Publications

Additional file 1: Table S1. The SNPâ s and their alleles in tolerant and susceptible bulk.

Time of flowering is a key adaptive trait in plants and is conditioned by the interaction of genes and environmental cues including length of photoperiod, ambient temperature and vernalisation. Here we investigated the photoperiod responsiveness of summer annual-types of Brassica napus (rapeseed, canola). A population of 131 doubled haploid lines derived from a cross between European and Australian parents was evaluated for days to flowering, thermal time to flowering (measured in degree-days) and the number of leaf nodes at flowering in a compact and efficient glasshouse-based experiment with replicated short and long day treatments. All three traits were under strong genetic control with heritability estimates ranging from 0.85-0.93. There was a very strong photoperiod effect with flowering in the population accelerated by 765 degree-days in the long day versus short day treatments. However, there was a strong genetic correlation of line effects (0.91) between the long and short day treatments and relatively low genotype x treatment interaction indicating that photoperiod had a similar effect across the population. Bivariate analysis of thermal time to flowering in short and long days revealed three main effect quantitative trait loci (QTLs) that accounted for 57.7% of the variation in the population and no significant interaction QTLs. These results provided insight into the contrasting adaptations of Australian and European varieties. Both parents responded to photoperiod and their alleles shifted the population to earlier flowering under long days. In addition, segregation of QTLs in the population caused wide transgressive segregation in thermal time to flowering. Potential candidate flowering time homologues located near QTLs were identified with the aid of the Brassica rapa reference genome sequence. We discuss how these results will help to guide the breeding of summer annual types of B. napus adapted to new and changing environments.

Developing new perennial pasture legumes for low-P soils is a priority for Australian Mediterranean agro-ecosystems, where soil P availability is naturally low. As legumes tend to require higher P inputs than non-legumes, the ability of these plants to fix N2 under varying soil P levels must be determined. Therefore, the objective of this study was to investigate the influence of soil P supply on plant N status and nodule formation in 11 perennial legumes, including some novel pasture species. We investigated the effect of applying soil P, ranging from 0 to 384 µg P/g dry soil, on plant N status and nodulation in a glasshouse. Without exogenous P supply, shoot N concentration and N : P ratio were higher than at 6 µg P/g soil. Shoot N concentration and N : P ratio then changed little with further increase in P supply. There was a close positive correlation between the number of nodules and shoot P concentration in 7 of the 11 species. Total nodule dry weight and the percentage of plant dry weight that consisted of nodules increased when P supply increased from 6 to 48 µg P/g. Without exogenous P addition, N : P ratios partitioned into a two-group distribution, with species having a N : P ratio of either >70 or <50 g/g. We suggest that plants with a high N : P ratio may take up N from the soil constitutively, while those with a low N : P ratio may regulate their N uptake in relation to internal P concentration. The flexibility of the novel pasture legumes in this study to adjust their leaf N concentrations under different levels of soil P supplements other published evidence of good growth and high P uptake and P-use efficiency under low soil P supply and suggests their potential as pasture plants in low-P soils in Australian Mediterranean agro-ecosystems warrants further attention.

Whether continuous ridge–furrow plastic film mulch (PM) and flat planting with PM is sustainable for soil water status and yield remain unknown. The study investigated effects of ridge–furrow PM applied in spring (RFMS) or autumn (RFMA), flat planting with no mulch (CK), flat planting with 60% mulch in spring (MS) or autumn (MA) on soil water and maize yield from 2016 to 2019. High yields in RFMA resulted from high soil water storage (SWS) consumption in 0–220 cm soil layer during the growing season, with main water supply for early plant growth coming from 0 to 80 cm layer and can be recovered from rainfall during later in the growing season. From 80 to 220 cm, SWS declined during growing season but recovered during next fallow season. The 2016 growing season had the lowest precipitation, and RFMA and MA had significantly more deep soil water consumption, which was replenished to normal levels in the following fallow season of 2016–2017. After four growing seasons, all PM treatments did not reduce deep soil water, compared to CK, or follow a declining trend over time, i.e., continuous cultivation with PM on Loess Plateau did not reduce soil water status.

Abstract Brassica rapa L. is a genetically diverse parent species of the allotetraploid species, oilseed rape ( B. napus ) and a potential source of drought tolerance for B. napus . We examined the effect of a 13‐day drought stress period during the early reproductive phase, relative to a well‐watered (WW) control, on subsequent growth and development in nine accessions of B. rapa and one accession of Brassica juncea selected for their wide morphological and genetic diversity. We measured leaf water potential, stomatal conductance, water use, and leaf and bud temperatures during the stress period and aboveground dry weight of total biomass at maturity. Dry weight of seeds and reproductive tissue were not useful measures of drought tolerance due to self‐incompatibility in B. rapa . The relative total biomass (used as the measure of drought tolerance in this study) of the 10 accessions exposed to drought stress ranged from 47 % to 117 % of the WW treatment and was negatively correlated with leaf‐to‐air and bud‐to‐air temperature difference when averaged across the 13‐day stress period. Two wild‐type ( B. rapa ssp. sylvestris ) accessions had higher relative total and non‐reproductive biomass at maturity and cooler leaves and buds than other types. We conclude that considerable genotypic variation for drought tolerance exists in B. rapa and cooler leaves and buds during a transient drought stress in the early reproductive phase may be a useful screening tool for drought tolerance.

The co-application of biochar and fertiliser has emerged as a strategy for improving soil quality and crop growth; however, the impact of the type of fertiliser added with biochar to the soil on leaching and retention of nutrients is not well studied. In this study, a leaching experiment was undertaken using a series of column lysimeters incorporating a wheat straw biochar (WSB) and two fertiliser types—chemical fertiliser (CF), or rock mineral fertiliser (MF). The results showed that CF and MF leached a similar amount of NH4+ with or without WSB, but the NO3– leaching occurred from CF-treated soil which was decreased by CF + WSB application. In contrast, NO3– leaching was not affected by WSB in MF-treated soil. Both CF and MF with or without WSB increased the cumulative leaching of P and K. Nevertheless, WSB application increased soil P and K contents after leaching, which was attributed to intrinsic nutrient release from biochar. Shoot growth and P and K uptake also increased with biochar amendment, whereas root growth and N uptake did not change. Therefore, the results highlight that biochar addition can improve nutrient retention and plant growth by reducing nutrient leaching, mainly dependent on biochar and fertiliser type combination used. It suggests that the adsorption properties of biochar for nutrient retention and subsequent release need to know before their broad application to soils as amendments.

The pea weevil, Bruchus pisorum, is one of the most intractable pest problems of cultivated field pea (Pisum sativum) in the world. Pesticide application, either as a contact insecticide spray to the field pea crop or fumigation of the harvested seed, is the only available method for its control. The aim of the study was to develop a quick and reliable method to screen for pea weevil resistance and increase efficiency in breeding for this important trait. Backcrossed progenies derived from an interspecific cross between cultivated field pea and its wild relative (Pisum fulvum, source of resistance for pea weevil) were subjected to natural infestation in field plots. Mature seeds were hand-harvested, stored to allow development of adult beetles, and then separated into infested and non-infested using a density separation method in 30% caesium chloride (CsCl). Susceptibility and resistance of the progenies were calculated based on this method and further confirmed by a glasshouse bioassay. Resistance in backcross populations improved considerably through selection of resistant lines using the density separation method. We found that the method using CsCl separation is a useful tool in breeding for pea weevil resistance. We were able to introgress pea weevil resistance from P. fulvum into cultivated field pea through backcrossing to produce several advanced pea weevil resistant lines following this procedure.