Heterosis is grown worldwide, mostly as a source of

Heterosis
refers to the phenomenon that progeny of diverse varieties of a species or
crosses between species exhibit greater biomass, speed of development, and
fertility than both parents. Various models have been posited to explain heterosis,
including dominance, over dominance, and
pseudo-over dominance. In this Perspective, we consider that it might be useful
to the field to abandon these terms that by their nature constrain data
interpretation and instead attempt a

progression
to a quantitative genetic framework involving interactions in hierarchical
networks. While we do not provide a comprehensive model to explain the
phenomenology of heterosis, we provide the details of what needs to be
explained and a direction of pursuit that we feel should be fruitful.

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Sunflower (Helianthus
annuus L.) is grown worldwide, mostly as a source of vegetable oil and
proteins. The main objectives of sunflower breeding programs are the
development of productive F1 hybrids with high seed and oil yield. Sunflower
oil yield is determined as the product of seed yield per unit area and the oil
percentage in grains. Therefore, consideration of both components is important
when breeding

for high oil
yield (Fick and Miller, 1997).

*

Seed oil and
hull content are the main characteristics determining oil yield in sunflower.
Oil content is a quantitatively inherited trait and it varies considerably depending
on cultivar and also environmental effects (Miller, 1987). There is a negative correlation
between hull and oil contents of seed. Miller and Fick (1997) indicated that
most of the increase in seed oil from past sunflower breeding and selection
resulted from decreases in hull percentage of seed. Pathak et al. (1983)

Detected
negative increases in oil content of sunflower hybrids and they concluded that
the reasons for that were possibly over dominance effects
of the genes conferring low oil content and the same
frequencies of these genes in hybrids and their parents.

Heterosis,
defined as the unusual growth and yield of heterozygous hybrids from two less
vigorous homozygous parents, has been explored during last 70 years.

 Heterosis can be considered as one of the most
important contributions of the genetics to agriculture, with large consequences
on agricultural yields.

 Farmers generally prefer hybrids developed by
utilizing heterosis to cultivars and grow them on large areas. Sunflower
hybrids predominate the sunflower productions in Turkey and in the world (Kaya, 2004).

Cultivated
sunflower is primarily grown from single-cross hybrid seed. Therefore, the
study was started with 25 F1 single-cross hybrids produced by crossing 5 male
restorer lines to 5 cytoplasmic male sterile (cms) lines in the breeding nursery of Trakya Agricultural Research Institute in Edirne
in 1999. The female lines (BAH4-A, BAH8-A, HA-89-A, 0704-A and 2453-A) and the
male lines (2644-R, 2284-R, 2280-R, 25711-R and R-01001) come from National
Sunflower Research

Materials
and Methods

Sunflower
seed: Seed of eight different genotype of the sunflower were received from Federal
Seed Certification and Registration Department, Swat. The experiment was conducted
on a sandy clay loam soil at Agricultural Research Institute, Tarnab and Peshawar
during autumn. Environmental temperature and physio- chemical properties of

the soil
were noted.

Increasing
seed and oil yields is the top priority of most sunflower breeding programs.
Getting benefit from use of heterosis is the main purpose in sunflower hybrid
breeding. The objectives of this study were to determine performance of
sunflower varieties and to measure the vigor of sunflower hybrids. In 2000 and
2001, sunflower hybrids were evaluated for four important yield components,
yield performance, standard and regular heterosis, and heterobeltiosis, in
Edirne – Turkey conditions. Based on observations in this research, seed yield
of hybrids was changed between 37 and 245 kg ha-1, oil yield between 17.6 and
118.8 kg ha-1, oil content between 38.0 and 50.8% and hull rate between 19.2 and
27.1%. The highest heterosis (288.3%) and heterobeltiosis  (98%) were found for oil yield.

The highest standard heterosis (21.2%) was
computed for seed yield. The lowest heterosis (–19.3%) and heterobeltiosis (-22.4%)
were observed for hull rate. The lowest standard heterosis (-22.0%) was
measured for oil yield. Regarding the studied traits, most favorable performances
we

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