The widespread application of ‘two-line’ hybrid rice, based on temperature- and photoperiod-sensitive genic male-sterile lines, plays an important role in ensuring global food security. Such lines are fertile in short-day/low-temperature conditions when used for self-breeding, and sterile in long-day/high-temperature conditions when used for hybrid seed production. However, fertility instability and low hybrid seed production of sterile lines are urgent problems. The aim of this study was to increase the stability of pollen sterility by studying the critical sterile-inducing temperature and stigma vitality of 97 newly selected male-sterile lines in China from 2017 to 2020. Sterility gene source analysis showed that 89.7% of the materials contained the tms5 sterile gene. After 6 days of treatment at 23.5°C during the reproductive period, 42 male-sterile lines were sterile. After 10 days of treatment at 23.5°C, the sterility of 12 sterile lines remained stable, indicating a high level of safety for hybrid seed production. After 10 days of low-temperature treatment at 19°C, the fertile pollen rate of 47 of the 97 sterile lines was >70%, indicating a high level of seed reproduction safety. Only six of these 47 male-sterile lines could maintain low fertility after 10 days of treatment at 23.5°C, indicating that they could be used safely for both hybrid seed production and sterile line reproduction. The results of delayed pollination showed that among the six lines, only Zhong 7S had high stigma vitality, and BYXA1S and H10S-2 had medium stigma vitality. Therefore, those three sterile lines have the potential for safe hybrid seed production and high-yield seed reproduction. Based on our research, we propose a new breeding standard of dual-purpose male-sterile lines to promote the development of two-line hybrid rice.

Context. In recent years, direct-seeded rice (DSR) cultivation methods have been widely adopted in Asia.

Aims. The objective of this study was to evaluate the grain yield, nitrogen use efficiency and associated plant traits of DSR in northeastern China.

Methods. A 2-year field experiment was conducted using two varieties under three cultivation methods (1) conventional transplanted rice (CTR); (2) wet direct-seeded rice (WDSR); and (3) dry direct-seeded rice (DDSR).

Key results. The grain yield of CTR and DSR ranged from 10.16 to 9.39 t ha⁻¹ and from 8.85 to 6.90 t ha⁻¹, respectively, accross varieties and years. The wide difference was attributed to the differences in spikelet number per panicle and biomass. Compared with the CTR, the DSR decreased the spikelet number per panicle, which resulted in lower spikelet number per m². Meanwhile, a significant positive correlation was observed between spikelet number per m² and nitrogen uptake. The nitrogen uptake of CTR and DSR ranged from 151 to 153 kg ha⁻¹ and from 96 to 132 kg ha⁻¹, respectively. The root biomass, root length and zeatin + zeatin riboside contents in roots were higher in CTR than DSR, which contributed to the higher nitrogen uptake.

Conclusions. These results suggest that DSR reduced nitrogen uptake, thereby resulting in decreased number of spikelets per panicle, and hence lower rice grain yield.

Implications. These findings have highlighted the deficiencies in direct seeded rice system, and further research is required to overcome these deficiencies.

Context. Annual ryegrass (Lolium rigidum) is a major weed of crop production in southern Australia that readily develops resistance to herbicides. Resistance increases both yield losses and control costs associated with this species.

Aims. This study aimed to gauge the extent and distribution of resistance to herbicides in L. rigidum across south-eastern Australian grain production systems by collecting seed from randomly selected fields.

Methods. A total of 1441 weed populations were collected through random surveys conducted over 5 years across 13 agricultural regions of four states with these samples then tested for resistance to eight herbicides from six modes of action.

Key results. Resistance to diclofop-methyl and sulfometuron-methyl was most common, being present in 64% and 63% of populations respectively. Glyphosate resistance was present in 4% of populations collected. Only 15% of populations collected were susceptible to all herbicides tested. Large differences in resistance occurred between the 13 regions surveyed with resistance to diclofop-methyl ranging from 15% to 86% of populations and sulfometuron-methyl from 12% to 96%. Resistance to post-emergent herbicides tended to be higher than pre-emergent herbicides. Multiple resistance was common with 60% of populations collected having resistance to two or more herbicide modes of action.

Conclusions. There were significant differences in the extent of multiple resistance in L. rigidum populations collected from individual regions suggesting that the rates of resistance evolution have differed between regions.

Implications. The high incidence of herbicide resistance in L. rigidum populations randomly collected from south-eastern Australian cropping fields highlights the need for the adoption of additional weed control practices to mitigate the impact of this species on grain production systems.

Context. Optimising nitrogen (N) management strategies for drill-sown rice crops is essential for minimising input costs for growers and reducing the environmental impact of rice production.

Aims. The study aimed to determine the recovery of fertiliser-N in drill-sown Australian rice crops, following current N fertiliser recommendations where two-thirds of the N is applied at sowing (pre-flood) and one-third at panicle initiation.

Methods. ¹⁵N-labelled urea was used to quantify N recovery by field-grown rice crops on a Sodosol and a Vertosol, and to determine the contributions of fertiliser-N applied pre-flood vs that applied at panicle initiation to total N fertiliser recovery on the Vertosol.

Results. Recovery of ¹⁵N fertiliser in grain + straw was ∼50% of applied N on both soils, with a further 20% recovered from roots and soil to a depth of 30 cm. Recovery of N fertiliser applied at panicle initiation (59%) was significantly higher than of N fertiliser applied pre-flood (43%), likely due to the presence of actively growing roots and higher plant N demand. Crops that received N fertiliser took up more native soil N than unfertilised crops on the Vertosol; hence, apparent fertiliser N recoveries were 10–15% higher than N fertiliser recovery determined using ¹⁵N-labelled urea.

Conclusions. The recovery of 50% of fertiliser-N in aboveground plant material indicates that N fertiliser use efficiency in drill-sown rice is similar to that of dryland cereal crops in Australia when best management practice guidelines for N fertiliser use are followed.

Context. Rotations in rainfed farming systems of southwest Australia have shifted towards intensified cropping and it is necessary to reassess soilborne pathogens and plant parasitic nematodes within this context.

Aims. We tested the hypothesis that these recent changes in rotations and agronomy have altered the efficacy with which rotations reduce the incidence of common root pathogens and plant parasitic nematodes.

Methods. We tracked changes in common pathogen DNA in soil and the incidence and severity of crop root damage in 184 paddocks, over 6 years from 2010 to 2015, and related this to farmer practices.

Key results. Overall, severe root damage was rare, with 72% of plant samples showing no damage or only a trace and only 1% severely damaged. We found that the reduction of paddocks in pasture and resultant very low weed populations, combined with early sowing, reduced persistence of pathogens and nematode pests. But some aspects of crop management had the opposite effect: high rates of herbicide, increased frequency of cereals and canola at the expense of lupin and increased N fertiliser use.

Conclusions. Current agronomic practices and the frequency of non-host crops in rotations appear to be effective in controlling common root pathogens and plant parasitic nematodes. But the aspects of agronomic management that increased populations of pathogens should be applied cautiously.

Implications. Studies such as this that link multiple productivity constraints, such as pathogens and nematode pests, weeds and nutrients, to management practices are important to understand the sustainability of current or proposed production methods.

Context. Yield losses in lentil (Lens culinaris ssp. culinaris Medik.) caused by weeds are estimated at 20–80%. In the absence of effective broad-spectrum herbicides, the menace of weed has emerged as a serious yield constraint in lentil.

Aims. Identification of tolerance to two broad-spectrum post-emergence herbicides, imazethapyr and metribuzin.

Methods. 221 lentil accessions were screened at the experimental research station of the International Center for Agricultural Research in the Dry Areas, Terbol (Lebanon) over four crop seasons (2014/15–2018/19). During the 2014/15 season, a preliminary screening experiment was conducted with 221 lentil accessions in an alpha lattice design with two replications, where accessions were treated at the pre-flowering stage at 150% of the recommended dose of imazethapyr (112.5 g active ingredient/ha) or metribuzin (315 g active ingredient/ha). Based on the preliminary results, 38 accessions were selected for further evaluation. In subsequent testing, the selected accessions were screened at 100% and 150% of the recommended doses of imazethapyr or metribuzin.

Key results. Herbicide treatments delayed the flowering time and maturation of tested lentil accessions. The plant height of selected tolerant accessions was reduced by 15% and 8% in the plots treated by imazethapyr and metribuzin, respectively. Reduction index (RIsy) was an effective tool to select for herbicide tolerance. Stability analysis indicated that two accessions (IG4400 and IG5722) performed under high rainfall environments while two other accessions (IG323 and IG4605) were adapted to low rainfall environments.

Conclusions. Four accessions (IG323, IG5722, IG4400, IG4605) were identified as independently tolerant to metribuzin and imazethapyr.

Implications. The identified herbicide-tolerant accessions can be used to develop herbicide-tolerant cultivars.

Context. Soybean cyst nematode is the most important pest of soybean (Glycine max (L.) Merr.) worldwide, causing serious yield losses. Lignin is a vital component of the cell wall that can provide resistance to cyst nematode. O-Methyltransferase (OMT) is a key enzyme involved in lignin metabolism in the phenylalanine pathway.

Aims. In this study, the soybean OMT gene family was systematically identified, and the expression response of GmOMT to abiotic and cyst nematode stresses was investigated.

Methods. In total, 67 OMT genes were obtained from the soybean genome through conserved structural domain alignment. GmOMT expression under abiotic stress of soybean was examined based on next-generation RNA sequencing (RNA-Seq). Comprehensive analysis of the genes was conducted, including gene structure, conserved structure, affinity, chromosomal localisation, functional prediction, Gene Ontology analysis, Kyoto Encyclopedia of Genes and Genomes analysis, promoter analysis, and expression pattern analysis.

Key results. The 67 GmOMT genes were identified and distributed among the 19 chromosomes. The GmOMT genes were classified into two categories: CCOMT subfamily and COMT subfamily. GmOMT genes from the same family shared similar gene structures and conserved structural domains, which have undergone strong purifying selection during evolution. The presence of multiple cis-responsive elements in the promoters of GmOMT genes suggested that members of the soybean OMT family may be involved in growth and developmental activities and resistance to stress in soybean.

Conclusions. GmOMT expression under abiotic stress showed that some of the genes may play a role in abiotic stress. Of them, GmCCOMT3 and GmCCOMT7 were closely associated with lignin synthesis based on both RNA-Seq and quantitative real-time PCR analysis.

Implications. These findings are valuable for elucidating the function of GmOMT in lignin metabolism and the relationship with SCN resistance.

Context. Enhancing grain yield and micro-nutrition contents in rice (Oryza sativa L.) through biofortification breeding is an efficient way to address micro-nutrient deficiencies in human.

Aims. QTL mapping for grain yield and micro-nutritional traits is prerequisite for developing new rice varieties.

Methods. QTLs for grain yield and micro-nutritional traits were identified using a backcross inbred lines (BIL) derived from an interspecific backcross of Xieqingzao B and Dongxiang wild rice (Oryza rufipogon Griff.).

Key results. A total of 16 and 29 QTLs were identified for grain Zn, Mn and Cu contents, including three for brown and milled rice, 10 for brown rice only, and three for milled rice only, and for grain related traits, respectively. Among grain micro-nutrient QTLs, three QTLs, qMn4, qMn6.2 and qZn6.2, showed genetic effects on both brown and milled rice.

Conclusion. Sixteen QTLs for grain related traits and eight QTLs for grain micro-nutrient content had O. rufipogon favourable alleles. A total 31 QTLs were clustered eight chromosomal regions. Importantly, two clusters, qZn4/qGW4 and qZn6.2/qMn6.2/qCu6.3/qGYP6.2, had the favourable wild alleles, suggesting that O. rufipogon alleles had synergistic effects on both yield component and micro-nutrient content.

Implications. These candidate QTLs could be useful for the improvement of grain yield and micro-nutrients through QTL pyramiding.

Context. Different environmental factors occurring during seed development could be responsible for maternal effects on seed dormancy. Understanding these effects on Digitaria sanguinalis (L.) Scop seeds would help to predict it’s seedling emergence.

Aims. To study D. sanguinalis maternal effects on seed dormancy level under environmental variations imposed by soybean (Glycine max L.) crop, changing (1) nutrient availability, (2) radiation and (3) soybean canopy presence during different phenological stages of the weed.

Methods. Field plots experiments under semi-controlled conditions were established to reach these objectives.

Key results. Among different factors evaluated, radiation was the most important factor, mainly during the reproductive stages of the weed. The reduction in solar radiation received by the mother plant diminished seed dormancy level even in those panicles receiving full sunlight in shaded plants.

Conclusions. Results suggest that solar radiation and temperature operate together in the mother plants to modify seed dormancy level.

Implications. Crop management decisions such as long crop cycles, late sowing date and narrow inter-row distances would reduce seed dormancy level and would anticipate a concentrated seedling emergence of the weed.