Mycorrhizas are symbiotic associations between the roots of plants and fungi. They come into existence when the plant's root system becomes infected with an appropriate fungus.

A disease can only occur when a virulent pathogen contacts a susceptible host under favourable environmental conditions. The incidence and severity of a disease reflects the occurence of these three factors. Plant breeders aid in disease control by developing resistant cultivars. Growers contribute to disease control by using farm management practices that reduce survival and dispersal of pathogens and/or modify the crop environment to make it less favourable for the pathogen.

The most outstanding features of recent seasons have been the relatively dry conditions experienced in most areas during growth and boll setting followed by unprecedently wet harvests. The variety scene has also seen major changes. Very little blight has occurred in DP90 as a result of the relatively dry conditions experienced allied to the successful lowering of seed-borne infection by the CSD clean seed program together with growers doing their best to avoid the disease by growing this blight-susceptible variety on clean fallow ground. Meanwhile there has been rapid changeover in the CSIRO varieties with the original Siokra 1-1 being replaced over the last two years by firstly Siokra 1-2 and then this year by the bigger-bolled, high yielding Siokra 1-4. In the same period Sicala 3-1 was replaced by Sicala 3-2. Now, for the coming season, the original big-bolled Sicala type has been replaced by the new small-bolled Sicala 33. In addition to Siokra 1- 4 and Sicala 33 there is the okra leafed Siokra L22 for hotter growing conditions and the normal leaf CS 189 which has performed well in bad Verticillium conditions in the Namoi Valley. Both these two varieties also show potential for dryland growing conditions.

The fungal disease Verticillium wilt has been of sporadic importance in irrigated cotton for many years. It has traditionally been most serious in cool seasons in parts of the Macquarie valley, around Wee Waa and on the Darling Downs. Crop rotation (particularly with cereals) and other cultural practices help to prevent buildup of the disease. After a period of relatively low Verticillium levels for much of the 80s, the disease has made a pronounced comeback in recent seasons. During the 1988/89 season the disease was common in almost all areas from Warren to Biloela. Last season Dr Stephen Allen even found quite severe outbreaks at Bourke where, because of the very hot summers, the disease would not be expected to flourish.

Again, as for previous conferences, we are providing an update of the ACCT results over the last two seasons. In both seasons 30 entries were tested at each of 12 sites (Warren, Breeza. Narrabri, Merah North, Bourke, Moree, Boggabilla, St George, Cecil Plains, Theodore, Biloela and Emerald) but in the 88/89 season the Biloela yield results were discarded because of 2,4-D damage.

Okay, so what should I talk about? Well, for one thing, what better than what I see as the eternal, ever-increasing breeding dilemma - that is, what and how many attributes should a breeder aim to improve in any particular breeding project and what weight or selection pressure should be placed on each

Plants encounter many environmental stresses such as droughts, flooding, extreme temperatures and high salt concentrations just to name a few. Some plants have been shown to respond to a particular stress by switching on a particular set of genes that then synthesise a set of proteins that assist the plant to survive the stress. Studying these genes and the proteins they encode will give us an understanding of how plants perceive their environment and the biochemical action needed for survival in that environment.

As cotton is naturally sensitive to a range of herbicides used for the control of broadleaf weeds, post-emergence suppression of such weeds is limited to relatively inefficient lay-by herbicides and mechanical means including interrow cultivation and hand chipping. Cotton cannot be treated with over-the-top applications of effective broadleaf herbicides such as Roundup and 2,4-D, and is, intact, often adversely affected by the drift of 2,4-D sprayed on grain crops in nearby fields. The introduction of genes for herbicide resistance by genetic engineering of cotton may not only provide resistance to this drift damage, but could also make possible the direct application of previously toxic herbicides to the cotton crop, thereby increasing the options for weed control.

The last year has seen a growing public concern over the use of chemical pesticides for the control of insect pests in cotton at a time when the Cotton Industry itself is still facing the real risk that these chemical pesticides will become ineffective due to the development of resistance by the insects. Improvements in the natural tolerance of cotton varieties to insect attack, by whatever means, should satisfy both parties by, one the one hand, reducing the need for pesticide application and its consequent deleterious impacts on the environment, and, on the other, by providing another weapon in the arsenal for the control of insects by an Integrated Pest Management strategy. One strategy that has been suggested, and currently under assessment by the breeders at Narrabri, is to increase cotton's Host Plant Resistance to Heliothis by breeding for the production of allelochemicals that the insects will find unpalatable. While this approach may be successful, the yield and quality penalties of producing these chemicals remains uncertain. We have adopted an alternative approach that will use genetic engineering to introduce into cotton genes for the production of insecticidal proteins that will be toxic to Heliothis larvae, but hopefully with little yield or quality penalty since the expression of these genes can be very tightly regulated to the cotton tissues at most risk to insect attack.

This project utilises information from Emerald and other irrigation districts in the State to develop a scheduling system, WATERSCHED, as part of a Cotton Management Decision Program. OBJECTIVES 1. To determine cotton yield response functions to differing levels of irrigation water and nutrients, to enable farmers to make better decisions on use of those input resources. 2. To develop a Cotton Management Decision Program which provides commercially relevant options of water scheduling and fertiliser application for extension officers, consultants and cotton growers, to optimise crop profitability. To increase the adoption by farmers of beneficial water management and fertiliser practices.