Agriculture Reference
In-Depth Information
TABLE 1.2
Plant Height, Grain Yield, and Lodging Rating of Traditional and Modern
Upland Rice Cultivars under Brazilian Conditions
Cultivar
Plant Height (cm)
Grain Yield (kg ha
−
1
)
Lodging Rating
a
Traditional
Rio Paranaíba
108
2780
3
Caiapó
105
2590
2
Guarani
98
2640
4
CNA 8054
108
2470
3
Average
105
2620
3
Modern
Progresso
86
2620
1
CNA 8172
86
2860
1
CNA 8305
91
2990
1
BRS Canastra
88
2870
1
Average
88
2840
1
Source:
Adapted from Morais, O P. 1998. Annual report of the project, “Breeding upland rice culti-
vars”. National Rice and Bean Research Center of Embrapa, Goiania, Brazil.
a
Higher values mean relatively more susceptibility to lodging and lower values mean more resistant
to lodging.
The creation of semidwarf cultivars spectacularly increased the yielding ability of many crops,
such as rice and wheat. For example, Table 1.2 compares the yields of older and taller traditional
cultivars of upland rice to modern, semidwarf cultivars of Brazil. Yields of the modern cultivars are
higher, in part, because they are less susceptible to lodging than the old ones. Similarly, lowland rice
cultivars used in the Philippines have, over the past 70 years, become shorter, in addition to having
smaller, more upright leaves and reduced sensitivity to photoperiod (Fageria et al., 2006). Panicle
weights initially became heavier, but later were made lighter with greatly increased panicle numbers.
In addition to lodging resistance, short-stature and sturdy culm cultivars give higher yields at
close plant spacing as compared to the taller cultivars. However, a taller plant has an advantage in
competing with weeds as compared to short-stature plant. In addition, grain yields decrease with
increasing water depth. Under such conditions, intermediate stature (100-130 cm) is considered
desirable over short stature (90-110 cm) for rice (Yoshida, 1981). Extremely dwarf height is also not
good, because grain yield increases quadratically with the increasing plant height (Fageria, 2007,
2009, 2014). A marked increase in harvest index and grain yield per day has been associated with
reduced plant height and earlier maturity (Evans et al., 1984). Evans et al. (1984) also reported that
despite these changes, there has been no change in the photosynthetic rate, CGR, or spikelet weight.
The plant height of 10 lowland rice genotypes grown under Brazilian conditions is presented in
Figure 1.6. The plant height of these genotypes varied from 94 to 111 cm, with an average value of
102 cm. Similarly, the plant height of 19 upland rice genotypes is presented in Table 1.3. Plant height
was significantly (P < 0.01) influenced by N and genotype treatments and across two N levels varied
from 93 to 118 cm among genotypes with an average value of 103 cm (Table 1.3). There was a sig-
nificant quadratic relationship between plant height (X) and grain yield (Y = −196.3034 + 3.2542 X
- 0.0097X
2
, R
2
= 0.65**) (Fageria et al., 2010). Hence, grain yield increases with increasing plant
height but there is a limit of this increase. When plant height is too low, it produces less dry matter,
and when it is too high, it may lodge and less responsive to N fertilization (Yoshida, 1981). This
means that intermediate plant height is a better compromise and this is confirmed by the fact that