Performance of canola quality Brassica juncea hybrids in low rainfall environments of Australia

© 2017 Dr. Babu Ram PandeyBrassica juncea L. Czern. and Coss. with equivalent oil and meal quality as B. napus L. canola (B. juncea canola) has been identified as an alternate Brassica oilseed crop for low rainfall areas in southern Australia. B. juncea canola generally out-yields B. napus in low yielding (less than 1.2 t/ha) environments where drought and heat stresses are common during the seed filling period. B. juncea canola has other desirable agronomical traits including better early vigour, blackleg tolerance and shatter tolerance compared with B. napus. Several cultivars of B. juncea canola have been released in Australia since 2007 when the first cultivar Dune was released. This has included herbicide tolerant (Clearfield®) cultivars such as SaharaCL and OasisCL. However, current cultivars need further yield improvements to become profitable in the target environments. Development of hybrid cultivars offers yield improvement of the crop as several studies have reported exploitable heterosis for yield in B. juncea. Seednet (previously Viterra) has recently commenced hybrid breeding of B. juncea canola in Australia. However, there is a lack of knowledge in relation to plant traits important for hybrid performance of B. juncea canola in low rainfall environments. Direct selections on yield under drought conditions are challenged by genotype by environment interactions leading to poor heritability and genetic gain. Inclusion of a yield-correlated physiological trait is highly desirable in such environments. In addition to seed yield, B. juncea needs to fulfil quality requirements to become an acceptable oilseed crop in Australia. Australian canola quality standard requires less than 2% erucic acid in seed oil and less than 30 µmoles total glucosinolates per g of oil free air dry meal. Other traits like oil content and oleic acid content above 60% are also important. Oil content determines price of the seed and oleic acid is highly desirable for health and quality of the products made using the oil. Most of these quality traits are affected by the growing environment particularly rainfall and temperature during seed filling. There is a lack of research on the stability of these quality traits under the low rainfall environments of southern Australia. To address the knowledge gap, glasshouse and field experiments were conducted from 2012 to 2014. The field experiments were conducted in low rainfall environments and under rain fed conditions in Victoria, South Australia and New South Wales. Four glasshouse experiments were conducted at the University of Melbourne (Parkville campus). The glasshouse experiments were grown in 50-75 cm long PVC tubes of 10 cm diameter. Two watering treatments, well-watered and water deficit, were imposed after the first open flower. The importance of pre- and post-anthesis biomass production of hybrids was studied for seed yield in Wimmera and Mallee regions of Victoria in 2012-2014. The study showed that pre-anthesis biomass production was more important for seed yield than post-anthesis biomass production in the environments with less than 250 mm annual rainfall. Post-anthesis and final biomass productions were more important than pre-anthesis biomass in relatively favourable environments (higher than 250 mm annual rainfall). The study also concluded that non-destructive methods of canopy cover measurements (digital photography and ceptometer) could replace direct biomass sampling at anthesis to predict seed yield of B. juncea canola in low rainfall environments. The canopy cover measurements were also associated with earliness in flowering. Heterosis of B. juncea canola was studied in three glasshouse experiments under well-watered and water deficit (from first open flower to maturity) conditions from 2012 to 2014. Two hybrids (HJM1Z-0027 and HJM1Z-2013) significantly out-yielded the control cultivar of B. juncea canola (OasisCL) and showed significant yield heterosis under water deficit conditions. Among the yield components, number of pods per plant was the most affected by water deficit whereas seeds per pod, thousand seed weight and harvest index were relatively stable. Earlier flowering with longer seed filling periods were also desirable traits for drought performance of the hybrids and parents. The study also compared four physiological traits (osmotic adjustment, leaf proline concentration, root depth and canopy temperature) for drought performance of B. juncea canola hybrids and parental lines in the glasshouse in 2013 and 2014. Canopy temperature of B. juncea canola hybrids was also measured in two field experiments at Horsham in 2014. The year 2014 was a dry year for Horsham. In the glasshouse, canopy temperature was negatively and consistently associated with seed yield in water deficit conditions. Root depth was not associated with yield under water deficit indicating that root depth was a constitutive trait or was a result of hybrid vigour of the hybrids. The field experiments also showed that seed yield was correlated with cooler canopy temperatures. B. juncea canola hybrids were evaluated under low rainfall environments of Victoria (Horsham, Beulah, Manangatang and Quambatook), South Australia (Lameroo, Minnipa, Lock and Mt Cooper) and New South Wales (Narrabri) in 2013 and 2014. The B. juncea canola hybrids were generally later flowering than the control cultivars of B. juncea canola and B. napus. Significant effects of location and genotype × location on flowering time indicated photoperiod sensitivity of the germplasm. Earliness in flowering was associated with improved seed yield of the hybrids. The hybrids consistently flowered earlier at Horsham than at other sites. A small number of hybrids significantly out-yielded all the control cultivars of B. juncea canola and B. napus at Horsham in 2014. The results indicated that B. juncea canola hybrids could be a potential Brassica oilseed crop in low rainfall environments if they are improved for better adaptation (earliness in flowering). The B. juncea canola hybrids were also subjected to assessment of seed and oil quality parameters. All the B. juncea canola hybrids maintained canola quality standard of less than 2% erucic acid and less than 30 µmol per g total glucosinolates at all the sites across Victoria, South Australia and New South Wales. With a wide genetic variation in oil and oleic acid content, the hybrids offered opportunities to select hybrids with better oil content and oleic acid than current B. juncea canola and B. napus control cultivars. Earliness in flowering was associated with improved oil content in the majority of the experiments (6 of 10) whereas the earliness in flowering was associated with improved oleic acid only in three experiments. The results indicated that hybrids of B. juncea canola could be a profitable Brassica oilseed crop in low rainfall environments of southern Australia from a yield and quality perspective. The study identified key yield components and plant traits important for yield under low rainfall environments. This is expected to be useful in breeding for juncea hybrids in future. As earliness in flowering had a strong positive effect on seed yield and oil content, future research should focus mainly on early flowering