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III. Economic Importance and Breeding Objectives

III. Economic Importance and Breeding Objectives

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PEANUT BREEDING



45



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

(Tai, 1972).

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.

C. PESTRESISTANCE



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

Peru.

(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).



46



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)

(Table 11).

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

Banks (1978).

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

Table I1

Wild Species of Arachis Immune to Pucciniu armhidis Speg."

~~~



Species

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.



Section



Origin



2 19823

33 1 194

262141

338448

262848

216233



Arachis

Arachis

Arachis

Triseminalae

Rhizomatosae

Rhizomatosae



Argentina

Argentina

Bolivia

Brazil

Brazil

Paraguay



PEANUT BREEDING



47



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

fungus.

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



48



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

resistance.

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).



PEANUT BREEDING



49



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

found.

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,

HERITABILITY,

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



50



J . C. WYNNE A N D W . C. GREGORY



remaining nine characters was not superior to selection for yield alone (Table

111).



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.



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