Infection of ryegrass by three rust fungi (Puccinia coronata, P. graminis and P. loliina) and some effects of temperature on the establishment of the disease and sporulation

Abstract

Experiments were conducted to examine the processes leading up to the infection of Lolium temulentum by crown rust (Puccinia coronata), stem rust (P. graminis) and brown rust (P. loliina), and the effects of temperature on these processes and sporulation. Uredia of all three rusts were produced freely if the adaxial leaf surface was inoculated, but did not form following inoculation of the abaxial surface. Light and scanning electron microscopy revealed abnormal growth of germlings on the abaxial surface which had amorphous sheet-like epicuticular waxes and very few stomata. On the adaxial leaf surface germ tubes of all the rusts orientated at right angles to the long axis of the leaf. However, the directional growth of germ tubes was often disrupted when they contacted the surface of bulliform cells at the base of leaf grooves. For P. loliina the optimum temperatures for urediospore germination and sub-stomatal vesicle formation were 12-16ЊC, and 8-20ЊC for appressorium formation. The optimum temperatures, for the same stages of fungal development, for P. coronata and P. graminis were higher. Urediospore production of P. loliina was higher at 10ЊC than at 25ЊC, but was similar at both temperatures for P. coronata.

Resistance to rust fungi in Lolium perenne depends on within-species variation and performance of the host species in grasslands of different plant diversity

“…Aeciospores germinate on the grass hosts. They initiate the outbreak of the disease, which is characterized by the proliferation of uredinia producing a vast amount of urediniospores, which spread within a few weeks, particularly in late summer and autumn (Roderick and Thomas 1997). Sexual reproduction of these fungi depends on an obligate host alternation.…”

“…Both pathogens are known to produce visible sporangia mainly in late summer and autumn (Roderick and Thomas 1997). Disease incidence was estimated visually in the Weld during 2-6 September 2003 (just before the second mowing) in each subplot.…”

Influência da luminosidade e da camada de cera epicuticular de superfícies de folhas de soja na infecção de Phakopsora pachyrhizi

“…No trabalho de Carver et al (1990) (Roderick & Thomas, 1997). A intensidade diferencial da ferrugem observado nas superfícies foliares não se correlacionou com as características da cera epicuticular.…”

Condições de ambiente favoráveis à germinação e à infecção de Puccinia substriata var. penicillariae em diferentes cultivares de milheto pérola

“…Para o patossistema milho (Zea mays L.) x Puccinia polysora Underw., Godoy et al (1999) observaram que a infecção das plantas foi favorecida por temperaturas de 23 o C e períodos de 2 a 24 h de molhamento foliar. Roderick & Thomas (1997) por pelo menos 5 h de molhamento foliar. Com base nos resultados observados no presente trabalho podese explicar o rápido progresso da ferrugem do milheto no plantio da seca no Estado do Rio de Janeiro e a habilidade do patógeno de infectar e colonizar o seu hospedeiro resultando em rápido progresso da doença sob condições favoráveis, mesmo que estas ocorram por períodos curtos.…”