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Over a 2-year period, disease incidence and severity caused by tomato-yellow-leaf-curl-virus (TYLCV) in lines of tomato (Lycopersicon esculentum) derived from interspecific hybridization with wild species of L. pimpinellifoliuim, L. hirsutum and L. peruvianum ranged from non to intermediate. The average fruit weight of these lines ranged from 25 to 90 grams. Crosses between TYLCV-resistant lines derived from the same wild species produced progenies similar to their parents in the level of resistance. However, progenies of 2-wild species combination showed little higher in levels of resistance than their parents. Analysis of F1, F2 and backcross populations from crosses of the most promising TYLCV-resistant lines with the susceptible cultivar showed that resistance appeared to be incomplete dominant and controlled by few genes.
Abstract
Twenty-seven accessions of four Lycopersicon species were evaluated for branched broomrape (Orobanche ramosa L.) resistance in a greenhouse pot experiment during 1988. The highest levels of resistance were found in accessions LA 372 and LA 1333 from L. peruvianum (L.) Mill.; LA 1380, LA 1599, LA 1581, and LA 1478 from L. pimpinellifolium Mill.; and LA 1311, LA 1228, and LA 1268 from L. esculentum var. cerasiforme. No appreciable levels of resistance were found among L. hirsutum Humb. and Bonpl. accessions. Percent of tomato plants with O. ramosa flower shoots could be used as a screening method for rapid testing of large collections of tomato germplasm.
A greenhouse experiment was conducted over two growing seasons to study the physical and mechanical properties of a recycled multilayer plastic cover and its effect on the production of greenhouse-grown tomatoes. Two experimental greenhouses were constructed, one covered with recycled multilayer film and the other with conventional virgin monolayer film. The air temperature under both covers was similar; the soil temperature in the recycled multilayer house was a few degrees lower in the afternoon hours to midnight than in the virgin monolayer house. The recycled multilayer film retained its strength and elasticity over a useful service life of 7 months (one growing season), after which severe degradation occurred as manifested by a 50% loss of elongation at break. During the useful lifetime of the film, haziness, light scattering, and light transmission of the recycled film was similar to the conventional film. The thermal analysis of the recycled film revealed a low stability against thermo-oxidative degradation and the infrared analysis indicated the presence of a measurable amount of degradation products, mainly carbonyl groups, in the recycled film in comparison with conventional film. During the useful lifetime of recycled film, yield components of the tomato crop were identical to the conventional film in both growing seasons. In conclusion, waste plastic recycling offers an attractive solution to nuisance environmental problems. However, the useful lifetime of recycled films needs to be improved.