No abstract

progenies from crosses to early maturing spring types in AusResistancetoMycosphaerellagraminicolacamalagento?Septoria tritici tralia and in Israel are reported to have failed (Rosielle and blotch, was identified in progenies of crosses with European winter Brown

Lettuce (Lactuca sativa L.) seeds are inhibited from germinating above an upper temperature limit that is dependent upon cultivar, growing conditions and seed treatments. Thermoinhibition is accompanied by an increasing sensitivity of germination to reduced water potentials (ψ). We have employed a water relations analysis (hydrotime model) of seed germination rates to investigate the basis of thermoinhibition. Germination rates can be characterized by the distribution of base water potentials among seeds in the population (ψb(g)) and a hydrotime constant indicating the total accumulated hydrotime (MPa · h) above the base required for radicle emergence. The hydrotime model adequately described germination time courses across a range of ψ at both high and low temperatures. Increasing temperature caused the ψb(g) distributions to become more positive, accounting for the greater sensitivity to ψ and inhibition of germination. Increases in embryo osmotic potential and in the turgor yield thresholds of both the radicle and the endosperm/pericarp envelope contributed to this change. Seed priming (prehydration and drying) treatments speeded germination by reducing the hydrotime requirement. Priming also resulted in smaller increases in ψb(g) at high temperature, alleviating thermoinhibition by lowering the embryo yield threshold sufficiently to compensate for the increased endosperm resistance. The beneficial effects of priming in lettuce appear to occur primarily in the embryo, rather than in the surrounding envelope tissues.

In 1989, a group of researchers, farmers and farm advisors initiated an interdisciplinary study of the transition from conventional to low-input and organic management of a 4-year, five-crop rotation. Crop yields initially varied among systems, but now appear to be approaching each other after a transition period that included the development of practices and equipment most appropriate for each system. Farming practices and crop production costs are carefully documented to compare the various systems' economic performance and biological risks. Supplying adequate N and managing weeds were challenges for the low-input and organic systems during the first rotation cycle, and experiments are being conducted on an 8-acre companion block to find solutions to these and other problems. Leading conventional and organic growers provide a much-needed farmer perspective on cropping practices and economic interpretations, because we try to provide “best farmer” management of each system. Research groups within the project are focusing on soil microbiology, economics, pest management, agronomy and cover crop management.

The 20-acre main experiment compared conventional, low-input and organic management using a 4-year, five-crop rotation of processing tomatoes, safflower, corn and wheat followed by double-cropped dry beans. Processing tomatoes, shown being mechanically harvested, were the key cash crop of the rotation. Cover-crop nitrogen supply and weed management were the most important challenges facing lowinput and organic farming systems when compared to conventional systems in the first 4 years of the Sustainable Agriculture Farming Systems project at UC Davis. Cover-crop timing and management using appropriate equipment were important for the success of transitional systems. The participation of local farmers ensured that optimal agricultural practices were used to manage all farming systems. Researchers regularly consulted gro wer-cooperators to determine "best farmer practices" of conventional, low-input and organic farming systems.