Introduction
Clonal selection at precommercial stages supports the commercial
production of sugarcane, complex hybrids of Saccharum spp.
Although production of sugar per unit area is a very important
characteristic, it is not the only factor on which sugarcane is
evaluated. In addition, the concentration of sugar and the fiber
content of the cane are analyzed. The time of year and the duration
that a clone yields its highest amount of sugar per unit area
can be very important, since sugarcane harvest seasons extend
from fall to spring. Because sugarcane is commercially grown in
plant and ratoon crops, clones are evaluated accordingly. Adaptability
to mechanical harvesting and seed cane cutting are important traits
in Florida.
Information about the stability of a clone's performance across
environments aids in selecting clones that will yield well across
all environments. Stability measurements also enable identification
of clones that will perform well in some but not all environments.
This stability factor is important in our evaluations because
of the wide range of environments for growing sugarcane in Florida.
As differences widen for such characteristics as temperature,
moisture, and soil, region-specific clones become necessary because
few clones produce high yields in markedly different environments.
Clones with desired agronomic characteristics also must be
productive in the presence of harmful diseases, insects, and weeds.
Some pests rapidly develop new, virulent races or strains. Clonal
resistance to such pathogens often changes over time, so no clone
can be considered permanently resistant. The selection team must
try not to discard clones that have sufficient resistance or tolerance
to pests, but it also must discard clones that are too susceptible
to pests to be grown commercially. Sugarcane growers in Florida
rely much more on tolerance than resistance to sugarcane diseases.
In the 1997 growing season, the top seven cultivars made up 75.5
percent of the total Florida sugarcane hectarage (Glaz
1997). Each of these seven cultivars, CP 80-1827, CP 72-2086,
CP 80-1743, CL 61-620, CP 73-1547, CP 70-1133, and CP 78-1628,
was susceptible to sugarcane rust, mosaic, leaf scald, or smut.
(Glaz et al. 1986) presented a formula
and procedure to help growers distribute their available sugarcane
cultivars while considering possible attacks of new pests.
The disease that has caused the most difficulty in Florida
in selecting resistant sugarcane cultivars is sugarcane rust,
caused by Puccinia melanocephala Syd & P. Syd. The
disease against which Florida sugarcane growers and scientists
have had the most success in selecting resistant cultivars is
sugarcane smut, caused by Ustilago scitaminea Syd and P.
Syd. Other diseases with which Florida sugarcane growers must
contend are leaf scald, caused by Xanthomonas albilineans
(Ashby) Dow; yellow leaf syndrome, caused by a luteovirus (Lockhart et al. 1996); and sugarcane
mosaic virus. Ratoon stunt disease (RSD), caused byClavibacter
xyli subsp. xyli, has probably been the most damaging,
although the least visible, sugarcane disease in Florida. Some
growers minimize losses from RSD by using hot-water treatments
to obtain disease-free seed cane. Scientists at Canal Point screen
clones for resistance to rust, smut, leaf scald, mosaic, RSD,
and eye spot, which is caused by Bipolaris sacchari (E.J.
Butler) Shoemaker. Eye spot is not currently a commercial problem
in Florida.
Damaging insects in Florida of long duration are the sugarcane
borer, Diatraea saccharalis (F.); the sugarcane wireworm,
Melanotus communis; and the sugarcane grub, Ligyrus subtropicus.
An insect discovered in Florida in 1990, the sugarcane lace bug,
Leptodictya tabida (Hall 1991),
has also become a pest, selectively feeding on some clones. In
1994, another insect pest new to commercial sugarcane fields in
Florida was found--the West Indian cane weevil, Metamasius
hemipterus (L.) (Sosa 1995). In
1994, this weevil caused particularly severe damage to several
plantings of CP 85-1382, a promising new clone described previously
in this series of reports.
Geneticists at Canal Point are working to incorporate borer
resistance into the breeding program by selecting for leaf pubescence
(a trait known to promote resistance) in elite sugarcane clones
(Sosa 1996). Currently, there are
no known commercial sugarcane cultivars with pubescent leaves.
Winter freezes are common in the region of Florida where much
of the sugarcane is produced. The severity and duration of a freeze
and the specific sugarcane cultivar are the major factors that
determine how much damage occurs. The damage caused by such freezes
ranges from none to death of the mature sugarcane plant. The sugar
content of these plants declines rapidly if temperatures return
to normal, warmer ranges soon after the freeze. Young, recently
planted and emerged sugarcane plants may die from severe freezes.
Beginning this year, this report includes reactions of sugar content
of mature sugarcane clones after a freeze.
A new emphasis for the Canal Point genetics program is to breed
and select sugarcane cultivars that enhance sugarcane's relationship
with the surrounding Everglades. Two strategies that are part
of the Canal Point program are to breed and select clones that
help reduce the phosphorus content of water discharged from Florida
sugarcane farms and that yield well in soils with higher water
tables.
Each year at Canal Point, about 100,000 seedlings are evaluated
from crosses derived from a diverse germplasm collection. [However,
reports from Mangelsdorf (1983) and
Deren (1995) contend that the genetic
base of U.S. sugarcane breeding programs is too narrow.] This
year, most of the parental clones in the Canal Point program originated
at Canal Point. Some of the clones used as parents this season
also came from Clewiston (Florida), Louisiana, and Texas. In addition,
several feral Saccharum officinarum and S. robustum
clones and interspecific hybrids of these clones were used as
parents.
About 10 percent of 100,000 seedlings from the seedling stage
are advanced to stage I, whence about 10 percent of the 10,000
clones are advanced to stage II. The 1,000 clones in stage II
were visually selected in the seedling and stage I phases. Once
selected as seedlings, clones are vegetatively or clonally propagated.
From this stage on in the selection program, all reproduction
is vegetative; hence, the clones used are genetically identical,
assuming no mutations or the unlikely formation and germination
of true seeds in the plots. From these 1,000 selected clones in
stage II, about 130 are selected for continued testing in replicated
experiments. Each of the first three stages is evaluated for 1
year in the plant-cane crop. The primary selection criteria for
the stage II and all subsequent stages are sugar yield, cane tonnage,
and disease resistance.
The stage III clones are evaluated for 2 years, in the plant-cane
and first-ratoon crops, at four locations. The 11 most promising
clones receive continued testing for 4 more years in the stage
IV experiments reported in this annual publication. Tai and Miller
(1989) also described this selection
program from the seedling to the stage IV phase. Clones that successfully
complete these experimental phases undergo 2 to 4 years of evaluation
and seed-cane increase by the Florida Sugar Cane League before
commercial release. Some of this evaluation occurs concurrently
with the evaluations described here.
Clones with characteristics that may be valuable for sugarcane
breeding programs are identified throughout the selection process.
Sugarcane geneticists in other programs often request clones from
Canal Point. From May 1997 to April 1998, Canal Point answered
requests for clones or seeds from El Salvador, Guatemala, Mexico,
Morocco, Nicaragua, Pakistan, Switzerland, and Thailand. Louisiana,
Maryland, South Carolina, Texas, and Virginia and six other locations
in Florida also received Canal Point clones.
The purpose of this report is to summarize the performance
of the clones in the plant-cane, first-ratoon, and second-ratoon
stage IV experiments sampled in Florida's 1997-98 sugarcane harvest
season.
United States
Department of Agriculture
Agricultural
Research Service
The material on this page is in the public
domain.
Original posting: April 19, 1999.
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