Verticillium and Fusarium Wilts of Cotton: Molecular Genetic Markers for Disease Resistance

Abstract

Verticillium wilt and Fusarium wilt, vascular diseases caused by the soil-borne fungal pathogens Verticillium dahliae and Fusarium oxysporumf.sp vasinfectum, respectively, are among the most important diseases of cotton (Gossypium spp. ), with the potential to cost the cotton industry millions of dollars in lost production. These fungi colonise the plant roots and penetrate the vascular tissues, where they proliferate in the vascular system and are eventually distributed throughout the plant. Plants infected with either Verticillium Fusarium display similar symptoms of chlorosis and necrosis of leaves, defoliation, stunting or plant death. Cross-sections of the stern reveal a brown or black centre which is due to the formation of meIanised products in the infected vascular system. However, chlorosis in Fusarium wilt tends to be in patches and vascular browning is more pronounced than in Verticillium wilt. In general, the symptoms of Fusarium wilt are much more severe and result in greater crop losses (Bell, 1992a and 1992b).

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Changes to the resistance management strategies for conventional insecticides and Bt transgenic cotton (1997/98 - 1998/99)

Abstract

The Australian cotton industry has been practising curative conventional insecticide resistance management and preventative Bt transgenic cotton resistance management for fifteen and two years now, respectively. The actual strategies are reviewed and reformulated at the end of each season at a series of industry meetings which include representatives of growers, consultants, researchers, resellers, agrochemical industry and aerial operators. The ACGRA (Australian Cotton Growers' Research Association) TIMS (Transgenic and insecticide Management Strategy) committee is responsible for coordinating this annual process for both strategies. The strategies outlined below are the result of the input of a large number of talented people, both within the TIMS committee but also throughout the wider cotton industry in general and their assistance and dedication is gratefully acknowledged.

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Do Degree Days accurately describe rates of cotton development

Abstract

Degree days are commonly used by industry and researchers to estimate expected crop development. This assumes that cotton's potential development is largely a function of temperature. Controlled environment studies show that the function currently used to calculate Degree Days does not accurately reflect the effect of high temperatures on development. Preliminary analysis of the data shows that the inclusion of an optimum temperature in the degree day function in addition to the base temperature of 12'C can make more consistent predictions of cotton development. Improving this function will enable better predictions of cotton development in a greater range of environments and seasons.

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The Living Soil: Soil microorganisms and their role in soil processes

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Soil organisms (biota) carry out a wide range processes that are important for soil fertility and health in both natural and managed agricultural soils. There is a two way relationship between the soil biota and agricultural production. As soil biota play a key role in a number of key nutrient transformation processes, crop residues form the essential supply of carbon (energy source) and nutrients for microbial activity

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Impact of insecticides in Ant Abundance in Cotton at ACRI

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Interest amongst cotton growers in incorporating beneficial insects into pest management is at an important stage in its development. Growers need reliable and cost effective tools to incorporate beneficials into ERM systems used on their own farms. However, while it is clear that beneficials are important in managing insect pests, we have little understanding of their quantitative contribution to the suppression of pest species. Research is still needed to quantify the effectiveness of beneficials, predict their impact on key insect pests, and where appropriate, investigate the impact of current management tactics

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Cotton Industry Briefing Paper

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The purpose of this paper is to outline the Australian cotton industry's concerns and position on the new US Farm Bill, currently being negotiated by the House of Representatives (House) and Senate and the potential ramifications for Australia, as an efficient producer and exporter of raw cotton. This paper will be used by an Australian Government and industry delegation that will visit Washington in early December to lobby against the Bill. The delegation will be led by the Minister for Agriculture, Fisheries and Forestry, The Honourable Warren Truss.

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Field Evaluation of Transgenic 2,4-D Tolerant Cotton

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The efficacy of transgenic, 2,4-D tolerant cotton, developed by CSIRO has been field tested over the past 2 seasons on an irrigated field at Premer, on the Liverpool Plains of NSW. The material tested was a single transgenic line in the Coker 315 cultivar containing an introduced 2,4-D degradation gene and it showed good tolerance to 2,4-D, even at high rates. The effects of spraying both transgenic and normal plants with 2,4-D were monitored in the 1996/97 season using visual damage symptoms and dry matter production. Dry matter cuts taken at the end of the season indicated complete tolerance of the transgenic line to 2,4-D at up to twice the normal field rate when applied during the vegetative growth stage. Good tolerance was also observed at flowering and boll-fill stages.

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An insight to Heliothis Thresholds for Ingard

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In managing insect pests growers are today faced with increasing insecticide resistance, a lack of new chemistry and increasing production costs. The introduction of transgenic Bacillus thuringiensis,(BT- Cr1lAc), technology will allow a general reduction in insecticide use. However it is important to delay resistance to conventional chemistry for as long as possible, as their use will play a critical role in managing/delaying resistance to transgenic (Ingard), plants. Therefore using appropriate heliothis thresholds for Ingard crops is important

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Industry Approach to Disease Control

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The confirmation of Fusarium wilt in a field north of Moree daring the 1996/7 season jolted the cotton industry. Major sections of industry were alarmed at the extent the disease had spread through many cotton production areas of Australia. Unlike most other diseases of cotton, Fusarium wilt poses more questions than answers on how the industry effectively manages and contains the disease in known affected areas. This paper concentrates on the industry's efforts to manage Fusarium wilt. In 1993 the fungus Fusarium oxysporum f.sp vasinfectum (fov) was isolated from cotton plants from the Darling Downs, and 1994 from the Boggabilla district. This disease has now been identified at other locations at Mungindi, Boggabilla, Goondiwindi, Moree, and daring 1998 at Garah, Miles and Theodore. Fusarium wilt has not been recorded in Central Queensland, St George or cotton production areas in the Namoi and Macquarie Valleys of New South Wales. Two distinctly different strains of Fusarium oxysporum f.sp vasinfectum (Fov) - Downs and Boggabilla, have been identified.

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Evaluation of companion crops as part of an integrated pest management package for GM cotton in the Kimberley

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Cotton was previously grown in the Ord during the 1960's and early 1970's. One major cause of the industry's demise was the development of insecticide resistance in Helicoverpa armigera (Heliothis). Although heliothis was not the major pest initially, pesticides targeting a range of other insects conferred resistance. Spray records indicate that whilst only 12 insecticide applications were required to grow the first crops, this rose to 21 sprays in 1971 and to an average of 40 sprays in the final season of 1974 (Michael and Woods 1980). As the development of genetically modified cotton (Ingard) progressed through the mid1990's, Department of Agriculture Western Australia, and Australian Cotton CRC scientists envisaged that it may be possible to develop a new cotton industry in the Ord. The new cotton industry would use integrated pest management (PM) and INGARD as the cornerstones of the system. Field trials evaluating PM systems commenced in 1996 and the first large scale trial(10-40ha) was conducted in 1997

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