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. Several of the clones with high
yields of sugar per hectare identified in this report will never
become commercial cultivars.
Deren et al. (1995) explain mathematically
how sugar yield is not the only economic factor on which sugarcane
yields are judged. 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 mechanical 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 only in some 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, and it 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 1998 growing season, not counting about 20 percent of the
area for which cultivars were not specified, the top seven cultivars
made up 91.9 percent of the total Florida sugarcane area (Glaz 1998). Each of these seven cultivars--CP
80-1827, CP 72-2086, CP 80-1743, CL 61-620, CP 73-1547, CP 78-1628,
and CP 70-1133--was susceptible to at least one of the following
sugarcane diseases: 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 and 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 by Clavibacter xyli subsp. xyli Davis,
Gillaspie, Vidaver, and Harris--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. Eye spot, caused by Bipolaris sacchari (E.J.
Butler) Shoemaker, 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. Stalk populations
may decline after severe freezes kill recently planted and emerged
sugarcane plants. Beginning last year, this report has included
reactions of sugar content of mature sugarcane after a freeze.
Updated information is included in table 1.
A new emphasis for the Canal Point genetics program is to breed
and select sugarcane cultivars that will enhance sugarcane's relationship
with the surrounding Everglades. Two strategies being pursued
are to breed and select clones that help to reduce the phosphorus
content of water discharged from Florida sugarcane farms (Glaz et al. 1997) and that will yield
well in soils with higher water tables.
Each year at Canal Point, approximately 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 from Canal Point. In addition, clones used as parents
this season came from Clewiston (Florida), Louisiana, Texas, and
Réunion, in the Indian Ocean. Also, 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 each plant (clone) is genetically identical
to its precursor, assuming no mutations or the unlikely formation
and germination of true seeds in our plots. From these 1,000 selected
clones in stage II, about 130 are selected for continued testing
in replicated experiments. The seedling stage, stage I, and stage
II are each evaluated for 1 year in the plant-cane crop at the
USDA Sugarcane Field Station in Canal Point. The primary selection
criteria for the stage II and all subsequent stages are sugar
yields, 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, all in commercial sugarcane
fields. 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 phase
to stage IV. Clones that successfully complete these experimental
phases undergo 2 to 4 years of evaluation and seed-cane increase
by the Florida Sugar Cane League, Inc., 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 1998 to April 1999, CP clones or seeds were
requested from and sent to Ecuador, Egypt, El Salvador, Morocco,
Pakistan, Peru, and Switzerland. California, Georgia, Kansas,
New York, and Texas, and five 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 in Florida's 1998-99 sugarcane harvest season.
United States
Department of Agriculture
Agricultural
Research Service
The material on this page is in the public
domain.
Original posting: June 20, 2000.
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