research only.
The period 1 April to 15 July 1988 had mean daily air temperatures 3.8 °C above and a precipitation sum 168 mm below the long-term normals of 13.3 °C and
239 Table 2. Root disease index and fresh vine weight of peas at peak bloom (29 June 1989) as related to treatments of soil compaction and prior crop of oats Previous crop ~'
Soil
Root disease
Fresh vine
compaction
index b
weight (g/10 plants)
2.0 b c
280 a
2.0 b
210 b
Oats Oats
+
Peas Peas
+
Std. error
2.7 a
92 c
2.7 a
66 c
0.08
17.9
a Peas with fallow after harvest in 1988 vs peas followed by a summer crop of oats in 1988 (see Fig. 1). b Disease index (pea roots infected): 1(0 - 10%), 2(11 - 25%), 3(26 -50%), 4(51 - 75%), and 5(76 - 100%). c Duncans multiple range using p = 0.01.
April
May
June
Plant growth and disease
July
E
G
5_
E
g
