Dryland Legume Pasture Systems: Boron tolerant annual medics

Part 1: Medic cultivars were grown in soil with high boron levels in a glasshouse, leaf damage symptoms recorded and cultivars allocated to different tolerance groups (Howie 2012).Part 2: The above identified that all spineless burr medic cultivars are susceptible to high boron levels. Screening wild accessions (supplied by the Australian Pasture Genebank) identified a burr medic accession with boron tolerance and vigorous growth. The boron tolerant accession was crossed with current spineless burr medic cultivars Scimitar and Cavalier. F2 plants with high early vigour were selected and a molecular marker used to identify homozygous boron tolerant plants. A single seed descent breeding method using speed breeding was used to obtain uniform lines. Lines were seed increased at Waite in 2018 and lines with the highest agronomic performance selected for 2019 field evaluation trials. A cohort of 16 boron tolerant lines along with their parents and barrel medic cultivars that differ in boron tolerance, were sown at Roseworthy and Minnipa. The trials were managed as best practice first year annual medics to maximise dry matter and seed production. Best practice consists of a high sowing rate (10 kg/ha), controlling broadleaf and grass weeds, monitoring and controlling insects and no grazing. Dry matter production was assessed and pods collected. Seed yield will be determined by April 2020.

第一部分：将苜蓿（Medic）品种种植于高硼（boron）水平的温室（glasshouse）土壤中，记录其叶片损伤症状，并将各品种划分为不同的硼耐受性分组（Howie, 2012）。
第二部分：前述研究表明，所有无刺蒺藜苜蓿（spineless burr medic）品种均对高硼环境敏感。通过对澳大利亚牧草基因库（Australian Pasture Genebank）提供的野生种质资源进行筛选，获得了一份兼具硼耐受性与旺盛生长特性的蒺藜苜蓿（burr medic）种质。将该硼耐受性种质与当前推广的无刺蒺藜苜蓿品种‘Scimitar’和‘Cavalier’进行杂交，筛选出苗期活力优异的F₂代植株，并利用分子标记鉴定出纯合硼耐受性植株。采用单粒传代结合快速育种技术，获得性状均一的育种株系。2018年于怀特（Waite）试验点对株系进行种子扩繁，筛选出农艺性状最优的株系用于2019年田间评价试验。选取16份硼耐受性株系及其亲本，以及硼耐受特性各异的截形苜蓿（barrel medic）品种，分别种植于罗斯沃西（Roseworthy）和明尼帕（Minnipa）试验点。试验按照一年生苜蓿第一年种植的最佳管理规范实施，以最大化干物质产量与种子产出。该规范具体包括：高播种密度（10 kg/ha）、阔叶与禾本科杂草防控、虫害监测与防治，且全程禁止放牧。研究人员已完成干物质产量测定与荚果收获，种子产量将于2020年4月前完成测定。