Colonization and sporulation of Peronospora viciae on cultivars of Pisum sativum

Abstract

The behaviour of Peronospora viciae was examioed on four pea {Pisum sativum) cultivars (Maro, Superb, Victory Freezer and Surprise) which appeared to exhibit varying degrees of resistance to this pathogen. Penetration into all cultivars was similar aod mainly by direct entry through the cuticle. The pathogen grew in a similar manner and at a similar rate in all the cultivars during the early stages (<96 h) of tissue colonization. As it approached the onset of sporulation its growth slowed down in the more resistant cultivars but in no instance were any hypersensitive or other host cell reactions observed. Greater differences between the cultivars were seen in the extent of sporulation, with the least resistant cultivar (Superb) bearing the largest number of sporangiospores. There was much less sporulation on the most resistant cultivar (Maro) and the process was more dependent on temperature than it was on Superb. The development of mature plant resistance occurred in a similar way and on a similar time-scale in all cultivars. The youngest leaflets on plants which were less than 8 weeks old at inoculation showed the least resistance to infection and colonization.

Ultrastructure of the host‐pathogen interface of Peronospora viciae in cultivars of pea which show different susceptibilities

“…The widespread lysis of hyphal cytoplasm *t advanced stages of infection observed by electron microscopy would reduce vital stainbg of these hyphae and possibly account for the apparent decline in leaf area colonized Mien scored by liglit microscopy (Dickinson *• Singh, 1982)., The death ofa large proportion of viable cytoplasm would clearly account for the reduced levels of sporulation observed on this cultivar. However, it is not known whether hyphal death is a cause or a consequence ofthe haustorium abnormalities described above.…”

“…Alternatively, it may he tliat the impairment of haustorial function (inability to absorb and translocate nutrients) causes premature senescence and lysis of the intercellular hyphae resulting in haustorium collapse. It is interesting that resistance in Maro is temperaturedependent, since it is largely overcome at high temperatures {Dickinson & Singh,, 1982),. It is possible that at higher temperatures the increased rate of uptake of material into haustoria may be sufficient to overcome the impairment indicated here.…”

Screening techniques and sources of resistance to rusts and mildews in grain legumes

“…Sporulation in partially resistant cultivars may also be more sensitive to temperature, while susceptible types can support sporulation from 4-24 • C (Dickinson & Singh, 1989;Pegg & Mence, 1970). Resistance has been noted to increase with the age of the plant (Dickinson & Singh, 1982;Stegmark, 1991) while Mence & Pegg (1971) noted that this process reversed during senescence. Independent of the age of seedlings, the leaves that were terminal and newly unfolded, or embryonic, developed the greatest amount of infection and sporulation (Stegmark, 1991) demonstrating that downy mildew is primarily a disease of young tissue.…”

“…Resistance to downy mildew in pea may affect the expression of disease through delayed sporulation, fewer conidia per unit area of fungal colony or unit of leaf area, degeneration of haustoria (Dickinson & Singh, 1982) or through the development of fewer haustoria (Clark & Spencer-Phillips, 1994). Sporulation in partially resistant cultivars may also be more sensitive to temperature, while susceptible types can support sporulation from 4-24 • C (Dickinson & Singh, 1989;Pegg & Mence, 1970).…”

Resistance to Peronospora viciae expressed as differential colony growth in two cultivars of Pisum sativum

“…Local infections are usually s>-mptomless before this occurs (Reiling, 1984) and the true extent of myeelial growth and oospore formation is not detected; partial resistance must therefore be assessed by microscopy of inoculated tissues (Lebeda & Reinink, 1991). This approach has been applied by Dickinson & Singh (1982) to P. viciae infections of cultivars where resistance was expressed late in colony development.…”