Genetic control of flowering time in lentil

Abstract

The transition to reproductive development is amongst the most significant in the developmental cycle of monocarpic plants. This transition, epitomised by the initiation of flowers, is of importance to agriculture. The wild progenitor of cultivated lentil, Lens culinaris subsp. orientalis, is a vernalisation responsive, facultative long day plant. The expansion of cultivated lentil, beyond the boundaries of its progenitor, coupled with the adoption of new agronomic practices, would have required the selection of landraces that were diverse in their response to both photoperiod and temperature. This diversity is reflected through the reported variation in flowering time observed in cultivated lentil. The genetic basis for this variation is of interest to plant breeding. The genetic control of flowering time in lentil however, is poorly understood. This study expands our current understanding of the genetic basis for the control of flowering time in cultivated lentil. The current understanding of the genetic control of flowering time in lentil is shaped by the discovery of the lentil Sn locus. It was then proposed that the genetic control of flowering time in cultivated lentil is a function of the lentil Sn locus and several minor loci. The lentil Sn locus was first characterised in cv. Precoz, an early-flowering cultivar that has been described to be photoperiod-insensitive. This study (Chapter 3), through the use of a candidate gene approach, proposes that the Arabidopsis ELF3 orthologue is the likely candidate for the lentil Sn locus, and concurs with the literature that the lentil Sn locus confers an early-flowering habit in its recessive state. It is also proposed that the lentil Sn is involved in the control of internode length, and early lateral branching. Additionally, the study suggests that the existing variation in flowering time observed in the unimproved lentil germplasm cannot be attributed to early-flowering habit conferred by the lentil Sn. The pilosae ecotype that characterises the Indian lentil germplasm has been previously described to be early flowering. This study (Chapter 4) investigated the genetic basis for the observed earliness in ILL 2601, a landrace that been evaluated to be amongst the earliest in the lentil germplasm. A segregating F2 population (n=173) was established between ILL 2601 and ILL 5588 (cv. Northfield), and a genetic linkage map was constructed from 734 `DArT-Seq^T`\\(^M\\) markers to identify loci contributing to the observed earliness through the use of Quantitative Trait Loci (QTL) mapping. The study identified two major loci controlling flowering time, and two major loci controlling the time to emergence from sowing, as being integral to the observed earliness in the Indian landrace. The four described loci have not been previously reported. This study (Chapter 5) additionally explored the genetic basis of the two major loci controlling flowering time in ILL 2601 through comparative genetics, and co-segregation analysis in segregating F3 populations. The study proposes that the non-coding genomic sequence in the intergenic region between the Medicago orthologues FTa1 and FTa2 as having a role in conferring ILL 2601 the early-flowering habit. The study also proposes that a legume-specific paralogue of the Arabidopsis PSEUDO-RESPONSE REGULATOR, PRR59c is the likely candidate for the second locus described to confer an early-flowering habit. Amongst the cultivated lentil germplasm, several accessions have been previously reported to be demonstrably late flowering. This study (Chapter 6) explored the genetic basis for the late flowering habit observed in cv. Indian Head. A Recombinant Inbred Line (RIL) population derived from a cross between cv. Indianhead and ILL 5588 was evaluated, and QTL determined in a genetic linkage map. Two loci contributing to the observed late flowering habit are proposed through this study. This study, on the whole, contributes significantly through its findings to the current understanding of the genetic control of flowering time, and flowering time variation in lentil.