week for 4 weeks with 250 ml liquid fer- tilizer solution (15-16-17, Peters Fertiliz- er Products, Fogelsville, Pennsylvania). Greenhouse temperatures were usually.
Journal of Nematology 18(3):385-392. 1986. © T h e Society of Nematologists 1986.
Influence of Pratylenchus penetrans on Plant Growth and Water Relations in Potato J. B. KOTCON AND R. LORIA~ Abstract: Plants of potato (Solanum tuberosum) cultivars Katahdin and Superior were inoculated with 0, 1,500, or 15,000 Pratylenchus penetrans. Transpiration, measured in the greenhouse with a porometer after 56 days of growth, was not significantly different a m o n g n e m a t o d e inoculum levels or between cultivars. T h e rate of xylem exudation from decapitated root systems of Katahdin plants inoculated with 1,500 or 15,000 P. penetrans and Superior plants inoculated with 15,000 P. penetrans was lower than from noninoculated plants. Root weight of Katahdin and Superior was not affected by P. penetrans inoculum level. Transpiration of plants inoculated with 0, 500, 5,000 or 50,000 P. penetrans was recorded weekly from 14 to 56 days after planting. No consistent effects of n e m a t o d e inoculum density on transpiration rate were observed. Root hydraulic conductivity was lower in Katahdin plants inoculated with 266 P. penetrans p e r plant and in Chippewa with 5,081 per plant than in noninoculated plants. Nematodes reduced leaf area of Superior, Chippewa, and Katahdin and root dry weight of Chippewa but had no effect on growth of Hudson, Onaway, or Russet Burbank plants. Assessing nematode effects on root hydraulic conductivity may provide a measure of the tolerance of potato cuhivars to nematodes. Key words: host-parasite relationships, leaf water potential, root lesion nematode, root hydraulic conductivity, Solanum tuberosum, potato, transpiration, water relations.
T h e root lesion nematode Pratylenchus penetrans (Cobb, 1917) Filipjev and Schuurmans-Stekhoven, 1941 causes substantial yield reduction of potato (Solarium tuberosum L.) in eastern North America (3,18). Compared with other crops, potatoes are relatively shallow rooted (8,13). Kotcon et al. (11) have demonstrated that both the length and volume of potato root systems are reduced significantly in fields infested with P. penetrans and other root-infecting pathogens. P. penetrans invades the cortex of feeder roots causing necrotic lesions and root discoloration. Acedo and Rohde (1) reported that the endodermis and stele are also invaded in some hosts and severe damage to vascular tissues occurs. Whereas morphological and histological changes provide visible evidence of root tissue damage, the effects of these changes on plant growth and yield have not been precisely defined. Root tissue damage is presumed to result in reduced water and nutrient uptake, but few quantitative measurements of altered Received for publication 26 April 1985. i Department of Plant Pathology, Cornell University, Long Island Horticultural Research Laboratory, Riverhead, NY 11901. Current address of senior author: Division of Plant and Soil Science, West Virginia University, Morgantown, WV 26506. We thank Barbara A. Kempter, Linda F. Matson, and George Vassilev for valuable technical assistance and D. A. Wilcox for advice on water relations. We also thank R. W. Smiley, W. F. Mai, and G. S. Abawi for critical review of the mar~xscript.
root function, resultant effects on host water relations, and subsequent growth retardation and yield loss have been made. Although resistance to P. penetrans is not known to occur in potato, some cuhivars have been reported to be relatively tolerant to this nematode. A resistant plant is one on which nematodes reproduce poorly; a tolerant plant is one that shows little injury, even under attack by large population densities of nematodes (19). Bernard and Laughlin (2) showed that Russet Burbank was most tolerant, Katahdin and Kennebec were intermediate, and Superior was least tolerant to P. penetrans in a field microplot study. T h e basis for tolerance to nematodes has not been identified; therefore, techniques for selecting nematode-tolerant cuhivars have been based on yield response under nematode pressure. Tolerance of crops to environmental stresses such as excessively high soil moisture, however, has been related to plant water relations. Tolerance to soil water logging in bean cultivars has been determined by analysis o f leaf xylem potential values (16). Leaf diffusive resistance has been used as an indicator of increased root resistance and flooding injury in rabbiteye blueberries (4). Few data are available, however, on the relationship of nematode tolerance and plant water relations. In this study we evaluated the influence of P. penetrans on transpiration and xylem 385
386 Journal of Nematology, Volume 18, No. 3, July 1986 exudation from root systems of the potato cultivars Katahdin and Superior. These two cultivars have been observed to differ in tolerance to this nematode. We also compared the influence ofP. penetrans on transpiration, root conductivity, and leaf water potential among six potato cultivars commonly grown in the northeastern United States. MATERIALS AND METHODS
T h e following procedures were used in all three experiments, unless indicated otherwise. Single-eye seedpieces were sprouted for 2 weeks in the greenhouse in moist vermiculite. Seedpieces with stems approximately 5 cm long were transplanted into plastic pots filled with 2,500 cm 3 steamed sand : soil (I:1) mix. Inoculum consisted of a water suspension of mixed age groups of P. penetrans which had been extracted from roots of field-grown rye (SecaIe cereale L.). Washed rye roots were incubated at 2022 C in aerated tap water for 1-3 weeks. T h e suspension was passed through a 300#m-pore sieve to remove the roots, and nematodes were concentrated by settling and decanting. Desired numbers of nematodes were applied with a syringe to the roots o f each plant at the time of transplanting. Plants were fertilized once each week for 4 weeks with 250 ml liquid fertilizer solution (15-16-17, Peters Fertilizer Products, Fogelsville, Pennsylvania). G r e e n h o u s e t e m p e r a t u r e s were usually 22 + 2 C but occasionally reached 30-35 C. High pressure sodium vapor lamps were used to provide supplemental lighting to maintain at least a 12-hour photoperiod. Transpiration was measured in the greenhouse with a steady state porometer (Model LI-1600, LI-COR, Inc., Lincoln, Nebraska). Leaf area was measured at harvest with a leaf area meter (Model 3000, LICOR, Inc.) Experiment 1: Plants of Katahdin and Superior were inoculated with 0, 1,500, or 15,000 P. penetrans per pot. At 56 days after transplanting, transpiration was measured on three leaflets of the uppermost fully expanded leaf of two plants in each treatment. Transpiration measurements were taken in the greenhouse at 1300 and 1500 hours and again the next day at 0900, 1100, 1300, and 1500 hours. Light intensity, measured with a quantum sensor
(Model LI-1905-I, LI-COR, Inc.), ranged from 200 to 1,100 #E m -2 sec-L T h e soil in each pot was thoroughly wetted and allowed to drain before measuring transpiration; no additional water was applied until the end of the measurement period by which time the soil moisture in some pots was depleted and plants had begun to wilt. T h e rate of xylem exudation from the root systems of decapitated plants was measured at harvest (60 days). Pots were watered to saturation and allowed to drain at 20 + 2 C for several hours before and during exudation measurements. Stems were cut near the soil line and xylem exudate was collected for 2-4 hours in a pipette attached to the stem with plastic tubing. Root fresh weight was determined at harvest. This experiment was repeated. This time, however, transpiration was measured on three leaflets on each of four plants per treatment. Readings were taken between 1300 and 1500 hours at 57, 58, and 59 days. Because skies were overcast, light intensity ranged from 120 to 480 ~E m -2 sec -~, which was lower than in the previous trial. Plants were watered daily, and symptoms of water stress were not observed. Root xylem exudation, leaf area, and root fresh weight were determined at 60 days as described previously. T h e transpiration rate of each plant was calculated as the mean o f all readings taken on the three leaflets. Data from both experiments were combined and analyzed by two-way analysis of variance assuming a randomized block design with experiments as blocks. Experiment 2: A second experiment was conducted to evaluate the influence of nematodes on transpiration of Katahdin and Superior throughout plant development. Four replicate plants o f each potato cultivar were inoculated with 0, 500, 5,000, or 50,000 P. penetrans. Transpiration was measured on the distal leaflet of the uppermost fully expanded leaf of each plant at weekly intervals beginning 28 days after transplanting. Soil moisture was adjusted to field capacity in the late afternoon, and measurements were taken the following day at 0900, 1100, 1300, and 1500 hours. This experiment was repeated with transpiration measurements taken weekly beginning at 14 days after transplanting. Both experiments were terminated at 60 days.
P o t a t o W a t e r R e l a t i o n s / P . penetrans: Kotcon, Loria 387 TABLE 1. Leaf area, rate of xylem exudation, and root weight of Katahdin and Superior potato plants inoculated with Pratylenchuspenetrans.
trans/
Leafarea (cm2/plant) Katahdin Superior
Water exuded (ml/hour) Katahdin Superior
0 1,500 15,000
2,013 a 2,023 a 1,881 a
0.495 b 0.168 a 0.195 a
P, peng-
plant
1,573 a 1,851 a 1,661 a
0.580 a 0.370 a 0.188 a
Root fresh weight (g/plant) Katahdin Superior 4.66 a 6.52 a 6.55 a
2.76 a 3.27 a 3.02 a
Meanof 4-6 plantsper treatment. Columnmeansfollowedby the sameletter do not differsignificantly(P = 0.05)according to Duncan'smultiple-rangetest. Data f r o m b o t h e x p e r i m e n t s w e r e comb i n e d and analyzed as a r a n d o m i z e d block design with e x p e r i m e n t s as blocks. Data f r o m each time and date w e r e analyzed separately by two-way analysis o f variance to d e t e r m i n e the significance o f variety and n e m a t o d e t r e a t m e n t effects. In addition, an analysis o f covariance was c o n d u c t e d using light intensity as a covariate. Experiment 3: Plants o f six c u l t i v a r s - Chippewa, H u d s o n , Katahdin, Onaway, Russet Burbank, and Superior--were transplanted into plastic pots (1,000 cm ~) c o n t a i n i n g steamed sand. Soil was infested by adding 0, 1.7, o r 17 g o f c o r n r o o t s infected with P. penetrans f r o m g r e e n h o u s e cultures. Pots o f c o n t r o l plants w e r e inoculated with 8.5 g o f n o n i n f e c t e d roots. Initial p o p u l a t i o n densities in soil were det e r m i n e d 2 weeks a f t e r transplanting by assaying all o f the roots and soil in six pots o f each t r e a t m e n t level with B a e r m a n pans using a 10-day incubation period. T r a n spiration was m e a s u r e d with a p o r o m e t e r on o n e leaflet p e r plant o f five plants p e r t r e a t m e n t . M e a s u r e m e n t s were m a d e twice a day at 25, 26, and 27 days a f t e r transplanting. Pots were sealed in p o l y e t h y l e n e bags a n d w e i g h e d daily to d e t e r m i n e whole plant transpiration. L e a f xylem potential on o n e leaf p e r plant was m e a s u r e d using a pressure b o m b (Soilmoisture E q u i p m e n t Corp., Santa Barbara, California) at 30 days a f t e r transplanting. Five plants p e r t r e a t m e n t w e r e harvested at 30 and 45 days a f t e r transplanting. Roots were washed gently a n d stems w e r e severed 1 cm above the soil line. H y d r a u l i c r o o t conductivity was d e t e r m i n e d by placing d e c a p i t a t e d r o o t systems in a 100-ml b e a k e r which was t h e n filled with water at 20 C. T h e b e a k e r was placed into a pressure b o m b , and t h e plant stem was i n s e r t e d t h r o u g h the p o r t in the top o f the c h a m b e r
and sealed. A 1-ml p i p e t t e was a t t a c h e d to the cut e n d o f the stem with r u b b e r tubing, and a small a m o u n t o f water was added. A f t e r a 5-minute equilibration p e r i o d , the pressure in the c h a m b e r was increased to 0.4 bars a n d xylem e x u d a t e was collected for 10 minutes. R o o t d r y weights and leaf areas were also measured. Data w e r e analyzed by three-way analysis-of-variance to d e t e r m i n e the significance o f data, cultivar, and n e m a t o d e t r e a t m e n t effects and interactions. RESULTS Experiment 1: T r a n s p i r a t i o n rates w e r e usually greatest b e t w e e n l l 0 0 and 1300 h o u r s and declined as light intensity and soil m o i s t u r e d e c r e a s e d later in the day. Mean transpiration rates did not differ significantly between nematode inoculum levels in e i t h e r cultivar. In the first trial, plants w e r e allowed to wilt. T h e m e a n transpiration rate o f K a t a h d i n plants was 0.816 m m o l m -~ sec -1, significantly (P = 0.05) less t h a n that o f S u p e r i o r which was 0.911 m m o l m -2 sec -1. In the s e c o n d trial, with well-watered plants, the m e a n transpiration rate o f Katahdin, 0.774 m m o l m -~ sec -~, was g r e a t e r (P = 0.05) t h a n that o f Superior, 0.589 m m o l m - * s e c -a. T h e rate o f xylem e x u d a t i o n f r o m r o o t systems o f decapitated n o n i n o c u l a t e d plants was similar for b o t h cuhivars in these exp e r i m e n t s ( T a b l e 1). H o w e v e r , K a t a h d i n plants inoculated with e i t h e r 1,500 o r 15,000 P. penetrans p e r pot e x u d e d less (P = 0.05) t h a n did n o n i n o c u l a t e d plants. T h e same t r e n d o c c u r r e d with Superior, alt h o u g h this d i f f e r e n c e was not statistically significant. R o o t fresh weight was significantly (P = 0.001) g r e a t e r f o r K a t a h d i n t h a n for Superior, b u t it was n o t significantly different a m o n g n e m a t o d e treatments. L e a f area o f K a t a h d i n was signifi-
388 Journal of Nematology, Volume 18, No. 3, July 1986
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Influence of Pratylenchus penetrans on the transpiration of leaves of Katahdin and Superior potatoes at 3, 5, and 7 weeks after transplanting. Error bars indicate the LSD (P = 0.05) for times when analysis of variance indicates a significant effect due to nematode treatment. FIG.
l.
cantly (P = 0.01) greater than that of Superior. T h e two-way variety-by-inoculum treatment interaction was not statistically significant for any parameter. Experiment 2: Mean transpiration rates generally were highest before midday and declined during the afternoon; however, this cycle varied from week to week (Fig. 1). Significant (P < 0.05) differences in transpiration rates were associated with cultivars, Katahdin having a greater mean transpiration rate than Superior at 3, 4, 5, 6, and 8 weeks after transplanting. Although statistically significant differences were observed among nematode treatments, these differences were not consistent from week to week or from hour to hour (Fig. 1). Significant (P = 0.03) varia-
tion in transpiration was attributed to covariation in light intensity between times of day but not between weeks or within any given time of day. Experiment 3: Mean initial population densities of P. penetrans were I, 266, and 5,081 per pot. Low population densities of nematodes were found in plants inoculated with corn roots assumed to be noninfected, but differences between treatment means were significant (P = 0.01). T h e average transpiration rate during days 25-27 after transplanting differed significantly (P = 0.05) among cultivars. Average leaf transpiration rates for Chippewa, Hudson, Katahdin, Onaway, Russet Burbank, and Superior were 0.506, 0.526, 0.671, 0.565, 0.269, and 0.706 mmol m -~ sec -1, respec-
Potato Water Relations/P. penetrans: Kotcon, Loria 389 TABLE 2. Influence o f Pratylenchus penetrans o n leaf area, r o o t dry weight, a n d r o o t system conductivity o f six p o t a t o cultivars at 30 a n d 45 days a f t e r transplanting. P, pe~e-
trans/ plant
Chippewa
Hudson
Katahdin
Onaway
Russet Burbank
Superior
1 266 5,081
162 a 136 a 136a
L e a f area ( c m 2 / p l a n t ) - - 3 0 days after p l a n t i n g 256 a 194 b 124 a 303 a 126 ab 176 a 258a 90a 157a
147 a 97 a 111 a
134 b 66 a 181 b
1 266 5,081
227 ab 262 b 169 a
L e a f a r e a ( c m ~ / p l a n t ) - - 4 5 days after p l a n t i n g 246 a 197 a 154 a 272 a 199 a 198 a 271 a 183 a 186 a
202 a 218 a 231 a
170 a 232 a 193 a
1 266 5,081
0.49 b 0.45 ab 0.36 a
0.73 a 0.77 a 0.79 a
1 266 5,081
2.53 b 2.46 b 1.33 a
R o o t dry weight ( g / p l a n t ) 0.62 a 0.37 a 0.54 a 0.43 a 0.50 a 0.37 a
Hydraulic conductivity (ml H ~ O / p l a n t / h o u r / b a r ) 3.22 a 2.37 b 2.13 a 4.06 a 1.31 a 2.30 a 2.86 a 1.22 a 2.08 a
0.37 a 0.36 a 0.42 a
0.28 a 0.25 a 0.42 a
1.90 a 2.01 a 2.07 a
1.78 a 2.11 a 1.84 a
Leaf area data are means of five replicates per treatment at each date. Root dry weight and hydraulic conductivity data are means of 10 replicates per treatment, five at 30 days after planting and five at 45 days after planting. Column means followed by the same letter do not differ significantly (P = 0.05) according to Duncan's multiple-range test.
tively (standard error of the difference [SED] = 0.070); and average whole plant transpiration rates were 12, 23, 9, 13, 8, and 12 grams per day, respectively (SED = 3.3). No significant differences in leaf transpiration or whole plant transpiration were attributed to nematode effects. Leaf xylem potential did not differ significantly among cultivars or nematode inoculum densities. Leaf area was significantly (P = 0.05) reduced by nematodes in the cultivar Katahdin at 30 days after transplanting and in Chippewa at 45 days after transplanting (Table 2). P. penetrans initial population densities had no significant effect on leaf area of Hudson, Onaway, or Russet Burbank. T h e two-way date-by-cultivar interaction was significant (P = 0.05); leaf area of Superior at 30 days after transplanting was lower in plants inoculated with 266 P. penetrans per pot than in the other two treatments; however, this trend was reversed at 45 days. Root dry weight of all cultivars was significantly (P = 0.05) greater at 45 than at 30 days. Effects of nematodes on root dry weight were not different at the two harvest dates; therefore, results were combined (Table 2). Root dry weight o f Chippewa was significantly lower in plants inoculated with 5,081 P. penetrans per pot
than in plants inoculated with a single P.
penetrans per pot. Katahdin responded similarly, but differences among nematode treatments were not significant. Root dry weights of all other cultivars were not affected by initial nematode population densities. Hydraulic conductivity of root systems was also significantly (P = 0.001) greater at 45 than at 30 days after transplanting in all cultivars. Effects of nematodes on conductivity were not different at the two dates; therefore, results were combined (Table 2). Hydraulic conductivity was significantly (P = 0.05) lower in Katahdin plants inoculated with 266 P. penetrans per pot and in Chippewa and Katahdin plants inoculated with 5,081 per pot than in plants inoculated with one nematode per pot. Hydraulic conductivity of Hudson, Onaway, Russet Burbank, and Superior did not differ among nematode treatments. When hydraulic conductivity was expressed per gram of root, rather than per root system, trends were similar but differences due to nematode effects were not significant. DISCUSSION
Initial population density o f P . penetrans had no consistent effect on transpiration rates in any potato cultivar tested in three
390 Journal of Nematology, Volume 18, No. 3, July 1986 experiments. Although fluctuations in soil Kimpinski (10) showed that P. penetrans, water potential in drying pots may have but not P. crenatus, reduced the uptake of masked small changes in transpiration rates, tritium-labelled water in infected potato the data indicate that the water status of plants. In tomato, root resistance was also the plants was not reduced sufficiently by positively correlated with M. hapla popunematode parasitism to stimulate measur- lation density, but only at low soil moisture able stomatal closure. (15). Increased root resistance observed in Other research indicates that nematode Meloidogyne-infected plants is assumed to parasitism can, but does not always, result be due to the formation of giant cells in in stomatal closure and, hence, reduced the stele, resulting in disruption o f the xytranspiration. Kaplan et al. (9) reported that lem (5,15). Histological studies of roots inP. penetrans had no significant effect on leaf fected with P. penetrans indicate that xylem diffusive resistance of sunflower during plugging with pectic materials occurs even daylight periods. However, diffusive resis- if nematodes are restricted to cortical cells tance of infected plants was greater than (21). Similar plugging of xylem has been that of noninfected plants at night. Meon suggested to explain transient decreases in et al. (15) reported increased diffusive re- hydraulic conductivity of maize roots insistance in tomatoes inoculated with 6,000 fected with Fusarium moniliforme (20). P. Meloidogyne javanica juveniles, but their penetrans infection of roots also causes study did not detect significant differences phenol accumulation, cell wall thickening in total transpiration between infected and in cortical cells, and granulation o f the ennoninfected plants at a lower (1,000/plant) dodermis (1). Such alterations in root anatinoculum level. These data are also con- omy and physiology could be expected to sistent with greenhouse studies on snap cause changes in cell permeability and, thus, beans infected with M. hapla in which tran- root hydraulic resistance. spiration rates were not affected by nemaPlant growth was not significantly aftodes at initial population densities of up fected by nematodes in experiments 1 and to 18,000 second-stage juveniles per plant 2. Leaf area of Katahdin was reduced by (23). P. penetrans at 30 days but not at 45 days Xylem exudation from decapitated root in experiment 3. Root dry weight of Chipsystems was reduced by nematode infec- pewa was also reduced. Plant growth of the tion in Katahdin but not in Superior plants other cultivars was not affected by initial in experiment 1. In decapitated root sys- nematode population density, except that tems not under pressure, as in experiment at 30 days leaf area of Superior plants in1, water enters roots entirely by osmosis. oculated with 266 P. penetrans was less than In this case, the driving force for root ex- that of plants with either a lower or a higher udation is the active accumulation of sol- initial inoculum density. T h e high final utes, chiefly minerals, in the root xylem population densities o f P. penetrans in the (12). Nematode effects on the rate of xylem inoculated treatments indicated that sucexudation in Katahdin could be due to cessful inoculation and invasion of roots either reduced root hydraulic conductivity was obtained in these experiments (unor reduced solute uptake or both. publ.). Plant growth in the greenhouse may In experiment 3, nematode infection re- have been limited by cultural and environduced xylem exudation from root systems mental conditions, thus preventing the full Of Katahdin and Chippewa but not Hud- expression of nematode-induced damage. son, Onaway, Russet Burbank, or Supe- Other studies have shown that Superior is rior. In transpiring plants or when root relatively intolerant ofP. penetrans (2,3,18) systems are under pressure, as in experi- and that significant yield losses to several ment 3, the pressure potential is the dom- cultivars occur under field conditions. Yield inant force and root hydraulic conductivity responses in field studies, however, are inbecomes important (12). Therefore, low consistent from one year to the next water flow t h r o u g h n e m a t o d e - i n f e c t e d (17,18). In addition, interactions with othKatahdin and Chippewa roots was due to er pathogens affect the amount of yield loss reduced hydraulic conductivity in the roots. under field conditions (14). Other researchers have found nematode Neither transpiration nor leaf xylem poinfection to affect water flow through roots. tential was affected by initial nematode
Potato Water Relations/P. penetrans: Kotcon, Loria 391 population density in our experiments. However, P. penetrans reduced root hydraulic conductivity in those cuhivars that also exhibited reductions in plant growth in the presence of this nematode. O u r data show that measurements of hydraulic root conductivity provide a sensitive parameter to evaluate the tolerance of potato cuhivars to P. penetrans under greenhouse conditions. However, significant effects of initial nematode population density on plant growth or water relations were not observed in Superior, contrary to previous reports of intolerance in this cultivar under field conditions (2,3,18). Effects of nematodes on plant water relations have been correlated with effects on plant growth in other studies. Evans et al. (7) demonstrated a significant correlation between reduced root system size in potato plants heavily infected with potato cyst nematodes (Globodera rostochiensis and G. pallida) and reductions in water and nutrient uptake and subsequent yields of potato cyst nematode-intolerant cultivars. Their study concluded that potatoes attacked by cyst nematodes were stressed for water and nutrients, even in well-irrigated plots, resulting in premature senescence o f foliage and, therefore, reduced yield. I n creased diffusive resistance in potato plants infected with potato cyst nematodes was observed under controlled conditions with intolerant but not with tolerant cultivars (22). However, differences between tolerant and intolerant cultivars were not observed under field conditions (6). Wilcox and Loria (23) found that root conductivity, leaf xylem potential, growth, and yield were reduced more by M. hapla in one snap bean cultivar than in another. This study has demonstrated that root xylem exudation is reduced by P. penetrans infection in some, but not all, potato cultivars under greenhouse conditions. Although nematode effects on root function appeared to be correlated to nematode intolerance, cultivar responses in the greenhouse were not always consistent with reported field observations. Environmental stresses may play an important role in the expression of nematode-induced changes in plant water relations and subsequent yield losses. Further research is needed to evaluate the relationship between tolerance to nematodes and plant water rela-
tions and to assess how environmental factors affect this relationship. LITERATURE CITED I. Acedo, J. R., and R. A. Rohde. 1971. Histochemical root pathology of Brassica olearacea capitata L. infected by Pratylenchus penetrans (Cobb) Filipjev and Schuurmans-Stekhoven (Nematoda: Tylenchidae). Journal of Nematology 3:62-68. 2. Bernard, E. C., and C. W. Laughlin, 1976. Relative susceptibility of selected cultivars of potato to Pratylenchus penetrans. Journal of Nematology 8:239242. 3. Bird, G. W. 1981. Management of plant parasitic nematodes in potato production. Pp. 223-243 in J. H. Lashomb and R. Casagrande, eds. Advances in potato pest management. Stroudsburg, Pennsylvania: Hutchinson Ross Publishing Company. 4. Davies, F. S., and D. Wilcox. 1983. Flooding tolerance of rabbiteye blueberry in Florida. HortScience 18:583 (Abstr.). 5. Dropkin, V. H., and P. E. Nelson. 1960. The histopathology of root-knot nematode infections in soybeans. Phytopathology 50:442-447. 6. Evans, K., K.J. Parkinson, and D. L. Trudgill. 1975. Effects of potato cyst-nematodes on potato plants. III. Effects on the water relations and growth of a resistant and a susceptible variety. Nematologica 21:273-280. 7. Evans, K., D. L. Trudgill, and N.J. Brown. 1977. Effects of potato cyst-nematodes on potato plants. V. Root system development in lightly and heavily infested susceptible and resistant varieties, and its importance in nutrient and water uptake. Nematologica 23:153-164. 8. Harris, P. M. 1978. Water. Pp. 244-277 in P. M. Harris, ed. The potato crop. The scientific basis for improvement. London: Chapman and Hall. 9. Kaplan, D. T., R. A. Rohde, and T. A. Tattar. 1976. Leaf diffusive resistance of sunflower infected by Pratylenchuspenetrans. Phytopathology 66:967-969. 10. Kimpinski,J. 1979. Root lesion nematodes in potatoes. American Potato Journal 56:79-86. 11. Kotcon, J, B., D. I. Rouse, and J. E. Mitchell. 1984. Dynamics of root growth in potato fields affected by the early dying syndrome. Phytopathology 74:462-467. 12. Kramer, P.J. 1983. Water relations of plants. New York: Academic Press. 13. Lesczynski, D. B., and C. B. Tanner. 1976. Seasonal variation of root distribution of irrigated, field-grown Russet Burbank potato. American Potato Journal 53:69-78. 14. Martin, M.J., R. M. Riedel, and R. C. Rowe. 1982. VertidUium dahliae and Pratylenchus penetrans: Interactions in the early dying complex of potato in Ohio. Phytopathology 72:640-644. 15. Meon, S., H. R. Wallace, andJ. M. Fisher. 1978. Water relations of tomato (Lycopersiconesculentum Mill. cv. Early Dwarf Red) infected with Meloidogynejavanica (Treub), Chitwood. Physiological Plant Pathology 13:275-281. 16. Nelson, R. B., D. W. Davis, J. P. Palta, and D. R. Laing. 1983. Measurement of soil water-logging tolerance in Phaseolus vulgaris L.: A comparison of screening techniques. Scientia Horticulturae 20:303313.
392 Journal of Nematology, Volume 18, No. 3, July 1986 17. Olthof, Th, H. A. 1983. Reactions of six potato cultivars to Pratylenchus penetrans. Canadian Journal of Plant Pathology 5:285-288. 18. Olthof, T h . H.A. 1984. Relative susceptibility o f six potato cultivars to the root-lesion nematode, Pratylenchus penetrans. First International Congress of Nematology, Guelph, Ontario, Canada (Abstr. 169). 19. Rohde, R. A. 1972. Expression of resistance in plants to nematodes. Annual Review of Phytopathology 10:233-252. 20. Schneider, R. W. 1984. Transient changes in hydraulic resistance caused in corn roots by Fusarium moniliforme. Phytopathology 74:1230-1233. 21. Shafiee, M. F., and W. R.Jenkins. 1963. H o s t -
parasite relationships of Capsicum frutescens and Pratylenchus penetrans, Meloidogyne incognita acrita, and M. hapla. Phytopathology 5 3 : 3 2 5 - 3 2 8 . . 22. Trudgill, D. L., and L. M. Cotes. 1983. Tolerance of potato to potato cyst nematodes (Globodera rostochiensis and G. pallida) in relation to the growth and efficiency of the root system. Annals of Applied Biology 102:385-397. 23. Wilcox, D. A., and R. Loria. 1986. Water relations, growth and yield in two snap bean cultivars infected with Meloidogyne hapla (Chitwood). Journal o f the American Society of Horticultural Science 11: 34-38.
Journal of Nematology 18(3):392-397. 1986. © T h e Society of Nematologists 1986.
Population Dynamics, Root Penetration, and Feeding Behavior of Pratylenchus agilis in Monoxenic Root Cultures of Corn, Tomato, and Soybean 1 R. V . REBOIS AND R. N . H U E T T E L 2
Abstract: Population dynamics, rate of root penetration, and external root feeding behavior of Pratylenchus agilis (Pa) in monoxenic cultures of intact corn seedlings and root explants of corn, tomato, and soybean were studied. In descending o r d e r o f suitability as hosts were I. O. Chief corn, Rutgers tomato, and Williams soybean. Soybean entries Kent, Pickett 71, PI 90763, and Essex were poor hosts. Numbers of eggs and vermiform Pa in the agar medium indicated total fecundity and host suitability. Agar, sand, or soil as support media did not appear to affect Pa root penetration, but the rate of corn root growth did. Whereas most vermiform Pa and eggs were in roots, substantial numbers appeared able to feed and complete their life cycle as ectoparasites on root epidermal cells and root hairs. Key words: corn, ectoparasite, feeding behavior, Glycine max, host, lesion nematode, Lycopersicon " esculentum, population dynamics, Pratylenchus agilis, resistance, root population, soybean, technique, tissue culture, tomato, Zea mays.
Pratylenchus agilis T h o r n e and Malek, 1968 (Pa) has been associated with soybean yield suppressions of 30% (4,7). In microplot studies (8,9), the Pa population development from good to poor hosts was as follows: corn (Zea mays L. cv. I. O. Chief) > tomato (Lycopersicon esculentum Mill cv. Marglobe) > soybean (Glycine max (L.) Merr. cv. Williams) > soybean cv. Essex. T h r e e years o f continuous cropping to Essex in microplots did not suppress Received for publication 3 July 1985. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty by the USDA and does not imply approval to the exclusion of other products or vendors that may also be suitable. 2 Nematologist and Microbiologist, Nematology Laboratory, Plant Protection Institute, USDA ARS NER, Beltsville, MD 20705. Present address of senior author: 2701 Muskogee Street, Adelphi, MD 20783. The authors thank B. L. Craddock for technical assistance.
yields. However, continuous cropping to corn or tomato, or 2 years of corn followed by Essex, resulted in damage in year 3 when the initial Pa infestation was one nematode per 150 cm 3 soil. Our objectives were 1) to determine in vitro population dynamics of Pa on various hosts under controlled conditions, 2) to determine if the feeding behavior was primarily ectoparasitic or endoparasitic, and 3) to compare the influence of sand, soil, and agar as support materials for root penetration by Pa. MATERIALS AND METHODS
Unless otherwise stated all operations were performed aseptically using sterile materials and demineralized water. All cultures were incubated at 28 C in the dark. Nematodes used in these studies were
