Wayne A. Burton

Assessment of genetic diversity in selected breeding lines and cultivars of canola quality Brassica juncea and their implications for canola breeding

AFLP markers were used to assess the genetic diversity of 77 breeding lines from three of the worlds major canola qualityBrassica juncea breeding programs from Canada (Agriculture and Agri-Food Canada and Saskatchewan Wheat Pool) and Australia (Agriculture Victoria). The objectives of the paper were to assess the genetic diversity within and between these three breeding programs and to assess genetic diversity of the canola quality germplasm as compared to mustard quality B. juncea. Fifteen lines of mustard quality B. juncea from India, China, Russia and Australia were also included in the investigation. Ten EcoR1/Mse1 based primer pairs generated 751 scorable fragments with an average of 26 polymorphic bands per primer pair (35%). Similarity coefficients were calculated using the Simple Matching coefficient and adendrogram was developed using the UPGMA procedure, resulting in germplasm being partitioned into five main groups. Line specific markers were discovered that have potential in enhancing the efficiency of individual breeding programs using breeding techniques like accelerated backcrossing. Further understanding the genetic diversity within and between programs has implications for future breeding and collaboration within and between the three programs.

Reaction of Brassica juncea (Indian mustard) lines to Australian isolates of Leptosphaeria maculans under glasshouse and field conditions

Brassica juncea (Indian mustard) lines from diverse geographical locations around the world and from Australian breeding programs were screened for resistance to the blackleg fungus, Leptosphaeria maculans, in both glasshouse and field trials. The five Australian L. maculans isolates used in glasshouse trials could be classified into two groups; those that attacked all B. juncea lines, and those that attacked none. All these isolates caused lesions on cotyledons of B. napus cultivars including Westar, Glacier and Quinta, suggesting that they are in Pathogenicity Group 4 as described by Koch et al. (1991). The two isolates that attacked B. juncea also attacked B. napus lines to a similar extent, but did not attack the two B. carinata lines tested. Brassica lines were sown in a blackleg disease nursery at Lake Bolac, Victoria, Australia, and five indicators of blackleg disease were measured (survival rate, disease rating, disease incidence, external and internal lesion length). All 92 B. juncea lines developed blackleg symptoms. Although they displayed a high disease incidence in the field, almost all of the B. juncea lines were more blackleg-resistant than a B. napus cultivar, Dunkeld, which is amongst the most resistant cultivars in commercial production in Australia. Four B. carinata lines were more resistant than any of the B. juncea lines, suggesting that this species may be a useful source of blackleg resistance in B. napus breeding programs.

Expression and relationships of resistance to white rust (Albugo candida) at cotyledonary, seedling, and flowering stages in Brassica juncea germplasm from Australia, China, and India

White rust (Albugo candida) is a highly destructive disease of oilseed Brassicas such as Brassica juncea and B. rapa. Most commercial B. juncea or B. rapa varieties are highly susceptible and yield losses from combined infection of leaves and inflorescences can be up to 20% or 60% in Australia and India, respectively. In Australia, canola-quality B. juncea has been developed to extend oilseed Brassica production into lower rainfall areas, with the first commercial B. juncea canola-quality variety planned for release in 2006. It is essential to identify useful sources of host resistance in B. juncea as breeding and/or selection of material for resistance is the most cost-effective method of delivering control for farmers. Three experiments were undertaken under controlled-environmental conditions to identify the best methods of characterising host resistance and to identify sources of resistance in B. juncea germplasm from Australia, China, and India. Forty-four B. juncea genotypes, viz. 22 from India, 12 from Australia, and 10 from China, were tested. Four Chinese genotypes (CBJ-001, CBJ-002, CBJ-003, CBJ-004) and one Australian genotype (JR049) consistently showed high resistance to A. candida across the different plant growth stages against a pathotype prevailing in Australia. Similarly, the most susceptible genotypes (viz. Indian genotypes RH781, RL1359, RH819) were extremely susceptible irrespective of the plant growth stage. Overall, although disease severity on cotyledons and leaves at the different growth stages was significantly and positively correlated, there was, however, no significant correlation between the number of stagheads and any of the other disease parameters measured. Our study demonstrates that controlled-environmental conditions are suitable for rapid identification of resistant genotypes and that genotypes with high levels of resistance can be reliably identified at the cotyledonary, seedling, or flowering stages.

Identification of variability in phenological responses in canola-quality Brassica juncea for utilisation in Australian breeding programs

Canola-quality Brassica juncea is a potential alternative crop species in lower rainfall Australian environments due to its superior heat and drought tolerance, disease resistance, and pod-shatter resistance compared with the currently grown B. napus species. Canola-quality types of B. juncea that are adapted to flower and mature before water deficits and high temperatures significantly limit yield potential are currently being developed. In this study, the variability in phenological characteristics in canola-quality B. juncea is assessed, with a view to identifying the potential for including a range of genetic phenological controls on the development of the crop to assist with adaptation. Vernalisation response was compared among 17 lines of B. juncea and 3 of B. napus, using a cold treatment of 2.6°C for 25 days. Leaf number, and duration to first flower and maturity were compared in response to the vernalisation treatments. To assess day length response, the same 20 genotypes were sown at five locations with a range of sowing times, and one controlled environment, where day length was artificially extended. Development stages were assessed and the duration of particular phenological phases determined in relation to time, thermal time, and photoperiod. The major factor controlling flowering in canola-quality B. juncea genotypes was day length, with only small responses to vernalisation detected. There was sufficient variability in these traits and in thermal time to flowering under long days (intrinsic earliness) within the current canola-quality germplasm in Australia to select early flowering genotypes with potential adaptation to low-rainfall environments.

Evidence from Genome-wide Simple Sequence Repeat Markers for a Polyphyletic Origin and Secondary Centers of Genetic Diversity of Brassica juncea in China and India

The oilseed Brassica juncea is an important crop with a long history of cultivation in India and China. Previous studies have suggested a polyphyletic origin of B. juncea and more than one migration from the primary to secondary centers of diversity. We investigated molecular genetic diversity based on 99 simple sequence repeat markers in 119 oilseed B. juncea varieties from China, India, Europe, and Australia to test whether molecular differentiation follows Vavilovs proposal of secondary centers of diversity in India and China. Two distinct groups were identified by markers in the A genome, and the same two groups were confirmed by markers in the B genome. Group 1 included accessions from central and western India, in addition to those from eastern China. Group 2 included accessions from central and western China, as well as those from northern and eastern India. European and Australian accessions were found only in Group 2. Chinese accessions had higher allelic diversity per accession (Group 1) and more private alleles per accession (Groups 1 and 2) than those from India. The marker data and geographic distribution of Groups 1 and 2 were consistent with two independent migrations of B. juncea from its center of origin in the Middle East and neighboring regions along trade routes to western China and northern India, followed by regional adaptation. Group 1 migrated further south and west in India, and further east in China, than Group 2. Group 2 showed diverse agroecological adaptation, with yellow-seeded spring-sown types in central and western China and brown-seeded autumn-sown types in India.

Heterosis of juncea canola under terminal drought conditions

To determine the levels of heterosis in F1 hybrids of juncea canola under well-watered and water deficit conditions, glasshouse experiments were conducted at the University of Melbourne, Parkville campus between 2012 and 2014. Three juncea canola hybrids, their parents and an open-pollinated juncea canola control cultivar (OasisCL) were grown. Plants were subjected to two treatments—well-watered and water deficit after first open flower to maturity. Measurements were recorded on days to various phenological stages, biomass production, seed yield and yield components. Yield heterosis was determined as superiority of F1 hybrids over mid parent and better parent. Two juncea canola hybrids—HJM1Z-2013 and HJM1Z-0027 out-yielded OasisCL and showed significant mid parent and better parent heterosis for seed yield under water deficit. Number of pods per plant was the major yield component affected by water deficit whereas seeds per pod, thousand seed weight and harvest index were stable. Water deficit had significant negative effects on biomass production at harvest. The study revealed the possibility of exploiting yield heterosis of juncea canola under terminal drought conditions. However, further experiments are recommended to verify the results as the results were from pot experiments in controlled conditions.