Evaluation of Pochonia chlamydosporia var. chlamydosporia as a control agent of Meloidogyne javanica on pistachio

The potential of isolates of Pochonia chlamydosporia var. chlamydosporia as biocontrol agents for root-knot nematodes was investigated in vitro and on pistachio plants. On potato dextrose agar, growth of all isolates started at temperatures above 10°C, reached maximum between 25 and 28°C and slowed down at 33°C. On water agar, all isolates parasitized more than 85% of the eggs of Meloidogyne javanica at 18°C after 3 weeks. Filtrates of isolates grown on malt extract broth did not cause more than 5% mortality on second-stage juveniles of M. javanica after 48 h of incubation. A single application of 10×10³ chlamydospores (produced on sand–barley medium) g^–1 soil, was applied to unsterilised soil planted with pistachio cv. Kalehghochi, and plants were inoculated with 3000 nematode eggs. After 120 days in the glasshouse, nematode multiplication and damage were measured. Ability of fungus isolates to survive in the soil and to grow on roots were estimated by counting colony forming units (cfu) on semi-selective medium. Fungal abundance in soil increased nearly 3-fold and 10×10³ and 20×10³ cfu g^–1 root of pistachio were estimated in pots treated with isolates 40 and 50, respectively. Strain 50 was more abundant in soil and on the roots, infected more eggs (40%) on the roots and controlled 56% of total population of M. javanica on pistachio roots, whereas isolate 40 parasitized 15% of the eggs on the roots and controlled ca. 36% of the final nematode population.     

The invasion and development of the cereal cyst-nematode, Heterodera avenae in the roots of autumn-and spring-sown cereals

Observations were made at 2 or 4 wk intervals from December to harvest on all stages of Heterodera avenae in winter oats growing on infested land. Second-stage larvae were present in all soil samples except on 5 and 20 July. Invasion and development of larvae was slow during winter. The nodal and seminal roots of winter oats were both heavily invaded by the nematode; larvae which invaded seminal roots tended to become male whereas those in nodal roots tended to become female. There was a small second invasion in August. Females were first observed on the roots of winter oats on 17 May, 214 days after the crop was sown and 62 days after the first fourth-stage larva was observed. The nodal roots of spring barley contained few H. avenae larvae whereas these roots were heavily invaded in winter wheat and oats. In spring barley the nodal roots were developing in June and July when few second-stage larvae were in the soil whereas in winter oats and wheat the nodal roots were growing rapidly in April when larvae were most numerous, and so were heavily invaded.     

Development of Heterodera glycines Life Stages as Influenced by Temperature

The effects of temperature on rates of development of Heterodera glycines egg and juvenile stages were examined as a basis for predicting generation times of the nematode on soybean. The relationship of temperature to H. glycines embryonic development between 15 and 30 C was described by a linear model, The calculated basal temperature threshold was 5 C. Thermal optimum for embryogenesis and hatch with low mortality was 24 C. Development proceeded to first-stage juvenile at 10 C and to second-stage juvenile at 15-30 C. Hatch occurred at 20-30 C. At 36 C, development proceeded to the four-cell stage, then the eggs died. The range of diurnal soil temperature fluctuation and accumulated degree-days between 5 and 30 C (DD5/30) had an impact on rate of development of juveniles in soybean roots. From early June to early July, H. glycines required 534 + 24 DD5/30 (4 weeks) to complete a life cycle in the field. During the midseason (July and August), life cycles were completed in 3 weeks and 429 ± 24 DD5/30 were accumulated. Late in the season (September to November), declining soil temperatures were associated with generation times of 4 weeks and slower rates of development.     

Alaboratory evaluation ofAnthocoris nemorum andA. nemoralis [Hem.: Anthocoridae] as predators ofPhorodon humuli [Hom.: Aphididae]

Anthocoris nemorum (L.) andA. nemoralis (F.) were reared on apterous hop aphids,Phorodon humuli (Schrank), at 20±0.5°C.A. nemorum andA. nemoralis killed an average of 255 and 174 aphids respectively during nymphal development, and the adults killed 37 and 33 per day respectively. Small anthocorid nymphs selectively killed small aphids but adult anthocorids and 5th instar nymphs killed aphids of every size. Mean development times from emergence to final moult were 22 and 16 days forA. nemorum andA. nemoralis respectively.     

Studies of the cereal cyst-nematode, Heterodera avenae under continuous cereals, 1974–1978. I. Plant growth and nematode multiplication

Population changes of Heterodera avenae and crop growth in a sandy loam soil were studied from 1974 until 1978; the nematode decreased plant growth but failed in two of the years to multiply on susceptible hosts. Spring oats were the most heavily invaded cereal and produced the smallest shoots. Second-stage juveniles invaded cereal roots in decreasing numbers: spring oats > autumn oats > spring barley > spring wheat > autumn barley > autumn wheat. Numbers of females developing on the different cultivars were in a similar order. Most females developed on roots in 1976 despite poor crop growth in the severe drought. Numbers of H. avenae in soil treated with oxamyl (Vydate) at 8.8 kg/ha a. i. were less in all years except 1975. In the dry winter and spring of 1975/76 nematode multiplication was prevented in soil treated with oxamyl before drilling in the autumn. In all years large numbers of females were produced on the roots of all cultivars but in 1975 and 1978 nematode populations declined because few females survived to form cysts containing eggs and their fecundity was reduced. Numbers of cysts after harvest were not affected by formalin (38% formaldehyde) applied as a drench at 3000 litres/ha in 1977 but fecundity doubled in treated soil, and nematode multiplication increased from 3.8 × in untreated plots to 18.6 ×. When the plots were irrigated in 1978 numbers of cysts and fecundity increased in formalin treated soil resulting in an increase in multiplication from 0.3 × to 14.6 ×. Fungal parasites attacking H. avenae females and eggs are considered responsible for the poor multiplication of the nematode.     

Persistence of a streptomycin-resistant variant of Corynebacterium insidiosum in soil and alfalfa roots in soil

Summary A pathogenic, streptomycin-resistant variant of Corynebacterium insidiosum, the alfalfa wilt bacterium, was used to determine the persistence of the bacterium in soil and in infected alfalfa roots buried in soil subjected to fluctuating temperatures and different moisture regimes. Use of streptomycin in the agar medium reduced the numbers of soil micro-organisms significantly and enabled colonies of C. insidiosum to be detected at low soil dilutions. In soils incubated at 20°C and moistened to field capacity, the pathogen was not recovered after 7 days from a Malmo silt loam but remained viable for 20 days in the A and C horizons and for 31 days in the B horizon of a Lethbridge silt loam. In excised alfalfa roots held in a Lethbridge silt loam, the pathogen persisted for 50 weeks in soil at the wilting point, regardless of temperature, and in soil subjected to temperatures fluctuating between -5 and +5°C, regardless of moisture. However, in excised alfalfa roots held at a mean temperature of 20°C and under saturated moisture conditions, C. insidiosum did not persist beyond 16 weeks. re]19730925     

Development of Meloidogyne chitwoodi on Wheat

Postinfection development of Meloidogyne chitwoodi from second-stage juveniles (J2) to mature females and egg deposition on ''Nugaines'' winter wheat required 105, 51, 36, and 21 days at 10, 15, 20, and 25 C. At 25 C, the J2 induced cavities and hyperplasia in the cortex and apical meristem of root tips with hypertrophy of cortical and apical meristem cell nuclei, 2 and 5 days after inoculation. Giant cells induced by late J2 were observed in the stele 10 days after inoculation. Clusters of egg-laying females were common on wheat root galls 25 days after inoculation. Juveniles penetrated wheat roots at 4 C and above, but not at 2 C, when inoculum was obtained from cultures grown at 20 C, but no penetration occurred at 4 C when inoculum was stored for 12 hours at 4 C before inoculation. In northern Utah, J2 penetrated Nugaines wheat roots in the field in mid-May, about 5 months after seedling emergence. M. chitwoodi eggs were first observed on wheat roots in mid-July when plants were in blossom. Only 40% of overwintered M. chitwoodi eggs hatched at 25 C.     

Root growth of subalpine and montane Eucalyptus seedlings at low soil temperatures

 This study examines the effect of different soil temperatures on root growth in seedlings of Eucalyptus pauciflora Sieber ex Sprengel subsp. pauciflora and Eucalyptus nitens (Deane & Maiden) Maiden. Seedlings were grown in a glasshouse in pots containing soil. Pots were held in water baths maintained at 3, 7 or 13°C, whilst shoots were exposed to ambient glasshouse temperatures. The experiments were designed to separate direct effects of soil temperature from effects due to differences in seedling size. In the first experiment, seedlings were grown to constant height (25 cm for both species), in the second to constant time (100 days for E. pauciflora and 64 days for E. nitens) and in the third experiment seedlings were transferred between soil temperatures. The rate of growth of both species increased with increasing soil temperature. E. nitens grew faster than E. pauciflora at 7 and 13°C, but E. pauciflora grew faster than E. nitens at 3°C. The rate of browning of roots increased with decreasing soil temperature and at a faster rate in E. nitens than E. pauciflora. Root length was highly correlated to root mass within diameter and colour classes (r² > 0.7). However, brown roots were heavier than white roots. Consequently, changes in root mass did not reflect changes in root length when the proportion of brown to white root also changed. For example, at a constant height of 25 cm at 3°C, E. nitens had greater root mass but lesser root length than E. pauciflora. E. pauciflora at 3°C grew faster, and had more root length and less brown roots than E. nitens. This supports the argument that E. pauciflora is better adapted than E. nitens to survive and grow at lower soil temperatures. Received: 16 December 1996 / Accepted: 2 April 1997     

Overwintering of Sphaerotheca humuli, the cause of hop powdery mildew

The ability of Sphaerotheca humuli to overwinter as cleistocarps in infected hop cones and leaves and in aerial buds on rootstocks was examined during the winters of 1970-1, 1971-2 and 1972-3. Periodical examination of cleistocarps, collected in October and overwintered in Terylene bags on the soil of a hop garden, consistently revealed two periods of maturation ending in November and in March, when over 50% contained eight, well-defined ascospores. In laboratory tests cleistocarps, kept either in the hop garden or dry at 4, 8 or 18^oC during the winter, could not be encouraged to dehisce earlier than April when naturally dehisced cleistocarps were first detected in the field. More ascospores were discharged from cleistocarps, and germination of ascospores in laboratory tests was greater, at 18 than at 4, 8 or 24^oC. Colonies of S. humuli arose on leaves of potted plants exposed to overwintered cleistocarps in the hop garden and were observed microscopically to originate from ascospores. However, a Burkard spore trap, operated amidst the cleistocarps in this garden in 1972 and 1973, failed to detect ascospores. Ascospores, discharged onto susceptible leaves in the laboratory, germinated but failed to produce colonies. It was demonstrated that S. humuli can perennate in aerial, dormant buds on hop rootstocks. Examination of buds in autumn revealed mycelium external to and between the bud scales. At budburst the mycelium was still present internally. Cleistocarps were occasionally associated with hibernating mycelium. Primarily infected shoots arose from plants bearing infected buds in conditions which precluded chance infection. Some evidence was obtained that conditions during the winter determine the success of survival in buds. The fungus appeared to be incapable of infecting a selection of weeds common to hop gardens and their vicinity.     

Flight activity of the damson–hop aphid, Phorodon humuli.

Flight activity of Phorodon humuli was monitored using suction traps, laboratory studies and mark and recapture experiments. Emigrants were trapped as they flew from a Myrobalan (Prunus cerasifera) hedge and among dwarf hops (Humulus lupulus). Daily flight curves were bimodal with 69% and 38% of emigrants caught in the morning peak near Myrobalan and among hops, respectively. The median period of flight activity was from 2 h after sunrise until 30 min before sunset. The lower temperature for flight was 13.5°C in the field and 14.9°C for take off in the laboratory. Variations in wind speed had little effect on flight activity explaining <2.5% of the total variance among insect counts. The percentage of emigrants on hop declined exponentially with time. The relationship, y= 10.9(±2.0) + 64.3(±2.3) × 0.92(±0.01)^t where t = daylight hours (standard error in parentheses), explained 98.3% of the variance. Hence, 62% of new arrivals flew within 1 day of arrival and 79% within 2 days. Similar numbers arrived as departed at 08:30, 10:30 and 12:30 h, but at 14:30 h twice as many arrived than departed and at 16:30 h, the accumulation was threefold. Daily flight curves of return migrants and males leaving hop were bimodal with 70% and 80%, respectively, trapped in the earlier peak. In the field, the median lower temperature for flight was 13.2°C for return migrants and a nonsignificantly different 12.8°C for males. The mean temperature for take off by return migrants was 15.7°C in the laboratory.     

Laboratory experiments on sugar-beet downy mildew (Peronospora farinosa)

The optimum conditions for Peronospora farinosa betae to produce spores were temperature 8–10 °C and relative humidity 90 % or more, but many spores were produced between 5 and 20 °C and between 80 and 90 % R.H. Most spores were formed in darkness after leaves were exposed to light for 6–8 h. Spores survived exposure to 60 % R.H. for up to 5 days, but were soon killed by temperatures above 20 °C. The germination capacity of spores collected from the field was often very small, but this could not be related to the weather. Most seedlings were infected when inoculated at the growing point and incubated in a saturated atmosphere between 3 and 15 °C for at least 8 h.     

Observations on the invasion and development of the pea cyst-nematode Heterodera goettingiana in winter field beans (Vicia faba)

A plot experiment to investigate the invasion, development and number of generations of Heterodera goettingiana on winter-sown field beans showed that, although second-stage juveniles invaded in October, white females did not appear until mid-May and only one generation occurred. The results are discussed in the context of temperature requirements for the development of this nematode.     

Mykoplasmaähnliche Organismen in Früchten proliferationskranker Apfelbäume Kurze Mitteilung

The potential of an in vitro technique to study root‐knot nematode infection on banana roots was investigated. Regenerated banana plants were placed horizontally on Gamborg B5 (GB5)‐medium and incubated under a light‐dark regime of 16h‐8h. Temperature fluctuated between 24 and 33 °C. Banana roots were inoculated with Meloidogyne incognita race 1 coming from roots of a transgenic tomato (Lycopersicon esculentum cv. Moneymaker) grown on GB5‐medium at 28 °C in complete darkness. Root‐knots appeared on primary and secondary banana roots two to seven days after nematode inoculation. After 28 days, egg masses protruded through the cortex and two days later juveniles hatched and reinfected banana roots. This method holds promise for dynamic studies of banana root infection with root‐knot nematodes.     

The trapping fungus Dactylaria Brochopaga: induction of trap formation,attraction, trapping and the development in some phytonematodes

All the six species of the phytonematodes induced traps directly on the spores of all the five isolates of Dactylaria brochopaga. The maximum rings induction was observed in the presence of second-stage juveniles of Meloidogyne incognita followed by Meloidogyne graminicola (J₂), Xiphinema basiri, Helicotylenchus dihystera, Tylenchorynchus brassicae and Hoplolaimus indicus. Maximum number of induced traps was recorded at temperature 28°C (98.3%) and pH 7 (96.7%) in the presence of H. indicus. In attraction assay, irrespective of the isolates of the fungus, all the six phytonematodes were attracted towards the fungal discs of the different isolates of D. brochopaga. Among all the five isolates, Isolate D attracted maximum (34.7%) number of nematodes closely followed by Isolate C (31.0%), whereas, Isolate A, B and E did not differ significantly. Maximum in vitro trapping was recorded in the case of M. incognita (J₂) followed by M. graminicola (J₂), H. dihystera and T. brassicae. The maximum ringing (pre-capturing), trapping and killing was recorded for the second-stage juveniles of M. incognita followed by M. graminicola, T. brassicae and H. dihystera. The inflation of ring cells did not occur immediately after ringing; however, the time between ringing and inflation varied with different nematodes species. Clear hyphae were observed in the invaded nematodes body after the content of nematode body was consumed. External growth of hyphae occurred only from the inflated cells of the constricting rings, which further developed several rings. Higher number of rings was observed in mycelia developed from bigger nematodes.     

Behaviour of the systemic nematicide oxamyl in plants in relation to control of invasion and development of Meloidogyne incognita

A single foliar application of oxamyl (12.5 μg) in acetone significantly reduced invasion of cucumber seedlings by Meloidogyne incognita juveniles for at least 21 days but did not affect the early stages of development of juveniles which had already invaded the roots. In contrast, application of oxamyl to the roots significantly reduced both invasion and development of juveniles. Concurrent studies using radiolabelled oxamyl showed that the amount of toxicant in the roots after 3 days was 13 times greater following root application than after foliar treatment. It is probable that oxamyl concentrates at the sites of nematode attack as an overall concentration of only 3 ng oxamyl g^-1 root was sufficient to prevent invasion. Much greater concentrations than this were required to affect the nematode in vitro. Oxamyl appeared to be lost from the roots into the soil principally in the form of its non-toxic oxime and it is suggested that the site of action following foliar application is at the root surface or outer cortex. Studies on the invasion behaviour of M. incognita juveniles on agar showed that the action of oxamyl had a sensory component.     

Failure of a Mycelial Formulation of the Nematophagous FungusHirsutella rhossiliensisto Suppress the NematodeHeterodera schachtii

Research was conducted to determine whether pelletized hyphae ofHirsutella rhossiliensissuppressed invasion of roots by the sugarbeet cyst nematodeHeterodera schachtiiin field microplots. The loamy sand in the microplots was infested withH. schachtiibut not withH. rhossiliensis.Alginate pellets, with or without hyphae ofH. rhossiliensis,were mixed into soil removed from the microplots (1 pellet/cm³of soil). The soil was placed in cylinders positioned vertically in microplots; cylinders (6/microplot) were 10.1 cm wide and 15.3 cm deep and contained 1200 cm³of soil. Pellets and soil also were placed in soil observation chambers, which were buried in the cylinders or kept at 20°C in moisture chambers in the laboratory. After 12 days, cabbage seeds were planted in each cylinder, and after 10 days of growth, the seedlings were removed from the soil andH. schachtiiin the roots were counted. The number ofH. schachtiiin roots was large and was unaffected by addition ofH. rhossiliensis.In soil observation chambers,H. rhossiliensisgrew vigorously from the pellets in heat-treated soil but not in nonheated soil, and enchytraeids and collembolans were observed near damaged pellets. We suspect that organisms, possibly including enchytraeids and collembolans, fed upon or otherwise inhibitedH. rhossil- iensis.     

Populations of Longidorus elongatus (Nematoda: Longidoridae) in two New Zealand soils under grazed pasture

Abstract

Information on the “needle nematode” Longidorus elongatus in New Zealand pastures has hitherto been limited. Monthly sampling of Pukepuke black sand and Manawatu fine sandy loam yielded L. elongatus populations up to 87 500 m^?2 (February) and 21 600 m^?2 (August). First stage juveniles appeared when soil temperature exceeded 15°C; females dominated populations every month and males were rare. Differences in abundance between soils may reflect the pore space available to these relatively large nematodes. Specimens survived 24 weeks storage at 5 and 15°C. While abundance tended to decline with depth, at 30–40 cm depth in Pukepuke sand, numbers increased, perhaps through the impact of groundwater levels on rooting patterns. In Pukepuke sand, plant species were associated with significantly different populations of L. elongatus, with Trifolium repens and T. subter‐raneum supporting more than Lolium perenne. More L. elongatus were found in grazed pasture with lower plant available P.     

Studies on halimeda. V. effect of temperature on chloroplast migration in this Siphonous green alga&*

Abstract

The effect of temperatures between 15 and 30°C on the daily cycle of chloroplast migration in Halimeda distorta and H tuna was determined from changes in segment pigmentation recorded by time‐lapse videography throughout the experiments. An un‐named opuntioid species was also tested between 20 and 35°C. Both the daily pattern and the amplitude of change in surface pigmentation, which were sustained for at least 5 days at 25°C, were unchanged at the higher temperatures. At 20°C the amplitude was considerably reduced but cyclical changes in surface pigmentation continued to occur throughout the 3‐day low temperature period. However, at 15°C even greater reduction in amplitude was observed together with a reduced rate of paling at the onset of darkness and absence of pre‐dawn re‐greening. Furthermore, at 15°C all daily changes in surface pigmentation had ceased by the second day in H tuna and by the third day in H distorta. These effects of lower temperatures were reversed when the plants were returned to 25°C, although after the 15°C treatment of H tuna the amplitude of the change in surface pigmentation in two of the three replicate plants was small on the first night back at 25°C whilst the third plant lost pigmentation progressively and was completely white, and apparently dead, two days later.     

Heterodera raskii n. sp. (Heteroderidae: Tylenchina), a Cyst Nematode on Grass, from Hyderabad,India

Heterodera raskii n. sp. is described and illustrated from specimens collected from roots of bulb grass, Cyperus bulbosus, in Hyderabad, India. The new species belongs to the ''goettingiana'' group and differs from closely related H. cyperi by the elongate ovoid shaped cysts and females, greater fenestral length, width, vulval slit, and absence of egg sac. The stylet knob shape was round in second-stage juveniles and posteriorly sloping in females and males of H. raskii n. sp., while it was anteriorly directed in second-stage juveniles and spherical in females and males of H. cyperi.     

The development of Puccinia hordei on barley cv. Zephyr

Germination of uredospores of Puccinia hordei was similar on cover-slips and on the first leaves of barley seedlings (cv. Zephyr) at 100 % r.h. over the range 5–25 °C, being greatest at 20 °C. At 15, 20 and 25 °C maximum germination was attained in 6 h. No uredospores germinated on coverslips in humidities below saturation. The numbers of pustules which subsequently developed on plants incubated at 5, 10, 15 or 18 °C and 100 % r.h. for varying periods up to 24 h, were directly related to rise in temperature and length of incubation. The time from inoculation to eruption of pustules (generation time) was 6 days at 25 °C, 8 days at 20 °C, 10 days at 15 °C, 15 days at 10 °C and 60 days at 5 °C. Pustule production on inoculated plants which had been kept at 5 °C was rapidly accelerated when they were transferred to 20 °C. Data obtained at constant temperatures were used to predict generation times of the fungus in the field. The productivity of pustules, determined as weight of uredospores, was examined at 10, 15 and 20 °C. Significantly more spores were produced at 15 than at 10 °C and most were produced at 20 °C. The results are discussed in relation to those obtained by other workers and to the development of brown rust in the field.