Agriculture Reference
In-Depth Information
by Jones in 1926 and hybrid rice research started in India in 1954 at the
Central Rice Research Institute, Cuttack, in Odisha State (Spielman et al.
2012); however, China was the
first country to develop the entire tech-
nology package needed to produce commercial hybrids (Li et al. 2009).
The grain yield increases due to the use of hybrid rice have helped China
feed an extra 60million people every year and allowed a reduction in land
area dedicated to rice by 14% while increasing total rice production
by 40% (Li et al. 2009).
A. Hybrid Rice and Direct Seeding
In Latin America, rice is planted using direct seeding and this has
profound implications for breeding and the use of hybrid rice as
compared with Asia. The
first difference appears in the amount of
seed used to plant a hectare. With inbred cultivars, the average seed rate
is 80
120 kg ha
1
, whereas the recommended seed rate for hybrid rice
under direct seeding is 30
-
40 kg ha
1
. This means that a hybrid must
have high initial vigor to close space quickly and compete with weeds.
At the same time, yield potential has to be very good even with such
a low seed rate. Good machinery is required because soil preparation
needs to be perfect, with adequate leveling and drainage to avoid
seedling losses. Similarly, precision planters are needed to adequately
control the depth of seed placement and distribution in the row.
Management of nitrogen must be adjusted from that of normal inbreds
due to the tendency of hybrids to lodge under direct seeding. Rice has
positive heterosis for plant height (Virmani 1994). As a consequence,
hybrids are usually taller than inbred cultivars. Under direct seeding,
competition between plants produces weak stems and surface seed
placement for good emergence favors shallow roots. This results in
higher lodging that is aggravated by the use of high rates of nitrogen,
especially during internode elongation. To avoid lodging, the rate and
timing of nitrogen fertilization have to be adjusted.
Another completely different aspect is the technology for seed pro-
duction. In transplanted rice, differences in
-
flowering time can be
accommodated by staggered planting. In contrast, under direct seeding,
it is not possible to do planting by machine once
flooding has begun;
as a result, only small differences can be managed under this system. In
mechanized seed production, pollen must move longer distances and
this has required the development of special technology such as the use
of helicopters to assist pollen movement. Excellent outcrossing capacity
is needed since the width of the rows of the female parent is higher than
in transplanted rice in order to accommodate mechanized harvest and to
