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- Author or Editor: Edward J. Ryder x
The similar titles of Namkoong’s paper and this one invite comparison, not so much for their similarity as for the differences in sampling rationale. The main difference is in the nature of the populations that are being sampled. The population in the field is usually far away. Further, it is of unknown size and its genetic makeup and complexity can only be guessed.
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.
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.
Big vein has been a problem for growers of lettuce (Lactuca sativa L.), particularly in the western United States, for many years. The principal symptom, vein clearing, lends an unsightliness to the lettuce that may reduce its market value (7). During periods of low temperatures, big vein may delay or prevent head formation and thus reduce the harvest recovery (4).
The artichoke is a popular vegetable in Italy, Spain, and France. The American consumer, upon first encountering this bristly vegetable, may wonder why. Dealing with the artichoke, either as a cook or around the dinner table, may seem more like a confrontation than a culinary venture, and the average artichoke novice may be happy with a stand-off.
Major reliance for protection of lettuce plantings from lettuce mosaic virus (LMV) in the United States is placed on a seed indexing procedure developed in California (1). The only major crisphead lettuce (Lactuca sativa L.) cultivar in the United States with resistance to lettuce mosaic has been ‘Vanguard 75’, released by the U.S. Dept. of Agriculture, cooperatively with the California Agricultural Experiment Station, in 1975 (3). ‘Vanguard 75’ is one of the important cultivars in the mid-February to early March harvest period in the desert districts of California and Arizona. It is also a major early cultivar in the spring season of the San Joaquin Valley. ‘Winterset’ is a new lettuce mosaic-resistant crisphead lettuce. It is suitable for the same periods and districts as ‘Vanguard 75’ and, in addition, is adapted for production in late winter in the desert.
In the last 2 decades, 2 cultivars of lettuce (Lactuca sativa L.) have dominated the western U.S. lettuce industry. The first, ‘Calmar’ was released by the University of California in 1960. For several years in the mid-1960's, it was planted on nearly all the spring, summer and early fall acreage in the Salinas Valley and other coastal districts in California. It is a large, vigorous cultivar of the Great Lakes type. The second, ‘Vanguard’, was released by the USDA in 1958 and for many years has been the mainstay cultivar for early spring production in the Imperial Valley and other desert districts. Each cultivar has spawned a group of selections, a ‘Calmar’ group and a ‘Vanguard’ group, which have increased the adaptive range of the original cultivars.
Lettuce mosaic virus (LMV), has been one of the most destructive diseases of lettuce (Lactuca sativa L.) in nearly all production areas of the world. One of the major goals of the USDA Lettuce Breeding Project in Salinas, California, has been to develop mosaic resistant cultivars. We began this program in 1959 with a search for sources of resistance. Three years later, we identified 3 resistant Plant Introductions from Egypt (3).