Pathogenic Effects of Pratylenchus scribneri

operated applicator and incorporated Waudo, S. W., and Norton, D. C. 1986. Pathogenic effects of Pratylenchus scribneri in maize into the top 4 cm of soil. Soil samples inbreds and related cultivars. Plant Disease 70:636-638. were taken from the top 25 cm of soil with a 2-cm-diameter soil probe at planting Maize inbreds C123Ht, C103, and Mol7Ht inoculated with 8,500 ± 500 Pratylenchus scribneri and in the inner rhizospheres of 10 developed dark brown, discrete lesions on their roots and had reduced root size and weight and extensively pruned root systems 90 days after inoculation in the greenhouse. Inbred B68Ht, randomly chosen plants per plot 40, 76, similarly treated, had the fewest nematodes and no visible pathological symptoms. In the field, the and 99 days after planting in 1983 and 99 nematode significantly (P= 0.05) reduced either weight, size, volume, or number and/or angle of and 101 days after planting in 1984. fibrous roots of some inbreds and hybrids. Inbred C123Ht and its related cultivars C103, Mo 17Ht, Root systems of four randomly chosen C123HtX Mo17Ht, and C123Ht× Cl03 supported some of the largest numbers of P. scribneriboth plants per plot were removed with a 20in the greenhouse and the field. In most instances, B37Ht and B68Ht had the fewest P. scribneri. cm-diameter modified turf patcher 76 days after planting in 1983 and 51 days after planting in 1984 for root parameter The lesion nematode (Pratylenchus sand, 24% silt, 16% clay, 2.3% organic assessment. Sampling 51 days after scribneri Steiner) is economically matter, and 7.4 pH). Each cultivar was planting was selected to minimize root important in many crops in the United replicated five times in a randomized destruction and to ensure removal of States (1,4,5,9-13). Although maize (Zea block design. Ten milliliters of water nearly whole root systems. Soil was mays L.) is a host of the nematode, containing 8,500 ± 500 P. scribneri were dislodged into a bucket and mixed information about the nematode's pipetted into a 2-cm-deep hole around the thoroughly before taking one 500-g pathogenicity in this crop is meager. seedling 1 day after planting. Cultivars sample per plot for nematode extraction. Colonization by P. scribneri of selected without nematodes served as controls. Again, P. scribneri in the soil were few inbreds that are or were commonly used Plants were fertilized with a teaspoonful and data are not reported. Washed root in the north central United States varied of Osmocote (14-14-14, NPK) 1 wk after systems were evaluated with a modificaconsiderably (14). Although related transplanting and watered as required. tion of Eiben's method (6) on a scale of cultivars possibly can respond similarly Light was supplemented with a 15-hr 1-4 from very small to very large root to P. scribneri, there is no work to verify fluorescent light period (1,132 /tE msystems. Root angle determination this. This work studies population s-l). based on measuring the angle between the changes of P. scribneri and assesses their Three months after inoculation, plant crown roots on the first and second upper pathogenic effects in maize inbreds and roots were removed from the soil, nodes and crown. Crown roots were related cultivars. washed, and rated. Plant tops and roots counted. Degree of fibrous root producwere dried at 90 C for 72 hr before being tion was evaluated on a subjective rating MATERIALS AND METHODS weighed. A sample (2-3 g) of dislodged of 1-4 from few to many fibrous roots. Greenhouse experiments. The P. fibrous roots was collected randomly, Roots were weighed after drying at 90 C scribneri were recovered from a maize and 100 cm 3 of well-mixed soil was taken for 72 hr. Root volume was determined field at Iowa State University Hinds for nematode extraction (2,8). Nematodes by water displacement (3). Research Farm, Ames, and were were counted with a Hawksley slide, and increased in maize inbred C123Ht in the nematodes per gram of dry root were calgreenhouse. Pathogenicity of the nemaculated. Soil populations of P. scribneri RESULTS tode was evaluated in seven maize were low and are not reported here. Greenhouse experiment. P. scribneri cultivars. Seeds were germinated on Field experiments. Eighteen maize population increase. Inbreds B37Ht, damp filter paper in petri dishes. Fiveinbreds in 1983 and eight in 1984 were B68Ht, and C103 had significantly (P = day-old seedlings were transplanted, one tested for nematode increase in loamy 0.05) fewer P. scribneri 90 days after per pot, into steam-sterilized soil (60% sand (81% sand, 12% silt, 7% clay, 2% inoculation in the greenhouse than did organic matter, 6.6 pH) naturally infested inbred C123Ht. Numbers of P. scribneri with P. scribneri. Other nematodes in C123Ht X Mol7Ht and C123Ht X JounalPaer 179 oftheIoa Aricltre nd present in small numbers were Xiphinema C 103 were intermediate to those in their Homra ae r Economic Exeimn StatIon, Amrclues Ia;d americanum Cobb, Helicotylenchus inbreds but were not significantly Project 2285. pseudorobustus (Steiner) Golden, and different (Table 1). Paratylenchus sp., for which data are not Pathogenicity of P. scribneri. Root Prescnt address of first author: Department of reported. Cultivars were replicated five systems of cultivars inoculated with P. Naiotai, Kenya.t nvriy .. Bx484 times each year in a randomized complete scribneri showed discrete, dark brown Naiob, ena.block design. Plots consisted of two lesions, extensive pruning, or reduced Accepted for publication 29iJanuary1986 (submitted adjacent rows 9.2 m long, 0.8 m apart, size (except B68Ht). The nematode for electronic processing). and planted at 42,000 seeds per hectare on caused a 3-32% reduction in root weight 8 May 1983 and 10 May 1984. Outer rows within cultivars, but differences were not The publication coats of this article were defrayed in part were bordered with inbred Mol7Ht. significant (Table 1). Cultivar B68Ht had by page charge payment. This article must therefore be In18,oehloftexprm ta arotwiticeseeutngrm hereby marked "advertisement" in accordance with 18 n18,oehl fteeprmna otwih nraersligfo U.S.C. § 1734 solely to indicate this fact. units of each cultivar were treated with nematode parasitism. Except for C 123 Ht aldicarb 15G. The nematicide was X C103 and B37Ht, P. scribneri also © 1986 The American Phytopathological Society applied in a 1 7.8-cm band at 2.4 kg a.i. / ha caused a 3-35% reduction in shoot 636 Plant Disease/Vol. 70 No. 7 Table 1. Numbers of Pratylenchus scribneri in roots, root weights, and shoot weights of 7 maize weight, but only Mo 17Ht was significant cultivars 90 days after inoculation (greenhouse) (Table 1). Field experiment 1983. P. scribneri P. scribneri/g Root Shoot population increase. Numbers of P. dry root Dry wt Percent Dry wt Percent scribneri per gram of dry root were Cultivara Inoculated Control (g) change (g) change significantly (P = 0.05) different only 99 C123Ht 64,421 0 3.2 19.6 days after planting in 1983 (Table 2). The 2.5 -25.0 17.7 -10.7 highest and lowest numbers of P. C123Ht X Mol7Ht 42,123 0 10.3 39.1 scribneri were obtained from C123Ht and 9.2 -12.0 38.1 -2.6 B68Ht, respectively, 99 days after C123Ht X C103 41,889 4 10.2 39.3 planting. Numbers of nematodes within 9.9 -5.0 39.8 1.3 the roots 40 and 76 days after planting Mo I7Ht 31,419 28 7.9 34.8 were not significant among cultivars, and 5.4 -32.0 21.2 -35.8 rankings were not consistent with C103 8,281 0 5.1 28.9 numbers at 99 days. Where inbreds and B68Ht 5,487 10 9.8 42.1 their hybrids could be compared, 12.6 29.0 37.0 -13.8 numbers of P. scribneri at 99 days were B37Ht 3,433 0 10.3 38.1 frequently significantly intermediate or 9.4 -8.9 38.3 0.5 less than the inbred containing the LSD (P= 0.05) 33,181 N.S. 4.6 9.2 greatest number of nematodes (Table 2). aEach cultivar was replicated five times and inoculated with 8,500 ± 500 P. scribneri. Field experiment 1984. P. scribneri population increase. Numbers of P. scribneri in roots differed significantly (P = 0.05) among many cultivars 51 and 101 Table 2. Numbers of Pratylenchus scribneri recovered from roots of 18 maize cultivars 40, 76, and days after planting (Table 3). Significantly 99 days after planting at Hinds Research Farm, Ames, IA, in 1983 fewer P. scribneri were recovered from cultivars treated with aldicarb than from untreated ones, especially at 51 days after Cultivar 40 Daysa 76 Days 99 Days planting, when the most P. scribneri were C123Ht 19179b 2,908 58,756 obtained from C123Ht and the fewest A632Ht 846 2,047 32,950 from B37Ht in plots not treated with Oh43 1,049 1,716 27,879 aldicarb. At 101 days after planting, the A619Ht 749 2,016 27,744 most P. scribneri were obtained from C123Ht X A619Ht 805 1,454 20,338 C123Ht, C123Ht X Mol7Ht, and C103, C123Ht X C103 1,208 8,742 19,258 and the fewest from B68Ht and B37Ht C 103 1,289 935 16,994 (Table 3). C123Ht X Mol7Ht 469 1,323 15,234 Pathogenicity of P. scribneri. For most B37Ht 103 303 12,227 cultivars, treatment with aldicarb, which Mol7Ht 418 2,245 10,296 B73Ht 995 1,088 9,158 provided varying degrees of nematode C123Ht X Oh43 1,060 1,251 7,880 control, resulted in root weight, size, and B73Ht0 2/02 691 1,151 6,150 volume increases 51 days after planting, B73Ht02/ 02 X Mo17Ht02/0 2 1,096 683 5,181 but most differences were not significant Mol7Ht02/ 02 1,029 10,922 5,140 (Table 3). Root weight of aldicarbB37Ht X A632Ht 1,092 6,962 4,372 treated C123Ht X Mol7Ht was signifiB37Ht X B73Ht 427 847 2,630 cantly (P = 0.05) heavier than that of B68Ht 565 296 1,560 untreated ones. Aldicarb-treated C 123 Ht LSD (P=0.05) N.S. N.S. 22,815 X C103 had a significantly (P = 0.05) a Days after planting. larger root system than untreated ones. bMeans of replicates. Numbers of crown and fibrous roots and Table 3. Numbers of Pratylenchus scribneri, maize root dry weight, size rating, volume, number of crown roots, and root angle, Hinds Researcb Farm, Ames, IA, 1984 51 Days after planting No.a of P. scribneri/g dry root Dry root No. of Fibrous bweight Size Volume crown root Root Cultivar Treatment 51 Daysb 101 Days (g) rating (ml) roots production angle CI123 Ht No aldicarb 18,989 52,626 3.2 1.7 6.5 16.8 1.9 32.0 Aldicarb 3,312 16,758 4.2 1.6 8.3 16.0 1.2 30.7 C123Ht X Mo17Ht No aldicarb 12,845 13,281 7.4 3.1 14.7 20.0 2.2 34.5 Aldicarb 1,565 2,203 12.2 3.4 22.1 20.3 2.1I 34.5 C103 No aldicarb 11,322 24,573 5.8 1.7 1 1.8 16.1 2.0 26.3 Aldicarb 669 9,116 4.8 2.1 10.3 14.1 1.9 30.7 B68Ht No aldicarb 9,437 4,626 5.1 2.2 10.1 20.9 1.7 38.0 Aldicarb 1,441 1,932 7.6 2.7 14.1 18.2 1.9 44.3 CI23Ht>< CI03 No aldicarb 7,816 16,159 5.1 2.1 10.8 16.8 2.2 33.3 Aldicarb 3,046 6,614 7.8 3.0 15.4 18.4 2.0 28.9 Mo17Ht02 /02 No aldicarb 6,840 14,115 4.4 2.0 9.1 19.2 2.2 28.9 Aldicarb 1,435 8,209 4.9 2.1 10.5 19.4 2.3 38.8 M oI7Ht No aldicarb 4,937 9,063 5.8 2.5 13.4 20.5 2.7 38.2 Aldicarb 4,155 3,232 5.9 2.7 12.2 20.0 2.3 34.9 B37Ht No aldicarb 3,913 7,848 9.9 2.9 16.8 26.6 2.6 37.4 Aldicarb 679 2, 168 8.8 3.4 15.9 26.3 2.3 36.5 LS D (P = 0.05) ""1,603 12,518 3.4 0.8 5.1 3.8 0.6 10.0 aNumbers are means of five replicates. bDays after planting. Plant Disease/July 1986 637 root angles of aldicarb-treated cultivars The resistant reactions of B37Ht and 5. Cobb, N. A. 1917. A new parasitic nema found were not significantly different from B68Ht to P. scribneri demonstrated by infesting cotton and potatoes. J. Agric. Res. those of untreated ones. A significantly the inability of the nematodes to induce 6. Eiben, G.J. 1968. A comparison of methods used (P = 0.05) negative correlation (r = 0.3) visible symptoms on B68Ht, the relative in evaluating corn for corn rootworm resistance. existed between numbers of P. scribneri superior root performance of B37Ht withDiss. Abstr. 28:3738-B. Univ. Mich. Microfilm and root weight 51 days after planting. out aldicarb treatment (Table 3), and 68-2816. 202 pp. aytheir inabldict toreatment (Targe numbs o 7. Georgi, L., Ferris, J. M., and Ferris, V. R. 1983. their inability to support large numbers of Population development of Praivienchus DISCUSSION P. scribneri confirm previous results (14). hexincisus in eight corn inbreds. J. Nematol. The ability of C 123Ht and Mo l7Ht to 15:243-252. support large numbers of P. scribneri is ACKNOWLEDGEMENTS 8. Jenkins, W. R. 1964. A rapid centrifugalconsistent with previous results (14) We wish to thank Pioneer Hi-Bred International flotation technique for separating nematodes B for providing support; A. Morad, D. Wixted, and J. from soil. Plant Dis. Rep. 48:692. Both C123Ht and Mol7Ht are also Edwards for assistance in data collection; and W. A. 9. Minton, N. A. 1965. Reaction of white clover and excellent hosts for P. hexincisus (14). A Russell, Department of Agronomy, Iowa State five other crops to Pratylenchus scribneri. Plant similar reaction of Mol7Ht to P. University, Crow's Hybrid Seed Co., Holden's Dis. Rep. 49:856-859. hexincisus also was found by Georgi et a I Foundation Seed, Inc., and Mike Brayton Seed 10. Rich, J. R., Thomason, I. J., and O'Melia, F. C. hexncny also wasviding fuds. 1977. Host-parasite interactions of Pratylenchus (7). The inbreds C123Ht and Mol7Ht Company forprovidingseeds. scribneri on selected crop plants. J. Nematol. have C103 in their parentage, which also 9:131-135. supported moderate to high numbers of LITERATURE CITED 11. Scribner, F. L. 1889. Diseases of the irish potato. I. Acosta, N., and Malek, R. B. 1981. SymptomaTenn. Agric. Exp. Stn. Bull. 2:27-43. P. scribneri (Tables 1-3). Hybrids tology and histopathology of soybean roots 12. Sherbakoff, C.D.,andStanley, W.VW. 1943. The C123Ht, Mo17Ht, and C123Ht X C103, infected by Pratylenchus scribneri and P. alleni. more important diseases and insect pests ofcrops derivatives of C123Ht, C103, and/or J. Nematol. 13:6-12. in Tennessee. Tenn. Agric. Exp. Stn. Bull. 186. Mol7Ht, also supported high numbers of 2. Bird, G. W. 1971. Influence of incubation 142 pp. solution on the rate of recovery of Pratylenchus 13. Smolik, J. D. 1978. Influence of previous P. scribneri both in the greenhouse and brachyurus from cotton roots. J. Nematol. insecticidal use on ability of carbofuran to the field (Tables 1 and 3). A common 3:378-385. control nematode populations in corn and effect genetic background is a possible 3. Bohm, W. 1979. Methods of Studying Root on corn yield. Plant Dis. Rep. 62:95-99. explanation for the ability of the related Systems. Springer-Verlag, New York. 188 pp. 14. Waudo, S. W., and Norton, D. C. 1983. exlanation suort highe number of therel d 4. Christie, J. R., and Birchfield, W. 1958. Population changes of Pratylenchus hexincisus cultivars to support high numbers of the Scribner's lesion nematode, a destructive and P. scribneri in maize inbred lines. Plant Dis. nematodes. parasite of amaryllis. Plant Dis. Rep. 42:873-875. Rep. 67:1369-1370. 638 Plant Disease/Vol. 70 No. 7