Delineating Marker-trait Associations for Fusarium Wilt in Chickpea using Axiom® Cicer SNP Array

Fusarium wilt (FW) caused by the Fusarium oxysporum f. sp. ciceri is a devastating disease of chickpea (Cicer arietinum L.). To identify promising resistant genotypes and genomic loci for FW resistance, a core set of 179 genotypes of chickpea was tested for FW reactions at seedling and reproductive stages under field as well as controlled conditions in the greenhouse. Our results revealed that at seedling stage, most of the genotypes were found resistant whereas, at the reproductive stage majority of the genotypes were found susceptible. Genotyping using a 50K Axiom®Cicer SNP Array and trait data of FW together led to the identification of 26 significant (p≤E-05) marker-trait associations (MTAs) for FW resistance. Among 26 MTAs, 12 were identified using trait data recorded in the field (3 at seedling and 9 at reproductive stage) and 14 MTAs were identified using trait data recorded under controlled conditions in the greenhouse (6 at seedling and 8 at reproductive stage). The phenotypic variation explained by these MTAs varied from 11.75 to 15.86% with an average of 13.77%. Five MTAs were classified as major, explaining more than 15% phenotypic variation for FW and two MTAs were declared stable, being identified in either two environments or at two growth stages. One of the promising stable and major MTAs (Affx_123280060) detected in field conditions at reproductive stage was also detected in greenhouse conditions at seedling and reproductive stages. The stable and major (>15% PVE) MTAs can be used in chickpea breeding programmes.

Genetic and cytogenetic mapping of DMI1, DMI2, and DMI3 genes of Medicago truncatula involved in Nod factor transduction, nodulation, and mycorrhization

The DMI1, DMI2, and DMI3 genes of Medicago truncatula, which are required for both nodulation and mycorrhization, control early steps of Nod factor signal transduction. Here, we have used diverse approaches to pave the way for the map-based cloning of these genes. Molecular amplification fragment length polymorphism markers linked to the three genes were identified by bulked segregant analysis. Integration of these markers into the general genetic map of M. truncatula revealed that DMI1, DMI2, and DMI3 are located on linkage groups 2, 5, and 8, respectively. Cytogenetic studies using fluorescent in situ hybridization (FISH) on mitotic and pachytene chromosomes confirmed the location of DMI1, DMI2, and DMI3 on chromosomes 2, 5, and 8. FISH-pachytene studies revealed that the three genes are in euchromatic regions of the genome, with a ratio of genetic to cytogenetic distances between 0.8 and 1.6 cM per microm in the DMI1, DMI2, and DMI3 regions. Through grafting experiments, we showed that the genetic control of the dmi1, dmi2, and dmi3 nodulation phenotypes is determined at the root level. This means that mutants can be transformed by Agrobacterium rhizogenes to accelerate the complementation step of map-based cloning projects for DMI1, DMI2, and DMI3.