Searching for Abiotic Tolerant and Biotic Stress Resistant Wild Lentils for Introgression Breeding Through Predictive Characterization

The Prospects of gene introgression from crop wild relatives into cultivated lentil for climate change mitigation

Crop wild relatives (CWRs), landraces and exotic germplasm are important sources of genetic variability, alien alleles, and useful crop traits that can help mitigate a plethora of abiotic and biotic stresses and crop yield reduction arising due to global climatic changes. In the pulse crop genus Lens, the cultivated varieties have a narrow genetic base due to recurrent selections, genetic bottleneck and linkage drag. The collection and characterization of wild Lens germplasm resources have offered new avenues for the genetic improvement and development of stress-tolerant, climate-resilient lentil varieties with sustainable yield gains to meet future food and nutritional requirements. Most of the lentil breeding traits such as high-yield, adaptation to abiotic stresses and resistance to diseases are quantitative and require the identification of quantitative trait loci (QTLs) for marker assisted selection and breeding. Advances in genetic diversity studies, genome mapping and advanced high-throughput sequencing technologies have helped identify many stress-responsive adaptive genes, quantitative trait loci (QTLs) and other useful crop traits in the CWRs. The recent integration of genomics technologies with plant breeding has resulted in the generation of dense genomic linkage maps, massive global genotyping, large transcriptomic datasets, single nucleotide polymorphisms (SNPs), expressed sequence tags (ESTs) that have advanced lentil genomic research substantially and allowed for the identification of QTLs for marker-assisted selection (MAS) and breeding. Assembly of lentil and its wild species genomes (~4Gbp) opens up newer possibilities for understanding genomic architecture and evolution of this important legume crop. This review highlights the recent strides in the characterization of wild genetic resources for useful alleles, development of high-density genetic maps, high-resolution QTL mapping, genome-wide studies, MAS, genomic selections, new databases and genome assemblies in traditionally bred genus Lens for future crop improvement amidst the impending global climate change.

Identification and Characterization of Resistance to Rust in Lentil and Its Wild Relatives

Lentil rust is a major disease worldwide caused by Uromyces viciae-fabae. In this study, we screened a large germplasm collection of cultivated lentils (Lens culinaris ssp. culinaris) and its wild relatives, both in adult plants in the field with a local rust isolate during 2 seasons and in seedlings under controlled conditions with four fungal isolates of worldwide origin. The main results from our study were the following: (1) a significant number of accessions with resistance based on hypersensitive reaction (reduced Infection Type (IT)) were identified in cultivated lentil and in L. ervoides, L. nigricans and L.c. orientalis. The IT scores showed a clear isolate-specific response suggesting race-specificity, so each fungal isolate might be considered a different race. Resistance was identified against all isolates what might be the basis to develop a standard differential set that should be a priority for rust definition and monitoring. (2) Interestingly, although at lower frequency than in L. ervoides and L. nigricans, the hypersensitive response was also observed within cultivated lentil, with accession 1561 (L.c. culinaris) displaying resistance to the four isolates making this accession a valuable ready-to-use resource for lentil resistance breeding. Resistance to all other rust isolates was also available within L.c. culinaris in an isolate-specific manner. Accession 1308 (L. ervoides) showed resistance against all isolates tested, as well as a reduced number of accessions belonging to other wild Lens species. (3) In addition, our screenings allowed the identification of several accessions with partial resistance (reduced Disease Severity (DS) despite high IT). Adult Plant Resistance resulting in reduced severity in adult plants in the field, despite high susceptibility in seedlings, was more frequently identified in L.c. culinaris, but also in L. nigricans and L.c. orientalis.

Climate change conditions the selection of rust-resistant candidate wild lentil populations for in situ conservation

Crop Wild Relatives (CWR) are a valuable source of genetic diversity that can be transferred to commercial crops, so their conservation will become a priority in the face of climate change. Bizarrely, in situ conserved CWR populations and the traits one might wish to preserve in them are themselves vulnerable to climate change. In this study, we used a quantitative machine learning predictive approach to project the resistance of CWR populations of lentils to a common disease, lentil rust, caused by fungus Uromyces viciae-fabae. Resistance is measured through a proxy quantitative value, DSr (Disease Severity relative), quite complex and expensive to get. Therefore, machine learning is a convenient tool to predict this magnitude using a well-curated georeferenced calibration set. Previous works have provided a binary outcome (resistant vs. non-resistant), but that approach is not fine enough to answer three practical questions: which variables are key to predict rust resistance, which CWR populations are resistant to rust under current environmental conditions, and which of them are likely to keep this trait under different climate change scenarios. We first predict rust resistance in present time for crop wild relatives that grow up inside protected areas. Then, we use the same models under future climate IPCC (Intergovernmental Panel on Climate Change) scenarios to predict future DSr values. Populations that are rust-resistant by now and under future conditions are optimal candidates for further evaluation and in situ conservation of this valuable trait. We have found that rust-resistance variation as a result of climate change is not uniform across the geographic scope of the study (the Mediterranean basin), and that candidate populations share some interesting common environmental conditions.

Evaluation and identification of advanced lentil interspecific derivatives resulted in the development of early maturing, high yielding, and disease-resistant cultivars under Indian agro-ecological conditions

The genetic base revealed by pedigree records of the majority of released cultivars appears to be narrow in major pulse crops, including lentils, because of the frequent use of the same parents and their derivatives in crop improvement programs. Therefore, corrective measures are needed to widen the genetic base by involving the genetic resources of a distinct gene pool. In this direction, rigorous efforts were made to introgress wild Lens taxa, L. culinaris ssp. orientalis, and L. ervoides into the backgrounds of cultivated varieties. Subsequently, genetic materials were advanced through the single seed descent method of breeding along with a rapid generation advancement (normal and off-season) approach. Two F_10:11 interspecific derivatives of lentils were evaluated in augmented block design at two locations, viz. International Centre for Agricultural Research in Dry Areas (ICARDA) and Sher-e-Kashmir University of Agricultural Sciences and Technology (SKUAST), India. The analysis of variance showed remarkable variability for all target characters at both locations. The heritability estimates were high, and correlation analysis exhibited a significant association between the majority of traits assessed at ICARDA and SKUAST, India. Further, SKUAST identified the most promising lines as "Jammu Lentil 144" and "Jammu Lentil 71." These derivatives were further validated separately for their agronomic potential and resistance against major biotic stresses. The results revealed that Jammu Lentil 144 and Jammu Lentil 71 produced 16.65 and 9.40% more seed yield than local and national checks, including earliness, by 25 and 15 days, respectively. These promising interspecific derivatives were also found to be resistant to fusarium wilt, root rot, pod borer, and aphid infestations. The standard agronomy of these cultivars has also been assessed consecutively for 2 years at SKUAST. Overall, the pre-breeding efforts have resulted in the development of early maturing, high-yielding, and disease-resistant lentil cultivars for the Jammu region of India.