In vitro flowering and seed formation in lentil (Lens culinaris Medik.)

Abstract

IntroductionGrain legumes, commonly known as pulses, are one of themost important agricultural crops worldwide. Pulses areamongst the ancient food crops that have been traditionallycultivated, particularly in Asia, Latin America, and Africa.In many developing nations, grain legumes are gainingincreased importance in view of the acute shortage in pro-duction of animal proteins and widespread protein malnu-trition (Bressani 1973). Apart from this, grain legumes arealso considered as the main source of protein for livestockfeed and inland fish production. Moreover, grain legumeshave the unique ability to fix nitrogen symbiotically therebyimprove overall soil fertility.Among the pulses, lentil is the most popular and ranksfirst in terms of human consumption in Indian subcontinent.The protein and nutritional qualities of lentil varieties havebeen reported to be superior to other pulse crops (Singh etal. 1968; Bhatty 1988). Thus lentil plays an integral role inagricultural systems of South Asian countries, with increas-ing annual demands due to its nutritional quality and popu-larity. Even so, this crop is typically characterized by lowyield potential.Several factors arebelieved toberesponsiblefor the reduced yields, including susceptibility to pests anddiseases, massive flower drop, and post-harvest losses(Erskine 1984). Diseases of lentil, at various stages ofgrowth, are caused by fungi, bacteria, viruses, and nematodeinfestations (Gowda and Kaul 1982).A number of attempts have been made to improve lentilvarieties using conventional breeding techniques, but theseefforts have failed to achieve desired results due to a narrowgenetic base and lack of available and suitable germplasmfor lentil improvement. Under these circumstances, there isconsiderable scope to embrace biotechnological approachesfor lentil improvement. Indeed, a number of studies havebeen previously conducted to develop suitable in vitro re-generation systems, and to explore the possibility of apply-ing biotechnology to lentil improvement programmes(Saxena and King 1987; Polanco et al. 1988; Warkentinand Mchughen 1993; Sarker et al. 2003).However, improvement of lentil through biotechnologi-cal methods has proven to be difficult due to its recalcitrantnature, particularly pertaining to the development of aneffective in vitro root induction system. Previous studieshave indicated that rooting in microsperma type of lentil isespecially difficult and appears to be a major constraint inobtaining fully regenerated plants through in vitro techni-ques (Khanam et al. 1995;Sarkeret al. 2003). Micro-grafting has been attempted to obtain in vitro-derived plant-lets (Gulati et al. 2001), but this approach was fraught withdifficulties especially in case of microsperma lentil varieties.Under these circumstances, in vitro flowering and fullydeveloped seed formation have been considered as a viablealternative to obtain plant progenies. It is believed that invitro flowering and pod production may significantly con-tribute towards the genetic improvement of lentil through abiotechnological approach.The main objective of the present investigation was todevelop an alternative regeneration system for Lens culina-ris Medik. from regenerated shoots of lentil, avoiding the invitro root formation stage. The necessary first step was todetermine suitable media for in vitro flowering and seedformation. Several reportsare available onin vitroflowering