RA 00110.pdf - OAR@ICRISAT

in about 30 accessions. Unlike monodii, the involucres
are tightly arranged on the inflorescence as in
pearl millet. Like monodii, the involucres readily
shatter. The dominant species in the fields and roadsides
of western Senegal is reported to be ssp. monodii
(Brunken 1977). This intermediate type should
theoretically be found wherever monodii and pearl
millet are or have been growing in the same area.
Stenostachyum should be almost as good a source
of genetic diversity for the same characteristics
as monodii, but an exception may be cytoplasmic
diversity, since it cannot be determined whether
pearl millet or monodii was the female parent (and
contributed cytoplasm) in the original cross. Stenostachyum
germplasm may be somewhat easier to
manipulate since it is partially domesticated. However,
the author prefers beginning with monodii in a
program to transfer germplasm from a wild to the
cultivated species, based on general observations of
genetic diversity in the two subspecies.
The secondary gene pool (Table 1) has only one
known species, P. purpureum or napiergrass (2n =
4x = 28). It is a sexual species. Napiergrass (A'A'BB
genomes) has the A genome in common with pearl
millet. The author's research has shown that the B
genome is dominant over the A' genome and masks
genetic variability (consequently phenotypic variability)
on the A' genome. Because of this relationship,
mutations have accumulated on the A' genome since
the beginning of the species with very little selection
pressure on the A'. As such, the A'genome should be
an excellent source of genetic variability. Napiergrass
readily crosses with pearl millet and produces sterile
triploid hybrids, but fertility can be induced by doubling
the chromosome number of the triploid to
produce a hexaploid. Napiergrass is a rhizomatous
perennial, with desirable characteristics, e.g., resistance
to most pests, vigorous growth, and outstanding
forage yield potential. Most of these characteristics
appear to be on the B genome. Interspecific hybrids
with pearl millet have immediate forage potential
but can also be used as bridges to transfer genes from
napiergrass to pearl millet.
The tertiary gene pool includes the remainder of
the wild Pennisetum species (Table 1). Examples of
species in this group can be found in Jauhar (1981)
and Stapf and Hubbard (1934). Crosses between
these species and pearl millet are difficult, but are
sometimes possible with special techniques. Interspecific
crosses are usually highly male and female
sterile, but fertility can be induced through chromosome
manipulation. This group includes both sexual
and apomictic species that are both diploids and
polyploids with base chromosome numbers of x = 5,
7, 8, and 9. There are both annual and perennial as
well as rhizomatous and nonrhizomatous species in
this group. Most have a protogynous habit of flowering.
Some useful characteristics of this group
include apomictic reproduction, perennial growth
habit, drought tolerance, cold tolerance, pest resistance,
and cytoplasm diversity. In addition to agronomic
characteristics, this tertiary group has excellent
germplasm for basic scientific research. As an
example, two species, P. orientale and P. villosum
have reported chromosome numbers of 2n = 18, 27,
36, 45, and 54 each for studying polyploidy effects.
Using the Wild Species
Germplasm from wild species is usually more difficult
to manipulate than germplasm within the cultivated
species. However, ease of manipulation and success
in using germplasm from wild species will vary both
within and between species, and can be affected by
both genotype and ploidy level. More success can be
expected when using wild species to improve a cultivated
species if:
• objectives are specific (with some flexibility),
• a team approach is used,
• good screening or selection techniques are available
for desired characteristics,
• alternative methods are tested,
• large populations are studied,
• highly heritable characteristic(s) are transferred,
and
• multiple cycles per year are possible.
These factors have helped to make utilization of
wild germplasm successful in the Grass Breeding
Program at Tifton, Georgia, USA. They also usually
become more important as breeding moves from
using wild subspecies in the primary gene pool to
using wild species in the tertiary gene pool. Until
recently, the wild species have not been used to
improve pearl millet.
In January 1980, the first crosses in the Grass
Breeding Program were made in the greenhouse
between pearl millet and three monodii (primary
gene pool) accessions sent by M. and Mme. A. Lambert,
French plant breeders in Senegal. Monodii
was used as the female parent to transfer the monodii
cytoplasm to pearl millet. The F 1 crosses planted
in the field in 1980 segregated for both rust-free
(Puccinia substriata var. indica) and leaf spot-free
36