Studies on the Isolation and Growth of Plant Rusts in Host Tissue Cultures and Upon Synthetic Media. I. Gymnosporangium

MORFOLOGIA, FUNÇÕES DOS SOROS E VARIAÇÕES DOS CICLOS VITAIS DAS FERRUGENS

RESUMO Os organismos vivos que são genericamente denominados ferrugens formam um amplo e complicado grupo. Mais de 100 gêneros que incluem cerca de 6.000 espécies são hoje conhecidos. Somente no Brasil são conhecidas cerca de 1.000 espécies pertencendo a 55 gêneros diferentes. As ferrugens pertencem ao grupo de organismos comumente denominados fungos, são organismos muito antigos. Sob o ponto de vista biológico, não há dúvidas de que as ferrugens foram bem sucedidas, tendo sido capazes de parasitar por um período tão longo, e com uma distribuição geográfica tão variada. Isso se deve ao fato de elas serem capazes de produzir diversas formas esporíferas que estão envolvidas em muito tipos complexos de ciclos de vida. Assim, essas variações permitem às ferrugens habilidades surpreendentes de adaptação em diferentes condições ambientais.

Signal exchange between higher plants and rust fungi

The rust fungi appear to have evolved a sophisticated complex of molecular interactions with their host plants that govern both plant resistance and susceptibility. It is suggested that many of these interactions relate to the maintenance and effective exploitation of biotrophy, and that host specificity and the obligacy of parasitism are a consequence of the resulting interactive molecular control of plant and fungal activities. For the dikaryon, plant signals are required for locating stomata and the formation of infection structures, haustorial mother cells, and haustoria. Host susceptibility to both the monokaryon and the dikaryon appears to involve the suppression of defensive secretory processes, the induction of cellular alterations in invaded cells, and, for the dikaryon at least, changes in nutrient translocation. Parasite-specific resistance involves cultivar-specific fungal signals (elicitors) of defense responses such as cell death and callose deposition. The nature of, and evidence for, the signals involved in these interactions are reviewed. Key words: biotrophy, elicitors, rust fungi, signal exchange.

GROWTH OF THE RUST FUNGUS PUCCINIA HELIANTHI ON TISSUE CULTURES OF ITS HOST

Rust-infected cotyledon, hypocotyl, and stem sections of sunflower seedlings were cultured on nutrient agar media. Callus growth from cotyledon sections was negligible, but hypocotyl and stem sections proliferated more or less freely. Infections arising from basidiospores produced an abundant tuft-like growth of haploid surface mycelium. Infections arising from urediniospores lacked almost entirely surface mycelial growth, but produced urediniospores in abundance, and finally teliospores.Copious aeciospore production occurred in some cultures where two basidiospore infections of different mating types coalesced. Later such compound infections produced urediniospores and teliospores. Tufts of mycelium developed on the new callus growth of some cultures. One of these calluses (examined cytologically) contained a number of more or less subnormal pycnia and aecia in different stages of development. Only a few sections produced callus tissue capable of surviving repeated subculturing. In the fourth set of subcultures from one such section, rust mycelium appeared as tufts on six of the calluses.