Raymond Cowley

Canola cultivar performance in weed-infested field plots confirms allelopathy ranking from in vitro testing

Crop competition and allelopathy are two cultural control options for possible inclusion in cropping systems. This research aimed to identify superior allelopathic canola genotypes through a two-year field study. First year screening results of 312 diverse Brassica genotypes showed genotypes differed significantly in their ability to suppress weed infestations. Crop plant height was correlated with the competitive ability of several genotypes, while other genotypes showed good weed-suppressive ability despite being short. Thirty-six of the genotypes grown in the field had been previously assessed for their allelopathic ability to inhibit the growth of annual ryegrass (Lolium rigidum) seedlings using an in vitro technique. The highly allelopathic genotypes: Av-opal, Sardi603, Rivette and Atr-beacon performed well against annual ryegrass in the laboratory and also against other species, including Capsella bursa-pastoris, Sisymbrium orientale and Hordeum leporinum in the field. The weakly allelopathic Barossa and X-06-6-3725 genotypes performed poorly both in the laboratory studies and in the field. The following year, field testing of selected genotypes at two sowing dates further suggested that the most allelopathic genotypes in the laboratory bioassay were generally those that suppressed weed numbers and their biomass in the field. The late sowing time increased the natural weed pressure leading to a decrease in both canola grain yield and quality. Many of the highly allelopathic canola genotypes, which caused low weed populations in the field, had relatively low grain yield. This suggests that the allelopathic trait is independent of local adaptation and yields potential under weed-free conditions. Ideally, cultivars with both high allelopathy and high competitive ability would be most useful to help farmers maximise yield and control weeds. Selection for allelopathy in canola shows potential as a future non-chemical weed control option and requires further investigation.

Breeding Lupinus albus for resistance to the root pathogen Pleiochaeta setosa

Pleiochaeta root rot (PRR) caused by Pleiochaeta setosa is a serious, widespread fungal disease in lupin crops, especially in Lupinus albus (broad-leaf lupin, or white lupin). PRR resistance is common in the gene pool of L. albus with various landraces from the Mediterranean region being the most resistant, and suitable for use in breeding new cultivars. Heritability of resistance is sufficient to make good gains from selection but only when controlled-environment (CE) screening is used. Field disease nurseries on loamy soil gave much lower heritability of resistance. Field disease nurseries had spatially variable spore counts despite continuous lupin cropping, and this was partly responsible (along with climatic conditions) for their reduced precision compared to tests conducted in a CE. Giving infected L. albus roots a single, most-severe-lesion score on a 0–9 scale was adequate for CE screening but not as precise or discriminating as the more time-consuming method of six scores per root. Replication in CE experiments was reduced to two pots of 16 seedlings each without sacrificing genotype discrimination.

Evidence that Diaporthe toxica infection of Lupinus albus is an emerging concern for the Australian lupin industry

Lupinus albus has been grown commercially in Australia since the 1970s and has long been regarded as resistant to phomopsis caused by Diaporthe toxica. Isolates capable of infecting L. albus were collected following an outbreak of phomopsis in 2004 in southern New South Wales. Glasshouse screening of L. albus cultivars with the pathogen revealed that genotypes differ in their response to D. toxica with some current cultivars having useful resistances. Several breeding lines and old cultivars were susceptible in either vegetative or reproductive tissue or both. The commonly grown commercial cultivar Kiev Mutant was moderately susceptible in all tissues assessed. A principle component analysis gave weak to moderate correlation (r = 0.14 to r = 0.54, depending on the two-way comparison) between vegetative and reproductive tissue, which is suggestive that resistance in different tissues may be under distinct genetic control. The germination of infected seed from the outbreak in 2004 was severely compromised, and much of the seed harboured the pathogen. A survey of 171 commercial seed samples from 2004 to 2006 showed that phomopsis discoloured seed was present in only 20 samples, all of them confined to southern New South Wales. While the pathogen presents a risk to L. albus cropping zones in southern New South Wales, it is not widely spread at this stage. However, vigilance is required to prevent infected seed from being sown so that the disease can be kept in check.

Application of multi-phase experiments in plant pathology to identify genetic resistance to Diaporthe toxica in Lupinus albus

Phenotyping assays in plant pathology using detached plant parts are multi-phase experimental processes. Such assays involve growing plants in field or controlled-environment trials (Phase 1) and then subjecting a sample removed from each plant to disease assessment, usually under laboratory conditions (Phase 2). Each phase may be subject to non-genetic sources of variation. To be able to separate these sources of variation in both phases from genetic sources of variation requires a multi-phase experiment with an appropriate experimental design and statistical analysis. To achieve this, a separate randomization is required for each phase, with additional replication in Phase 2. In this article, Phomopsis leaf and pod blight (caused by Diaporthe toxica) of Lupinus albus was used as a case study to apply a multi-phase experimental approach to identify genetic resistance to this pathogen, and demonstrate the principles of sound experimental design and analysis in detached plant part assays. In seven experiments, 250 breeding lines, cultivars, landraces, and recombinant in-bred lines from a mapping population of L. albus were screened using detached, inoculated leaves, and/or pods. The experimental, non-genetic variance in Phase 2 varied in magnitude compared to the Phase 1 experimental, non-genetic variance. The reliability of prediction for resistance to Phomopsis pod blight was high (mean of 0.70 in seven experiments), while reliability of prediction for leaf assays was lower (mean 0.35–0.51 depending on the scoring method used).

Penetration and symptom development of Pleiochaeta root rot in susceptible and resistant Lupinus albus cultivars

Pleiochaeta root rot caused by Pleiochaeta setosa is a major threat to the Australian lupin industry. Although Pleiochaeta root rot-resistant Lupinus albus varieties have been bred, there is no information on the likely mechanism of this resistance. Susceptible (Kiev mutant) and resistant (P25758) albus lupin cultivars were inoculated with spores of P. setosa strain PS6-1 and the infection process studied microscopically. No specialised penetration structures were observed on the roots, and infecting hyphae entered roots of both cultivars by growing directly between root surface cells. Lengths of conidial germ tubes on resistant hosts was significantly longer than on susceptible hosts, suggesting that a component of the resistance is via reduced host recognition by the pathogen.

Evaluation of resistance to Phomopsis stem blight (caused by Diaporthe toxica) in Lupinus albus

Historically, in Australia, Phomopsis stem blight in Lupinus albus crops is rare. However, in 2004 an outbreak of this disease occurred in southern New South Wales affecting stems, pods and seeds of the cultivar Kiev-Mutant. This virulent outbreak represents a potential threat to the Australian lupin industry. The current research was therefore initiated to optimise disease screening protocols for evaluation of the disease. Screening for resistance to Phomopsis stem blight is important because stubble is a potential high source of inoculum in no-tillage systems, and grazing of Phomopsis infected stubble can cause lupinosis in stock animals. A single spore isolate of the fungal pathogen Diaporthe toxica collected from the 2004 outbreak was used to assess the levels of disease resistance in stem tissue in L. albus cultivars in some experiments and in other experiments field-infected stubble was used as inoculum. Resistance of current L. albus cultivars, breeding lines, and landraces to D. toxica was assessed in both glasshouse and field experiments in 2007 and 2008. The results showed that resistance existed in some cultivars and several germplasm accessions. Environmental effects and possible differences in pathogen race structure lead to some poor correlations of resistance ratings between different experiments (ranging from r = −0.489 to 0.800, depending on the experiment and tissue assessed). In field experiments consistent expression of the disease was dependent on rainfall. Screening in an irrigated disease nursery improved the methodology. Nevertheless, results suggest that it will be possible to develop new L. albus varieties that are resistant to Phomopsis stem blight should the disease become widespread in south-eastern Australia.

Identification of QTLs associated with resistance to Phomopsis pod blight (Diaporthe toxica) in Lupinus albus.

Phomopsis blight in Lupinus albus is caused by a fungal pathogen, Diaporthe toxica. It can invade all plant parts, leading to plant material becoming toxic to grazing animals, and potentially resulting in lupinosis. Identifying sources of resistance and breeding for resistance remains the best strategy for controlling Phomopsis and reducing lupinosis risks. However, loci associated with resistance to Phomopsis blight have not yet been identified. In this study, quantitative trait locus (QTL) analysis identified genomic regions associated with resistance to Phomopsis pod blight (PPB) using a linkage map of L. albus constructed previously from an F8 recombinant inbred line population derived from a cross between Kiev-Mutant (susceptible to PPB) and P27174 (resistant to PPB). Phenotyping was undertaken using a detached pod assay. In total, we identified eight QTLs for resistance to PPB on linkage group (LG) 3, LG6, LG10, LG12, LG17 and LG27 from different phenotyping environments. However, at least one QTL, QTL-5 on LG10 was consistently detected in both phenotyping environments and accounted for up to 28.2% of the total phenotypic variance. The results of this study showed that the QTL-2 on LG3 interacts epistatically with QTL-5 and QTL-6, which map on LG10 and LG12, respectively.

Use of remote sensing to determine the relationship of early vigour to grain yield in canola (Brassica napus L.) germplasm

Abstract. Early crop vigour in canola, as in other crops, is likely to result in greater competition with weeds, more rapid canopy closure, improved nutrient acquisition, improved water-use efficiency, and, potentially, greater final grain yield. Laborious measurements of crop biomass over time can be replaced with newer remote-sensing technology to aid data acquisition. Normalised difference vegetation index (NDVI) is a surrogate for biomass accumulation that can be recorded rapidly and repeatedly with inexpensive equipment. In seven small-plot field experiments conducted over a 4-year period with diverse canola germplasm (n = 105), we have shown that NDVI measures are well correlated with final grain yield. We found NDVI values were most correlated with yield (r >0.7) if readings were taken when the crop had received 210–320 growing degree-days (usually the mid-vegetative phase of growth). It is suggested that canola breeders may use NDVI to objectively select for vigorous genotypes that are more likely to have higher grain yields.

Response of canola (Brassica napus L.) and mustard (B. juncea L.) to different watering regimes

In arid and semiarid winter crop growing regions of southern Australia, low rainfall, high evaporation, and low soil moisture storage are the limiting factors for crop production. In this region canola ( Brassica napus L.) is principally grown in rotation with wheat and pasture species. Some field studies have indicated Indian mustard ( Brassica juncea L.) to be more drought tolerant than canola and therefore considered to be better adapted than canola to short season environments. A field experiment was conducted at Wagga Wagga in NSW to determine the effect of two soil moisture regimes on water use efficiency, harvest index, seed and oil quality of cv. Oasis of Indian mustard and cv. Skipton of canola. Significant year × stress and species × stress interaction effects were observed for grain yield, harvest index, seed weight, biomass water productivity, and grain water productivity. Irrigation during the post flowering period resulted in 50% and 200% increases in canola grain yield in the first year (year with higher in-crop water) and the second year (year with low in-crop water), respectively. For mustard, these values were 7% and 45%, respectively. Stressed mustard resulted in higher grain yield than stressed canola while irrigated canola performed better than irrigated mustard. High mustard biomass production resulted in lowering its harvest index. Generally, the biomass water productivity of mustard was higher than that of canola. Grain yield-based water productivity of stressed mustard was higher than that of stressed canola while irrigated canola had higher water productivity than irrigated mustard. When rainfall and actual evapotranspiration drop below some thresholds, mustard becomes a favourable crop. Generally, effects due to the water treatments (stressed v irrigated) were much larger than the differences due to species.

Changes in farming practices impact on spore release patterns of the blackleg pathogen, Leptosphaeria maculans

Abstract. Blackleg disease is caused by the stubble-borne pathogen Leptosphaeria maculans and results in significant yield losses in canola (Brassica napus) worldwide. Control of this disease includes breeding for resistance, fungicides and cultural practices including stubble management. In recent years, cropping systems have changed with the introduction of no-till farming and inter-row sowing, and it is unknown what impact these changes have had on stubble retention. The aim of this study is to investigate the impact of inter-row sowing on stubble retention and spore release. The use of inter-row sowing resulted in 25–48% of stubble remaining standing (vertical) in fields after 1 year. Furthermore, spore release was significantly (P < 0.05) delayed in stubble that remained vertical in the field compared with stubble lying down, with total spore release from vertical stubble 66% less than from horizontal stubble. The impact these changes have on the epidemiology of blackleg disease remains unknown.