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III. Economic Importance and Breeding Objectives
Hammons, 1971). Virginia-type peanuts produce oil with a lower linoleic acid
content and tend to have greater oil stability than Spanish or Valencia types.
Hybrids from subspecific crosses also vary in chemical composition of the oil
Khan et al. (1974) examined the refractive indices of oil from hybrids and
segregating populations of six peanut crosses in order to assess fatty acid compositions of the groups. The iodine values were under the control of a few additive
genes and thus highly heritable. A wide range of genetic variability in iodine
value in the F2 populations of these crosses indicated that selection could improve
quality and stability of oil.
Peanut seeds contain about 26% protein and the resulting peanut meal about
twice that percentage (Woodroof, 1966). Although variation in the protein level
has been demonstrated for a wide range of genotypes (Holley and Hammons,
1968; Young and Hammons, 1973), little breeding work to exploit this variation
has been reported.
In many countries there is a concerted effort to develop cultivars resistant to
leafspots and rust, two of the most important diseases of peanuts worldwide.
Norden (1973, 1980) reviewed the progress and difficulties encountered in breeding for disease resistance in peanuts. The progress in breeding for resistance to
several important pests is summarized in what follows.
I . Disease Resistance
a. Rust. Peanut rust, caused by Puccinia arachidis Speg., has become established throughout Asia, Australia, and much of Africa and has occurred with
increasing frequency in the United States (Hammons, 1977). Sources of resistance to rust were identified over a decade ago (Bromfield and Cevario, 1970;
Bromfield, 1974; Hammons, 1977). According to Hammons (l977), the resistant sources consist of three breeding lines, which are as follows:
(a) Tarapoto (PIS 259747,34 1879,350680,38 1622,405 132) originating from
(b) Israel line 136 (PIS 298115 and 315608), which was selected from the
cultivar Virginia Odom (Cook, 1972). Bromfield and Bailey (1972) concluded
that the resistance of PI 2981 15 was controlled by two recessive genes. Fourteen
progeny from the cross of PI 298 1 15 and an unknown pollen parent identified as
FESR 1-14 were released as rust-resistant germ plasm.
(c) DHT 200 (PI 314817), which was collected from Peru and is being considered for release in Australia (Shorter, 1978).
J . C. WYNNE AND W . C. GREGORY
At ICRISAT, Subrahmanyam et al. (1980) have screened over 4000 lines of
cultivated peanuts for their rust reaction in the field and screenhouse. The resistance of Tarapoto and Israel line 136 was confirmed and several additional
resistant germ plasms were identified. Two land races, NC Ac 17090 and EC
76446 (292), were more resistant than previously identified resistant sources.
Several species of Arachis also have been shown to be resistant to rust,
developing no symptoms when tested in India by Subrahmanyam et al. (1980)
b. Cercospora Leafspots. Cercospora leafspots, the most common disease
of peanuts, are caused by Cercospora arachidicola Hori (early leafspot) and
Cercosporidium personatum (Berk. and Curt.) Deighton (late leafspot). Potentially valuable sources of resistance to C. arachidicola were identified in cultivated peanuts in Georgia (Sowell et a l . , 1976). Resistance was confirmed by
Foster et al. (1980), who proposed to increase the level of resistance using
recurrent selection and a detached leaf technique developed by Melouk and
Monasterios et al. (1978) evaluated the reaction of 180 peanut accessions for
resistance to leafspot caused by both C. arachidicola and C . personatum. Of the
genotypes screened, 14 had very few lesions caused by C . arachidicola, 10 had
very few caused by C. personatum, and 15 had few lesions from either pathogen.
Nigam et al. (1980) found that several accessions resistant to rust were also
resistant to late leafspot.
The wild species of Arachis are also resistant to leafspot (Abdou et al., 1974;
Gregory et a l . , 1973; Moss, 1980). Sharief et al. (1978) inoculated three species
of Arachis and three of their F, and F2 hybrids with spore suspensions from C.
arachidicola and C. personatum. They concluded that variation in disease tolerance resulted from multifactonal genetic differences in the hosts. The authors
suggested that introgression of genetic factors from the two resistant Arachis
species studied ( A . chacoense Krap. et Greg. nom. nud. and A . cardenasii Krap.
et Greg. nom. nud.) into the genomes of A . hypogaea could increase host
Wild Species of Arachis Immune to Pucciniu armhidis Speg."
A . duranensis Krap. et Greg. nom. nud.
A . correntina (Burk.) Krap. et Greg. nom. nud.
A . cardenasii Krap. et Greg. nom. nud.
A . pusilla Benth.
A . sp. 9661
A . sp 10596
"After Subrahmanyam et a l . (1980).
USDA PI No.
33 1 194
resistance in the cultivated peanut. Smartt et al. (1978) advocated maximizing
resistance by selection in the A . chacoense x A . cardenasii population before
attempting gene transfer to the cultivated species.
Hexaploids from crosses of cultivated peanuts with A . chacoense, A . cardenasii, and other diploid species have been exposed in field trials to C. permnatum in India and C. arachidicola in Malawi (Moss, 1977, 1980). Lines from
the hexaploids of A . hypogaea x A . cardenasii were found to be resistant to both
pathogens (Moss, 1977, 1980). Stalker et al. (1979) also reported resistant
selections to both pathogens in 40-chromosome derivatives from an A . hypogaea
x A . cardenasii hybrid population.
c . Ajlatoxin. Aflatoxin produced by Aspergillus jlavus (Link) Fries is a
major problem facing the peanut industry in the United States. Mixon and Rogers
(1973) and Mixon (1976) found two Valencia accessions (PI 337394 and
337409) and several breeding lines resistant to seed colonization by two
aflatoxin-producing strains of A.j7avus. LaPrade (1974) found that an intact testa
is required for resistance, the testa appearing to act as a mechanical barrier to the
Many additional factors seem to influence susceptibility of seeds to invasion
by Aspergillus (Bartz et al., 1978). Therefore breeding of resistant cultivars has
proven difficult. Seeds of genotypes resistant to invasion by A.flavus under field
growth contained aflatoxin concentrations equal to genotypes easily colonized
when the two were stored under humid conditions (Wilson et a l . , 1977). Nevertheless, Mixon (1976, 1980) has developed a productive line resistant to colonization.
d . Rosette Virus. Rosette virus is transmitted by an aphid (Aphis craccivora
Koch.). Cultivars resistant to rosette were developed in Senegal and the Upper
Volta (Gillier, 1978). These cultivars are being used as source of resistance to
deveiop cultivars adapted to other growing areas of Africa.
e . Southern Stern Rot. No presently available lines of peanuts appear to be
highly resistant to stem rot caused by Sclerotium rolfsii Sacc. Garren (1964)
concluded that the Virginia cultivar NC 2 was the least susceptible to this disease
and lines of the fastigiate type were the most susceptible. This observation was
confirmed by Muheet et al. (1975). Despite breeding efforts to develop resistant
cultivars at several institutions (Lin, 1959; Beute et a l . , 1976), except for NC 2
(Gregory, 1970), no cultivars resistant to stem rot have been released.
f. Cylindrocladium Black Rot. Cylindrocladium black rot (CBR) is caused
by a soil-borne fungus, Cylindrocladium crotalariae (Loos) Bell & Sobers.
Valencia types are most susceptible and Spanish types are most resistant to CBR
(Wynne et al., 1975b; Coffelt, 1980b). NC 3033 and Va GPl have been released
as resistant germ plasm (Beute et al., 1976; Coffelt, 1980a). Advanced breeding
lines resistant to CBR have been developed in North Carolina using an accelerated breeding program (Wynne, 1976b). Backcrossing to an adapted cultivar to
J. C. WYNNE A N D W. C. GREGORY
improve quality may be required before cultivar release. Hadley et al. (1979)
studied the F, , F2, and parental generations from a four-parent diallel cross (two
resistant to black rot, Argentine and NC 3033, and two susceptible, NC 2 and
Florigiant) under greenhouse conditions to determine the inheritance of CBR
resistance. Because general combining ability was significant for both generations, indicating that CBR resistance is primarily controlled by additive genetic
effects, they proposed that genetically distinct sources of resistance be combined
to produce genotypes with superior CBR resistance. Such material should buffer
potential pathogen adaptation to overcome resistance.
g. Nematodes. Lesion nematodes. Smith et al. (1978a) evaluated six
peanut introductions and two commercial cultivars (Starr and Spancross) for
resistance to lesion nematodes [Pratylenchus brachyurus (Godfrey) Felip Sch.
Stek] under field conditions. Three introductions were found to have some
Root-knot nematodes. Minton and Hammons ( 1975) conducted greenhouse
tests for resistance to root-knot nematodes, Meloidogyne arenaria (Neal) Chitwood, a major parasite of peanuts in the southeastern United States. None of 479
entries tested showed resistance to the nematode.
Banks (1969) tested about 400 accessions of cultivated peanuts and 33 species
collections for resistance to the northern root-knot nematode, Meloidogyne hapla
Chitwood. Although differences in susceptibility among the cultivated lines were
observed, Banks (1969) concluded that resistance was not great enough to be
useful in developing resistant cultivars. One wild species from section
Rhizomatosae, PI 262286, had a moderately high level of resistance, but this
species has not yet been successfully hybridized with cultivated peanuts.
h. Other Diseases. Peanut breeders are also attempting to develop cultivars
resistant to Verticillium wilt (Verticillium sp.), Sclerotina blight [Sclerotinia
sclerotiorum (Lib.) DeBary], Webb blotch (Phoma arachidicola), collar rot
(Diplodia gossypina), and pod breakdown (Pythium sp.). Resistant lines have
been reported for Verticillium wilt (Smith, 1961; Frank and Krikun, 1969; Khan
et al., 1972, 1974), Sclerotina blight (Porter et al., 1975), collar rot (Porter and
Hammons, 1975), and Webb blotch (Smith et al., 1978b).
2 . Insect and Mite Resistance
a . Southern Corn Rootworm. The southern corn rootworm (Diabrotica undecimpunctata howardi Barber) is the most destructive insect pest of peanuts in
the Virginia-Carolina production area. The cultivar NC 6 has a high enough level
of resistance to rootworm to eliminate the need for insecticide application in most
soils of the region (Campbell et al., 1977). NC 6 is also moderately resistant to
the potato leafhopper (Empoascafabae Harr.), although sources with a higher
level of resistance have been isolated (Campbell et al., 1976).
b . Lesser Cornstalk Borer. The lesser cornstalk borer, Elasmopalpus lignosellus (Zeller), is a major insect pest on peanuts in the southeastern and
southwestern United States. Leuck and Harvey (1968) screened germ plasm for
lesser cornstalk borer resistance but their results were inconclusive. Smith et al.
(1980) screened seedlings of 490 genotypes for their reaction to lesser cornstalk
borer larvae under greenhouse conditions. Eighty entries gave a significantly
better reaction than the check cultivar, Starr.
c. Mites. Johnson et al. (1977) have found resistance to the two-spotted
mite, Tetranychus urricae Koch, a major pest of peanuts in North Carolina
during dry seasons in several species of Arachis. No evidence of highly resistant
commercial cultivars was reported. Several of the wild species of Arachis were
found to have resistance approaching immunity.
d . Thrips. Young et al. (1972) screened 872 peanut entries for resistance to
tobacco thrips, Frankliniella fusca (Hinds). Only moderate resistance was
Immature and adult thrip populations in the buds and flowers of developing
peanut plants were studied by Tappan and Gorbet (1979) to evaluate thrip damage. They concluded that thrip control on peanuts is not economical because
injurious populations occur too early in the growing season to influence yields.
e . Fall Armyworms. Leuck and Hammons (1974) observed that the nutrition
of the host plant can influence the expression of resistance to armyworm
[Sportoptera frugiperda (J. E. Smith)]. They conducted a study using three
growth media and various fertilizer combinations and found that armyworm
preferred foliage of peanuts grown in Tifton loamy sand field soil over that of
peanuts grown in washed sand or vermiculite. The data also showed that fall
armyworm resistance varied with the types of fertilizer and with vigor and
appearance of the single cultivar utilized in the study. Resistance to fall armyworm has been reported (Duke, 1980).
IV. BREEDING AND QUANTITATIVE GENETICS
A . VARIABILITY,
A N D CORRELATION
Bernard (1960) estimated genetic and environmental variability for several
traits, including seed yield, number of pods, and weight per seed in the F,
through F4 generations of 4 crosses between 8 diverse cultivars and 15 crosses
between 6 F4 selections from the first group of crosses. Seed size (weight per
seed) had a higher estimate of heritability than did seed yield. Several traits were
correlated with yield, but a selection index including yield and any or all of the
J . C. WYNNE A N D W . C. GREGORY
remaining nine characters was not superior to selection for yield alone (Table
Syakudo and Kawabata (1965) found that genotypic correlations among 15
characters in the 6 possible crosses of Virginia-, Valencia-, and Spanish-type
peanuts were higher than phenotypic correlations. Estimates of broad-sense heritability were low for all traits of economic importance.
Lin (1966) also found that estimates of heritability for number of pods and
seed yield were relatively low. He reported that the major portion of genetic
variance among F2 and F3 progenies of a Spanish X Virginia cross was due to
dominance effects for number of pods and yield. Estimates of broad-sense heritability for an Fs bulk population were higher for yield and number of pods in
high planting densities than in low densities (Lin et al., 1971).
Martin (1967) obtained narrow-sense heritability estimates of approximately
70% for oil content, shelling outturn, and yield using F, and backcross progenies
between two cultivars. He reported that cultivar differences were due to two pairs
of alleles for oil content, one for shelling outtum and five for seed weight. Oil
content was not correlated with yield.
Coffelt and Hammons ( 1974) reported correlation coefficients and heritability
estimates for nine components of yield in an F2 population between Argentine
(Spanish type) and Early Runner (Virginia type). The characters measured were
number of pods and seeds per plant, pod and seed weight per plant, 100-seed
weight, length and breadth of 10 pods, number of seeds per pod, and pod
length-to-breadth ratio. They found highly significant positive correlations between number of pods and pod weight, number of seeds and seed weight, pod
weight and number of seeds, pod and seed weights, and number of seeds and
seed weight. Selection for increases in any of the four characters, number of
pods, pod weight, number of seeds, or seed weight, should result in a corresponding increase in the remaining traits. Pod breadth was also significantly
correlated with 100-seed weight. Other significant correlations were obtained,
but they were small in magnitude. Broad-sense estimates of heritability for
100-seed weight, pod length, pod breadth, and the pod length-to-breadth ratio
were high (71-90%). Low heritability estimates were observed for number of
pods, pod weight, number of seeds, seed weight, and seeds per pod.
Tai and Young (1975) studied the inheritance of protein content and oil content
using six cultivars and their F2 populations. They concluded that both protein
content and oil content were quantitatively inherited. Correlations between protein content and oil content were negative and varied from nonsignificant to
highly significant in the various populations. Holly and Hamrnons (1968) had
previously reported a tendency for a reciprocal relationship between oil content
and protein content. However, enough exceptions were found for the 26 cultivars
tested to invalidate an absolutely negative relationship between oil and protein.