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  • Author or Editor: A.G. Stone x
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Many factors affect the potential for composts to provide biological control of diseases caused by soilborne plant pathogens. Heat exposure during composting kills or inactivates pathogens and weed seeds if the process is monitored properly. Unfortunately, most beneficial microorganisms also are killed by this heat treatment. Conditions must be provided after peak heating that enhance natural recolonization of composts by biocontrol agents. The raw feedstock, the environment in which the compost is produced, as well as conditions during curing and utilization, determine the potential for recolonization by this microflora and the induction of disease suppression. Controlled inoculation of compost with biocontrol agents has proved necessary to induce consistent levels of suppression on a commercial scale. Compost stability is another important factor. Immature composts serve as food for pathogens and increase disease even when biocontrol agents are present. On the other hand, excessively stabilized organic amendments, such as highly decomposed peats, do not support the activity of biocontrol agents and disease therefore develops. Finally, salinity, C to N ratio, and other factors affect suppressiveness. Each of these factors will be discussed.

Free access

Abstract

The trend towards total mechanization of the production of processing tomatoes is creating many new problems. This paper describes one which may become very important as the practice of direct seeding in the field partly replaces the use of transplants.

Open Access

Abstract

Fifty-eight cultivars of tomatoes were screened for the occurrence of high pH fruit. Although large differences in pH were found between and within cultivars, no pH values high enough to permit the growth of Clostridium botulinum were obtained. pH and titratable acidity were not highly correlated. Tomato acidity data obtained from 57 locations in 23 states for 356 cultivars and 212 breeding lines were compiled and analyzed to identify trends. These data show that small-fruited, light colored and “new” cultivars are not low in acid, as is commonly believed. A few high pH data points (pH ⩾ 4.7) were associated with specific cultivars, locations, and conditions (overripening). The response of some higher pH cultivars to acidulation with citric acid was determined; a linear relationship between pH and added acid was found. These data were used to evaluate several methods of acidulation recommended for home canners.

Open Access

Abstract

The potato aphid (Macrosiphum euphorbiae) is a common insect pest of tomatoes. This insect damages the plants by sucking the sap from the leaves and by transmitting plant viruses The severity of aphid infestations on tomatoes varies from season to season and within a season. They are generally most severe during periods of cool weather.

Open Access

Abstract

When cultivars and accessions of the cultivated tomato, Lycopersicon esculentum Mill., and related species, were evaluated for resistance to a leaf miner, Liriomyza munda Frick, in greenhouse and field cage tests, the screening tests revealed several lines of L. esculentum having genes for adult nonpreference or larval antibiosis or both. All accessions of L. hirsutum Humb. & Bonpl. and L. hirsutum f. glabratum C. H. Mull, were virtually immune to attack in both greenhouse and field tests. Lycopersicon pimpinellifolium (Jusl.) Mill, demonstrated a considerable level of antibiosis in the greenhouse, but was not promising in the field. All accessions of L. peruvianum var. dentatum Dun. and L. glandulosum C. H. Mull, tested were susceptible. The commercial cv. VF 145B was nonpreferred in the field.

Open Access

Abstract

Potentially useful levels of resistance to the leafminer, Liriomyza sativae Blanchard (= munda Frick), in Cucumis melo L. were identified in greenhouse and field studies in different years and widely separated locations. Resistant lines were identified as those having the least number of mines per leaf in a given test. Two apparently distinct sources of resistance were found in Plant Introduction (PI) 282448 from Africa and PI 313970 from India. In a single test of F1 hybrids the resistance of PI 282448 appeared to be controlled by recessive genes, while that of PI 313970 appeared to be controlled by partially dominant genes. Plant introductions from Central Asia and East Asia were, in general, the most susceptible.

Open Access

Compost offers the potential to suppress root rots and vascular wilts caused by soilborne plant pathogens, as well as plant diseases affecting aerial plant parts. Many factors affect the degree of control obtained. They include the decomposition level (stability) of the compost, the types of microorganisms colonizing the organic matter after peak heating of the compost, plant nutrients released by the compost (fertility), its salinity, loading rates, and other factors. Biocontrol agents in composts induce suppression through various mechanisms, including competition, antibiosis, hyperparasitism, and the induction of systemic resistance in the plant (roots as well as foliage) to pathogens. Examples of each of the effects are reviewed.

Free access

Abstract

Acidity was measured on ripe and overripe samples of 16 cultivars of tomato (Lycopersicon esculentum Mill.) ‘Ace’ and ‘Garden State’ were the lowest in acidity. In some samples of ‘Garden State’, 25% of the individual ripe fruits exceeded pH 4.8. Overripe tomatoes, tomato tissue infected with Alternaria and anthracnose, and fruits obtained from dead vines were also abnormally high in pH.

Open Access