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  • Author or Editor: Kenneth L. Deahl x
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Abstract

Intercropping is a well-established practice for increasing production of many agronomic crops from a given land area (5). The land equivalent ratio (LER) is a standard measure of the overall production gain from intercropping and is defined as the land area needed for monocropping to produce the maximum of each crop per unit of land area for intercropping (5). Tomatoes have been investigated as intercrops with cabbage (2), corn (1), cucumber (4). and okra (3). In most of these systems, overall production was greater in intercropping than in monocropping (LER >1.0); however, tomato yields were reduced substantially. The objectives of this research were; a) to determine whether tomato and a short-season crop such as snap bean could be intercropped with minimum impact on tomato and b) to evaluate the performance of four fresh-market tomato cultivars of different maturity and growth habit for intercropping with snap beans.

Open Access

The oomycete, Phytophthora infestans, is a devastating pathogen of potato worldwide. Several genotypes of P. infestans are able to infect other cultivated and weed species of the family Solanaceae and cause symptoms similar to late blight. Changes in P. infestans populations have stimulated investigations to determine if potato strains from new immigrant populations infect nonpotato hosts more often than those from the older population. Expansion of the effective host range may be one of the mechanisms involved in pathogenic changes in natural populations of P. infestans and to determine its significance, it is necessary to establish if the pathogen strains on nonpotato hosts represent distinct genotypes/populations or are freely exchanging with those on potato. This article reports characterization of P. infestans isolates from four solanaceous hosts (black nightshade, hairy nightshade, petunia, and tomato) growing within and around fields of blighted potatoes in four U.S. locations and one U.K. location and their comparison with isolates collected from adjacent infected potatoes. Isolates were characterized for mitochondrial DNA haplotype, mating type, metalaxyl resistance, allozymes of glucose-6-phosphate isomerase and peptidase, and DNA fingerprint with the RG57 probe. Analysis showed close similarity of the petunia, hairy and black nightshade isolates to potato isolates. However, tomatoes from New Jersey and Pennsylvania, respectively, were infected by two distinct and previously unreported pathogen genotoypes, which had quite different fingerprints from P. infestans isolates recovered from nearby infected potatoes. Potato growers should be aware that both weed and cultivated solanaceous species can be infected with P. infestans and may serve as clandestine reservoirs of inoculum. Because some of these plants do not show conspicuous symptoms, they may escape detection and fail to be either removed or treated and so may play a major role in the introduction and spread of pathogens to new locations.

Free access

Late blight, caused by Phytophthora infestans, affects tomatoes and potatoes in Florida during the winter–spring crop season. During the 2005 season, severe late blight epidemics were observed in Florida prompting our survey. Isolates from 2005 to 2007 were characterized phenotypically based on growth on three media, mating type, pathogenicity, and sensitivity to metalaxyl and genotypically based on two isozymes, mitochondrial DNA (mtDNA), and genomic profiling using the RG57 probe. Isolates collected in this survey were all A2, mtDNA Ia, and either 100/100 (2005), or 100/122 (2006/2007) at the Gpi locus, and homozygous 100 at the Pep locus. Novel genotypes infecting tomato in Florida were observed based on the Gpi locus and RG57 genomic profile. We propose US-20 for the collection of clonal isolates recovered during the 2005 season and US-21 for clones recovered during 2006 and 2007. In addition to these novel genotypes recovered from tomato, one isolate was recovered from potato representing the US-8 clonal lineage. The findings of the survey in south Florida and their implications are presented.

Free access