Summary. The response of cvv. Russet Burbank and Kennebec potatoes to different levels of residual and applied phosphorus (P) was compared on krasnozem and duplex soils in the Central Highlands of Victoria. Field experiments were conducted at 12 sites over 3 years to examine the effects of applied P (banded at planting) at rates up to 475 kg/ha on yield, petiolar P concentrations, tuber size, number of tubers/plant and specific gravity. The relationships between yield response and fertiliser P required to optimise yields with Olsen P and P adsorption isotherms were also determined. Application of P significantly (P<0.05) increased yields at 11 of the 12 sites for cv. Russet Burbank and at 6 of the 9 sites for cv. Kennebec. Based on data for all sites, there was a significant (P<0.001) Mitscherlich relationship between yield response to applied P and Olsen P. This relationship was significantly (P<0.05) different for each cultivar. The critical Olsen P concentration was 27 mg/kg for cv. Kennebec. However, for cv. Russet Burbank the relationship had not plateaued, although our Olsen P concentrations ranged from 5–46 mg/kg. For cv. Russet Burbank there was a significant (P<0.05) negative linear relationship between the amount of applied P required to achieve 95% of maximum yield and Olsen P concentrations. However, there was no significant (P>0.05) relationship between the amount of applied P required to achieve 99% of maximum yield and Olsen P concentrations. For these krasnozem and duplex soils, the predictive models of either yield response or the amount of applied P required to optimise yield, were not significantly (P>0.05) improved by including P sorptivity measures. At yield-responsive sites there were significant (P<0.05) changes in the proportion of tubers >280 g for both cultivars. However, the only quality parameter adversely affected by applied P was specific gravity. There were significant (P<0.05) Mitscherlich relationships between relative yield and petiole P concentrations for both cultivars. The following critical petiole P ranges have been proposed to assist in the assessment of the P status of cv. Russet Burbank crops in Victoria: 0.45–0.57% at a tuber length of 5–10 mm; 0.35–0.47% at a tuber length of 35–45 mm and 0.21–0.26% at a tuber length of 75–85 mm. The use of petiole sampling for assessment of the P status of potatoes before the 5–10 mm tuber stage is not recommended. The critical P range for cv. Russet Burbank was higher than the critical P range for cv. Kennebec at a 5–10 mm tuber length. The practical implications from this work are that Olsen P is a good indicator of a site’s potential yield response to applied P fertiliser. However, at those soil P concentrations where a yield response is expected, Olsen P is of little value to predict the amount of P fertiliser required to achieve maximum yields. We have established that separate calibration curves are required for cvv. Russet Burbank and Kennebec to define their critical Olsen P concentrations on krasnozem and duplex soils. This is the first work in Australia showing critical nutrient ranges for petiolar P over time in cv. Russet Burbank.

No abstract

No abstract

Cut Geraldton waxflower (Chamelaucium uncinatum Schauer) flowers are often infected with Botrytis cinerea. Release of infection from quiescence can cause ethylene production by invaded host tissues and result in flower abscission. Postharvest floral organ abscission is a major problem for the commercial waxflower industry. Methyl jasmonate (MeJA) occurs naturally in plant tissue and has a signalling role in eliciting induced systemic resistance against disease. MeJA treatments have been shown to suppress B. cinerea infecting cut rose flowers. The present experiments investigated the potential of exogenous MeJA treatments for B. cinerea management on harvested waxflower. MeJA treatments of 10 and 100 µL liquid MeJA/L of air applied to cv. Purple Pride and 1 µL MeJA/L to cv. Mullering Brook gave reductions in disease severity for uninoculated stems. However, concentrations of 100 µL MeJA/L applied to Purple Pride in addition to 1 and 10 µL MeJA/L applied to Mullering Brook increased the incidence of floral organ fall. Flower abscission upon treatment with MeJA may be due to induced systemic resistance-associated upregulation of ethylene biosynthesis. MeJA treatments had no direct effect on B. cinerea hyphal elongation in vitro. Collectively, these results show that while MeJA treatment may elicit defence in waxflower against Botrytis, the chemical also causes floral organ fall. Thus, exogenous MeJA treatments do not have potential for B. cinerea management on harvested waxflower.

The effects of method, time and number of cultivations on root diseases and yield of wheat were studied in a field experiment, in 1985, on a calcareous sandy loam in the Victorian Mallee. The incidence and severity of rhizoctonia root rot (Rhizoctonia solani) were higher in direct-drilled wheat than in wheat sown after cultivation. Compared with direct drilling, the severity of rhizoctonia root rot in seedlings was reduced by 40% with cultivation 20 weeks before sowing; by 70% with cultivation 1 day before sowing; and by 90% with 2 cultivations, the first at 16 weeks and the second 1 day before sowing. Cultivation generally increased the incidence of common root rot (Bipolaris sorokiniana) but had no significant effects on the severity of damage by the cereal cyst nematode (Heterodera avenae) or the number of nematode cysts produced, compared with direct drilling. The incidence and severity of root diseases, and the number of H. avenae cysts produced, were not significantly different in wheat sown after rotary hoeing than in wheat sown after scarifying. The severity of damage by H. avenae, the number of nematode cysts and the incidence of common root rot were higher (45, 70 and 36%, respectively) when scarifying was done 1 day before sowing, compared with scarifying 20 weeks earlier. Differences in sowing depth probably caused this effect since seed was sown deeper (as indicated by subcrown internode lengths) and plant emergence was less in the latter treatment. The timing and number of cultivations with a rotary hoe, however, did not significantly affect the severity of damage by H. avenae, the number of nematode cysts or the incidence of common root rot. The incidence of common root rot was correlated (r = 0.71) with the subcrown internode lengths, indicating that the deeper the seed was sown the greater the proportion of plants with the disease. Dry weight of seedlings and grain yield were negatively correlated (r = -0.79 and -0.66) with the severity of damage caused by H. avenae. Plant dry weight and grain yield were, however, not correlated with the severity of rhizoctonia root rot or the incidence of common root rot.