Environmental Engineering Reference
In-Depth Information
or burning of stubbles, and use of chemical products when necessary. For
M. fimbriolata
biological
control with
Metarhizium anisopliae
is also an alternative (Dinardo-Miranda 2008a).
Nematodes of the genera
Meloidogyne
and
Pratylenchus
also attack sugarcane. Resistant variet-
ies usually are not an efficient way to control nematodes but management practices such as crop
rotation when sugarcane is replanted, and application of organic matter help to decrease the popula-
tion of nematodes. In areas where the attack is intense chemical control may be necessary (Dinardo-
Miranda 2008b).
Fungi diseases that affect sugarcane include rust (
Puccinia melanocephala
), smut (
Ustilago sci-
taminea
), eye spot (
Bipolaris sacchari
), red rot (
Colletotrichum falcatum
or
Glomerella tucuma-
nensis
), pokkah-boeng (
Fusarium
), and pineapple disease (
Thielaviopsis paradoxa
). The most
important method of controlling fungi diseases is through the use of resistant varieties. Additional
measures, which are effective with some diseases, include roguing of diseased stools, burning or
plowing out trash or stubbles, and heat treatment of cane seeds (Santos 2008).
Resistant varieties are also the most important method of control of bacteria diseases such as
ratoon stunting (
Clavibacter xyli
) and leaf scald disease (
Xanthomonas albilineans
), or viruses such
as sugarcane mosaic virus and yellow leaf disease. Periodic surveys of nurseries and heat treatments
may also be useful to prevent the spread of some diseases (Almeida 2008; Gonçalves 2008).
Despite the great number of pests and diseases that affect sugarcane, chemical control is applied
in less extent than in many other crops because of the effectiveness of biological control methods
and especially of resistant varieties. Fungicides and bactericides are seldom used in sugarcane.
21.4 suGarcane PhysIoloGy
In spite of the fact that sugarcane became one of the main sources of sugar and ethanol in the
world, its physiology has been poorly studied in relation to other grass species. Sugarcane plants
can be obtained from seeds, germination can be easily obtained in vitro and the structure of
the seeds and seedlings of sugarcane is typical of other grasses. Seedlings can be an excellent
model to study and understand several aspects of gene expression, biochemistry physiology.
For biotechnology purposes though, sugarcane seeds are not useful because what we call sugar-
cane is not a single species, but a polyploid hybrid. This makes the seed method of reproduction
inappropriate for crop cultivation. Crops are planted from clones of designed varieties using
stem cuttings. The same plant stays in the field for an average of 5 years. Yields decline with
age and after a while it becomes aneconomical so the crop must be replanted. One of the most
important physiological events related to sugar production is the drought stress that occurs in
wintertime. From the agricultural viewpoint, it is well known that the stress is necessary to
induce senescence (by ethylene) of the top shoot of the plant and the consequent storage of
sucrose in the stem. Accumulation of sucrose is related to photosynthesis, sink-source relation-
ships, flowering, and water stress. Water stress depends on the level and rate it developed. When
applied slowly it leads to developmental changes such as a reduction in leaf expansion and the
closing of leaf stomata. Photosynthate translocation is not reduced until the stress becomes
severe. Combined, the effect of drought is to lead to accumulation of carbohydrates in the
leaves and in storage sinks of the sugarcane plant (Hartt 1936). The accumulation of sucrose in
storage parenchyma of sugarcane is called ripening. Ripening is caused by the gradual decrease
of tissue moisture, reduction of cell expansion, and the formation of new internodes without
much inhibition of photosynthesis. Reduced consumption of sucrose for metabolic energy and
new cell formation leads to increased sucrose content (Gosnell and Lonsdale 1974). Sugarcane
managing includes the use of drought and growth inhibiting stresses to ripen the crop before
harvest.
Sugarcane photosynthesis is based on the so-called Kranz syndrome anatomy. Instead of using
the C
3
pathway system, in which CO
2
is converted directly by the enzyme ribulose bisphosphate
carboxylase (RUBISCO) into organic acids containing three carbon atoms, sugarcane leaves
