pollinated and bulked to begin development of PR5BR
 (photoperiod-insensitive). During 1978 and 1979, seeds
 from F2 plants were bulked and grown under long days at
 Isabela where the population was subject to random
 mating. In 1980, 1981 and 1982 the population was grown
 under long days at Isabela. At the end of each random
 mating cycle, male sterile plants were selected for
 resistance to anthracnose, rust, fusarium root and stalk rot,
 zonate leaf spot, sugarcane borer and lodging. PR5BR is
 photoperiod insensitive, and should be a source of both
 B-lines maintainerss) and R-lines (restorers). Seed of this
 population is available in small quantities from TARS.
 Other sorghum populations developed in cooperation with
TARS are as follows: RP1R and RP2R (Ross et al., 1977); RSP3BR
(Craig et al., 1979); Three Pairs (A and B) of Sorghum Lines with
Az Cytoplasmic-Genic Sterility (Schertz et al., 1981); GPT2RB
(Duncan et al., 1982); and NP22 (Gorz et al., 1984).


Agronomic Studies
 During the last decade a series of studies on sorghum grain
yield have been conducted in Puerto Rico. Wahab et al. (1976),
Sotomayor-Rios and Miller (1977), and Sotomayor-Rios and
Weibel (1978) reported yields averaging 4,000 kg ha-'.
Sotomayor-Rios and Lugo-L6pez (1978) reported grain yields
which ranged from 4,504 to 6,884 kg ha-' in studies of nitrogen
application and timing. Split application of the maximum quan-
tity of N (280 kg ha-') resulted in the highest crude protein con-
tent. Near maximum yields (almost 90%) were found with one
application of 56 kg ha-' N. In cooperation with Texas A&M
University, Sotomayor-Rios et al. (1984) evaluated 15 grain
sorghum cultivars with potential for the tropics on an Oxisol and
on a Vertisol. The hybrids ATx634 x 76CS490, ATx623 x
RTAM428 and ATx378 x RTx430 were the highest yielding en-
tries during the plant and ratoon crops. Cultivars such as these
appear capable of yields of over 8-10 tons in a 240-day period
under two consecutive harvests. Better resistance to the local
diseases and insects should raise the yield potentials of sorghum
even higher.
 We have studied the development, selection and testing of
sorghum x sudan and sorghum x sorghum forage hybrids in
Puerto Rico (Sotomayor-Rios and Telek, 1977; Sotomayor-Rios
and Santiago, 1981; Sotomayor-Rios et al., 1981; Torres-Cardona
et al, 1983; Sotomayor-Rios and Torres-Cardona, 1982;
Sotomayor-Rios et al., 1983; Torres-Cardona et al., 1984;
Sotomayor-Rios and Torres-Cardona, 1984a; and Sotomayor-Rios
and Torres-Cardona, 1984b). Locally developed single and three-
way forage sorghum hybrids (Torres-Cardona et al., 1983) are
capable of producing over 25 tons of dry forage ha-' with about
10% crude protein in only 180 days. The excellent dry forage
yield potential, relatively low HCN-p values and high protein
content of these hybrids, make them adaptable to intensive
forage production schemes in the tropics. Forage sorghum height
and leaf area have been highly correlated with forage yields in
Puerto Rico (Sotomayor-Rios and Torres-Cardona, 1984a; and
Sotomayor-Rios and Torres-Cardona, 1984b). Forage quality im-
provement depends on increasing digestibility and animal intake.
Improved quality is shown by increasing in vitro dry matter disap-
pearance (IVDMD), higher protein, and adequate levels of essen-
tial minerals. Decreasing non-digestible constituents, eliminating
or lowering toxic components, and developing disease resistant
genotypes will contribute to obtaining a forage of improved
quality. Studies conducted at TARS are aimed at the develop-
ment of lines or cultivars with higher IVDMD, possessing the
brown midrib character (bmr). This gene has been associated
with lower lignin content and increased digestibility compared to
normal sorghum genotypes (Gourley and Lusk, 1978).


Bird, Insect, Disease and Nematode Problems
 The most serious pests of sorghum in Puerto Rico are birds and
insects. Birds cause damage from the milk stage to maturity,
especially on small scale winter plantings. Generally, the grain
sorghums most susceptible to bird damage are the white and
yellow-seeded varieties, while the brown types (high tannin) are
the most resistant. Brown seeded, high tannin sorghums have the
disadvantage of reduced feed value for monogastric animals. To
protect grain sorghums from bird damage under experimental
conditions, breeders have used various methods. The application
of bird repellents and the use of an alarm-method have not been
effective in keeping the birds from attacking the sorghum grain.
 The most important insects attacking sorghum in Puerto Rico
(Barbosa, Pedro, Personal communication) are the sorghum
midge, Contarinia sorghicola; and sorghum webworm, Celama
sorghiella; and Stenachroia elongella, the old world webworm.
Other economically damaging insects on local sorghum include:
the corn earworm, Heliothis zea; the fall armyworm, Spodoptera
frugiperda; the sugarcane borer, Diatraea saccharalis; the lesser
cornstalk borer, Elasmopalpus lingnosellus; the corn aphid,
Rhopalosiphum maidis, and the chinch bug, Blissus leucopterus.
 Limited research on sorghum diseases has been reported in
Puerto Rico (Alconero et al., 1977; Powell et al., 1977; and Hep-
perly et al., 1982). The main field diseases affecting sorghum in
Puerto Rico are rust (Puccinia purpurea Cke), anthracnose (Col-
letotrichum graminicola [Cesati] G. W. Wilson), root and stalk
rot (Fusarium moniliforme Sheid), gray leaf spot (Cercospora
sorghi Ellis and Everhart), zonate leaf spot (Gloeocercospora
sorghi Bain and Edgerton), leaf blight (Helminthosporium tur-
cicum Pass), downy mildew (Sclerospora sorghi Weston and Up-
pal) and maize dwarf mosaic virus (MDM). Grain molds and
storage decay are serious contraints to production of quality
sorghum seed under the humid tropical island climate.
 The world losses due to nematode damage requires more atten-
tion in sorghum production areas. Limited research on the effect
of nematodes on sorghum has been conducted in Puerto Rico.
Bee-Rodriguez and Ayala (1977) reported on the interaction of
Pratylenchus zeae with four soil fungi. The authors concluded
that, under greenhouse conditions, a population consisting of
1,500 P. zeae in 20-cm pots were pathogenic on sorghum and
suppressed top and root growth. Hernandez-Catalan (1977)
evaluated 10 sorghum lines (selected from PR2BR population) for
nematode resistance. He found that the average yield of the 10
sorghum lines when planted in soil treated with Dasanit (Fen-
sulfothion) at the rate of 33.7 kg ha-' (active ingredient) yielded
about 3,095 kg ha-' of grain. The same ten lines, however, yield-
ed an average of 2,650 kg ha-' of grain when planted on the soil
not treated with Dasanit. Ayala and Bee-Rodriguez (1978)
described the field symptoms of nematode susceptibility in
sorghum of plants growing at the TARS Isabela experiment farm.
These authors reported that two to three weeks after germination
most plants turned purplish, wilted and died in a few days, a
symptom typical of dieback. The roots turned deep red and the
cortex was loosened. Nematodes of the species P. zeae were in-
variably associated with the symptoms.


Black Layer Studies
 Quinby (1972) and Eastin et al. (1973) studied the use of black
layer (BL) formation in grain sorghum as an indicator of
physiological maturity. Weibel et al. (1982) reported on the rela-
tionship of BL to sorghum kernel moisture content and max-
imum kernel weight in nine hybrids in Puerto Rico. In most cases
BL formation and maximum dry weight occurred at the same
time or within one maturity stage. They concluded that BL for-
mation can be used as a good indicator of physiological maturity
and maximum dry weight under tropical conditions.


VOL. XX-PROCEEDINGS of the CARIBBEAN FOOD CROPS SOCIETY


291