Since the comprehensive review by Aycock in 1966 (15), numerous papers on various aspects of the biology and ecology of the soilborne plant pathogen Sclerotium rolfsii Sacco have been published, and many different methods have been tested to control the diseases it causes. This wealth of published informa­ tion over the last 18 years attests to the worldwide importance of this pathogen on many dicotyledonous crops and several monocotyledonous species (8, 15, 139, 168, 187) . Diseases caused by S. rolfsii are especially rampant in the tropics and subtropics and in areas of the southern and southeastern US where temperatures are sufficiently high to permit the growth and survival of the fungus. Yet despite more or less continuous research over the 93 years since the report by Rolfs in 1892 on S. rolfsii on tomato (see 15), this pathogen continues to plague growers and cause considerable economic loss. Control efforts have often met with limited success, due in part to the extensive host range, prolific growth, and ability to produce large numbers of sclerotia that may persist in soil for several years. Furthermore, control measures effective for a particular crop or area may not be adaptable elsewhere due to regulatory or economic con­ straints. This review summarizes the pertinent literature on the biology, ecology, and control of S. rolfsii (including S. delphinii) published since 1965. Articles prior to 1965 are not included, since an extensive bibliography can be found in Aycock's monograph (15) . In addition, some of the published information has been outlined by Domsch et al (69) and Mordue (160) . I also evaluate research

The Biology, Ecology, and Control of Sclerotium Rolfsii

Seed treatments are used on many crop seeds for a variety of purposes. The greatest use of seed treatments has been to provide an inexpensive insurance against rotting of planted seeds by soil fungi such as Pythium spp. and Rhizoctonia solani. Seed treatments for many other purposes are being de­ veloped and used. Increasingly, commercial seed treaters are beginning to view seed treatments as a means to substantially increase the value of the seed and to improve plant growth and productivity. Examples of other types of seed treatments are: (a) treatment with systemic chemicals that can translocate into the seed to control deep-seated plant pathogens. Several chemicals also translocate to the above-ground portions of the seedling and protect against foliar diseases; (b) treatment with microor­ ganisms that can proliferate on the seed, transfer to the root and fix N2, enhance uptake of nutrients, protect the subterranean plant portions against attack by soil-inhabiting fungi, and/or increase plant growth; (c) physical treatments that control seedbome pathogens; (d) seed coatings or pellets that can improve seed shape for planting or provide other benefits; (e) physiolog­ ical seed treatments that enhance germination rate and plant performance; and (j) various treatments that affect seed moistUre relationships and result in improved seed storability or performance.

Concepts and Technologies of Selected Seed Treatments

Publisher Summary There has been a large upsurge in interest in biological disease control recently, reflecting increasing environmental concern over pesticide use. This chapter discusses the ecological considerations, which comprises of suppressive soils, organic amendments and cornposts, monoculture decline, physical and chemical practices, and role of fauna in natural biological disease control. There has been a gradual increase in the number of commercial biocontrol agents on the market for the control of soil–borne plant pathogens over the last few years and only one product, Dagger–G, a Pseudomonaspuorescens marketed by Ecogen, Inc, Lanhorne, PA, USA, for the control of Rhizoctonia and Pythium damping–off of cotton, has been withdrawn from sale because of poor shelf–life of the material. The chapter discusses that chemicals still dominate the disease control market and some consideration should be given to research areas likely to improve further the commercial uptake of biological disease control agents. Consequently, optimizing realistic screening procedures is a first step, which can be refined to target specific types of antagonists. Once specific antagonists have been identified, they can be developed further by consideration of inoculum production, formulation, storage and application, ideally linking the expertise of scientific researchers with industrial partners. Molecular biology has helped identify the modes of action of many biocontrol agents. A considerable effort is currently underway to improve biocontrol efficacy of microorganisms through the use of molecular biology.

Developments in the Biological Control of Soil-borne Plant Pathogens

Improving the efficacy of biocontrol agents against soilborne pathogens

The effects of biological, chemical and integrated control on the formation of selerotia ofRhizoctonia solani on new potato tubers were studied in experimental fields. Sprouts of seed tubers, sprouted in daylight, were inoculated withVerticillium biguttatum, an ecologically obligate mycoparasite ofR. solani. Fungicides were mixed with the top soil. Biological control byV. biguttatum increased the percentage of harvests with less than 5% loss due to grading from 24% (non-inoculated) to 56%. Fungicides at the recommended rates usually gave good results but lower doses were less effective in sand than in loam soils. When fungicides were combined with biological control, the results were often, better: harvests with less than 5% sorting loss increased from 56 to 81%. Integrated control with pencycuron at 25% of the recommended rate was about equal to chemical control with pencycuron at full rate. The advantages of integrated control are discussed.

Control of Rhizoctonia solani in potato by biological, chemical and integrated measures

Coating iris bulbs with a preparation ofTrichoderma harzianum was highly effective under greenhouse conditions in reducing incidence of diseases caused byRhizoctonia solani andSclerotium rolfsii. In field experiments with irises for bulb production, the incidence ofR. solani in plants and bulbs was effectively reduced (up to 93%), and the yield increased (by 35–41%), by applyingT. harzianum either as a bulb coating or broadcast application (biological treatment), treating soil with pentachloronitrobenzene (PCNB; quintozene) (chemical treatment), or solarizing the soil by mulching it with transparent polyethylene sheets (physical treatment) prior to planting. Combined treatments,i.e., chemical-biological or physicalbiological, were the most effective.T. harzianum bulb treatment and broadcast application in field plots increasedTrichoderma population density in the soil by 4–27 times.

A. Kalfon

Papers

Integrated control of soilborne and bulbborne pathogens in Iris