Trent Potter

Zinc efficiency of oilseed rape (t Brassica napus and t B. juncea) genotypes

Twenty five genotypes of oilseed rape (canola and mustard) were tested under varied supply of Zn (+Zn: 2 mg kg−1 soil, -Zn: no Zn added) in two pot experiments in soil culture to determine the genotypic variation in tolerance to the Zn-deficient conditions, that is, to identify the Zn-efficient genotypes. On the basis of performance of genotypes in pot experiments, ten genotypes were tested in 1995 for their performance under varied supply of Zn (+Zn: 3.5 kg ha−1, -Zn: no Zn added) on a Zn-deficient field in South Australia.Zn efficiency (ratio of shoot dry matter in -Zn to shoot dry matter in +Zn treatment and expressed in percentage) in pot Experiment 1 varied from 35% for 92-13 to 74% for Siren. Narendra, Dunkeld, Barossa, Oscar and Xinza 2 performed well under -Zn treatment. Zn efficiency in Experiment 2 varied from 32% for Wuyou 1 to 62% for Pusa Bold. Pusa Bold and CSIRO-1(mustard genotypes) were the most efficient in terms of dry matter production among all the oilseed rape genotypes tested. Root dry matter accumulation was significantly higher in Zn-efficient genotypes. Zn efficiency (ratio of seed yield in -Zn to seed yield in +Zn and expressed in percentage) in field experiment varied from 62% for Huashang 2 to 76% for Dunkeld. With few exceptions, the ranking of genotypes in pot and field experiments indicates similarity in their response to Zn deficiency. There looks to be genetic control over Zn concentration in tissues. Zn-efficient genotypes had lower Zn concentration in roots and higher Zn concentration in youngest fully opened leaf blades, indicating a better transport of Zn. This, together with a higher Zn uptake, appears to be the basis of expression of Zn efficiency.

Reaction of a range of Brassica species under Australian conditions to the fungus, Leptosphaeria maculans, the causal agent of blackleg

A range of Brassica species was screened for resistance to Leptosphaeria maculans, the causal agent of blackleg. The lines were assessed in 8 disease nurseries in 4 canola growing regions of Australia and in 1 glasshouse trial, with a view to identifying alternative sources of resistance to L. maculans for Australian breeding programs. Lines were screened for degree of internal and external blackleg symptoms during both the seedling and adult plant growth stages. Correlation for resistance with ranking between disease nurseries was very strong (0.41-0.98). Brassica carinata and B. nigra were the most resistant species in the disease nurseries, being even more resistant than B. juncea. The 7 European winter B. napus lines tested were significantly more resistant than the 7 Australian spring B. napus lines, with another crucifer, Sinapis alba, being intermediate in resistance between the European and Australian B. napus lines. The same ranking of lines from most to least resistant was also seen when cotyledons and stems were inoculated in the glasshouse with 2 well-characterised Australian isolates. With the exception of the B. napus susceptible control Westar, all lines had similar frequencies of seedling survival in the nurseries. However, mature plants of these lines varied significantly in their degree of resistance. This indicates that screening for seedling survival is not useful in selecting L. maculans resistant lines in Australia. The Brassica lines with the B genome, especially B. carinata, and the winter B. napus types are now being used as sources of resistance in Australian breeding programs.

Long-season canola ( Brassica napus L.) cultivars offer potential to substantially increase grain yield production in south-eastern Australia compared with current spring cultivars

Abstract. Average yield of canola in the high-rainfall zone (HRZ) of southern Australia are about half the predicted potential yield based on seasonal water supply. Current cultivars of canola that are available to growers were not bred specifically for the HRZ and tend to be short-season types aimed at escaping water stress during grain filling in the drier regions of the cropping belt. In the HRZ, these cultivars fail to utilise all available growing-season water due to early maturity. Field experimentation and crop simulation studies across the HRZ landscape of south-eastern Australia were used to determine the increased yield potential of longer-season canola cultivars compared with short-season cultivars. In this study the Catchment Analysis Tool spatial modelling framework was used to determine the expected canola yields of three cultivars across the entire HRZ of south-eastern Australia. Hyola50 (‘spring-short’) was used to represent the current recommended spring-type canola cultivar within the HRZ and was evaluated against an unreleased long-season spring-type cultivar CBI8802 (‘spring-long’) and a newly released winter-type cultivar Taurus (‘winter’). Spring-long outperformed spring-short across much of the study area. Yield advantages of winter over spring-short were mainly confined to the coastal fringe of Victoria and Tasmania and small pockets in New South Wales where at one location the average yield over 50 growing seasons exceeded spring-short by up to 60% or 1.4 t/ha. The superior performance of spring-long, (up to 17% or 0.9 t/ha at one location) was over a wider area than winter (26.4 compared with 8.8 million ha for winter) and although the magnitude of the yield increase over spring-short was not as great as winter at some locations, the overall result determined that spring-long had the greater production potential. The superior performance of spring-long beyond the HRZ challenges the trend of selecting earlier maturing cultivars by current breeders following the abnormal sequence of dry years in an attempt to minimise yield loss due to water stress during grain filling. This study has provided breeders, growers and advisors with information on where in the HRZ a longer-season canola cultivar can be grown to improve overall crop productivity. It has also provided evidence that new canola types may be required to maximise grain yields not only for the HRZ but potentially also in lower rainfall regions.

Yield performance of late-maturing winter canola (Brassica napus L.) types in the High Rainfall Zone of southern Australia

Abstract. Area and production of canola (Brassica napus L.) in the High Rainfall Zone (HRZ) of southern Australia has increased significantly over the past decade. Varieties available to growers have not been bred specifically for the HRZ and are generally adapted to the drier regions of the cropping belt. Field experiments were conducted at Hamilton in south-west Victoria in 2005, 2006 and 2008 to identify canola traits and management suited to the HRZ of southern Australia. Nine varieties with different reported maturities (winter and spring types) were sown at either two times of sowing and/or under different nitrogen (N) fertiliser regimes. Dates of key phenological development were recorded, dry matter was determined at bud, flowering and maturity and grain yield and yield components were determined at harvest. Plant traits and climate data were assessed in relation to grain yield. Yields of the winter types were either significantly (P < 0.05) greater or not significantly less than the spring types in all 3 years and similar to those reported under experimental conditions in Europe. This was despite the winter types flowering up to 35 days later than the spring types and spring rainfall being approximately half that of the long-term average. In general, the winter types had greater early vigour, greater dry matter production at the bud, flowering and maturity stages and were taller than the spring types. Regression analysis showed positive relationships between grain yield and pod density and plant size (dry matter and plant height). Plant size was influenced by variety, time of sowing and N fertiliser application rates. Crops in the HRZ were able to sustain more seeds per pod at larger canopy sizes and pod densities than those achieved in the northern hemisphere. Despite the number of pods per g of dry matter at flowering being nearly double that reported in the UK, there was little apparent reduction in the number of seeds per pod. It is possible that higher solar radiation and warmer minimum temperatures in the HRZ of Australia provide conditions more favourable for growth before, and during grainfill. This indicates that different dry matter production and yield component targets may be appropriate for canola in this environment especially in more typical seasons. It is likely that growers will need to sow new, later maturing varieties earlier and with higher rates of N fertiliser than is current practice in Australia. This study indicates that winter types may have the potential to provide improvements to the yield of canola in the HRZ either through the direct importation of varieties from overseas or through the identification and incorporation of desired traits into existing material. It is recommended that a wider range of germplasm be assessed over a greater geographical area to identify traits and management practices to optimise phenology and canopy structure. This information can be used to help inform breeders on crop improvement priorities as well providing tailored management practices to maximise grain yields for this environment.

Continuing innovation in Australian canola breeding

Abstract. Innovation has been integral in the development of the current Australian canola (Brassica napus L.) industry. From the initial introduction of poorly adapted Canadian germplasm, Australian breeders have developed high yielding, high quality, disease-resistant canola cultivars. The Australian canola industry has transitioned from being reliant on imports to becoming one of the world’s major exporters of canola. This review details the progressive innovations in the Australian canola breeding programs from the initial introduction of rapeseed to more recent developments including herbicide resistance, hybrid cultivars, speciality oil types and genetically modified canola.

Assessing progress in breeding to improve grain yield, quality and blackleg (Leptosphaeria maculans) resistance in selected Australian canola cultivars (1978–2012)

Abstract. Canola breeding in Australia began in the early 1970s with the first cultivars being released in the late 1970s. Thirty-four non-herbicide-tolerant canola cultivars, released in Australia between 1978 and 2012, were evaluated for improvements in yield, quality, blackleg resistance and adaptation to Australian environments. The cultivars were sown at three sites in 2008 and one site in 2014. In addition, blackleg susceptibility was assessed in two independent blackleg experiments in 2008. Yield improvement averaged 21.8 kg ha–1 year–1 (1.25% year–1) but ranged from 8 to 39.1 kg ha–1 year–1 at the lowest to the highest yielding sites, respectively. Although the yield gain shown by our study was for conventional canola only, the different herbicide-tolerant types are derived by incorporating the herbicide tolerance genes into Australian germplasm and so the rate of genetic gain would be expected to be similar for all herbicide tolerance types. Oil and protein concentrations have increased by 0.09% year–1 and 0.05% year–1, respectively, whereas glucosinolate concentration was reduced to between 7 and 16 μmoles per gram of meal by the mid-1990s. Cultivars released before 2002 all had low to moderate resistance to the blackleg isolates present in the fields during the experimental period but more recent releases had improved survival under heavy blackleg pressure due to the incorporation of additional or different resistance genes. The data suggests that at least 25% of the yield improvement achieved by the breeding programs over 30 years was associated with improved blackleg resistance and the remainder with gains in other aspects of potential grain yield. The private breeding companies in Australia will need to continue to produce cultivars with high yield potential and deploy blackleg resistance genes wisely in order to maintain the yield improvements required to remain competitive in global markets.

Seeding rate and cultivar effects on canola (Brassica napus) competition with volunteer wheat (Triticum aestivum)

Abstract. Canola (Brassica napus L.) is an important rotational crop in the temperate cropping zone of southern Australia. Herbicide-resistant weeds are rapidly spreading and reducing canola grain yield and quality. Crop competition is a useful tool for reducing weed costs and dependence on herbicides, and retarding the spread of herbicide resistance. The potential interaction of canola seeding rate and cultivar for weed management has not been quantified in Australia. A field experiment was conducted in three environments to examine the impact of two contrasting canola cultivars (a low vigour type and a high vigour hybrid) at four seeding rates (10–100 plants/m2) on volunteer wheat (∼50 plants/m2). Significant but variable effects of crop seeding rate, cultivar and weed were detected on canola density and grain yield, and on the suppression of volunteer wheat. The canola hybrids suppressed volunteer wheat more than the less vigorous cultivars in all the experiments. There was no benefit of increasing canola seeding rate above the normally recommended rate of 40 plants/m2 for weed suppression. The seed production of volunteer wheat on average doubled when canola density dropped from 40 to 10 plants/m2. Treatment effects on canola grain yield losses from weeds were less than those on weed suppression. The grain yield of both cultivars was reduced between 30% and 40% with weeds at a canola density of 40 plants/m2 and plateaued above this density in weedy conditions. Maintaining canola plant establishment and using competitive cultivars is critical to avoiding weed seedbank replenishment, and reducing canola yield losses from weed competition.