Genetic diversity and structure of landrace of lablab (Lablab purpureus (L.) Sweet) cultivars in Thailand revealed by SSR markers

A de novo chromosome-scale assembly of the Lablab purpureus genome

Introduction

Lablab (Lablab purpureus (L.) Sweet), an underutilized tropical legume crop, plays a crucial role in global food and nutritional security. To enhance our understanding of its genetic makeup towards developing elite cultivars, we sequenced and assembled a draft genome of L. purpureus accession PK2022T020 using a single tube long fragment read (stLFR) technique.

Results and discussion

The preliminary assembly encompassed 367 Mb with a scaffold N50 of 4.3 Mb. To improve the contiguity of our draft genome, we employed a chromatin contact mapping (Hi-C) approach to obtain a pseudochromosome-level assembly containing 366 Mb with an N50 length of 31.1 Mb. A total of 327.4 Mb had successfully been anchored into 11 pseudomolecules, corresponding to the haploid chromosome number in lablab. Our gene prediction recovered 98.4% of the highly conserved orthologs based on the Benchmarking Universal Single-Copy Orthologs (BUSCO) analysis. Comparative analyses utilizing sequence information from single-copy orthologous genes demonstrated that L. purpureus diverged from the last common ancestor of the Phaseolus/Vigna species approximately 27.7 million years ago. A gene family expansion analysis revealed a significant expansion of genes involved in responses to biotic and abiotic stresses. Our high-quality chromosome-scale reference assembly provides an invaluable genomic resource for lablab genetic improvement and future comparative genomics studies among legume species.

Epicuticular wax chemicals of Lablab purpureus subsp. bengalensis influence short-range attraction and oviposition responses in Aphis craccivora and Aphis gossypii

Lablab purpureus subsp. bengalensis (Jacq.) Verdc. is an important legume of India and Africa. Both aphids, Aphis craccivora Koch and A. gossypii Glover (Hemiptera: Aphididae), are important herbivorous pests of this legume crop. These viviparous females lay nymphs on the leaf surface of this legume plant. Therefore, it is of considerable interest to study whether leaf surface wax chemicals (long-chain alkanes and free fatty acids) of this legume plant served as short-range attractants and oviposition stimulants in both females to lay nymphs. Twenty-one n-alkanes from n-C12 to n-C35 and 11 free fatty acids from C12:0 to C22:0 were identified in leaf surface waxes. Nonacosane and nonadecanoic acid were the most abundant among n-alkanes and free fatty acids, respectively. Both females were attracted towards one leaf equivalent surface wax against the control solvent (petroleum ether) in short Y-tube olfactometer bioassays. A synthetic blend of tetradecane, pentadecane, tetracosane, tridecanoic acid, tetradecanoic acid, and heneicosanoic acid comparable to one leaf equivalent surface wax served as short-range attractants and oviposition stimulants in A. craccivora; whereas a synthetic blend of tetradecane, hexadecane, docosane, nonadecanoic acid, and arachidic acid comparable to one leaf equivalent surface wax acted as short-range attractants and oviposition stimulants in A. gossypii. These results can provide the basis for efficient pest management strategies of A. craccivora and A. gossypii against L. purpureus subsp. bengalensis using host plant leaf surface wax compounds. Further, SEM studies of antennae and forelegs of both aphids were conducted to observe sensilla structures, which help in chemoreception.

Molecular Analysis of Genetic Diversity and Structure of the Lablab (Lablab purpureus (L.) Sweet) Gene Pool Reveals Two Independent Routes of Domestication

In this study, genetic diversity and structure of 474 cultivated and 19 wild lablab (Lablab purpureus) accessions. were determined using 15 nuclear and 6 chloroplast SSR markers. The overall gene diversity was relatively low (0.3441). Gene diversity in the wild accessions (0.6059) was about two-folds greater than that in the cultivated accessions. In the wild accessions, gene diversity was greatest in the southern Africa, followed by East Africa. In the cultivated accessions, gene diversity was highest in the eastern Africa. The results suggested that South Africa is the center of origin and East Africa is the center of domestication of lablab. Different cluster analyses showed that 2-seeded-pod cultivated accessions (ssp. uncinatus) were clustered with wild accessions and that 4-(6)-seeded-pod cultivated accessions (ssp. purpureus and bengalensis) were intermingled. UPGMA tree suggested that ssp. purpureus and bengalensis were domesticated from 4-seeded-pod wild accessions of southern Africa. Haplotype network analysis based on nuclear SSRs revealed two domestication routes; the ssp. uncinatus is domesticated from 2-seeded-pod wild lablab (wild spp. uncinatus) from East Africa (Ethiopia), while the ssp. purpureus and bengalensis are domesticated from 4-seeded-pod wild lablab from Central Africa (Rwanda). These results are useful for understanding domestication and revising classification of lablab.

Breeding potential of lablab [Lablab purpureus (L.) Sweet]: a review on characterization and bruchid studies towards improved production and utilization in Africa

Lablab (Lablab purpureus) [Lablab purpureus (L.) Sweet] is termed a lost, underutilized and neglected crop in Africa. Despite the multipurpose use, production, consumption and research are still limited. Wide genetic diversity of lablab germplasm exists in Africa. Diversity studies provide significant information for subsequent research programs and improvement. The advent of genotyping and sequencing technologies has enabled the identification of unique and agronomically important traits. Application of next-generation sequencing on lablab as a pioneer orphan crop is currently underway. This has enabled description of the whole genome, generation of reference genome and resequencing that provide information on variation within the entire genome. Information from these technological advances helps in identifying potential traits for biotic and abiotic stress for further breeding programs. Storage pests specifically bruchids (Callosobruchus spp.), are considered a major obstacle in lablab production. Screening of available genotypes for bruchid resistance and studies on the physical and biochemical factors that confer resistance in lablab is required. Applying advanced technologies provides precise and reliable identification of the novel markers responsible for bruchid resistance allowing for introgression of important genes to breeding programs. This review provides a detailed analysis on the characterization of lablab and the information on bruchid resistance vital for breeding farmer-preferred varieties that possess agronomically beneficial traits. Concerted efforts and research on this neglected crop will enhance its production, utilization and consumption.