- Meadowfoam (Limnanthes alba) is an oilseed crop with unique chemical characteristics. The ability to identify physiological maturity (PM) and harvest maturity HM of the crop would permit timely harvest of high quality seeds. However, changes of oil contents, fatty acid profile and glucosinolate contents, as well as seed quality during these maturity stages are unknown.
The objectives of this research were to: 1) determine the PM (highest dry matter content) and HM (seed moisture content 16% or less) of two meadowfoam cultivars Ross and MF189, using physiological and morphological indicators, 2) measure seed quality (germination and vigor) at PM and HM, 3) assess oil contents and fatty acid profile at different stages of seed development, 4) evaluate glucosinolate levels at different seed maturity stages, 5) explore methods of breaking dormancy in freshly harvested seeds, and 6) genetic study to screen for high oil content genotypes using single nucleotide polymorphism (SNP) markers linked with high oil content. Ross and MF189
meadowfoam cultivars were used in studies 1 to 5 at two locations, Hyslop and Lewis Brown farms near Corvallis, Oregon. Studies were repeated for two years 2013 and 2014. Seeds from each cultivar were sampled twice each week from anthesis until HM. Oil contents during different stages of seed development were determined using NMR. The fatty acid profile was determined by ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometer (UPLC-QTOF-MS). The glucosinolate (GSL) content was determined using HPLC. Seed viability was assessed by the tetrazolium test (TZ) and the standard germination test (SGT), and seed vigor was measured by the accelerated aging test (AAT) during different stages of maturity.
The time from anthesis to PM ranged between 33 and 40 d. The time from PM to HM ranged between 7 and 11 d, depending on the weather conditions, cultivars and locations.
At PM, seeds turned to brownish green to light brown and could be marked with fingernail and the canopy was dark green. At HM, seeds were brown, hard, and canopy turned brown. At PM, the maximum seed dry weight (SDW) ranged between 833 to 1036 mg per 100 seeds. The SDW did not change significantly between PM and HM. At PM, seed moisture content (SMC) ranged from 280 to 430 g kg⁻¹, and from 80 to 160 g kg⁻¹ at HM. Seeds reached maximum viability at HM with an average of 94% compared to 88% at PM as measured by the TZ test.
The viability by SGT ranged between 67% and 86%. The difference in results between TZ and SGT, to a large extent, was due to seed dormancy. The AAT was not reliable test for assessing seed vigor of young seeds, probably due to the effect of high temperature and relative humidity.
The oil contents at PM ranged from 27.6% to 28.5% at Lewis Brown farm, and from 25.4% to 26.2% at Hyslop farm in 2013, and from 26.6% to 28.9% at Lewis Brown farm and from 27.9% to 28.8% at Hyslop farm in 2014. The oil contents at HM ranged from 27.8% to 28.8% at Lewis Brown farm, and from 25.1% to 26.3% at Hyslop farm in 2013, and from 28.7% to 29.3% at Lewis Brown farm and from 28.2% to 28.9% at Hyslop farm in 2014.
Seed oil contained long-chain fatty acids including 20:1, 22:1(5), 22:1(13), and 22:2(5, 13). The contents of fatty acids did not differ significantly after reaching PM until HM. Fatty acid content of 20:1 increased dramatically with an average of 8.9% at 12 DAA to 21.1% at PM in both cultivars and years. The average contents of fatty acid 22:1(5) from 12 DAA to PM ranged from 0.9% to 5.2% and fatty acid 22:1(13) ranged from 2.4% to 7.7% in both cultivars and years. The average content of fatty acid 22:2 (5, 13) ranged from 3.0% to 12.8% in both cultivars and years. These results suggest that meadowfoam seed can be harvested at PM or at HM without significant change in seed oil content or fatty acid composition.
Seed meal contains glucosinolate (GSL), which have allelopathic effects and have potential for use as bio-herbicides in organic farming. The GSL contents of Ross at Lewis Brown farm were 0.0 μmol g⁻¹ (seed dry wt. basis) starting from seed formation until PM. At HM, when SMC was approximately 15%, the GSL content reached an average of 97.8 μmol g⁻¹ in 2013, and 81.9 μmol g⁻¹ in 2014, respectively. A similar trend was observed
in MF189 in the same location, but the content at HM was 103.9 μmol g⁻¹ in 2013, and 89.4 μmol g⁻¹ in 2014, respectively. Similarly, at Hyslop farm, the GSL content of Ross at HM remained 0.0 μmol g⁻¹ until PM, and then increased to 103.7 μmol g⁻¹ at HM in 2013, and 69.2 μmol g⁻¹ at HM in 2014, respectively. Likewise, it remained 0.0 μmol g⁻¹ at PM, and jumped to 85.9 and 83.7 μmol g⁻¹ at HM in 2013, and 2014 respectively for MF189 at Hyslop farm. The GSL contents reached highest levels at HM in both cultivars, locations, and years. Therefore, if the objective is to use the meal as a bioherbicide, it is recommended not to harvest the crop before HM.
Freshly harvested seeds of meadowfoam may have low germination because of dormancy. Breaking dormancy treatments included: 1) pre-chilling seeds at 2ºC and 5ºC for 5 d, 2) heat at 45ºC for 7 d and 50ºC for 3 d, 3) soaking for 24 h at room temperature (21ºC), 4) germinating seeds with gibberellic acid solution 0.05% (500 ppm), and 5) untreated control. After applying the dormancy breaking methods, seeds were germinated at 10ºC for 14 d. Seeds treated with 0.05% gibberellic acid solution and seeds treated with pre-heat at 45ºC for 7 d resulted in an average germination of 94% for MF189 grown in Lewis Brown in both years, and 90% for seeds treated with GA and 91% seeds treated with pre-heating treatment in Ross. Seeds that were grown at Hyslop farm, which received the same gibberellic acid and pre-heating treatments resulted in an average germination of 83% for MF189 and 84% for Ross. The higher germination at Lewis Brown farm compared to Hyslop farm may be due to better environmental and soil fertility conditions during the growing seasons.
Genotypes with high and low oil content were selected from OMF58 C6 and GJPool. To identify and validate single nucleotide polymorphism (SNP) markers linked with high oil content, ninety-five samples were genotyped using genotyping by sequencing (GBS) from Illumina HiSeq 2000 sequencer. Trait analysis by association, evolution and linkage (TASSEL) universal network enable analysis kit (UNEAK) generated 5180 SNP markers. A genome wide association analysis was conducted for oil content and SNP markers using TASSEL 5.0 software. The most significant markers were validated using KBiosciences allele specific polymorphism. The studies showed that GBS can be used as a powerful approach to discover SNPs in meadowfoam.