Evidence for the occurrence of induced resistance to pitch canker,caused by Gibberella circinata (anamorph Fusarium circinatum), in populations of Pinus radiata

Pitch canker, caused by Gibberella circinata, was discovered in California in 1986. Although initially quite damaging to Monterey pines (Pinus radiata), the severity of pitch canker has moderated in areas where the disease was first observed and some trees appear to have recovered completely. The absence of symptoms on trees that were once severely affected implies they have become more resistant to the disease. Experimental work has shown that P. radiata can manifest systemic induced resistance (SIR) in response to infection by the pitch canker pathogen and observations of disease remission may indicate that SIR is operative under natural conditions as well. As a test of this hypothesis, the susceptibility of trees in remission was assessed by inoculating them with G. circinata and recording the extent of lesion development. In addition, randomly selected trees in areas that differed in residence time of pitch canker were inoculated to determine if trees with a longer period of exposure to the pathogen were more resistant to the disease. The results of these tests showed that 89% of trees observed to be in remission sustained very limited lesion development, consistent with resistance to pitch canker. Furthermore, trees in areas where pitch canker was well established tended to be more resistant than trees in areas where the disease was of more recent occurrence. In sum, these findings support the view that SIR occurs in P. radiata and is contributing to a moderation of the impact of pitch canker under natural conditions.     

Characterization of field‐evolved resistance to Bacillus thuringiensis‐derived Cry1F δ‐endotoxin in Spodoptera frugiperda populations from Argentina

BACKGROUND

Transgenic maize (Zea mays L.) event TC1507 (Herculex^® I insect protection), expressing Cry1F δ‐endotoxin derived from Bacillus thuringiensis var. aizawai, was commercialized in 2003 in the Americas. Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) susceptibility to Cry1F was monitored annually across several regions in Argentina using diagnostic concentration bioassays. Reduced performance of TC1507 maize against S. frugiperda was reported in 2013. A resistant population was established in the laboratory and the dominance of Cry1F resistance was characterized.

RESULTS

During 2012–2015, high‐survivorship of several populations was observed in the resistance monitoring program. Reciprocal crosses of a Cry1F‐resistant population with a Cry1F‐susceptible population were evaluated to calculate effective dominance (D_ML) based on mortality levels observed at 100 µg/ml Cry1F. Two additional dominance levels (D_LC and D_EC) were calculated using lethal (LC₅₀) or effective concentration (EC₅₀) derived from concentration–response bioassays. Estimates indicated that Cry1F resistance in S. frugiperda in Argentina was either highly recessive (D_ML = 0.005) or incompletely recessive (D_LC < 0.26 and D_EC < 0.19).

CONCLUSION

This study is the first documented confirmation and characterization of S. frugiperda Cry1F field‐evolved resistance in Argentina. The resistance to Cry1F in S. frugiperda populations collected in Argentina, is autosomal and incompletely recessive similar to the resistance reported in Brazil. © 2017 The Authors. Pest Management Science published by John Wiley © Sons Ltd on behalf of Society of Chemical Industry.     

Relative susceptibility of four species of African mahogany to the shoot borer Hypsipyla robusta (Lepidoptera: Pyralidae) in the moist semideciduous forest of Ghana

We examined the relative susceptibility of four mahogany species, Khaya ivorensis, Khaya anthotheca, Entandrophragma angolense, and E. utile, to Hypsipyla robusta attack. Seeds were obtained from one to three parent trees for each species. The research was conducted in the moist semideciduous forest zone in Ghana and used a randomized complete block design. Tree height and diameter and height to first branch were measured until 24 months after out-planting in the field. H. robusta damage was assessed by counting the numbers of shoots attacked, branches, and dead shoots. Khaya spp. grew better but experienced more attack than Entandrophragma spp. The relative susceptibility to H. robusta attack, from most to least, of the four species was: K. anthotheca > K. ivorensis > E. angolense > E. utile. At 24 months, the mean number of shoots attacked per tree ranged from 1.0 for an E. utile seed source to 3.6 on for a K. anthotheca seed source. At 15 months, K. anthotheca and K. ivorensis started branching at about 1.5 m, but height of clear trunk increased over time due to self-pruning. As K. anthotheca grew taller, the number of H. robusta attacks per tree declined. This suggested that selection of genotypes and species that are tolerant of H. robusta attack based on infestation of young plants may not be appropriate. Genetic factors more completely reflecting the response of different species and genotypes to H. robusta attack may manifest themselves at later growth stages.     

Flow‐mediated movement of freshwater catfish,Tandanus bostocki,in a regulated semi‐urban river,to inform environmental water releases

Movement and migration of fish are critical for sustaining riverine fish populations. Water resource development alters natural flow regimes and can disconnect habitats and interfere with hydrological cues for fish movement. Environmental flow releases can counter these impacts, but to be effective they must be based on quantitative flow–biota relationships. We used radio‐telemetry to investigate the association between flow and movement of Tandanus bostocki, a plotosid fish endemic to south‐western Australia. Movement was assessed for 15 adult fish at three temporal scales: weekly, daily and bihourly to reveal seasonal patterns in movement, movement around individual flow pulses, and to describe changes in home range respectively. We used a predictive modelling approach to assess the importance of discharge and other covariates on the directional distance travelled or linear home range size. Our seasonal and flow pulse study revealed that T. bostocki undertook larger downstream movements during higher flows and smaller upstream movements during lower flows. Daily movements tended to be downstream on the ascending limb of flow pulses and upstream on the descending limb. Flow‐dependent movements at weekly or daily time scales were relatively modest (typically hundreds of metres) and were moderated by time of year and gender; however, fish underwent a synchronised 1‐km movement upstream during the known reproductive period in October. The home range study revealed that T. bostocki had larger home ranges (night‐time foraging) when baseflow was elevated. These results can assist the design of customised environmental flows in the study river and other flow‐regulated rivers.     

Endocrine responses in mares and geldings with high body condition scores grouped by high vs. low resting leptin concentrations

Previous observations from this laboratory indicated that horses with high BCS could have resting plasma leptin concentrations ranging from low (1 to 5 ng/mL) to very high (10 to 50 ng/mL). To study the possible interactions of leptin secretion with other endocrine systems, BCS and plasma leptin concentrations were measured on 36 mares and 18 geldings. From mares and geldings that had a mean BCS of at least 7.5, five with the lowest (low leptin) and five with the highest (high leptin) leptin concentrations were selected. Jugular blood samples were collected twice daily for 3 d from the 20 selected horses to determine average resting hormone concentrations. Over the next 12 d, glucose infusion, injection of thyrotropin-releasing hormone (TRH), exercise, and dexamethasone treatment were used to perturb various hormonal systems. By design, horses selected for high leptin had greater (P < 0.0001) leptin concentrations than horses selected for low leptin (14.1 vs. 2.8 +/- 0.92 ng/mL, respectively). In addition, mares had greater (P = 0.008) leptin concentrations than geldings. Horses selected for high leptin had lower (P = 0.027) concentrations of GH but higher (P = 0.0005) concentrations of insulin and thriiodothyronine (T3) than those selected for low leptin. Mares had greater (P = 0.0006) concentrations of cortisol than geldings. There was no difference (P > 0.10) in concentrations of IGF-1, prolactin, or thyroid-stimulating hormone (TSH). Horses selected for high leptin had a greater (P = 0.0365) insulin response to i.v. glucose infusion than horses selected for low leptin. Mares had a greater (P = 0.0006) TSH response and tended (P = 0.088) to have a greater prolactin response to TRH than geldings; the T3 response was greater (P = 0.047) in horses selected for high leptin. The leptin (P = 0.0057), insulin (P < 0.0001), and glucose (P = 0.0063) responses to dexamethasone were greater in horses selected for high leptin than in those selected for low leptin. In addition, mares had a greater (P < 0.0001) glucose response to dexamethasone than geldings. Cortisol concentrations were decreased (P = 0.029) by dexamethasone equally in all groups. In conclusion, differences in insulin, T3, and GH associated with high vs. low leptin concentrations indicate a likely interaction of these systems with leptin secretion in horses and serve as a starting point for future study of the cause-and-effect nature of the interactions.     

Hormonal patterns in normal and hyperleptinemic mares in response to three common feeding-housing regimens

We previously reported that a rise in plasma leptin concentrations followed the rise in insulin and glucose in meal-fed horses, whereas horses maintained on pasture had little fluctuations in hormonal patterns. We have also described a hyperleptinemic-hyperinsulinemic condition that occurs in about 30% of our light horse mares of high body condition maintained on pasture. The present experiment was designed to 1) study the effect of 3 common feeding-housing regimens on leptin and other metabolic hormones in mares and 2) determine whether the hyperleptinemic condition interacted with these regimens. Six light horse mares with high body condition (average score = 7) were assigned to 2 simultaneous 3 x 3 Latin squares, 1 with normal mares (leptin = 0.1 to 6 ng/mL) and 1 with mares displaying hyperleptinemia (>10 ng/mL). Three feeding-housing regimens were compared: ad libitum pasture, ad libitum native grass hay in an outdoor paddock, and single morning feedings of a pelleted concentrate and hay at 0700 in a barn. Five days of acclimation to the feeding regimens were followed by a 36-h period of hourly blood collection to characterize the hormonal characteristics. Leptin concentrations were elevated (P < 0.001) in mares predetermined to be hyperleptinemic compared with normal mares, regardless of the feeding regimen. Leptin was greatest (P < 0.01) in mares on pasture and least in mares fed hay. Variations over time (P < 0.01) were present for all hormones and metabolites studied. Glucose and insulin concentrations were greatest (P < 0.01) in mares on pasture, with meal-fed mares exhibiting an immediate rise in plasma concentrations of both after feeding. Mares on hay had low and constant concentrations of glucose, insulin, and leptin, with no apparent fluctuations. Cortisol, prolactin, and IGF-I did not differ with leptin status, whereas GH differed due to feeding-housing regimen (P < 0.02); there was also an interaction of leptin status and feeding-housing regimen for GH concentrations (P = 0.094). It was concluded that 1) estimates of hormonal secretion in horses based on frequent sampling, depending upon the hormone in question, can be profoundly affected by the feeding-housing regimens, and 2) the hyperleptinemic condition persists under differing conditions of feeding-housing.     

Temporal variation in contamination of pine engraver beetles with Fusarium circinatum in native Monterey pine forests in California

The relative importance of beetle species associated with Fusarium circinatum‐infected Monterey pines was investigated in three Monterey pine forests along the coast of central California, USA from April to November in 2004 and 2005. Fusarium circinatum was frequently isolated from Ips mexicanus and I. plastographus. The mean percentage isolation based upon numbers of I. mexicanus and I. plastographus carrying propagules of F. circinatum was 17·7 and 10·9% in 2004 and 16·7 and 17·3% in 2005, respectively. The mean percentage isolation was high in the spring and early summer and low in late summer and autumn in all three locations for both species. Isolation was higher from beetles emerging from harvested F. circinatum‐infected pine‐stems than for trapped beetles, 42·4% for I. mexicanus and 45·9% for I. plastographus. The mean (± SE) propagule load of trapped I. mexicanus was 269·5 (± 14·1) in 2004 and 281·7 (± 35·7) in 2005 and was 216·1 (± 28·9) in 2004 and 251·9 (± 28·4) in 2005 for I. plastographus. Mean propagule loads decreased from May to November in all locations for both species. Propagule loads of beetles emerged from infected stems were lower than that of trapped beetles, with means of 89·4 (± 23·2) and 93·0 (± 23·2) for I. mexicanus and I. plastographus, respectively. Thus beetles must acquire fungal propagules from more than one infected host. These results also suggest that higher contamination rates and propagule loads in spring and early summer may indicate a higher risk of pitch canker transmission, relative to late summer or autumn.     

Association of the pitch canker fungus, Fusarium subglutinans f.sp. pini, with Monterey pine seeds and seedlings in California

The causal agent of pitch canker disease of pines, Fusarium subglutinans f.sp. pini , is a recent introduction to California. The work presented here demonstrates that this pathogen is seed-borne in Monterey pine ( Pinus radiata ). The pathogen was isolated from up to 83% of seeds collected from cones on recently infected branches. Seedling emergence from infested Monterey pine seeds was 9%, compared with 67% for uninfested seeds. The fungus was isolated more frequently from seedlings originating from diseased branches than from symptomless branches. However, more than 50% of seeds from symptomless Monterey pine branches produced symptomless seedlings from which the pathogen was isolated. It is hypothesized that F. s . pini is carried within the seeds, where it may remain dormant until germination. The implications of these findings for the regeneration of native and landscape-planted Monterey pines, and for the transport of this non-native pathogen in pine seeds and seedlings to previously uninfested areas, are discussed.