Can fatty acids and oxytetracycline protect artificially raised larvae from developing European foulbrood?

A quantitative assay for the transmission of European foulbrood (EFB) in artificially raised larvae was developed. This assay was used to determine the concentration of oxytetracycline (OTC) required to prevent larvae from developing EFB and whether 8 fatty acids (undecanoic, lauric [dodecanoic], myristic, myristoleic, ricinoleic, ricinelaidic, homo-y-linolenic and 13,16,19-docosatrienoic acids) which had previously been demonstrated to inhibit the growth of Melissococcus plutonius cultures, could protect larvae from developing EFB. The larval assay involved grafting individual larva (less than 24 hours old) into a single well in a micro-titre plate. Each larva was fed 10 μL of basic larval diet (BLD) containing 500 000 M. plutonius organisms. After 3 days the larvae were also fed 60 000 Paenibacillus alvei spores (a common secondary invader associated with EFB) in 10 μL BLD. The combination of these two organisms was required to reliably produce symptoms typical of that seen in field cases of EFB. Most larvae infected using this protocol died from EFB. To determine the efficacy of OTC, EFB infected larvae were fed 0, 1, 2.5, 5 10 or 20 μg/mL of OTC. Treatment with 1 μg/mL lowered the mortality rate from 93.75% to 69.5%. Treatments with 2.5 μg/mL to 10 μg/mL reduced the mortality rate further whereas treatment with 20 μg/mL reduced the rate to the same as the negative control. Larvae fed 20 or 200 μg/mL of each of the eight fatty acids were not protected from developing EFB

Efficacy of Chemicals for the Potential Management of the Queensland Fruit Fly Bactrocera tryoni (Froggatt) (Diptera: Tephritidae)

This study investigated alternative in-field chemical controls against Bactrocera tryoni (Froggatt). Bioassay 1 tested the mortality of adults exposed to fruit and filter paper dipped in insecticide, and the topical application of insecticide to adults/fruit. Bioassay 2 measured the mortality of adults permitted to oviposit on fruit dipped in insecticide and aged 0, 1, 3, or 5 days, plus the production of offspring. Bioassay 3 tested infested fruit sprayed with insecticide. The field bioassay trialed the mortality of adults exposed to one- and five-day insecticide residues on peaches, and subsequent offspring. Abamectin, alpha-cypermethrin, clothianidin, dimethoate (half-label rate), emamectin benzoate, fenthion (half- and full-label rate), and trichlorfon were the most efficacious in bioassay 1, across 18 tested insecticide treatments. Overall, the LT50 value was lowest for fenthion (full-label rate), clothianidin, and alpha-cypermethrin. Fenthion, emamectin benzoate, and abamectin had the greatest effect on adult mortality and offspring production. Infested fruit treated with acetamiprid, fenthion, and thiacloprid produced no/very few offspring. Alpha-cypermethrin demonstrated good field efficacy against adults (one day post treatment: 97.2% mortality, five day post treatment: 98.8% mortality) and subsequent offspring (100% across one and five day post treatments), comparable to that of fenthion (full-label rate) (100% mortality for offspring and adults across both post treatments). Alpha-cypermethrin is a possible alternative to fenthion against B. tryoni; as a pyrethroid, it may not be desirable if adjunct biological control is imperative. Thiacloprid and Acetamiprid may be useful as a post-harvest treatment

Docked tail length is a risk factor for bacterial arthritis in lambs

Arthritis is commonly observed in lambs at slaughter, resulting in losses due to carcase downgrading, trimming or condemnation. The condition arises on-farm and is thought to be influenced by a number of predisposing factors, which vary in their ability to be addressed by sheep producers. The aim of this study was to investigate whether there is a link between tail length and arthritis in lambs. If there is, leaving a longer tail stump when docking may be a cost-effective way of reducing the prevalence of joint infections in lambs. The study was conducted at an abattoir in South Australia and included 63,287 carcases. This study found a correlation between short-docked tails (fewer than three coccygeal vertebrae remaining) and bacterial arthritis in lambs. Other risk factors for arthritis included breed and the regional source of the lambs, but not age. The constraints of data collection within the abattoir did not allow the effects of tail docking method, sex or whether male lambs had been castrated on the prevalence of bacterial arthritis to be determined. The bacterium most commonly isolated from abnormal joints was Erysipelothrix rhusiopathiae, followed by Streptococcus spp., including Streptococcus suis

Docked tail length is a risk factor for bacterial arthritis in lambs

Arthritis is commonly observed in lambs at slaughter, resulting in losses due to carcase downgrading, trimming or condemnation. The condition arises on-farm and is thought to be influenced by a number of predisposing factors, which vary in their ability to be addressed by sheep producers. The aim of this study was to investigate whether there is a link between tail length and arthritis in lambs. If there is, leaving a longer tail stump when docking may be a cost-effective way of reducing the prevalence of joint infections in lambs. The study was conducted at an abattoir in South Australia and included 63,287 carcases. This study found a correlation between short-docked tails (fewer than three coccygeal vertebrae remaining) and bacterial arthritis in lambs. Other risk factors for arthritis included breed and the regional source of the lambs, but not age. The constraints of data collection within the abattoir did not allow the effects of tail docking method, sex or whether male lambs had been castrated on the prevalence of bacterial arthritis to be determined. The bacterium most commonly isolated from abnormal joints was Erysipelothrix rhusiopathiae, followed by Streptococcus spp., including Streptococcus suis

Peach rootstocks differ in their growth responses to both high and low root temperatures

This paper examines the hypothesis that both high and low root zone temperatures (RZT) reduce growth in peaches and that peach rootstocks differ in their growth responses to RZTs. This hypothesis was tested by growing plants of five peach rootstocks, Fay Elberta, green leaf Nemaguard, Golden Queen, Okinawa and a redleaf Nemaguard at constant RZTs of 5, 13, 21, 29°C and a diurnally variable RZT of 29/21°C. For the pooled data, over the RZT range 5-29°C, the relationship between RZT and total growth (TG) could be described as bell shaped curve peaking near 21°C, with the mathematical relationship between the two being ln TG = 2.080 + 0.015RZT 2 - 0.0004RZT 3 (r2 = 0.82, p<0.001). The growth of plants whose roots were exposed to the diurnally variable RZT was similar to that of plants exposed to a constant RZT of 29°C; the reduced growth in both groups being attributed to exposure to unfavourable RZTs for part or all of the day. Significant differences in RZT induced growth responses among rootstocks were observed. These trials demonstrate that both sub- and supraoptimal RZTs, independently of air temperature and light intensity, reduce growth and that peach rootstocks differ in their responses to RZTs. This research has implications for future rootstock development and selection, orchard management practices and for the development of models examining peach tree growth and development, particularly with respect to the effects of potential changes in the global climate

Difference in yield and persistence among perennial forages used by the dairy industry under optimum and deficit irrigation

Perennial ryegrass (Lolium perenne L.) is the dominant forage grazed by dairy cows in Australia; however, poor persistence has led to an increasing interest in alternative forages. This study was conducted to identify more productive and/or persistent perennial forage species than perennial ryegrass. We evaluated 15 perennial forages under optimum irrigation (I1) and 2 nominated deficit irrigation (I2, 66% of irrigation water applied to I1; I3, 33% of irrigation water applied to I1) regimes, over 3 years at Camden, NSW (34830S, 1508390E), on a brown Dermosol in a warm temperate climate. The forages were: perennial ryegrass, cocksfoot (Dactylis glomerata L.), phalaris (Phalaris aquatica L.), prairie grass (Bromus catharticus M. Vahl), tall fescue (Schedonorus phoenix (Scop.) Holub), kikuyu (Pennisetum clandestinum Hochst. ex. chiov.), paspalum (Paspalum dilatatum Poir.), birdsfoot trefoil (Lotus corniculatus L.), lucerne (Medicago sativa L.), red clover (Trifolium pratense L.), strawberry clover (Trifolium fragiferum L.), sulla (Hedysarum coronarium L.), white clover (Trifolium repens L.), chicory (Cichorium intybus L.), and plantain (Plantago lanceolata L.). Under non-limiting conditions of water and fertility, tall fescue, kikuyu, and prairie grass had the highest mean annual yield over the 3 years of this experiment (24.8–25.5 t dry matter (DM)/ha), which was significantly greater (P < 0.05) than perennial ryegrass (21.1 t DM/ha). Kikuyu was significantly higher than all forages under the extreme I3 deficit irrigation treatment, with mean annual yields of 17.0 t DM/ha. In contrast, the mean yield of white clover was significantly lower (P < 0.05) than of any other forage at only 5.0 t DM/ha, a 70% decline in yield compared with I1. Lucerne was the most tolerant species to deficit irrigation, with a mean annual yield decline (P < 0.05) between the I1 and I3 treatment of only 22%. This study has shown that there are large differences in the relative yield potential of forages and, importantly, indicates the possibility of increasing yield of perennial forages by at least 2-fold on commercial farms, by improving water, and fertiliser management. However, while yield is an important criterion for choosing dairy forages, it is only one factor in a complex system, and choice of forages must be considered on a whole-farm basis and include water-use efficiency, nutritive value, costs of production, and risk

Leaf development, net assimilation and leaf nitrogen concentrations of five Prunus rootstocks in response to root temperature

Rootstocks differentially influence tree physiology and these differences may be due to varying responses to root zone temperature (RZT). To determine if this is the case, the physiology, leaf development and nitrogen relationships of five different Prunus rootstocks with chill requirements between 100 and 1100 h were examined during and after growth at RZTs of 5, 12 and 19 °C for 6 weeks. RZT correlated positively with leaf numbers, expansion rates and final leaf area, and significant differences existed among the rootstocks in the magnitude of these parameters at different RZTs. In particular, leaf expansion and area were less affected at low RZT in the low chill varieties. Net assimilation (An), leaf nitrogen (N%) and photosynthetic nitrogen use efficiency (An/N) also correlated positively with RZT: again, there were differences in the magnitude of these parameters among the rootstocks. No associations amongst An, N% or An/N could be found for the rootstocks; hence, they all differed in their physiological responses to RZT. Low RZT alone was sufficient to reduce An and decreased both leaf area and photosynthetic activity. Leaf expansion was related to N%, as the varieties with the lowest N% also had the lowest expansion rates. Infrared thermography of the cv. Golden Queen showed a negative correlation between RZT and leaf temperature with leaves of plants at the lowest RZT being 2 °C warmer than ambient whilst those at the highest RZT were 2 °C cooler than ambient. These differences were due to transpiration, as transpiration for the variety used decreased with reducing RZT. Transpiration from the other rootstock varieties was lowest at the 5 °C RZT but, depending on variety, at 12 °C was either higher, lower or the same as that from plants whose roots were at 19 °C. Together, the results of this study explain some of the rootstock-induced changes in tree growth and suggest the need to incorporate seasonal changes in RZT into development models for peaches

High and low root zone temperatures at bud-break reduce growth and influence dry matter partitioning in peach rootstocks

Previous studies with actively growing peach [. Prunus persica (L.) Batsch] rootstocks have shown that low root zone temperatures (RZTs) affect growth and partitioning of dry mass. However, whether plants show similar responses at other phenological stages has not been examined, nor has the influence of high RZTs. Consequently, we examined the effects of high and low RZTs on dry matter accumulation and its partitioning using five rootstocks (Fay Elberta, Green Leaf Nemaguard, Golden Queen, Okinawa and Red Leaf Nemaguard) that were emerging from dormancy. The rootstocks were grown at diurnally variable (29/21 °C) or at constant RZTs of 5, 13, 21 and 29 °C; the above ground parts were at a day-time temperature of 27 °C and a night-time temperature of 21 °C. Total growth and its components could be described by cubic functions of RZT, all of which were maximised at a RZT of ~21 °C. Thus, both sub- and supra-optimal RZTs reduced growth and influenced dry matter partitioning independently of air temperature and light intensity. At ~21 °C, the root mass ratio was maximised whilst the leaf, stem and shoot mass ratios were minimised. With the exception of their roots, the growth of plants exposed to diurnally variable 29/21 °C RZTs was similar to those whose roots were constantly maintained at 29 °C with root growth being intermediate between that of plants whose roots were kept constantly at 21 or 29 °C. The partitioning of growth, however, was similar to that at a constant RZT of 21 °C. The rootstock cultivars differed in response to RZT with respect to total growth and in partitioning. This research illustrates that the growth of plants exiting dormancy is significantly influenced by RZT. The different responses of the rootstocks to RZT offer an explanation for comparative differences in tree growth and development of rootstock-scion combinations at different locations, particularly in the spring. The data also indicate that RZTs should be incorporated into tree growth and development models for peaches and has implications for the mitigation of the deleterious effects of global changes in climate on peach tree growth

Impact of marker dye on adult eclosion and flight ability of mass-produced Queensland fruit fly 'Bactrocera tyroni' (Froggatt) (Diptera: Tephritidae)

Sterile Queensland fruit flies Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) are commonly marked with fluorescent dye to assist with subsequent identification after release and recapture. The impact of dye on adult eclosion and flight ability was tested using eight concentrations of dye (Swada, Fiesta Astral Pink) from 0 to 4.5 g/L of pupae. There was no significant difference in eclosion rates between undyed pupae (control) and pupae dyed at a concentration of 1.0 g/L. For dye concentrations of 1.5–4.5 g/L, adult eclosion rates declined from 85.7% to 77.4% and were significantly different from the control. Flight ability indices ranged from 92.1% to 83.3%. There was no significant difference in flight ability between control pupae and those dyed at 1.0 g/L and 3.5 g/L pupae, but other pupae from other dye concentrations were significantly different from the control. Pupal weight ranged from 8.3 to 10.2 mg and there was no significant relationship between pupal weight and adult eclosion or flight ability.4 page(s

Growth and its partitioning in Prunus rootstocks in response to root zone temperature

Rootstocks for stone fruit varieties differentially influence tree physiology and one possible explanation for these differences is that varieties vary in their response to root zone temperature (RZT). To examine the effects of RZT, two trials using actively growing plants of five different Prunus rootstocks with chill requirements between 100 and 1100 h were undertaken. Plants were grown at RZTs of 5, 13 and 19 °C for 6 weeks after which total dry matter accumulation and its partitioning amongst roots, stems and leaves was determined. In general, the magnitude of total dry matter and its component parts positively correlated with RZT and significant differences were found among varieties in the magnitude of total dry matter accumulation. Individual varieties ranked differently at the three RZTs with respect to total dry matter: in general, the same ranking was also seen in the ranking of each growth component. RZT significantly influenced partitioning causing differences in leaf, stem and root mass ratios. These differences were greatest at low RZTs and became less as RZT increased. Several patterns of partitioning were found. Firstly, the low chill varieties (Okinawa and Flordagold) were little affected by RZT with similar partitioning occurring at each RZT. Secondly, the higher chill varieties, Green Leaf Nemaguard (GL), Golden Queen (GQ) and Fay Elberta (FE), reacted more strongly to RZT and were particularly affected by the lowest RZT. For these varieties, the root mass ratio rose and stem mass ratio fell as RZT increased. However, with respect to leaf mass ratio, two different trends were found: the leaf mass ratio for FE and GQ positively correlated with RZT whilst the relationship for GL was negative. These findings suggest that the response to RZT is related to a variety's chill requirement; offer an explanation for differences in performance of rootstock-scion combinations at different locations; and will aid the development of more accurate tree performance models by taking RZT into account