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Edward J. Ryder

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Edward J. Ryder

Genes for flowering time appear to be relatively common in lettuce and other Lactuca species. These include previously described major genes Ef-1 an Ef-2, other genes of discrete effect and genes acting in a quantitative manner. Our goals in studying the flowering time phenomenon are: 1)describe the inheritance of the traits, 2) establish their relationship to each other, and 3) elucidate their evolutionary significance.

The PI 175735 (L. serriola) is an accession with narrow leaves, spines and anthocyanin. Its flowering time is daylength related; it is early flowering under long days and late flowering under short days. It was crossed with the late flowering line C-2-1-1, which is homozygous for both late alleles in the Ef system. The F1 is late under short days and early under long days. The F2 population and F3 families were grown under long day conditions in the greenhouse, Segregation in the F2 was 3 early: 1 late. Among F3 families from early plants, segregation was 1 homozygous early: 2 segregating. Within segregating families, the ratio was again 3:1. The evidence suggests a single gene with earliness dominant.

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Edward J Ryder

Lettuce mosaic has been a serious virus disease for lettuce in all locations worldwide where lettuce has been grown. Consequently, the disease and its virus have been well studied. Lettuce plants react to lettuce mosaic virus in a variety of ways. The most common susceptible reaction is an overall vein clearing and mottling, followed by leaf recurving, leaf distortion, and stunting. However, some susceptible types manifest a mild mottling with little additional distortion. Others develop a necrotic reaction, which may be severe, mild, or seasonal. Finally, there are at least three resistant reactions, most frequently appearing as a systemic infection manifested with restricted yellowish lesions. Research is ongoing to sort out the various reactions and their genetic bases. This report describes the inheritance of the severe necrotic reaction and its relationship to the resistant reaction conferred by the allele mo-1. Several previous crosses among necrotic types indicate that the same necrotic allele is operating except that found in `Bibb'. Several crosses were studied. The cross `Salinas' (mot.) × `Crisp As Ice' (nec.) showed that necrotic is due to a single dominant allele. The cross `Salinas 88' (res.) × `Maikonig' (nec.) produced three phenotypes in F2, indicating the action of two loci. The crosses PI 251245 (res.) × `Prizehead' (nec.) and `Vanguard 75' (res.) × `Prizehead' disclosed two recombinant phenotypes, mottled and resistant-necrotic. Necrotic is dominant to nonnecrotic in both susceptible and resistant phenotypes. The genes are inherited independently.

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Edward J. Ryder

Resistance to lettuce mosaic (LMV) in current cultivars of lettuce is due to a single recessive gene, momo, in one of two allelic forms. The nature of the resistance may be described as resistance to multiplication and spread in the plant. Resistance is systemically manifested as small irregular yellowish areas on the leaf. This compares to the usual expression of susceptibility: vein clearing, followed by mottling, leaf margin recurving, and later stunting and yellowing. A cos-like stem lettuce from Egypt, `Balady Aswan', is susceptible to LMV, but reaction to the virus is a milder one than the usual susceptible reaction. Segregating generations from crosses with normal susceptible and resistant lines were analyzed. The data suggest a single gene for reaction type, with mild dominant or partially dominant to severe. Selection of lines from crosses with the resistant type allows the breeder to select resistant and mild alleles together, which confers a higher level of resistance than momo alone. Plants with the combined reaction either show no symptom or show the resistant symptom very late.

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Edward J. Ryder

Three chlorophyll deficiency traits in lettuce (Lactuca sativa) are reported. One, chlorophyll deficient-3 (cd-3), is quite yellow in the seedling stage, and controlled by a single recessive allele. Chlorophyll deficient-4 (cd-4) has sectors of yellow-green and green in the true leaves. It is inherited as a single recessive, and may be allelic to chlorophyll deficient-2 (cd-2). Sickly (si) is stunted, yellow, and partially necrotic, and is also controlled by a single allele. Virescent (vi) is epistatic to cd-4 and the latter is partially lethal. Linkage and additional epistatic relations with previously named chlorophyll deficient genes and other traits are discussed.

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Edward J. Ryder

In an earlier study, two genes controlled flowering time in certain lettuce crosses. Early alleles (Ef-1, Ef-2) at both loci are partially dominant; flowering time in the greenhouse ranges about 100 days from double dominant to double recessive. Crosses between C-2-1-1, a double recessive line, and four cultivars were analyzed to study further the distribution of these genes. Empire and Salinas flower at the same time as C-2-1-1, while Vanguard 75 and Prizehead are earlier than C-2-1-1. Empire × C-2-1-1 and Salinas × C-2-1-1 showed unimodal distribution in F2, indicating segregation of several genes or environmental variation. A linear relationship between F2 plant values and F3 family means from both crosses suggested a polygenic basis. The F2 distribution of Prizehead × C-2-1-1 was similar but showed a greater range of flowering times. An additional major gene was indicated in Vanguard 75 × C-2-1-1, with earliness recessive.

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Edward J. Ryder

Segregation data from crosses between necrotic and mottled lettuce (Lactuca sativa L.) parents showed that a single gene controls the difference in type of reaction to lettuce mosaic virus: necrosis is dominant to mottled. Segregation data from crosses between resistant and necrotic parents differed, depending on the necrotic parent. In crosses with the necrotic cultivar Prizehead, there were two independent genes, one controlling necrotic vs. mottled and the other resistant vs. susceptible. In a cross with the necrotic cultivar Maikonig, resistance was epistatic to necrotic, suggesting a second necrotic allele. Crosses among necrotic cultivars indicated a single gene for the necrotic reaction, with the possibility of more than one necrotic allele. Necrotic alleles identified are named Necrotic-1m and Necrotic-1p.

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Edward J. Ryder

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.

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Edward J. Ryder

In crosses of lettuce (Lactuca sativa L.) between parents producing a mild or susceptible reaction to lettuce mosaic virus, a single gene segregated. The heterozygote reacted in an intermediate manner. In crosses between mild-reacting and resistant parents, the mild reaction gene and the resistant gene segregated independently. The resistant and mild alleles together produced a new phenotype that is usually symptomless. The gene symbol proposed is Mi'Mi, where Mi' gives the mild phenotype. Breeding is in progress to combine the mild and resistant traits in new lettuce cultivars.