Principles of Plant Genetics and Breeding

for emasculation, which is done in the bud stage. To
emasculate, the bud is grasped between the thumb and
index finger. Next, the petal in front of the keel and
the sepal on the side of the standard are folded down.
The standard petal is opened with the forceps and the
wing petals are pulled out and down. The standard is
held back with the thumb and index finger while the
operator pulls the keel free of the stigma and anthers.
Alternatively, the keel and wing petals may be removed
all together. The anther and the stamens are removed to
complete the emasculation. If an emasculated flower
will not be immediately pollinated, the hypanthium is
tagged (e.g., with a small thread).
Pollination
Pollen collected between 5 and 7 a.m. is most viable.
Flowers are artificially pollinated in the morning to early
afternoon. The keel may be detached and used as a
brush to directly deposit the pollen onto the stigma.
Some operators transfer the pollen with a camel hair
brush or the tip of the forceps. The environment may
be humidified, but care should be taken not to dislodge
the pollen. Pollen may be collected and stored under
desiccated condition in a cool place (6°C) for up to
about a week without losing viability.
Fertilization occurs between 12 and 16 hours after
pollination, after which the ovary elongates as the intercalary
meristem at its base grows. The peg eventually
penetrates the soil where it develops into a mature
peanut fruit. An identification wire may be tied to the
peg from the emasculated flower before it penetrates
the soil.
Boerma, H.R., and R.S. Hussey. 1992. Breeding plants for
resistance to nematodes. J. Nematol. 24:242–252.
Hyman, B.C. 1990. Molecular diagnosis of Meloidogyne
species. J. Nematol. 22:24–30.
BREEDING PEANUT 535
References and further reading
Seed development and harvesting
Seed is mature for harvesting after about 55–65 days,
depending on the environment and cultivar. Peanuts are
ready to be harvested when 65–70% of them are mature.
Early harvesting results in shriveled kernels. At proper
maturity, the kernels display the distinct texture and
color of the variety, the inside of the shell beginning
to color and show dark veins. Harvesting is easier in
sandy soils, and occurs with less loss of pods with smallpodded
than large-podded varieties.
Common breeding objectives
Some of the major objectives in peanut breeding are as
follow:
1 Yield potential and stability. Breeders are interested
in high crop yield per se, but also a stable yield with
adaptation to various agroecological zones. High
shelling percentage is important. Early maturity is
desired in some production areas.
2 Disease resistance. Important diseases of peanut
include foliar ones such as leaf spot (caused by
Cercospora spp.). Stem and peg rots (caused by
Sclerotium rolfsii) and charcoal rot (caused by
Rizoctonia spp.) are economic diseases in some production
area.
3 Insect resistance. Important insect pests include
leafhoppers, corn earworm, cutworms, and tobacco
thrips.
4 Product quality. Peanuts consist of 40–48% oil and
25–30% protein, making the crop a major source of
vegetable oil and plant protein. Breeding high oil
content is an important objective.
Isleib, G., and G. Kochert. 1994. Introgression from A. cardenasii
germplasm lines. Crop Sci. 33:1418.