Heterologous expression of Septoria lycopersici tomatinase in Cladosporium fulvum: effects on compatible and incompatible interactions with tomato seedlings.

The anti-fungal, steroidal, glycoalkaloid saponin, alpha-tomatine, is present in uninfected tomato plants in substantial concentrations, and may contribute to the protection of tomato plants against attack by phytopathogenic fungi. In general, successful fungal pathogens of tomato are more resistant to alpha-tomatine in vitro than fungi that do not infect this plant. For a number of tomato pathogens, this resistance has been associated with the ability to detoxify alpha-tomatine through the action of enzymes known as tomatinases. In contrast, the biotrophic tomato pathogen Cladosporium fulvum is sensitive to alpha-tomatine and is unable to detoxify this saponin. This paper describes the effects of heterologous expression of the cDNA encoding tomatinase from the necrotroph Septoria lycopersici in two different physiological races of C. fulvum. Tomatinase-producing C. fulvum transformants showed increased sporulation on cotyledons of susceptible tomato lines. They also caused more extensive infection of seedlings of resistant tomato lines. Thus, alpha-tomatine may contribute to the ability of tomato to restrict the growth of C. fulvum in both compatible and incompatible interactions.

Aetiology of yam (Dioscorea rotundata) tuber rots held in traditional stores in Nigeria: importance of Fusarium spp. and yam beetle.

The extent and causes of yam (Dioscorea rotundata) tuber rots were investigated in Igalaland, Nigeria. Rots were found to be associated with prior physical damage in almost all cases. Numerous fungal species were isolated from the infected lesions of which Fusarium spp. predominated, not Botrydiplodia theobromae as previously reported in other studies. None of the fungi was able to infect undamaged yams in laboratory experiments. The damage was caused by both biotic and abiotic factors of which the yam beetle (Heteroligus meles) was the largest single cause. There were significant differences in the frequency with which different varieties of yam were attacked by H. meles and found to be infected with Fusarium spp. In an independent survey of farmers' experience of yam rots, varieties that scored well correlated with apparent resistance to the beetle and Fusarium spp. These studies highlight the importance of yam beetle infestation and the need to have independent methods for varietal authentication.

An investigation of microtubule organization and functions in living Drosophila embryos by injection of a fluorescently labeled antibody against tyrosinated alpha-tubulin.

Rhodamine-labeled monoclonal antibodies, which react with tyrosinated alpha-tubulin (clone YL 1/2; Kilmartin, J. V., B. Wright, and C. Milstein, 1982, J. Cell Biol., 93:576-582) and label microtubules in vivo (Wehland, J., M. C. Willingham, and I. Sandoval, 1983, J. Cell Biol., 97:1467-1475) were microinjected into syncytial stage Drosophila embryos. At 1 mg/ml antibody concentration, the microtubule arrays of the surface caps became labeled by YL 1/2 but normal development was found to continue. The results are compared with the data from fixed material particularly with regard to interphase microtubules, centrosome separation, and spindle and midbody formation. At 5 mg/ml antibody concentration the microtubules took up larger quantities of antibodies and clumped around the nuclei. Nuclei with clumped microtubules lost their position in the surface layer and moved into the interior. As a result, the F-actin cap meshwork associated with such nuclei either failed to form or subsided. It is concluded that microtubule activity is required to maintain the nuclei in the surface layer and organize the F-actin meshwork of the caps.