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  • Author or Editor: Edward J. Ryder x
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Abstract

Two sources of resistance to lettuce mosaic are described. Resistance is inherited as a single recessive gene. The same gene occurs in both sources. Symptoms on resistant plants are small chlorotic areas distributed sparsely on leaf surface. Later leaves may have more severe symptoms.

Open Access
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Abstract

Achene color and leaf-type genes are linked, with p = 0.34. Achene color and male-sterility genes are linked, with p = 0.39. Leaf-type and male-sterility genes are independently inherited. Achene color and virescent chlorophyll-deficiency genes are linked, with p = 0.03. Thirty-four other linkage comparisons showed independent inheritance.

Endive-type leaf and chlorophyll deficiency are each regulated by recessive alleles. Three separate recessive alleles control albinism.

Open Access
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Abstract

The Salinas River and the valley through which it flows are deceiving to the casual traveler driving through on a summer day. If he looks down while crossing one of the bridges over it, the river is quite unimpressive. The bed seems to be largely overgrown with weeds. The trickles and pools of water seem to have no movement. The traveler is likely to forego a second look and to relegate it to the far reaches of his mind with all the other dry streambeds of the West.

Open Access
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Abstract

In 5 spring trials, the percentage of lettuce plants (Lactuca sativa L.) showing big vein symptoms was consistently low for the resistant line 72-136 and consistently high for the susceptible ‘Great Lakes 65.’ Results were less consistent for the moderately resistant ‘Merit’ and for ‘Calmar.’ During periods of low temperatures a lower percentage of big vein infected plants than healthy plants was harvested. Results were variable at high temperatures but, in general, differences were less.

Open Access
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Abstract

Two new lettuce genes are described and named: chlorophyll deficient-2 (cd-2) and Early flowering (Ef). Brown pericarp is either a pleiotropic effect of plump involucre (pl) or is caused by a closely linked gene. White pericarp (w) is epistatic to brown. Endive-like leaf (en) and white pericarp are linked, with P = 0.47. Virescent (vi) and fringe (fr) are linked, with a recombination value of p = 0.25. Genes for spininess and anthocyanin color are linked. Endive, white, virescent, fringe, and male sterile-6 (ms-6) form a linkage group. Three other double recessives have interactive relationships. Endive and fringe together are phenotypically extreme endive; virescent and golden (go) together are golden; golden and chlorophyll deficient-2 are golden and partially lethal.

Open Access
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Abstract

A partially dominant allele for early flowering in lettuce (Lactuca sativa L.) reduces flowering time by about one-half. This property is useful in backcross breeding procedure to accelerate the transfer of useful alleles to a desired recurrent parent. Application of the technique to transfer resistance to lettuce mosaic is described through 4 backcrosses. Generalization of the technique for other species is discussed.

Open Access
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Two new lettuce (Luctuca sativa L.) genes are described and named truncated leaf (tn), and sickly (si). A gene for reflexed involucre is identical to that previously described in wild lettuce (L. serriola L.). Mosaic reaction (me) and light green (lg) are linked, with P = 0.448. Six gene pairs tested for linkage are independently inherited. Sickly is epistatic to light green.

Free access
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Abstract

Three new lettuce (Lactuca sativa L.) genes were described and named: shiny green (Sgsg), salmon (Sasa), and apple green (Agag). Plump involucre and male sterile are linked, with p = 0.345. Plump involucre and Early flowering are linked closely, with p approaching zero. Twenty-five gene pairs tested for linkage were independently inherited. In achene color, the order of recessive epistasis is white > yellow > brown. The double-recessive combination vivicd-2cd-2 (virescent and chlorophyll deficient) is phenotypically virescent and partially lethal.

Open Access
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Abstract

Variation in flowering times within genotype classes of the Early Flowering (Efef) gene in lettuce (Lactuca sativa L.) suggested that more than one gene may govern flowering time. Segregation from crosses between earlier and later plants in the early class indicated a second discrete flowering time gene. This gene was confirmed in F3 family analyses and in subsequent progeny comparisons. The first gene is renamed Early flowering-1 (Ef-lef-1) and the second is named Early flowering-2 (Ef-2ef-2). The consequences of the presence of the second gene in cultivars and in the backcross breeding procedure are discussed. Flowering time is influenced by daylength and temperature.

Open Access
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Abstract

Mosaic-susceptible and -resistant lettuce cultivars and breeding lines were evaluated for seed transmission of the virus. Two methods of indexing were used: the seedling method, in which seedlings from infected plants were observed; and the Chenopodium method, in which a local lesion host, C. quinoa, was inoculated with seed samples ground in buffer solution. Susceptible lines transmitted at a rate averaging about 2% per plant. Over 90% of resistant lines failed to transmit the virus; the rest transmitted at extremely low rates, averaging 0.49% in one experiment. The parent plant’s environment appears to affect the transmission rate. Low day temperature results in a higher rate than high.

Open Access