Interactions of aphid herbivory and nitrogen availability on the total foliar glycoalkaloid content of potato plants.

In plant growth room (PGR) and open-air pot (OAP) experiments, potato cvs King Edward and Maris Piper were grown under two nitrogen levels or two different nitrogen release patterns. Plants were subjected to infestation by peach potato aphids Myzus persicae (Homoptera: Aphididae). Total glycoalkaloid (GA) levels were measured in the foliage of both infested and non-infested plants, before, during and after aphid infestation. In the PGR experiment, aphid infestation reduced the amounts of total GAs in both cultivars. This reduction is attributed to the sugar deficiency induced in the plants owing to the dense aphid colonization. Results from the OAP experiment showed a temporal increase of GAs produced by potato cv. King Edward plants subjected to aphid infestation. Elevated amounts of nitrogen in the nutrient solutions (PGR experiment) reduced total GAs, while no differences were observed between manure and fertilizer treated plants (OAP experiment). It is concluded that the source of available nitrogen does not affect foliar GA synthesis in potatoes, and as a consequence, does not affect its endogenous chemical defense against insect herbivory. The case for insect-induced chemical defense mechanisms as triggered by low rates of aphid infestation is discussed.

Mycotoxin production in a carbendazim-resistant strain of fusarium sporotrichioides.

Mycelial yield and production of three trichothecenes, namely T-2 toxin, diacetoxyscirpenol (DAS) and neosolaniol (NEO) were compared in control (CS) and carbendazim-resistant strains (RS) ofFusarium sporotrichioides. Each strain was exposed to graded concentrations of carbendazim (0, 1, 2, and 4 µg/ml media) for 2, 5 and 7 days under shake-culture conditions at an incubation temperature of 25°C. Mycelial yield was significantly (P<0.001) affected by strain, carbendazim concentration and incubation time. The strain differences in mycelial mass at 2 days (P<0.05) became more pronounced at 5 and 7 days of incubation (P<0.001). However, mycelial growth differences between the two strains were greatest following exposure to carbendazim, with the effects becoming more divergent with time. Combined results for the three incubation times showed dose related effects in carbendazim inhibition of T-2 toxin production by CS isolates. In contrast, RS cultures exposed to the 2 µg/ml addition of carbendazim significantly increased T-2 toxin production (P<0.05 or better). At 1 and 4 µg/ml additions, T-2 toxin inhibition occurred but the effect was less marked than in the CS series. RS yielded more DAS than CS at 5 days (P<0.05) and at 7 days (P<0.01) of incubation. The major component of this strain difference arose from the effects of the 2 µg/ml addition of carbendazim (P<0.01). NEO production was also higher in RS than in CS, with the difference becoming progressively more pronounced from day 5 (P<0.05) to day 7 (P<0.01) of incubation. However, these differences reflected enhanced NEO output with carbendazim addition of 4 µg/ml (P<0.05) in day 5 extracts and of both 2 µg/ml (P<0.01) and 4 µg/ml additions (P<0.05) in day 7 samples. Moreover, the ratio of NEO to T-2 toxin production was affected by an interaction involving incubation time, strain and carbendazim dose (P<0.05 or better). On day 5, this ratio was greater in CS exposed to 2 µg/ml, but at 4 µg/ml, the ratio was higher in RS. It is concluded that carbendazim resistance induced genuine differences in the synthesis of T-2 toxin and NEO. It is suggested that the strain difference may reside in the conversion of NEO to T-2 toxin which may be sensitive to fungicide concentration. This would imply that carbendazim resistance induces changes in the terminal rather than initial phases of trichothecene biosynthesis.

3-Acetyl deoxynivalenol and esterase production in a fungicideinsensitive strain ofFusarium culmorum.

3-Acetyl deoxynivalenol (3-ADON) and esterase production were determined in a strain ofFusarium culmorum insensitive to the fungicide, difenoconazole. Following further exposure to this fungicide for different periods of time, the initiation of 3-ADON production was observed to be accelerated in the insensitive strain compared to a control (sensitive) strain of the phytopathogen. In particular, 3-ADON appeared in insensitive cultures within 21 days of incubation with fungicide levels of 1 to 4 µg/ml media and at 43 days with difenoconazole levels of 6 and 10 µg/ml. However, in the control strain, 3-ADON production was delayed until 28 and 57 days for the respective doses of fungicide. For these times and fungicide levels, the overall production of 3-ADON by the insensitive strain was significantly different from the zero values recorded with the control strain (P<0.05). Moreover, although difenoconazole was generally effective in depressing 3-ADON synthesis in both strains, the suppression was not significant (P>0.05) for the insensitive strain at 43 and 57 days of incubation with fungicide added at 1 µg/ml. In a parallel experiment, total esterase production was observed to increase progressively over time and at consistently higher levels for the insensitive strain from day 14 onwards so that by day 35 the strain difference was significant (P<0.05). Although the increase with time occurred in both strains, this enhancement appeared at 14 days in the insensitive strain (P<0.05) but delayed until 21 days in the control strain (P<0.05). In conclusion, these investigations have demonstrated the persistence of 3-ADON production and enhanced levels of total esterases in a strain ofF. culmorum insensitive to difenoconazole. Furthermore, it is proposed that changes in esterase profiles might be of diagnostic value in identifying toxigenic strains of differentFusarium species.

3-Acetyl deoxynivalenol production in a strain ofFusarium culmorum insensitive to the fungicide difenoconazole.

The production of the mycotoxin, 3-acetyl deoxynivalenol (3-ADON), was investigated in a strain ofFusarium culmorum insensitive to the systemic fungicide, difenoconazole. On exposure to graded concentrations of the fungicide, the insensitive strain continued to synthesise 3-ADON when difenoconazole levels of 100 and 200µg/ ml media were used. In contrast, a control (sensitive) strain ceased production of 3-ADON at difenoconazole levels of 100 µg/ml. Differences between the two strains were also observed for 3-ADON production with time. Following incubation with fungicide at 0.1 µg/ ml, 3-ADON production occurred more rapidly in CS than in IS cultures. This is the first report of increased persistence and alteration of the pattern of production of a mycotoxin following the development of fungicide insensitivity in a fungal phytopathogen.

Determination of mimosine and 3-hydroxy-4(1h)-pyridone in Leucaena, avian excreta and serum using reversed-phase ion-pair high-performance liquid chromatography.

The estimation of mimosine and 3-hydroxy-4(1H)-pyridone in Leucaena leucocephala, Leucaena seeds, chick excreta and chick serum using reversed-phase ion-pair high-performance liquid chromatography was investigated. Isocratic elution of both compounds was achieved in 11 min using sodium octyl sulphate as the pairing agent in a pH 2.25 buffer. Good recoveries of both mimosine and 3-hydroxy-4(1H)-pyridone in all but serum samples were obtained.

Blood pyruvate carboxylase activity as a criterion of biotin status in young pigs.

A basal diet containing isolated soybean protein was supplemented with 100 and 500 microgram biotin/kg and another basal diet containing hen-egg albumen was supplemented with 1300 microgram biotin/kg. The five diets were fed to groups of young pigs from four to 12 weeks old. Growth depression or skin or foot lesions characteristic of biotin deficiency were not seen but the undersurfaces of the hooves of pigs given the basal albumen diet were unusually soft. Blood pyruvate carboxylase activity showed a maximum response to dietary biotin at six weeks but by 12 weeks there was no response to supplemental levels greater than 100 microgram/kg. Plasma biotin concentration gave a good indication of biotin intake at all ages.

Utilization of dried microbial cells grown on methanol in a semi-purified diet for growing pigs.

1. Twenty-four pigs (mean body-weight 44 kg) were used to determine the digestibilities of energy, nitrogen and amino acids in dried microbial cells (DMC) grown on methanol and in white fish meal (WFM). N utilization and the excretion of various nitrogenous compounds were also studied. 2. Semi-purified diets containing DMC, WFM or no protein source were offered at the rate of 1 kg fresh food/d. Daily N intakes were 26-5, 24-7 and 0-65 g respectively. 3. Mean metabolic faecal N determined with the protein-free diet was 1-11 g/d (1-26 g/kg dry matter (DM) eaten) for the two experiments. The corresponding endogenous urinary N value was 2-91 g/d. 4. Daily urinary N output of pigs given the diet with WFM was significantly greater than that of pigs given the diet with DMC, with the result that N retention, net protein utilization and biological value were higher for pigs given DMC. 5. Apparent and true digestibility of amino acids were higher for the diet with DMC than for the diet with WFM. 6. N excretion in the form of ammonia, urea, uric acid and allantoin accounted for 81, 91 and 99% of the total N excreted by the groups given the protein-free diet, DMC and WFM respectively. Pigs given DMC excreted greater quantities of allantoin-N and less urea-N than pigs given WFM.

Requirements of the young turkey for sulphur amino acids and threonine: comparison with other species.

1. The requirements of the 3-week-old turkey for the sulphur containing amino acids and for threonine were estimated to be 0.83% and 0.94% respectively in diets containing 12.5 MJ ME/kg. 2. It is suggested that the growth responses of rats and slow-growing chicks and of fast-growing chicks and young turkeys to daily intakes of the sulphur containing amino acids and of threonine are similar.

Amino acid requirements of the young turkey: leucine, isoleucine and valine.

1. The leucine, isoleucine and valine requirements of the 3-week-old turkey were determined in a factorial experiment and were found to be 1-42, 0-84 and 1-21% respectively in semi-purified diets containing 12-5 MJ ME/kg. 2. It is suggested that the efficiency with which turkeys and chicks utilise isoleucine and valine is similar, and that a daily intake of about 325 mg of valine would sustain a rate of growth of about 23 g/d in both species.

Amino acid requirements of the young turkey: lysine and arginine.

The arginine and lysine requirements for maximum growth of the 3-week-old turkey, determined in a factorial manner, were 1-75% arginine and 1-55% lysine. 2. It is demonstrated that the arginine required to support a growth rate of about 20 g/d is similar in turkeys and chicks, suggesting that the efficiency with which dietary arginine was utilised for growth is similar in both species.