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Alfalfa leaf rust caused by the fungal pathogen Uromyces striatus compromises forage yield and quality. We investigated the genetic basis of leaf rust resistance in alfalfa using an F1 mapping population segregating for resistance to the disease in addition to segregation for fall dormancy (FD) and winter hardiness (WH). The objective of this work was to map quantitative trait loci (QTL) associated with alfalfa leaf rust resistance using genotyping-by-sequencing (GBS) SNP markers in the biparental F1 mapping population. The female parent 3010 displayed susceptibility to rust while the male parent CW 1010 was moderately resistant. The mapping population consisted of 184 F1 progenies that were planted with the parents in a randomized complete block (RCBD) design with three replications at Watkinsville and Blairsville, GA. Four clones generated from stem cuttings of each genotype were planted in each replication. Phenotyping rust severity (RS) was based on the NAAIC visual rating scores of 1–5. RS and FD exhibited a negative phenotypic correlation (r = −0.26). RS and WH also exhibited a negative correlation (r = −0.27) suggesting that the dormant and winter hardy genotypes were more susceptible to leaf rust than the non-dormant and cold sensitive. Four QTL for alfalfa leaf rust resistance and one QTL for rust susceptibility were identified in the CW 1010 genetic map while three QTL for rust susceptibility were identified in the 3010 parent. The most important QTL Us-RustR1 explained 13% (R2 = 0.13) of the phenotypic variance. This study suggests that leaf rust resistance in alfalfa is most likely incomplete and has polygenic inheritance. Comparative genome analysis of QTL regions using sequences of significant SNPs revealed homology to M. truncatula sequences that were previously reported for their role in plant defense mechanisms. Validation of the QTLs in different genetic backgrounds as well as fine mapping of the QTL regions would be the next step of this research. The markers presented in this study would be valuable resources for alfalfa genetic improvement via marker-assisted selection (MAS). • Eight QTLs associated with alfalfa rust resistance were detected using GBS of a pseudo-testcross mapping population. • In this population, the inheritance of rust resistance caused by Uromyces striatus was polygenic and incomplete. • The sequences of QTL SNPs exhibited homology with genes associated with fungal diseases defense in M. truncatula. • Alfalfa rust severity correlated with FD and WH, but the relationship might be specific to the population. [ABSTRACT FROM AUTHOR]

Understanding key adaptation traits is crucial to developing new cultivars with broad adaptations. The main objective of this research is to understand the genetic basis of winter hardiness (WH) and fall dormancy (FD) in alfalfa and the association between the two traits. QTL analysis was conducted in a pseudo-testcross F1 population developed from two cultivars contrasting in FD (3010 with FD = 2 and CW 1010 with FD = 10). The mapping population was evaluated in three replications at two locations (Watkinsville and Blairsville, GA). FD levels showed low to moderate correlations with WH (0.22–0.57). Assessing dormancy in winter is more reliable than in the fall in southern regions with warm winters. The mapping population was genotyped using Genotyping-by-sequencing (GBS). Single dose allele SNPs (SDA) were used for constructing linkage maps. The parental map (CW 1010) consisted of 32 linkage groups spanning 2127.5 cM with 1377 markers and an average marker density of 1.5 cM/SNP. The maternal map (3010) had 32 linkage groups spanning 2788.4 cM with 1837 SDA SNPs with an average marker density of 1.5 cM/SNP. Forty-five significant (P < 0.05) QTLs for FD and 35 QTLs for WH were detected on both male and female linkage maps. More than 75% (22/28) of the dormancy QTL detected from the 3010 parent did not share genomic regions with WH QTLs and more than 70% (12/17) dormancy QTLs detected from CW 1010 parent were localized in different genomic regions than WH QTLs. These results suggest that the two traits have independent inheritance and therefore can be improved separately in breeding programs. [ABSTRACT FROM AUTHOR]

Molybdenum (Mo) is a critical micronutrient for nitrogen (N) fixation in legumes. Low pH limits the availability of Mo, thereby reducing nodulation and N fixation. This study investigates the effect of Mo supplementation on alfalfa nodulation and its correlation with root and shoot biomass in low-pH soil. Three experiments were conducted in the greenhouse, involving 14 genotypes of alfalfa subjected to four different treatments, unlimed low-pH soil (5.2) with Mo applied (lithium (Li)−Mo+), low-pH soil (5.2) without Mo (Li−Mo−), limed soil (pH 7.3) with Mo applied (Li+Mo+), and limed soil (pH 7.3) without Mo (Li+Mo−). Foliar application of Mo resulted in a significant increase in nodule counts in the 14 alfalfa cultivars grown in low-pH soil (5.2) even though to a lesser extent than in limed soil with neutral pH (7.3). The increase in number of nodules correlated positively with plant root weight and upper plant biomass. [ABSTRACT FROM PUBLISHER]

In the article [1], in 'Methods' section and 'G x E and heritability' subsection, there is an error in the formula of heritability (H2). [ABSTRACT FROM AUTHOR]