Agriculture Reference
In-Depth Information
TABLE 8.13
Rating of Diseases Occurrence (Brown Spots, Grain Discoloration, Blast, and
Rhizoctonia solani
) in Irrigated Rice According to Date of Sowing in the State of
Rio Grande do Sul of Brazil
Probability of
Disease
Occurrence (%)
Grain Yield
(Mg ha
−1
)
Whole Grains
(%)
Sowing Date
Disease Rating
1 October-10 October
35
Very low to low
8.30
64
15 October-30 October
45
Low
8.15
63
1 November-11 November
65
Low to medium
8.00
62
15 November-30 November
65
Medium to high
7.45
59
1 December-12 December
75
High to very high
6.65
56
Source:
Adapted from Grohs, D. P. et al. 2010. Criterion for diseases management in irrigated rice
.
IRGA Technical
Bulletin/Technical Report 7, 48p, Cachoeirinha, Rio Grande do Sul, Brazil: IRGA.
Note:
The cultivars planted were BR IRGA 410 and IRGA 417.
8.6 QUANTITATIVE GENETICS AND MOLECULAR APPROACH TO IMPROVE
NITROGEN USE EFFICIENCY
Quantitative genetics and molecular approach have been considered as important strategies in
developing crop cultivars having a higher N use efficiency (Malik and Rengel, 2013). Molecular
genetics can be used to identify key elements controlling the process of N remobilization. Nitrogen
remobilization efficiency is subject to genetic variability (Malik and Rengel, 2013). Nitrogen remo-
bilization from vegetative parts to grain is an important strategy in improving the yield of crops
(Fageria et al., 2011a). Nitrogen remobilization in crop species can be manipulated by modifying
physiological traits and the use of transgenic plants or mutants with modified capacity for N or car-
bon assimilation and recycling (Masclaux-Daubresse et al., 2001, 2010; Malik and Rengel, 2013).
Significant variation in N remobilization from vegetative parts to grain has been reported for wheat
and corn (Kichey et al., 2007).
Improvement in plant components that contribute to grain formation and filling can increase
the total grain yield in cereals (Singh, 2013). A number of plant characteristics, including plant
height, number of tillers, time of anthesis, number of panicles per plant, panicle length, number
of grains per panicle, and size of grain, contribute to the final yield. Both classical and molecular
genetics have provided information regarding the genes that control several important yield-con-
trolling traits (Singh, 2013). In sorghum, six genes attributed to maturity (Rooney et al., 2000) and
four genes responsible for dwarfism (Hadley, 1957) have been identified by classical genetics while
controlling regimes of the genome for plant height (Rami et al., 1998), maturity (Lin et al., 1995),
number of tillers (Paterson et al., 1995), seed weight (Pereira and Lee, 1995), panicle characteristics
(Pereira and Lee, 1995), and stay green (Tao et al., 2000).
The identification of quantitative trait loci (QTL) for many morphological traits, grain yield, and
its components under different N levels (low and high) has been reported for many crop species (An
et al., 2006; Malik and Rengel, 2013). Grain yield, grain protein content, and leaf senescence are
genetically controlled and that prompted mapping QTL for leaf senescence on various plant species
(Malik and Rengel, 2013). In wheat (Joppa et al., 1997), barley (Mickelson et al., 2003) identified
QTL related to N remobilization from senescing leaves for grain filling. Colonization of QTL for
flag leaf remaining green and grain yield was confirmed by Verma et al. (2004) in wheat, and these
traits are positively correlated in a phenotype. Similarly, in rice, Jiang et al. (2004) reported 46 QTL
for stay-green-related traits and reported a positive correlation between stay-green and grain yield.
