Nematode Community Structure in a Vineyard Soil

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Abstract: Distribution of the nematode community in a California vineyard was ... densities of plant-parasitic nematodes were found in the vine row, with the ...
Nematode Community Structure in a Vineyard Soil H. FERRIS and M. V. MC KENRY ~

Abstract: D i s t r i b u t i o n of the n e m a t o d e c o m m u n i t y i n a C a l i f o r n i a v i n e y a r d was s t u d i e d over a 13-month period. O m n i v o r o u s a n d m i c r o b i v o r o u s n e m a t o d e s were s i m i l a r l y d i s t r i b u t e d in t he ro ot zone, w i t h greatest densities o c c u r r i n g betwee n vine rows a n d n e a r the soil surface. G re a t e s t densities of p l a n t - p a r a s i t i c n e m a t o d e s were f o u n d i n the vine row, w i t h the i n d i v i d u a l species differing in t h e i r vertical d i s t r i b u t i o n . T o t a l n e m a t o d e biomass was greatest b e t w e e n rows n e a r the surface. Biomass of p l a n t parasites was greatest in t he u p p e r 30 cm of soil in the row, w he re a s biomass of m i c r o b i v o r e s was greatest in this region b e t w e e n rows. Of the p l a n t - p a r a s i t i c ne ma todes, the v a r i a b i l i t y in d i s t r i b u t i o n a m o n g vines was greatest for Paratylenchus hamatus a n d least for Meloidogyne spp. Key Words: Vitis vinilera, Paratylenchus hamatus, t r o p h i c groups, biomass.

A study on the seasonal variation of plant-parasitic nematode populations in a California vineyard (4) also provided data on the distribution, biomass, and population dynamics of the various nematode species and trophic groups in the soil. Such information has been collected in many locations, usually natural woodlands and grasslands (5, 7, 8, 10) rather than in agroecosystems. This paper includes information on (i) the spatial distribution and seasonal variation of trophic groups of nematode species in the grapevine root zone; (ii) the biomass distribution of nematodes in various trophic groups and taxa; (iii) the variability of distribution of nematodes in and between root zones; and (iv) comparisons between the microbivore and omnivore groups and the plant-parasite group. M A T E R I A L S AND M E T H O D S T h e study was conducted in an ownrooted, 37-year-old irrigated vineyard of ' T h o m p s o n seedless' grapevines (Vitis vini[era L.). Details of the site, soil physical conditions, vineyard cultural practices, and sampling technique and pattern were presented previously (4). Soil samples were taken from the vineyard 15 times at 28-day intervals from six vines on each date. At the start of the investigation, vines for each date were selected at random. T h e same vine was never sampled twice in order to avoid errors introduced by root damage Received for publication 27 February 1975. Assistant Nematologists. Department of Nematology, University of California, Riverside 92502. The assistance of G. Eanes, N. Kundtz, P. Naylor, D. Nielsen, C. Pratt, R. Small, and G. Stewart is gratefully acknowledged. Supported in part by USDA-CSRS Grant 316-15-63 and the California Grape Growers.

during previous sampling. Sampling positions were 30 and 90 cm from the vine trunk in the row, and 30, 90, and 150 cm from the trunk between rows in a line perpendicular to the row. At each position, samples of about 700 cm 3 soil were taken at 15-cm intervals to a depth of 120 cm with a 7.5-cm diam auger. A total of eight samples was taken at each position, and 40 samples were taken from each vine. Nematodes were extracted from soil samples by sugar-flotation-sieving (3). Estimates of densities of Meloidogyne eggs and of the distribution of organic material in the soil were obtained by a modified eggextraction technique (2). Population densities were determined for each plant-parasitic species, whereas nonparasitic species were assigned to two trophic groups: (i) microbivorous bacterial feeders, and (ii) stylet-bearing omnivorous forms (largely Dorylaimida) which feed primarily on algae, bacteria and fungi (7, 8). Nematode distribution data for the various trophic groups were summarized as group means over the whole sampling period. T h e percentage of each trophic group or taxon distributed at each depth across the whole root zone was calculated and correlated with the distribution of organic material. Seasonal fluctuations of nematodes were summarized as an average of the total community for the six vines on each sampling date. Measurements for the biomass study were made on nematodes collected at the J u n e sampling. Nematodes extracted from each 15-cm depth interval in sampling positions 90 cm from the trunk in the row and 120 cm from the trnnk between rows, for each of three vines, were killed and fixed in 151

132 Journal of Nematology, Volume 8, No. 2, April 1976 5% formalin. U p to 70 individuals of each type at each d e p t h were measured for length and width. Fewer than 70 were measured when species were scarce at a particular depth or location. Plant parasites were measured by species, whereas microbivores a n d omnivores were measured by trophic group. N e m a t o d e eggs and endoparasitic stages of the life cycle were n o t included in biomass measurements. Biomass of each group or taxon at each position was determined by using the average of mnnbers for the months of May, June, and July' 1973 at the a p p r o p r i a t e depths and positions and c o m p u t e d by the formula of Andrassy (1). N e m a t o d e counts were adjusted for extraction efficiency (10) and recorded as n u m b e r per m'-' of soil 15 cm thick (150 liters of soil). T h e n u m b e r of nematodes in the 40 samples of 500 cm a soil processed from a vine were totaled. T h i s total provided a p a r a m e t e r to determine variability of nematode distribution for each species or trophic group. T h e m e a n and standard deviation for the totals were calculated for each species or trophic g r o u p for each sampling date. A coefficient of variation was calculated from these means and standard deviations. T h e m e a n coefficients of variation over the 15 sampling periods were used as measures of variability of distribution for species and trophic groups.

RESULTS

Spatial Distribution: Spatial distribution data are presented as an average over the 15 sampling periods. (In Fig. 1, 2, each bar represents an average of 90 samples). Omnivores and microbivores, being concentrated near the soil surface, (Fig. l-A, B) were similarly distributed, whereas plant parasites (Fig. I-C) were spread to greater depths. Densities of plant parasites were ~reater in the plant row t h a n between rows, but the greatest densities of microbivores and omnivores were found between rows. Microbivores and omnivores showed little variation in horizontal distribution, whereas parasites were in greater densities closer to the vine, at least in the u p p e r 30 cm. Of the individual plant-parasitic taxa, Xiphinema arnericanum Cobb (Fig. 2-B) was concentrated in the area u n d e r the

ridge of soil in the vine row to 45 cm. Although Meloidogyne spp. (Fig. 2-A) were more widely distributed, they increased in n u m b e r closer to the ridge in the u p p e r soil regions. Paratylenchus hamatus T h o r n e & Allen (Fig. 2-C) occurred at all depths except for the top 15 cm between rows. T h i s species, however, was very sporadic in its distribution within an individual root zone and between vines. T h e greatest densities of microbivorous nematodes found in the u p p e r regions of soil were closely correlated with percentage of organic material in the soil (Fig. 3-A). Omnivorous nematodes and plant parasites were concentrated in higher numbers at slightly greater depths. W i t h i n the parasitic group, the highest numbers of most species were found between 15 and 30 cm, and tile p r o p o r t i o n distributed below the 100 cm d e p t h was low in all cases except for P. hamatus (Fig. 3-B). Seasonal Variation: P o p u l a t i o n densities of omnivore and microbivore communities followed similar seasonal patterns (Fig. 4-A, B). Tile variation a m o n g tile six vines on each date, as represented by the standard deviation, also followed similar patterns. Differences were greater in population densities within tile plant-parasitic g r o u p between s u m m e r and winter (Fig. 4-C). W h e n counts of Meloidogyne spp. eggs were included in the plant-parasitic nematode totals, variability a m o n g the six vines increased markedly. Nematode Biomass: T o t a l n e m a t o d e biomass in the row (Fig. 5-A) was less than that between rows (Fig. 5-B) near the soil surface, but the decrease with d e p t h was a b o u t the same rate. T h e p l a n t parasites had tile greatest biomass near the soil surface in tim row, whereas tim omnivores had the smallest (Fig. 5-C). O m n i v o r e biomass surpassed that of the parasites and microbivores at 45-cm d e p t h by increasing as the others decreased. All three groups declined to low levels of biomass below 90 cm. T h e percent contribution of each g r o u p to the total n e m a t o d e biomass in the row (Fig. 5-E) was variable between 30 and 90 cm. Above 30-cm depth, the parasites contributed the most to n e m a t o d e biomass, whereas the microbivores had the greatest contribution to biomass below 90 cm. Between the rows, the biomass of microbivores

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ill tile top 45 cm of soil far exceeded that of the omnivores and tile parasites (Fig. 5-D). Below 45 cm, the contributions were variable with increasing depth. T h e contribution of the parasite group to the total nematode biomass between rows was miniscule (Fig. 5-F). Of the parasite group, X. americanum dominated the biomass in the top 45 cm o[ soil in the row (Fig. 5-G). Paratylenchus hamatus had little contribution to the total

biomass. Meloidogyne spp. larval biomass generally varied little with depth but was very low in the top 15 cm of soil. Biomass values between rows were low for all species of the parasitic group (Fig. 5-H).

Variability of Nematode Distribution: T h e m e a n coefficient of variation for the groups of six vines was higher for P. hamatus than for the other parasitic nematodes, including Meloidogyne eggs, as evaluated by Duncan's Multiple Range Test

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C o m m u n i t y Structure in a Vineyard: Ferris, Mc Kenry 135 (Table 1). T h e coefficient of variation for

X. americanurn was greater than that for MeIoidogyne larvae. T h e coefficients of variation a m o n g vines for the trophic groups and higher parasitic taxa were not significantly different (Table 1). DISCUSSION Distribution of microbivorous, omnivorous, and parasitic nematodes in the soil was compatible with the distribution of their food sources. Organic litter resulting from fallen leaves and berries was concentrated near the soil surface in the row. T h e associated microflora and microfauna provided a food source for the microbivores and omnivores in this region. Soil microbes associated with annual surface applications of chicken manure and vine prunings between the rows provided food for microbivores and omnivores in this area. Greatest densities of root material occurred in the plant row (4). T h e use of biomass in community structure studies gives a better indication than does numerical data of the total metabolism attributable to each trophic group and its importance in organic turnover and oxygen consumption in the soil ecosystem. Biomass also gives a better indication of the a m o u n t of food material required to support each group. However, the metabolic rate of the individual species in each trophic group is also important in such studies and has not been considered here. Generally, the smaller the organism, the greater its metabolism per gram of biomass (11), and thus the smaller the biomass which can be supported at a particular trophic level. T h e microbivorous nematodes were not only a b u n d a n t but had a large biomass near the soil surface, particularly between rows. I n contrast, the omnivores, also a b u n d a n t near the surface, had a relatively small biomass in the upper 20-30 cm of the soil. J "~

However, individuals in this trophic g r o u p were larger at greater depths and contribnted more to the total biomass. This fact emphasizes the impotrance, as shown by Wasilewska (8), of body size as well as numbers in biomass determinations. This relationship between body size and population density was also noted with the parasitic group. Xiphinema americanurn was numerically fewer than the Meloidogyne larvae ill the upper soil region but made a far greater contribution to the parasitic nematode biomass. This ocurrence does not suggest that the biomass of a parasitic species supported by a plant is proportional to the damage caused. Inclusion of endoparasitic stages and eggs of Meloidogyne spp. in the determinations would have given a more accurate determination of biomass of this taxon. It would also have increased the proportional contribution of the plant parasites to the total nematode biomass at all depths sampled. In June, there probably were relatively few active Meloidogyne females in the roots and egg densities were at their lowest level (4). T h e influence of females and eggs on biomass would have been greater in September. T h e microbivorous and omnivorous nematodes were at their greatest densities during the fall and winter months after the annual replenishment of organic material to the soil. These trophic groups also probably responded to the postharvest irrigation after the warm dry soil conditions prior to harvest. Production of feeder roots by grapevines in the spring (9) causes a seasonal variation in food availability for parasites. This is one of the factors determining seasonal changes in parasitic nematode densities and biomass. Paratylenchus hamatus was less uniformly distributed than the other parasitic nematodes in the vineyard. T h e r e were large variations in numbers between vines, and the distribution within the root zone

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FIG. 3-4. 3) Percent distribution with depth. Points are based on 450 samples taken at each depth over a 13-month period. 3-A) Nematode trophic groups. 3-B) Components of the plant-parasite trophic group. Bars denote LSD values (P=0.05) for comparisons between nematode groups at each depth. 4) Seasonalvariation in nematode trophic groups in a vineyard soil. Points plotted represent the total nematode counts from 40 samples of 500 cm3 soil taken throughout the root zone and averaged across six vines on each date. Bars represent the standard deviation for the six vines on each date. 4-A) Microbivorous nematodes. 4-B) Omnivorous nematodes. 4-C) Plant-parasitic nematodes.

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1. ANI)RASSY, I. 1959. Die R a n m i n h a l t s - u n d ( ; e w i c h t s b e s t i m m u n g der Fadenwiirmer (Nematoden). Acta Zool. Acad. Sci. H u n g . 2:1-15. 2. BYRD. D. W., JR., H. FERRIS, and C. J. NUSBAUM. 1972. A m e t h o d for estimating h u m hers of eggs of Meloidogyne spp. in soil. J. Nematol. 4:266-269. 3. BYRD, D. ~V., JR., C. J. NUSBAUM, and K. R. BARKER. 1966• A rapid flotation-sieving technique for extracting nematodes from soil• Plant Dis. Rep. 50:954-957. 4. FERRIS, H., and M. V. MC KENRY. 1974. Seasonal fluctuations in the spatial distribution of nematode p o p u l a t i o n s in a California vineyard. J. Nematol. 6:203-210. 5. J O H N S O N , S. R., J. M. FERRIS, and V. R. FERRIS. 1974. Nematode c o m m u n i t y structure of forest woodlots: III. Ordinations of taxonomic groups and biomass. J. Nematol. fi:118-126. 6. RASKI, D. J., W. H. H A R T , a n d A. N. KASIMATIS. 1973. Nematodes and their control in vineyards. Calif. Agric. Exp. Stn. Circ. No. 533 (Revised), 20 p. 7. T W I N N , D. C. 1974. Nematodes. Pages 421-425 in C. H. Dickinson, and G. J. F. Pugh, eds. Biology of p l a n t litter decomposition, Vol. 2, Academic Press, l,ondon.

C o m m u n i t y Structure in a Vineyard: Ferris, Mc Kenry 137 8. W A S I L E W S K A , L. t971. Neutatodes of the d u n e s in the K a m p i n o s forest, ii. C o m n n n t i t y s t r u c t u r e hased on n u n t h e r s of i n d i v i d u a l s , state of binmass a n d r e s p i r a t o r y m e t a b o l i s m . Ekol. Pol. 19:651-688. 9. W I N K L E R , A. J. 1962. G e n e r a l V i t i c u l t u r e .

Univ. Calif. Press, Berkeley, 633 p, lit. YEAI'I.'S, (;. ~,V, 1972. N e m a t o d a of a D a ni s h heech forest. I. M e t h o d s a n d g e n e r a l analysis. Oikos 23:178-189. 11. Z E U T H E N , E. 1953. O x y g e n u p t a k e a n d body size in organisms. Q. Rev. Biol. 28:1-12.

Effects of Oxime Carbamate Nematicides on Development of Heterodera schachtii on Sugarbeet ARNOLD

E. STEELE l

Abstract: T r e a t m e n t of sugarbeet, Beta vulgaris L., w i t h aldicarb, a l d i c a r b sulfoxide, or a l d i c a r b sulfone 10 days after p l a n t s were i n o c u l a t e d w i t h lteterodera schachtii p r e v e n t e d d e v e l o p m e n t o[7 the n e m a t o d e , b u t second-stage larvae p e n e t r a t e d the roots. T h e s e c he mi c a l s ha d no m e a s u r a b l e effects on n e m a t o d e s in p l a n t s t r e a t e d 15 days a l t e r i n o c u l a t i o n . T h e tests e s t a b l i s h e d t h a t soil t r e a t m e n t s of a l d i c a r b are directly or i n d i r e c t l y l e t h a l to larvae d e v e l o p i n g w i t h i n roots of sugarbeet. Heterodera schachtli failed to develop on root slices of red table beet grow n in soil t r e a t e d w i t h a l d i c a r b or a l d i c a r b sulfoxide. S i m i l a r t r e a t m e n t of p l a n t s w i t h a l d i c a r b sulfone or o x a m y l d i d not affect s u b s e q u e n t d e v e l o p m e n t of H. schachtii on root slices of treated plants. Key 14"ords: o x a m y l , aldicarb, sttgarbeet n e m a t o d e , c u l t u r e , storage root slices.

Studies at this laboratory (7) have established that aldicarb [2-methyl-2(methylthio) propionaldehyde-0- (methylcarbamoyl) oxime], with or without hatching agents, temporarily inhibits hatching of Heterodera sehachtii Schmidt. Normal rates of hatching occur when the aldicarb is removed. Invitro treatment of second-stage larvae (L2) with aldicarb or aldicarb sulfoxide [2methyl-2-(methylsulfinyl)propionaldehyde 0(methylcarbamoyl)oxime] prevented invasion of tim larvae, whereas aldicarb sulfone [2-methyl-2-(methylsulfonyl)propionaldehyde-0-(methylcarbamoyl) oxime] had no effect. Although the study showed that aldicarb acts as a systemic agent to control H. schachtii, the results did not reveal whether aldicarb is nematicidal or nemastatic within plants. This paper reports results of additional tests on the modes of action of aldicarb, aldicarb sulfoxide, aldicarb sulfone, and oxamyl [methyl N'-N'-

Received for publication 6 October 1975. 'Nematologist, Agricultural Research Service, United States Department of Agriculture, P. O. Box 5098, Salinas, California 93901. Mention of a proprietary product does not constilule a guarantee or warranty of tile product by the U. S. Department o[ Agriculture, and it does not imply approval to the exchtsiou of other products that may also be suitable.

dimethyl-N-(methylcarbamoyl)oxy-l-thiooxamimidate]. M A T E R I A L S AND M E T H O D S Aldicarb and its by-products (aldicarb sulfoxide and aldicarb sulfone) were compared [or their effects on development of Heterodera schachlii in roots of sugarbeet (Beta vulgaris L.). Analytical grades of these chemicals of 99% purity were utilized (Union Carbide Corporation, Salinas, California 93901). In the first study, sugarbeet seedlings germinated in steam-sterilized sand were transplanted to individual styrofoam cups containing 300 g o [ steam-sterilized sand-soil mixture (prepared by adding 1 part sand to 4 parts clay loam soil). At this time, 30 broken cysts, each with about 250 eggs and larvae, were added to the soil. Ambient temperatnres in the growth chamber, in which the experiment was conducted, were regulated to maintain soil temperatures at 24C -+ 0.5 during both 16 h o[ high intensity illumination (about 55,974 lux), and 8 h o [ darkness. After I0 and 15 days, the plants were removed, carefully washed, and placed in funnels containing either distilled water or a 5/~g/ml aqueous solution o[ each test chemical. T h e root system of each seedling was supported in