Effects of Sodium on Potassium Nutrition in Three Tropical Root Crop Species

The potassium (K) nutrition and high K requirement of tropical root crops may be affected by their sodium (Na) status, as has been observed in a number of plant species. Solution culture was used to study the effects of K and Na supplies in tannia [Xanthosoma sagittifolium (L.) Schott.], sweet potato [Ipomoea batatas (L.) Lam.] and taro [Colocasia esculenta (L.) Schott]. At low K supply, Na ameliorated symptoms of K deficiency and increased growth in tannia, and to a lesser extent in sweet potato, but not in taro. None of the species responded to Na at adequate K supply. Differences in response to Na were attributed to differences in Na translocation to plant tops. At maximum Na supply, the Na concentration in index leaves averaged 1.82% in tannia, 0.205% in sweet potato, and 0.0067% in taro. An increase in the supply of Na resulted in a shift in the critical K concentration for deficiency (i.e., 90% of maximum yield) in index leaves from 2.9% to 1.2% in tannia, and from 4.8% to 2.5% in sweet potato. The critical K concentration in taro was 3.3%, irrespective of Na supply. To overcome the problem in tannia and sweet potato of determining the critical concentration relevant to a leaf sample of unknown K status, a relationship was established for each species relating the critical K concentration to the concentration of Na in the index leaves.     

Volatile losses of sulfur from intact plants

Losses of volatile sulfur (S) compounds were measured from intact plants of 22 species including tropical and temperate crop and pasture species grown under glasshouse conditions. All species released substantial amounts of S during a 22‐hour collection period. The amounts lost ranged from 0.13 μg S g dry weight of shoot^‐1 22 hours^‐1 in barrel medic to 2.68 μg S g dry weight of shoot^‐1 22 hours^‐1 in rape. These losses represented 0.005% of the total S in the shoot in barrel medic and 0.92% in rape. There was no obvious division between temperate and tropical species in terms of the amounts of volatile sulfur compounds released, but the evidence suggested that tropical species released a different spectrum of volatile sulfur compounds from temperate species. Thus in tropical grasses and legumes, a higher proportion of the total volatiles was recovered in cold traps, whereas in temperate grasses and legumes, a higher proportion of the total volatiles was recovered in activated carbon traps located after the cold traps. When all 22 species were considered together, the amount of volatile S lost was not correlated with the S concentration in the shoot. Extrapolation of these short term observations in the glasshouse to longer term losses under field conditions suggests that losses of volatile S from fields of alfalfa, Rhodes grass, and wheat may be in the order of hundreds of grams of S ha^‐1 year^‐1, while losses from fields of cotton may be in the order of thousands of grams of S ha^‐1 year^‐1.     

Sterile solution culture techniques for aluminum toxicity studies involving organic acids

Microbial degradation of low molecular weight organic acids can be a serious source of error in solution culture experiments concerned with the protection of plant roots by these compounds against aluminum (Al) toxicity. Under normal glasshouse conditions, the problem was not solved by sterilisation of the various components of the solution culture system and surface sterilisation of the soybean and mungbean seeds. Of four water soluble antibiotics tested, streptomycin, rifampicin, and trimethoprim were phytotoxic at concentrations ≥ 50 mg/L; cefotaxime, while not phytotoxic up to 150 mg/L, gave poor control of microbial growth in 2‐day root elongation tests with mungbean. However, addition of 30 mg/L cefotaxime plus 20 mg/L trimethoprim at planting and a further 30 mg/L cefotaxime after one day was effective in controlling microbial numbers and preventing significant loss of added citrate to the solutions. At these concentrations the antibiotics were non‐phytotoxic and appeared not to cause any complexation of Al. Use of the method showed that citrate, L‐malate, and oxalate were highly effective detoxifiers of Al in solution.     

Rare earth elements and plant growth: II. Responses of corn and mungbean to low concentrations of lanthanum in dilute,continuously flowing nutrient solutions.

Corn (Zea mays cv. Hycorn 82) and mungbean (Vigna radiata cv. Berken) plants were grown for 14 d in dilute nutrient solutions containing constant lanthanum (La) concentrations from 0 to 1.37 μM. Solutions were maintained at pH 4.5 to prevent precipitation of La. Lanthanum at 0.63 μM increased the root growth of corn by 36% and 0.19 μM La increased mungbean root growth by 21% relative to controls. However, no beneficial effects of La on the total dry matter yield of either plant species were demonstrated; that of corn was unaffected, whilst that of mungbean was reduced by over 30% at solution La concentrations greater than 0.19 μM.

Roots of both plant species accumulated 20 to 150 times higher concentrations of La than the shoots. The highest La concentrations in roots were 1775 mg/kg in corn and 2955 mg/kg in mungbean. Where La was added to the nutrient solutions, concentrations of La in the shoots ranged from 9 to 16 mg/kg for corn and from 34 to 52 mg/kg for mungbean. The oldest leaves of both plant species accumulated higher La concentrations than found in the remainder of the shoots. Both plant species demonstrated an ability to restrict the uptake of La into the shoots, as the concentrations of La in the shoots increased only slowly with increasing concentrations of La in the roots and in the nutrient solution. The data suggest critical shoot and root La concentrations of the order of 34 and 775 mg/kg respectively, for toxicity in mungbean. Critical La concentrations for toxicity in corn must be grsater than 16 mg/kg in shoots and 1775 mg/kg in roots.     

The effect of fungicides on sugar beet infected with beet mild yellowing virus

Studies were made in 1989, 1990 and 1991 to establish whether carbendazim (MBC) had a direct therapeutic effect on sugar beet plants infected with beet mild yellowing virus (BMW), resulting in detectable yield benefits. In a field trial in 1989 virus-infected plots treated with carbendazim gave a significantly higher yield, of 0.66 t sugar/ha, than virus-infected plots sprayed with sulphur to control powdery mildew. This response to carbendazim in virus-inoculated plots was not repeated in subsequent trials in 1990 and 1991, and a glasshouse study showed no apparent effect on virus concentration within inoculated plants. Neither was any effect of carbendazim on symptom development observed in any of the trials or glasshouse experiments.     

Evidence for absence of equine arteritis virus in the horse population of New Zealand

AIM: To summarise investigation and laboratory data collected between 2001 and 2011 to provide evidence that equine arteritis virus is not present in the horse population of New Zealand.

METHODS: Analysis was carried out on results from laboratory tests carried out at the Ministry for Primary Industries Animal Health Laboratory (AHL) for equine arteritis virus from horses tested prior to being imported or exported, testing of stallions as part of the New Zealand equine viral arteritis (EVA) control scheme and testing as part of transboundary animal disease (TAD) investigations for exclusion of EVA. Horse breeds were categorised as Thoroughbred, Standardbred or other.

RESULTS: A total of 7,157 EVA serological test records (from import and export testing, EVA control scheme testing and TAD investigations) were available for analysis between 2005 and 2011. For the three breed categories a seroprevalence of ≤1.6% at the 95% confidence level was determined for each category. Between 2001 and 2011, as part of the EVA control scheme, the EVA status of 465 stallions was determined to be negative. During 2005–2011 EVA was excluded from 84 TAD investigations.

CONCLUSIONS: There was no evidence of equine arteritis virus being present in the general horse population outside of carrier stallions managed under the EVA control scheme.

CLINICAL RELEVANCE: Equine arteritis virus is absent from the general horse population of New Zealand.