Agriculture Reference
In-Depth Information
The spin-offs from the base populations, derived by single-plant selec-
tion within the F
2:5
families derived from selected F
2:4
families evaluated
in the FYT, are used to feed fresh variability into the elite population,
as well as other elite materials identi
ed from external sources of diver-
sity. Similarly, the spin-offs from the elite population constitute the set
of elite lines submitted to multienvironment trials, from which new
cultivars are selected.
4. Genetic Gain.
The genetic gain of the Brazilian upland rice breeding
programwas estimated for the period 1984
2009, based onmeta-analysis
of multienvironment trials of advanced lines (Breseghello et al. 2011).
Although in the beginning of that period there was no signi
-
cant grain
yield progress, gains accelerated toward the end of that period, up to
45 kg ha
1
from 2002 to 2009, corresponding to 1.44% per year. Besides
the grain yield gain, there was a reduction of 6.35 days in duration of the
cycle and a reduction of 13 cm in plant height over the 25-year period.
Those ancillary changes contributed to the improvement of land use
ef
ciency and a reduction in canopy lodging.
The period of higher genetic gain for grain yield coincides with the full
implementation of the recurrent selection scheme in the breeding
program. In the early phase of the program, crosses were made based
on suppositions about the combination ability of parents. Currently,
every cycle of crossing builds upon the gain made in previous cycles.
The near homogenization achieved in the elite population regarding
plant height, duration of cycle, and grain quality allows the application
of higher selection pressure on yield, which accelerated genetic gain in
recent years.
Additional grain yield gains are expected based on the evaluation of
the upland rice elite population in recent years. The mean yield of F
2:4
families evaluated in the FYT from 2003 to 2012 advanced an average
of 79.1 kg ha
1
per year, corresponding to a rate of 2.66% per year
(Fig. 5.2). During this period, no signi
cant change in plant height and
duration of the cycle was observed. The yield progress observed in the
recurrent selection of the elite population should impact the yield
potential of inbred lines entering multienvironment trials in the fol-
lowing years.
5. Characteristics of Brazilian Upland Rice Cultivars.
Most modern
Brazilian upland rice cultivars have a cycle of maturity between 100
and 120 days, plant height between 90 and 100 cm, a moderate number
of tillers, with a narrow angle of insertion, long panicles, moderate
resistance to common diseases (blast, brown spot, leaf scald, and grain
