Genetic Control of Resistance to Tan Necrosis Induced by Pyrenophora tritici-repentis, Races 1 and 2, in Spring and Winter Wheat Genotypes

ABSTRACT The symptoms of tan spot of wheat, caused by Pyrenophora triticirepentis, include a tan necrosis component and an extensive chlorosis component. Since tan spot has become the major component of the leafspotting disease complex of wheat in western Canada, the need for resistant cultivars has increased. This study was conducted to determine whether the resistance to tan spot found in a diverse set of spring and winter wheat genotypes was due to resistance genes not previously reported. The genetic control of resistance to necrosis induced by P. triticirepentis race 1 and race 2 was determined, under controlled environmental conditions, for spring wheat genotypes Erik and 86ISMN 2137 and winter wheat genotypes Hadden, Red Chief, and 6B-365. Plants were inoculated at the two-leaf stage and disease reaction was assessed based on lesion type. Tests of the F(1) and F(2) generations, and of F(2:3) and F(2:8) families, indicated that one recessive gene controlled resistance to the necrosis component of tan spot caused by both race 1 and race 2 in each cross studied. Lack of segregation in crosses between the resistant cultivars indicated that the resistance gene was the same in all of the cultivars.     

The Direct Injection Technique for Preparing the Spray Mix - A Method for Reducing Safety and Hygiene Problems in Plant Protection?1

In the past, industry and research institutes have produced a number of technical proposals to improve sprayer technique, and development in this area has been very successful. The «closed sprayer-system>>, the pesticide flushing system, flow regulation systems and updated stirring arrangement are examples of many different practicable improvements. A completely new approach to improving application technique is the « direct injection of pesticides >>: contrary to normal practice the tank of the sprayer is filled with pure water only. The pesticide is introduced in concentrate form into a separate tank and injected into the water flow produced by the equipment pump during the application process. The advantages of this technique include no direct handling of the active substance concentrate; no problems with liquid-stirring; no pesticide residues. A commercial sprayer equipped with a metering device prototype and a newly developed constant pressure fitting is described as an illustrative example of prospective design of a « direct-injection >> system. A number of other technical possibilities exist for putting this method into practice. The advantages of this technique have to be paid by an additional capital outlay but they offer the chance to reduce safety and hygiene problems in chemical plant protection.     

Systemic Resistance Induced by Trichoderma spp.: Interactions Between the Host, the Pathogen, the Biocontrol Agent, and Soil Organic Matter Quality

ABSTRACT Several factors affect the ability of Trichoderma spp. to provide systemic disease control. This paper focuses on the role of the substrate in which plants are grown, resistance of the host to disease, and the ability of introduced Trichoderma inoculum to spread under commercial conditions. Several reports reveal that foliar disease control provided by Trichoderma spp. is more effective on plants grown in compost-amended media compared with in lower-in-microbial-carrying-capacity sphagnum peat media. In Rhododendron spp., host resistance affects control of Phytophthora dieback provided by Trichoderma spp. For example, T. hamatum 382 (T382) significantly (P = 0.05) suppressed the disease on susceptible cv. Roseum Elegans while plant vigor was increased. The disease was not suppressed, however, on highly susceptible cvs. Aglo and PJM Elite even though the vigor of these plants was increased. Using a strain-specific polymerase chain reaction assay under commercial conditions, it was demonstrated that introduced inoculum of T382 did not spread frequently from inoculated to control compost-amended media. Other Trichoderma isolates typically are abundant in control media within days after potting unless inoculated with a specific Trichoderma isolate. Thus, the low population of isolates that can induce systemic resistance in composting and potting mix environments may explain why most compost-amended substrates do not naturally suppress foliar diseases.