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A technique involving Restriction Fragment Length Polymorphism (RFLP) was used to observe the DNA fragment polymorphism between a bean cultivar with I/I genotype and a bean cultivar with i/i genotype. The I gene encodes immunity to bean common mosaic virus (BCMV).

Powdery mildew of wheat, Erysiphe graminis f. sp. tritici attacks wheat during periods of rapid growth, high levels of nitrogen fertilizer, high humidities, and cool temperatures. Yield losses due to mildew are caused by reduction in photosynthesis, increase in respiration and transpiration, impairment of heading and grain filling, and loss of plant vigor and growth.

In order to respond to the low economic and harvesting yields caused by diseases that attack the tomato, we considered using tomato varieties resistant to late blight (Phytophthora infestans) of tomato (Lycopersicon esculentum) and potato (Solanum tuberosum). The evaluation of the percentage of infestation was performed with tomato leaflets over a 168 hour period. The percentage of infestation was recorded every eight hours from the time of inoculation until maximum infestation was reached. The methodology applied was at random and included six treatments and five replications. The experiment consisted of collecting healthy leaflets from five improved varieties and one local variety of tomato. After collection, the leaflets were disinfected and inoculated in petri dishes on both sites of the midrib with Phytophthora infestans at concentrations of 1 x 107 conidium/mL. The commercial variety (Santa Cruz Kada Gigante) presented the lowest average infestation rate (50%) during the evaluation stage from time of inoculation up until 120 hours. After 120 hours, the leaflets of this variety also reached maximum infestation. A comparison of the study conditions to the scale of resistance values shows it must belong to a moderately resistant variety with horizontal resistance genes to this fungal disease.

Resistant (65-410 and 65-393) and susceptible (breeders Lahontan) alfalfa seedlings were infected with the Northern root-knot nematode, Meloidogyne hapla. Infected roots were fixed, stained, and embedded in plastic for ultrastructural investigations. Sections of plastic embedded tissue, cut at 0.5-1.5 microns for light microscopy investigations, were stained with various histochemical stains to determine the chemical composition of the nematode-altered tissues. In the susceptible cultivar, giant cells were formed by enlargement of nematode-stimulated cells without cell wall lysis. The giant cells became multinucleate by karyonkinesis without cytokinesis. Proplastids in the giant cells became structurally altered to form tubular complexes. The resistant plants usually responded to the nematodes by a hypersensitivity reaction followed by extensive wall buildup in cells surrounding the infection sites. Nematodes often remained in the necrotic tissues.

No description available.

No description available.

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No description available.