The per cent. The oil obtained is

The
oleiferous Brassica species, generally referred to as rapeseed-mustard,
are one of the economically important agricultural commodities. India’s combined volume of exports of rapeseed-mustard
seed oil is almost 10.07% of the total vegetable oilseeds. World output of rapeseed-mustard crops rose from about
36 million tonnes in 2001-02 to 67.9 million tons in 2015-16 (www.fas.usda.gov.in). However, the demand for rapeseed-mustard oils continues to escalate
steeply due to increasing consumption and diversion of bioenergy use.

Crop
Brassicas are important sources of edible oil with the lowest amount of
saturated fats and leafy vegetables rich in minerals and antioxidative
property. It is
traditionally grown in India since about 3500 BC. Rapeseed-mustard
is an important group of oilseed crops accounting about one-fourth of the total
oilseeds production in India.
It includes toria (B. rapa L. var. toria), brown sarson (B. rapa L.
brown sarson), yellow sarson (B. rapa  L. var. yellow sarson), Indian mustard (B.
juncea L. Czern and Coss), black mustard (B. nigra) and taramira (Eruca
sativa / vesicara Mill.) species. These along with non-traditional
species like gobhi sarson (B. napus L.) and karan rai (B. carinata
A. Braun) have been recorded to be grown since ancient time. These
species are predominantly grown on varied soils of diverse agro-climatic
regions in the country. Among
all these species, Indian mustard contributes more than 80% of the total
rapeseed-mustard production and 27% of edible oil pool of the country (Singh et
al., 2013).

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Brassica
juncea (L.) is mainly
self-pollinating, although an average of 7.5 to 30 per cent out-crossing does
occur under natural field conditions (Abraham, 1994; Rakow and Woods, 1987). It
is widely believed that Brassica juncea (2n=36,
AABB) was first evolved in the Middle East where its ancestral parental species
Brassica rapa (2n=20, AA) and Brassica nigra (2n=16, BB) were
hybridized naturally (Prakash and Hinata, 1980). The
oil obtained from the seed is edible and contains several important nutritional
components. The oil content of seeds ranges from 40-50 per cent. The oil
obtained is the principle cooking medium and excellent source of chemical
industry such as lubricants, and in the manufacture of a variety of products
like rubber, soap, plastic, nylon. The cake obtained from oil extraction is utilized
as cattle feed which improves the quality of milk and other animal produce. The
seed and oil are used as a topping in the preparation of pickles and for
seasoning curries and vegetables. In Northern India, mustard oil is mainly utilized for human consumption
(Vaghela et al., 2011).

During the last decade, the yield of mustard in India
is almost static, hovering around 1-1.2 tonnes/ha, which is much below than the
world’s average of 1.98 tonnes/ha. The
area, production and productivity of rapeseed-mustard was 5.76 million ha, 6.82
million tonnes and 1184kg/ ha respectively during 2015-16 (Agriculture Statistics at Glance,
2016). During 2013-16, the world average production of 2144 kg/ha and highest average yield of
3640 kg/ha by European Union shows  that
India needs to fill the large gap of 85% over world average
(www.nmoop.gov.in) where tapping heterotic capability of crop through
hybrids essentially prompts improvement.

In
the past, by using conventional breeding methods like mass selection, pure line
selection, disruptive selection and intervarietal hybridization some
improvements in the genetic potential of the varieties have been obtained. In many
cases, selection and reselection were widely followed in the low yielding local
land races, and progenies of hybrids. As a result the rate of increment in
yield per unit area has been rather slow. The yield level has almost reached a
plateau in these crops. Therefore, a precise genetic understanding of
inheritance of yield and of physiological characters that determine the
potential yield could be helpful in developing future high yielding
varieties/hybrids of these crops. It has also been realized that reassessment
of traditional breeding methods, based on valid genetic information of crop
yield would be necessary for obtaining visible gains in their production
(Thurling, 1974).

Survey
and study of genetic variability is a logical way to initiate any breeding
programme. Genetic variation is the basis of progress in plant breeding
programme as it determines the scope of selection. The genetic facts are
inferred from observations on phenotypes. Since phenotype is an artifact of the
joint effect of genotype and environment, non-genetic component exerts large
influence on genetic variability. The exploitable variability is, consequently,
required to be judged through various genetic parameters like heritability and
others. Such a study appears to be extraordinarily important for planning genetic
improvement in Indian mustard. The study of genetic variability ensures
identification of traits that offer potential scope for improvement through
selection. In crop improvement programme the importance of a character is
determined by the magnitude of its influence on the economic product.

For a sound breeding programme, it is
also a pre-requisite to evaluate the nature of gene action associated with
expression of different agronomically important traits, acertain the
potentiality of the parents in hybrid combinations, and in the isolation of
promising F1 hybrids for further exploitation in breeding programmes.
In this regards, the precise information on combining ability is rather more important
in identifying the parents for their use in crop improvement programme. Griffing’s
(1956) biometrical analysis has been widely used to aid plant geneticists in
selection of parents for hybridization programmes. In most instances, the evaluation
provides reliable information on combining ability of parent i.e. the capability of the parents to
produce superior progenies following hybridization, and the magnitude of
additive and non-additive gene action.

Heterosis breeding in crop plants has been the most
successful technique among numerous technical options available to the
geneticists and plant breeders for the improvement of productivity in crop
plants. This phenomenon though now not fully understood genetically to this
point, has yet enabled the plant scientists to enhance the performance of
several economic traits. Heterosis in mustard has been recognized as a means of
improving yield and other vital traits. In oilseed Brassicas many studies have
reported the extent of heterosis for seed yield ranging from 13 to 91% in B. juncea L. (Verma et al. 2011, Yadava et al.
2012 and Meena et al. 2015). It was
also observed that hybrids between genetically distant groups showed more
heterosis than within the group combinations. Significant levels of heterosis
for yield contributing parameters has also been pronounced.

One
of the major constraints limiting productivity of rapeseed-mustard is damages
caused by biotic and abiotic factors. These crops
are damaged by different diseases like white
rust, Alternaria blight, downy mildew and Sclerotinia blight at distinctive
tiers of plant growth. Most of the available rapeseed-mustard cultivars are
susceptible to these diseases. Therefore, breeding for resistant varieties
incorporating genetic resistance is the most economical and preferable ways of
reducing yield losses due to diseases. Information on the nature and mode of
inheritance of resistant genes and their stability under different
agro-climatic conditions is imperative for effective usage of resistance within
the breeding programme.

White
rust, a fungal disease caused by Albugo
candida is important disease of oilseed Brassicas
in India. Resistance to this disease in several sources/lines in Indian mustard
has been reported to be controlled by few major genes (Verma and Bhowmic, 1989;
Paladhi et al., 1993, Sachan et al. 2012, Verma, 2014). The
resistance to this disease is also reported to be quantitatively inherited
conditioned by minor genes (Edward and Williams, 1982). In B. juncea though several sources of resistance have been described
(Saharan et al., 1988), but information
on the incorporation of resistance to agronomically superior cultivars has met
with limited success, probably due to their poor agronomic background. Further
the new sources of resistance especially of local origin offer great promise.
One new line named PWR 15-8 developed at Pantnagar is under intensive
investigation and use in breeding programme. Therefore, unraveling genetic
control of white rust resistance of this new line will be very useful for its
effective and efficient utilization in mustard improvement.

Yield
is the ultimate product of action and interaction of number of yield components
which are govern by a large number of genes having small effects and are
greatly influenced by environment. The effect of small individual genes cannot
be estimated instead only cumulative effects of gene action can be estimated
for any of the attributes. The information on the nature of gene action could
be helpful in predicting the effectiveness of selection in a population. A
distinct knowledge about type of gene effect, its magnitude and composition of
genetic variance i.e., additive,
dominance and epistasis helps in formulating an effective and sound breeding
programme.

Generation
mean analysis has proved to be an important technique to estimate different
genetic parameters. The concept of generation mean analysis was developed by
Hayman (1958) for the estimation of genetic components of variation. Evaluation
of this approach is based on at least six different generations of a cross,
viz., parents, F1, F2 and backcrosses (BC1 and
BC2). This method provides information about additive, dominance and
epistatic interactions.