Variability and Trait Association Studies for Late Leaf Spot Resistance in a Groundnut MAGIC Population

Globally, late leaf spot (LLS), a foliar fungal disease is one of the most important biotic constraint in groundnut production. Multi-Parent Advanced Generation Inter Cross (MAGIC) groundnut population was developed in a convergent crossing scheme using eight founder parents to develop a mapping population for multiple traits includes LLS. The experiments conducted in light chamber using detached leaf assay, and disease field screening nurseries at two locations (ICRISAT and ARS, Kasbe Digraj) showed significant variability for LLS resistance and component of resistance traits. Total 10 MAGIC lines with longer incubation (>11.0 days) and two MAGIC lines with longer latent period (>27 days) than the resistant parent, GPBD 4 were identified. The MAGIC lines, ICGR 171413, and ICGR 171443 with a lesion diameter of <1 mm and 4.10–5.67% of leaf area damage can be valuable sources for the alleles limiting the pathogen severity. A total of 20 MAGIC lines recorded significantly superior for disease score at 105 DAP_I (5.60–6.89) compared to resistant check, GPDB 4 (6.89). Further studies to determine the type and number of genes controlling the LLS component traits in groundnut will be useful for improvement of resistance to LLS. Genomic selection approach can be valuable in groundnut breeding to harness the minor alleles contributing to the component traits of LLS resistance.

Mapping Revealed Two Additive QTLs and Fourteen Epistatic QTLs for Late Leaf Spot Resistance in a Cultivated Groundnut Breeding Line VG 9514.

A late leaf spot resistant breeding line VG 9514 was bred through interspecific hybridization between Arachis hypogaea L. and Arachis cardenasii. Genetic study involving segregation for late leaf spot resistance in F2 and recombinant inbred line population of a cross between VG 9514 X TAG 24 revealed duplicate recessive resistance for the disease. Integration of newly developed SSR markers from A02 chromosome with existing linkage map generated a new genetic linkage map with 278 markers and 2679.1 cM map distances. QTL mapping involving this genetic linkage map and phenotypic field score of late leaf spot identified two major consensus additive QTLs in the A02 chromosome of cultivated groundnut. Epistatic interaction between these two major QTLs was also noticed through an epistatic QTL analysis in Ici-Mapping 4.1. In all the fourteen epistatic QTLs, a common component locus was remained within the major additive QTL at 90 cM in chromosome A02. Sequence analysis within the major additive QTL peaks revealed open reading frame of genes that code LRR domain containing proteins which are involved in disease resistance in crop plants.

Combining Ability Analysis of Late Leaf Spot Resistance and Other Agronomic Traits in Nine Groundnut Genotypes

Late leaf spot (LLS) Phaeoisariopsis personata (Berk. and Curtis) Deighton is one of the most important foliar diseases of groundnut worldwide including Nigeria. The genotypes were used to estimate the general combining ability (GCA) and specific combining ability (SCA) for yield components and late leaf spot (LLS) resistance. Four susceptible genotypes (SAMNUT 23, SAMNUT 24, SAMNUT 25 and SAMNUT 26) were used as females and five resistant genotypes (ICGV 12991, ICGV 7878, FDR-F7 82, FDR-F7 67 and FDR-F7 61) were used as males using line x tester mating design with three replications. The parents and progenies were evaluated for late leaf spot resistance. Highly significant negative general combing ability (GCA) effects were recorded for disease incidence in SAMNUT 25 (-0.05), indicating the genotype is a good general combiner for late leaf spot (LLS) and SAMNUT 26 (-5.90) is a good general combiner for LLS disease severity. ICGV 12991 (-12.00), FDR-F7 67 (-.68) and FDR-F7 61 (-2.23) genotypes are good general combiner for late leaf spot (LLS) disease resistance (disease incidence and severity), among the crosses, significant and negative SCA effects were obtained for most of the crosses i.e SAMNUT 24 x FDR-F7 67 and SAMNUT 24 x FDR-F7 61 for late leaf spot (LLS) resistance indicating that they are good specific combiners for late leaf spot (LLS) resistance. The ratio of the general combining ability (GCA) and specific combing ability (SCA) variances indicated the preponderance of specific combining ability (SCA) variance over general combining ability (GCA) variance for disease incidence and severity, indicating the role of non-additive gene effect and it may be due to difference in genotypes used as parents.