Effects of Inducers of Systemic Acquired Resistance on Reproduction of Meloidogyne javanica and Rotylenchulus reniformis in Pineapple.

The potency of the inducers of systemic acquired resistance (SAR), acibenzolar-s-methyl, DL-alpha-amino-n-butyric acid (AABA), DL-beta-amino-n-butyric acid (BABA), gamma-amino-n-butyric acid (GABA), p-aminobenzoic acid (PABA), riboflavin, and salicylic acid (SA), in reducing reproduction of Meloidogyne javanica and Rotylenchulus reniformis in pineapple was investigated. All inducers were applied as foliar sprays to 1-mon-old pineapple plants (20 ml/plant) grown in 22-cm-diam. pots in the greenhouse. Two days after application, 10,000 eggs of M. javanica or R. reniformis were inoculated onto the plants. Six months after inoculation, nematode reproduction was measured. Acibenzolar decreased R. reniformis egg production by 58% compared to the nontreated control (P

Effect of Conditioning Treatments on the Survival of Radopholus similis at High Temperatures.

Heat treatments are an environmentally safe method for eliminating quarantine pests from tropical foliage. Conditioning heat treatments can induce thermotolerance against subsequent and otherwise phytotoxic temperatures in tropical foliage, allowing heat treatments to be even more effective. However, if thermotolerance is also induced in nematodes of quarantine significance like Radopholus similis, heat treatments would be rendered ineffective. A lethal thermal death point (LT(99.9)) was established for R. similis by recording mortality at 25 (control temperature), 43 degrees C, 45 degrees C, 47 degrees C, or 49 degrees C after a 0, 1-, 2-, 4-, 6-, 8-, 10-, 12-, or 15-minute exposure. In a second experiment, nematodes were conditioned at 35, 40, or 45 degrees C for 0, 15, 30, 60, 120, and 180 minutes, allowed to rest for 3 hours, and then challenged at 47 degrees C for 5 minutes. No nematodes survived the challenge heat treatment; rather, nematode mortality was hastened by the conditioning treatment itself. In a third experiment, R. similis inside anthurium roots were conditioned at 25 degrees C or 40 degrees C for 15 minutes and then treated at 45 degrees C for up to 8 minutes. Mortality of conditioned and unconditioned nematodes was similar (P > 0.1). Conditioning treatments increase plant thermotolerance but do not induce thermotolerance in R. similis. Heat treatments have promise as disinfection protocols for quarantines.

Esterase Polymorphism in Meloidogyne konaensis.

The continual detection of a slow (I1) esterase band in greenhouse cultures of Meloidogyne konaensis isolated from the field led to a hypothesis that the nematode may be polymorphic for esterase. A survey of coffee fields demonstrated at least four esterase phenotypes were present in Meloidogyne recovered. An F1 phenotype predominated (60% of the females), but an I1 phenotype was also common (30% of samples). A series of greenhouse and laboratory experiments were undertaken to understand this polymorphism. Esterase phenotype was not affected by development at 22 masculine, 25 masculine, or 33 masculineC on tomato. Two different esterase phenotypes (I1 and F1-I1) were detected after M. konaensis was grown on tomato for several generations, even in single-egg-mass lines derived from an F1 female. Three isolates of M. konaensis differing in esterase phenotype (F1, I1, and F1-I1) did not differ morphologically but did differ in their parasitic ability. Only the F1 isolate parasitized Coffea arabica. The F1-I1 isolate had greater reproduction on Lycopersicon esculentum and Cucumis sativus than either the I1 or F1 isolate. The mechanism of the development of the polymorphism has yet to be determined. However, the F1 esterase may be useful as a marker for future research on parasitism of coffee by M. konaensis.

Plant Nutrient Partitioning in Coffee Infected with Meloidogyne konaensis.

Two experiments were conducted to assess nutrient partitioning in coffee (Coffea arabica cv. Typica land race Guatemala) infected with Meloidogyne konaensis. Nutrient levels were quantified from soil, roots, and leaves. In the first experiment, 500-cm3 aliquants of a Kealakekua Andisol were infested with four initial population densities of M. konaensis ranging from 0 to 1,500 freshly hatched second-stage juveniles. Coffee plants (~3 months old) were transplanted into the soil and grown for 25 weeks. Plants responded to nematode infection with decreases (P < 0.05) in concentrations of Ca, Mg, P, and B and increases (P < 0.05) in concentrations of Mn, Cu, Zn, and Ca/B in the roots. Mn and Cu uptake by roots was decreased (P < 0.05) by nematode infection even though concentrations of Mn and Cu increased (P < 0.05) in the roots. Concentrations of Ca and Mg also decreased (P < 0.05) in the leaves, whereas the concentration of Zn increased (P < 0.05). In the second experiment, the soil was amended with Zn at 0 or 5 mg/kg soil and infested with M. konaensis at 0, 100, 1,000 or 10,000 eggs/1,200 cm(3) soil. Three-month-old coffee seedlings of similar height were weighed and transplanted into pots and then placed in a greenhouse and grown under 50% shade for 23 weeks. Concentrations of P, K, Ca, Mg, Mn, B, and Zn increased in roots of nematode-free plants growing in Zn-amended soil. The beneficial effects due to the Zn amendment were not apparent in nematode-infected plants. Mn, B, and Zn uptake by coffee roots and P and B concentrations in coffee leaves responded similarly. Management of M. konaensis is necessary to achieve optimal nutrient management in coffee.

Intercropping Cover Crops with Pineapple for the Management of Rotylenchulus reniformis.

Effect of cover crops intercropped with pineapple (Ananas comosus) on Rotylenchulus reniformis population densities and activity of nematode-trapping fungi (NTF) were evaluated in two cycles of cover crop and pineapple. Sunn hemp (Crotalaria juncea), rapeseed (Brassica napus), African marigold (Tagetes erecta), or weeds were intercropped with pineapples. Beds planted with sunn hemp or rapeseed had lower population densities of R. reniformis than African marigold, weeds, or pineapple plots during cover crop growth, and the subsequent pineapple-growing periods. Rapeseed was a good host to Meloidogyne javanica and resulted in high population densities of M. javanica in the subsequent pineapple crop. Fireweed (Erigeron canadensis) occurred commonly and was a good host to R. reniformis. Bacterivorous nematode population densities increased (P

Effects of Acibenzolar-S-Methyl Application to Rotylenchulus reniformis and Meloidogyne javanica.

Effects of acibenzolar-s-methyl, an inducer of systemic acquired resistance in plants, on Rotylenchulus reniformis and Meloidogyne javanica in vitro and in vivo were determined. A single foliar application of acibenzolar at 50 mg/liter (5 ml of solution per plant) to 7-day-old cowpea or soybean seedlings decreased R. reniformis and M. javanica egg production by 50% 30 days after inoculation. The mechanism of acibenzolar on plant-parasitic nematodes was then investigated. Acibenzolar at 50 to 200 mg/liter did not affect movement of R. reniformis and M. javanica or penetration of second-stage juveniles (J2) of M. javanica on cowpea. However, M. javanica development was slowed and fecundity was reduced in plants treated with acibenzolar. On average, 50% of J2 that penetrated acibenzolar-treated cowpeas developed into mature females with eggs, whereas the other 50% exhibited arrested development. The number of eggs per egg mass was 450 in water-treated cowpeas, whereas the number declined to 250 in acibenzolar-treated plants. Acibenzolar may be responsible for stimulating the plants to express some resistance to the nematodes.

Management of Rotylenchulus reniformis in pineapple, Ananas comosus, by intercycle cover crops.

The effects of intercycle cover crops on Rotylenchulus reniformis population densities in pineapple were evaluated in one greenhouse and two field experiments. In the greenhouse, Crotalaria juncea, Brassica napus, and Tagetes erecta were planted for 3 months and then incorporated. These treatments were compared to weedy fallow with or without 1,3-dichloropropene (1,3-D) in three soils (Makawao fallow, Wahiawa fallow, and Wahiawa pineapple) naturally infested with R. reniformis. All cover crop incorporation suppressed R. reniformis numbers in cowpea more than did the weedy treatment in the Makawao (P < 0.05) but not in the Wahiawa soils. Crotalaria juncea treatment increased bacterivorous nematodes and nematode-trapping fungal population densities more than the other treatments in Makawao fallow and Wahiawa pineapple-planted soils. The field trials included the same plants as well as Sinapis alba. Treatments with Crotalaria juncea and 1,3-D maintained lower R. reniformis population densities on pineapple longer than other cover crops or weedy fallow treatments. Crotalaria juncea could have suppressed R. reniformis because it is a poor host and because it enhances nematode-trapping fungi when incorporated into soil. Treatment with 1,3-D reduced microbial activities but produced the greatest pineapple yield.

Interactions Between Rotylenchus reniformis and Pineapple mealybug wilt associated virus-1 in Pineapple.

The individual and combined effects of Pineapple mealybug wilt associated virus-1 (PMWaV-1) infection in pineapple, Ananas comosus, and Rotylenchus reniformis on pineapple growth were evaluated under greenhouse and field conditions. Under greenhouse conditions, no effect of PMWaV-1 infection on pineapple growth or nematode reproduction was observed. Under field conditions, the interaction of PMWaV-1 and nematodes was evaluated in plant and ratoon crops. In the plant crop, pineapple in plots treated with the nematicide 1,3-dichloropropane showed increased vegetative growth, whereas virus infection had no effect on vegetative growth. Nematodes reduced the average fruit weight (P = 0.01), whereas PMWaV-1 infection did not (P > 0.14). However, more fruit in the largest size classes (sizes 7 and 8) were produced in PMWaV-1-free plots than in PMWaV-1-infected plots (P = 0.03). The average fruit weight decreased in the presence of virus or nematodes. The smallest fruits were from PMWaV-1-infected plants infested with R. reniformis. More early-ripening fruit (30%) were produced by plants infected with PMWaV-1 than by PMWaV-free plants (P < 0.05). PMWaV-1 infection may be one of the reasons for asynchronous fruit ripening, which is a top limiting factor for pineapple production in Hawaii. In the ratoon crop, PMWaV-1 infection reduced fruit weight by 9% (P < 0.01), whereas nematode effects were similar across treatments (P > 0.10). More fruit in the three largest size categories were produced in PMWaV-1-free plots than in PMWaV-1-infected plots (P < 0.01). PMWaV-1 infection reduced the number of fruit produced in the ratoon crop (P < 0.02). An interaction (P < 0.03) between R. reniformis and PMWaV-1 infection status was detected in the ratoon crop. The fewest fruit were produced in plots with PMWaV-1-infected plants that were nematode infected.

Effect of Gamma-irradiation and Heat on Root-knot Nematode, Meloidogyne javanica.

Effects of gamma-irradiation on the root-knot nematode Meloidogyne javanica were investigated. A dose of 7.5 kGy killed all second-stage juveniles (J2) within 1 day after treatment. Egg hatch was completely inhibited at 6.25 kGy. A bioassay on tomato measuring galling and egg production was used to determine the infectivity of irradiated J2 and J2 hatched from irradiated eggs. The J2 and eggs irradiated with a dose of 4.25 kGy did not induce galls or reproduce on tomato plants. When nematodes were exposed to combined irradiation and heat treatment, no synergistic effect on J2 or eggs was measured. Heat treatment at 49 degrees C for 10 minutes or 20 minutes without irradiation immobilized J2 and prevented egg development. Irradiation rates needed to kill or incapacitate M. javanica were high and may be impractical as a quarantine measure.

Root-knot Nematode Management in Dryland Taro with Tropical Cover Crops.

Twenty-two cover crops were evaluated for their ability to reduce damage by root-knot nematode, Meloidogyne javanica, to taro, Colocastia esculenta, in a tropical cropping system. Cover crops were grown and incorporated into the soil before taro was planted. Barley, greenpanic, glycine, marigold, sesame, sunn hemp, and sorghum x sudangrass DeKalb ST6E were poor or nonhosts to the nematode as measured by low population changes of nematodes in soil between cover crop planting and taro planting. Alfalfa, buckwheat, cowpea, lablab, Lana vetch, mustard, oat, okra, rhodes grass, ryegrain, ryegrass, siratro, sweet corn, and wheat allowed nematode populations to increase dramatically. Taro yields were greatest in the marigold plots and lowest in the ryegrain plots. Taro corm weight decreased with increasing initial nematode population (Pi) (r = 0.22, P = 0.056). Siratro, ryegrass, and Blizzard wheat plots had higher taro yield than plots with similar Pi's but planted to other cover crops. These cover crops may have antagonism to other soil microorganisms or their decomposition products may be toxic or adversely affect the nematodes. Cover crops can be an effective and valuable nematode management tactic for use in minor tropical cropping systems such as taro.

Axenizing and Culturing Endomigratory Plant-Parasitic Nematodes using Pluronic F127, Including its Effects, on Population Dynamics of Pratylenchus penetrans.

A non-chemical technique for surface sterilizing plant-parasitic nematodes for aseptic cultures is described. The method is most applicable to nematodes with active migratory infective stages and requires only a few starting specimens. Rate of achieving a primary aseptic culture with the technique ranged from 60%-100% depending on the conditions of the specimens collected for culturing. Aseptic cultures of species of Meloidogyne, Rotylenchuluz, Pratylenchus, and Radopholus initiated with the method remained contamination-free after 12 months of maintenance in tomato root explant or alfalfa callus cultures. Further studies of Pluronic F127, a polyol gel medium employed in the technique to confine the spread of contaminating bacteria or fungi associated with the nematodes, showed that the polyol gel was a suitable support medium for culturing corn root explant, alfalfa callus tissues, and consequently Pratylenchus species including P. agilis, P. brachyurus, P. scribneri, and P. penetrans. During the course of 10 months, P. penetrans reared in polyol-base medium followed a standard biological growth curve, multiplied to a higher population density, maintained a similar female-to-male ratio, and possessed a similar tendency to reside inside or outside host tissues as did P. penetrans reared in agar-base medium. The percentages of P. penetrans juveniles in the sub-populations residing outside or inside the host tissues reared in polyol-base medium also were similar to and fluctuated temporally in like manner as those reared in agar-base medium. Members of these sub-populations from the polyol- or agar-base were equally infective and reproductive after 9 months of culturing.

Occurrence of Pasteuria-like Organisms on Selected Plant-Pamsitic Nematodes of Pineapple in the Hawaiian Islands.

Soils from 320 sites representing diverse undisturbed habitats from five Hawaiian Islands were assessed for occurrence of Pasteuria-like organisms. Mean annual rainfall at sites ranged from 125-350 cm, elevation from 69-2,286 m, and annual mean temperature from 12-24 C. Seven different natural communities were represented: wet lowland, mesic lowland, wet montane, mesk montane, dry montane, mesic subalpine, and dry alpine. Pasteuria spp. in a soil sample was detected by baiting with infective stages of Helicotylenchus dihystera, Meloidogyne javanica, Pratylenchus brachyurus, and Rotylenchulus reniformis, followed by cultivation of the nematodes on pineapple plants for 10-11 months. All nematode baits except R. reniformis were readily recovered from the soil samples. A sample was considered Pasteuria-positive if at least 5 % of the nematode specimens showed endospore attachment. Thirteen percent of all samples were positive for Pasteuria-like organisms. The frequencies of association between Pasteuria spp. and Meloidogyne, Helicotylenchus, or Pratylenchus species were 52%, 24%, and 24%, respectively. Positive samples were more prevalent on the older islands of Kauai and Oahu (75%), in lowland communities (61%), and in areas with introduced vegetation (60%). More than 27% of the positive samples were associated with plant species in a few selected families that included Meliaceae and Myrtaceae. Occurrence of Pasteuria spp. seemed to be positively associated with mean annual rainfall or temperature, but negatively associated with elevation.

Evaluation of ethoprop and tetrathiocarbonate for reniform nematode control in pineapple.

Ethoprop and disodium tetrathiocarbonate (TTC) were evaluated as replacements of fenamiphos and 1,3-dichloropropene (1,3-D) for control of Rotylenchulus reniformis on pineapple in Hawaii. Treatments were established in a field on the Del Monte Fresh Fruit (Hawaii) plantation in spring 1991. Preplant soil treatments consisted of fumigation with 1,3-D at 226 kg a.i./ha and TTC at 135 kg or 270 kg a.i./ha. Postplant nematicides for the 1,3-D treated plots were fenamiphos (3.4 kg a.i./ha trimonthly) and ethoprop (3.4 or 6.7 kg a.i./ha monthly). Tetrathiocarbonate was applied postplant to the TTC-treated plots every 2 months at 67 kg a.i./ha. Nematode population densities were monitored in all plots at 3-month intervals. Tetrathiocarbonate was not effective in reducing the preplant soil population densities of R. reniformis or limiting subsequent nematode damage to the plants. Ethoprop and fenamiphos reduced nematode damage, resulting in greater yield in the first and second crop harvests (P < 0.05). Ethoprop was an effective alternative to fenamiphos for control of R. reniformis in pineapple.

Comparison of Single- and Double-chisel Injection Methods for the Control of Rotylenchulus reniformis in Pineapple.

The efficacy of 1,3-dichloropropene (1,3-D) applied with one or two chisels was determined for control of Rotylenchulus reniformis on pineapple. The soil was fumigated with 1,3-D at 157 liters/ha with either a single chisel 46 cm deep or two chisels 41 cm deep in replicated experiments conducted in four commercial fields. Soil samples were collected before fumigation and 45 days afterward from three depths and three positions. The three depths were 0-15, 16-30, and 31-45 cm; and the three positions were the center of the bed, plant line, and interbed area. The single-chisel injection was comparable to the two chisels in percentage control of R. reniformis. Satisfactory control was achieved in three fields (percentage reduction from untreated = 79, 81, and 83) but not in the fourth field. The highest level of control was at the lowest soil depth (31-45 cm) nearest the points of injection. Among the sampling positions, control in the interbed area was generally the lowest. A single-chisel injection may be recommended because of the slightly enhanced control.

Fitness Components and Selection of Biotypes of Heterodera glycines.

Survival of biotypes of Heterodera glycines was studied in microplots and in the field. The field population was subjected to various cropping sequences. Viability of eggs overwintered in microplots was determined each spring by percentage hatch, percentage of hatched eggs penetrating roots, and numbers of females developing on Peking and PI 88788 soybeans. Eggs from the field were collected in the spring and fall and assayed for ability to develop on Peking and PI 88788. Hatch of isolates overwintered in the microplots averaged 13% in May 1989 and 19% in 1990. No differences in hatch were detected among the isolates in 1989. Numbers of juveniles penetrating susceptible roots averaged less than 20% of the hatched eggs each year. An isolate of a biotype parasitic on susceptible soybeans and the resistant soybean PI 88788 penetrated roots more successfully than other biotypes. A second isolate from North Carolina, parasitic on susceptible soybeans, PI 88788, and the resistant soybean Peking experienced selection against development on Peking during two winters. Only 17 % of the expected numbers of females developed on Peking from this isolate. In the microplot experiment, parasitism of PI 88788 and Peking had a selective disadvantage (selection coefficient) of s = 0.29 and 0.62 over all isolates, respectively. In the field experiment, the relative numbers of cysts on Peking and PI 88788 increased between the spring and fall on soybean, then decreased over the winter and under corn. Selection coefficients against parasitism of PI 88788 and Peking averaged 0,19 and 0.3 in the field population. In neither experiment did juveniles lose their ability to parasitize susceptible soybeans.

Development of Heterodera glycines as Affected by Alachlor and Fenamiphos.

A series of greenhouse experiments was conducted to elucidate the postinfection development of Heterodera glycines in response to applications of alachlor and fenamiphos. The rate of H. glycines maturation on a susceptible soybean cultivar was not altered by 1.0 mug alachlor/g soil but was completely inhibited by 1.0 or 1.5 mug fenamiphos/g soil. An alachlor-fenamiphos combination allowed development after an initial 300-degree-day delay. Nematode maturation on the resistant soybean cultivar Centennial with 1.0 mug alachlor/g soil was similar to that observed on an untreated resistant control. Twice as many females matured on Centennial plants growing in alachlor-treated soil as on untreated Centennial plants. Fenamiphos in combination with alachlor (1.0 mug a.i./g soil) allowed development on Centennial at half the rate of the resistant control. This antagonism between alachlor and fenamiphos on development may help to explain late season population resurgence of H. glycines observed with field application of these pesticides.

Effect of Planting Date, Alachlor, and Fenamiphos on Heterodera glycines Development.

The effects of alachlor (2.25 kg a.i./ha) and fenamiphos (2.25 kg a.i./ha) on the penetration and development of Heterodera glycines were examined on Glycine max cultivars Deltapine 105 planted 29 April, 29 May, and 29 June 1986 and Deltapine 105 and Centennial planted 15 May, 15 June, and 15 July 1987. Penetration was lowest on the third planting of soybeans and on fenamiphos-treated plants. Development from second-stage juveniles to adult females required 270 (1986) and 260 (1987) DD20/32 on roots from the first planting control and alachlor treatments. Fenamiphos, alone or with alachlor, retarded development in Deltapine 105 (1986) and in Centennial (1987). Males matured in roots from the second planting in 190 (1986) and 180 (1987) DD20/32 regardless of treatment or cultivar. No development occurred in roots from the third planting until 400 DD20/32 in 1986, but in 1987 development was similar to that in roots from the second planting. Nematode development was similar in alachlor-treated and control roots regardless of planting date. Fenamiphos restricted nematode penetration on most planting dates and slowed development. Simultaneous applications of alachlor and fenamiphos usually also inhibited development.