Factors related to productivity and persistence of lucerne (Medicago sativa) genotypes with different fall dormancy levels: a review

The lucerne productive and nutritional potential make it the most used forage legume worldwide. This wide use leads genetic improvement programs to increasingly select the main requirements for a given edaphoclimatic condition. However, in Brazil, the research on genetic improvement of lucerne has been limited over the years, which has hindered the production of this species and the domination of other legumes in animal production, as estilosantes and pigeon pea. This literature review aimed to present results from countries such as New Zealand and Australia that lead the world ranking, as weel as Argentina, in the cultivation of this crop and that can be used as showcase to understand the management of lucerne. From extensive bibliometry analyses in the period between 1963 and 2021, variables as persistence and phyllochron in these countries indicate that it is possible to produce lucerne with similar productivity, longevity and quality in Brazil. Nevertheless, to leverage this production, not only genetic improvement should be aimed, but also research and dissemination of knowledge on the ideal management of defoliation and, mainly, on the choice of the genotype and dormancy level to be cropped by the producer.

Whole-Genome Sequencing on 220 Alfalfa (Medicago sativa L.) Accessions Identified Loci Associated with Fall Dormancy

Fall dormancy (FD) is one of the most important traits of alfalfa (Medicago sativa) for cultivar selection to overcome winter damage. Regrowth plant height following autumn clipping is an indirect way to evaluate FD. Although transcriptomics, proteomics analysis, and QTL mapping have revealed some important genes correlated with FD, the genetic architecture of this trait is still unclear. There are no applicable genes or markers for selection, which hinders progress in the genetic research and molecular breeding for the trait. We conducted whole-genome sequencing (WGS) on 220 alfalfa accessions at 10x depth. Among the 875,023 SNPs, seven of them were associated with FD using genome-wide association study (GWAS). One SNP located on chromosome 6 is in linkage disequilibrium with dehydration-responsive element-binding protein 1C (DREB1C). Furthermore, seven DREB genes are clustered in this region, one of which has previously been shown to enhance freezing tolerance in the model plant Medicago truncatula. The candidate genes uncovered by our research will benefit the transgenic and CRISPR-Cas9 research of FD in alfalfa. This gene will also be useful for marker development and assisted selection of FD for alfalfa.

Dynamics of aerial and perennial biomass of two lucerne cultivars with different fall dormancy subject to two severities of cutting during the establishment phase

The aim of this study was to quantify the impact of two cutting severities on the dynamics of aerial and perennial (root plus crown) biomass of lucerne (Medicago sativa L.) plants of two cultivars of contrasting fall dormancy rating during the establishment phase. We worked at Unidad Integrada Balcarce with two cultivars of lucerne (non-winter dormant: FD10; semi-winter dormant: FD6) and two cutting severities (40 and 100 mm) defining four treatments (FD6-40 mm, FD6-100 mm, FD10-40 mm and FD10-100 mm) under a completely randomized design. In both cultivars, increasing cutting severity produced a reduction in leaf area and number of nodes in the residual, resulting in a reduced production of aerial biomass during regrowth, given a reduction on shoot number. On the other hand, the effect of increased cutting severity on perennial biomass was only observed in plants of FD10 cultivar. This cultivar showed less perennial biomass when cut at 40 mm than at 100 mm, while no differences were observed between cutting heights in FD6 cultivar.

Phenotypic Diversity and Productivity of Medicago sativa Subspecies from Drought-Prone Environments in Mediterranean Type Climates

The phenotypic diversity and productivity of a diverse alfalfa (M. sativa subspp.) panel of cultivars, landraces and wild relatives with putative drought tolerance were evaluated in two Mediterranean environments (central Chile and Southern Australia). In Chile, 70 accessions were evaluated in rainfed conditions and in Australia 30 accessions under rainfed and irrigated conditions, during three growing seasons. Large phenotypic variation was observed among and within subspecies for NDVI, stem length, intercepted PAR and forage yield. Principal component analysis indicated that the first two principal components (PC) accounted for 84.2% of total variance; fall dormancy, taxa, and breeding status were closely related to the agronomical performance of alfalfa accessions. Forage yield varied largely among accessions across years and locations. A linear relationship was found between annual forage yield and annual water added to the experiments (R2 = 0.60, p < 0.001). The GxE analysis for forage yield allowed the detection of the highest yielding accessions for each of the two mega-environments identified. The accessions CTA002 and CTA003 showed greater forage yield in both Chile and Australia environments. It is concluded that new breeding lines derived from crosses between cultivated alfalfa (M. sativa subsp. sativa) and wild relatives belonging to the primary (M. sativa subsp. falcata) and tertiary (M. arborea) gene pool, achieve outstanding agronomical performance in drought-prone environments.

Whole-Genome Sequencing on 220 Alfalfa (Medicago sativa L.) Accessions Identified Association of DREB1C Gene with Fall Dormancy Height

Fall dormancy (FD) is one of the most important traits of alfalfa (Medicago sativa) for cultivar selection to overcome winter stress. Although transcriptomics, proteomics analysis, and QTL mapping have revealed some important genes correlated with FD, the genetic architecture of this trait is still unclear. There are no applicable genes or markers for selection, which hinders progress in the genetic research and molecular breeding for the trait. We conducted whole-genome sequencing (WGS) on 220 alfalfa accessions at 10x depth. Among the 875,023 SNPs, four of them were associated with FD height using GWAS. One SNP located on chromosome 6 is in linkage disequilibrium with dehydration-responsive element-binding protein 1C (DREB1C). Furthermore, seven DREB genes are clustered in this region, one of which has previously been shown to enhance freezing tolerance in the model plant Medicago truncatula. The candidate genes uncovered by our research will benefit the transgenic and CRISPR-Cas9 research of FD in alfalfa. This gene will also be useful for molecular marker development and marker-associated breeding of FD for alfalfa.

Resistance to the alfalfa weevil in the Iranian collection of Medicago sativa

The Iranian collection of Medicago sativa (alfalfa, 502 accessions) was evaluated under field conditions to identify variation in resistance to the alfalfa weevil (Hypera postica Gyllenhal) between accessions over 4 years. Twenty-one accessions were identified as resistant (score 3) to semi-resistant (score 5) based on K-means cluster analysis. These materials were grouped into 10 groups by means of Duncan's Multiple Range Test. Susceptibility to alfalfa weevil was significantly correlated with some of the agro-morphological traits such as plant height (r = 0.314, P<0.01), regrowth rate (r = 0.435, P<0.01) and fall dormancy score (r = 0.284, P<0.01). In general, the resistant germplasm originated from elevated regions at high latitudes, where a co-evolution between the plant and the pest may have taken place. Multiple regression analysis showed a positive linear relationship between susceptibility to the alfalfa weevil and traits such as growth habit, plant height, length and width of the central leaflet and regrowth rate. The resulting bi-plot based on factor analysis ranked accessions for susceptibility to the pest. The identified germplasm should prove useful in alfalfa breeding programs to develop accessions resistant to the alfalfa weevil.

Contribution of Mitochondrial Structure and Respiratory Metabolism to The Cold-Resistance of Alfalfa Seedling Root

Background: Fall dormancy of alfalfa is significantly associated with its cold tolerance, while root, the main body of alfalfa for overwintering, is critical for the cold resistance of alfalfa. The effect of low temperature on mitochondrial ultrastructure and respiratory metabolism of alfalfa seedling root with different fall dormancy was examined, to study the root cold resistance mechanism by which fall dormancy affects alfalfa cold tolerance. Results: Low temperature induced mitochondrial swelling, and the decline of ATP and accumulation of H 2 O 2 in alfalfa seedling root. Both the Cytochrome pathway (CP) and Alternative pathway (AP) respiratory rate were restrained and mETC complex I, II, III and IV activities were inhibited directly by low temperature in both kinds of alfalfa seedling root, while the decline of mETC complex II and III activities were more serious in Gannong No. 5. These results indicated that the damage of mitochondrial structure and the inhibition of mETC complex I , II, III and IV activities directly by low temperature declined the ATP synthesis and aggravated the ROS accumulation, which inhibit the growth of alfalfa seedling root. Moreover, the lower damage on mitochondrial structure and mETC complex II, III activities and higher the percent of AP to total respiratory rate lead to the lower ATP lack and H 2 O 2 accumulation, which contributed to the root growth of Xinmu No.4 seedling. Conclusions: Low sensitivity of mitochondrial structural stability and mETC complex II, III and Alternative respiration to low temperature contributed to the root cold resistance of alfalfa with low fall dormancy grade.

Correlation Analysis of Alfalfa Varieties Based on Production Performances, Winter Survival Rates and Fall Dormancies

Selection for fall dormancy (FD) in alfalfa can impact other traits, such as dry matter yield (DMY), winter survival rate (WSR) and chemical compositions. Nine alfalfa varieties were mowed during the early flowering stage from 2015 to 2018. The results showed that the WSRs of both Zhongmu No. 2 and Caoyuan No. 3 exceeded 95% and there was a significant negative correlation between the FD rating and WSR (-0.988; P less than 0.01). The four-year average DMY of Zhongmu No. 2 was the highest (11,912 kg ha-1). The crude protein contents of Caoyuan No. 3 and Zhongmu No. 2 were both greater than 20%. Zhongmu No. 2 had the lowest acid detergent fiber (30.2%) and neutral detergent fiber (48.4%) contents as well as the highest relative feed values (126). Zhongmu No. 2, Adrenalin, Gold Empress and Caoyuan No. 3 (FD 1-4) were the optimum alfalfa varieties for planting in Hohhot, Inner Mongolia, China.