Introduction
Macaroni wheat (Triticum durum Desf.) is the second
important wheat species of India but the exploitation of genetic
information has not been very well demonstrated as compared to bread
wheat. Durum (macaroni) wheat is highly valued for production of
semolina and pasta products like macaroni, spaghetti, vermicelli,
couscous, burghul and frekeh. These preparations are popular in North
America, Europe particularly and African countries and thus impart
bright prospects to durum wheat from the export point of view (Tandon
1994). In recent years in India there has been a renewed interest in
durum cultivation because of newly devolved dwarf, rust resistant
durums for irrigated areas. However, earliness, high yield potential
and superior grain quality (bold, golden, hard and lustrous grains)
are yet to be explored for higher profitability. This necessitated
acceleration of improvement in this species. An efficient breeding
program is needed to break down the present plateau of productivity
through improvement of durum wheat varieties. Direct components of
grain yield in wheat were reported to be tillers per plant, grain
yield per spike and kernel weight (Srivastava et al. 1982; Singh and
Rana 1989; Joshi 1997). By improving these direct and some other
indirect components, grain yield can be improved in durums. The
knowledge about the nature and magnitude of gene effects may greatly
help in formulating plant breeding program, since such a knowledge
not only tells about the relative importance of different kinds of
gene effects (additive, dominance and epistatic) in the control of
characters but also provides information about the cause(s) of
heterosis (Jinks 1955; Hayman 1958; Brim and Co-ckerham 1961; Gamble
1962; Hill 1966; Matinzinger 1968; Stuber and Moll 1974). In the
present study, an attempt has been made to estimate various kinds of
gene effects through generation mean analysis and to know the
relative importance of these gene effects in the control of grain
yield per spike in durum wheat under normal and late sown
environment. The information based on the nature and magnitude of
gene action controlling inheritance of character like grain yield per
spike which is ultimately related to productivity would aid in the
choice of effective and efficient breeding methods and thus,
accelerate the pace of its genetic improvement for grain yield in
durums. Present study deals with such endeavour.
Materials and methods
The experimental material generated from six diverse parents, comprised three crosses namely, Cocorit71 x A-9-30-1, HI8062 x JNK-4W-128 and Raj911 x DWL5002. Twelve basic generations viz. two parents, F1 and F2, first backcross generations with both parents (BC1 and BC2), Where BC1 was the cross between F1 x female parent and BC2 was F1 x male parent, their selfed progenies (BC1F2, BC2F2) and second backcross generations i.e. the BC1 and BC2 plants again crossed with both original parents (BC1 x female parent; BC1 x male parent and BC2 x female parent; BC2 x male parent). All these populations were raised together in randomized block design with three replications at 30cm x 15cm spacing under normal and late sown environments in the same cropping seasons at Research farm of Rajasthan cultural University, Agricultural Research Station, Durgapura, Jaipur. Each parent and F1 generations was sown in 2 rows, each backcross generation in 4 rows and F2 and the second cycle of backcrosses in 6 rows of 5 m length. Grain yield per spike (g) of the main tiller was recorded on 15 random plants in each parent and F1, 30 plants in each backcross generations and 60 plants in each F2 and second backcross generations in both environments.
The data of each population in both environments were analyzed separately by joint scaling test of Cavalli (1952) to determine the nature of gene action. Components of heterosis in the presence of digenic interactions were calculated as suggested by Jinks and Jones (1958) and trigenic interactions were calculated as suggested by Hill (1966).