CHAPTER ONE
1.0 Introduction
Cultivated sunflower (Helianthus annuus L.) is an annual,
herbaceous (2n=34) and a cross pollinated crop, native to North America. It is
a member of the Asteraceae family and it is regarded as the fourth most
important oilseed crop grown worldwide after soya beans, palm and edible
rapeseed (canola) (Moghaddasi, 2011; Sujatha et al., 2012). Sunflower is
cultivated on about 18 million hectares worldwide with an annual seed
production of 40 million tons (FAOSTAT, 2015). Its seeds are known for their
high oil (25 – 48%) and protein (23 – 35%) content and thus used in
confectionary and animal feed (Imran et al., 2015). It is used as an ornamental
plant due to the attractiveness of its flower (Mayor et al., 2010). Sunflower
seeds have abundant health benefits which can be attributed to the high levels
of polyunsaturated and monounsaturated fats, phytosterols, tocopherols,
protein, copper, folates, iron, zinc, and vitamin B (Nandha et al., 2014; Roche
et al., 2010). Its oil is used as raw materials in many industries due to the
presence of four commercially important fatty acids namely, palmitic, stearic,
oleic, and linoleic acids (Lee et al., 2010).
Gene variability within a species enables the development of
new improved varieties with improved characteristics. Therefore, the success of
genetic improvement of sunflower depends on the magnitude of genetic
variability which enables the selection of desirable genotypes for breeding
purpose (Cvejic et al., 2011). In addition, realizing the need for the
imperativeness of low-input agriculture being proffered for the 21st century,
farmers require a suite of improved crop varieties that are genetically diverse
in terms of climate change resilience, input use-efficiency, high yielding
potential, resistance to biotic and abiotic stresses, enhanced nutritional and
other important quality attributes (Tester and Langridge, 2010; Waines and
Ehdaie, 2007). However, the envisaged genetically diverse portfolios of
sunflower crop varieties are often unavailable to farmers due to its extreme
narrow genetic base (Seiler and Frederick, 2011). This makes its improvement
through conventional breeding method alone difficult. In view of this, the
induction of genetic variability for sunflower crop, particularly in the era of
increasing global food crisis and changing climatic regimes is, therefore,
highly desirable.
Mutagenesis is an important tool in plant breeding for
increasing genetic variability and consequently, broadening the genetic base of
germplasms (Ndou et al., 2013). Spontaneous mutations occur naturally in crops
but, its rate is low and cannot always be exploited for breeding, thus the need
for induced mutagenesis (Jain and Suprasanna, 2011). Mutations in plants can be
induced using chemical or physical mutagens and the effectiveness and
efficiency of any induced mutagenesis experiment are direct results of the
choice of appropriate mutagen treatments (Rupinder and Kole, 2005).
Almost all mutagens have the property of reacting with DNA
and thereby bringing about changes in nucleotide sequences. However, the mode
of action of each mutagen is distinct. Besides, a mutagen may effectively bring
about mutations, but the accompanying undesirable effects like lethality or
sterility may decrease its efficiency (Shagufta et al, 2013). Thus, in order to
exploit induced mutagenesis for crop improvement, a preliminary determination
of the treatment that would yield the greatest amount of desirable mutation
while at the same time, producing the least density of undesirable effects is
necessary (Xin et al., 2008; Mba et al., 2010). Chemical mutagens as compared
with physical mutagens offer high mutation rate and predominantly, point
mutations (Cvejic et al., 2011). Among chemical mutagens, ethyl methane
sulfonate (EMS) is the most powerful and effective mutagen for creating
mutations in plants (Cvejic et al., 2011).
Mutagenesis has become an important crop improvement tool
available to breeders with no regulatory restrictions imposed as with
genetically modified crops (Parry et al., 2009) with mutant varieties readily
accepted by consumers. Sunflower mutants with altered agronomic traits have
been created through the use of induced mutations amongst which includes; early
maturing, short stature, larger head diameter, thinner husk, high oil content,
cytoplasmic male sterile (CMS) lines and many more (Sabetta et al., 2011;
Cvejic et al., 2015; Mostafa, 2011). Mutagenesis, in conjunction with
conventional breeding methods could result in mutant varieties with desirable
traits that can be used to broaden the genetic base of sunflower and to improve
its various agro-morphologically important traits. There is paucity of
information on the response of sunflower varieties developed by IAR, Samaru to
different EMS doses, as well as, effective mutagen dose for induction of
variability. The present study was focused on increasing the genetic
variability within selected sunflower varieties using EMS and selecting mutants
with important agro-morphological traits for further improvement. In view of
these, the objectives of this study were to:
assess the response of the sunflower varieties to different
EMS doses and determine optimal EMS doses for desirable mutation
estimate genetic variability for agronomic traits among M2
mutants and identify some desirable mutants for oil content and other agronomic
traits
assess the degree of association among oil content, grain
yield and other agronomic traits
assess the degree of similarity among the mutants for the studied agronomic traits.