Effects of temperature and growth stage on the reaction of some wheats to brown rust attack

El-Azzabi, Taher Sadek (1982) Effects of temperature and growth stage on the reaction of some wheats to brown rust attack. University of Southampton, Doctoral Thesis.

Abstract

Relatively little work has been done in this Country on Puccinia recondite. The present study was undertaken to provide a better understanding of the behaviour of brown rust, on winter wheat cultivars in this Country. Brown rust has numerous stages in its developments many of these had previously been studied, but some gaps remained which needed further investigation. Germination, appressorium formation and penetration on these three different rust isolates 74/2, 74/11, and 76/28 on nine winter wheat cultivars, Maris Ranger, Maris Huntsman, Maris Fundin, Kinsman, Sportsman, Armada, Flanders, Waggoner and Hobbit at 10, 15 and 2cPC at 24 and 48 hours incubation at 100% RH, on the second, fifth and flag leaves were studied. The results showed that germination, appressorium formation and penetration levels rate low at 10°C and increased with an increase in temperature and incubation period. At around the optimum 20 C, the processes were complete in 24h and increasing the incubation periot had little effect. There were some significant differences between the effect of isolates on different cultivars, and between the cultivars in their response to the germination, appressorium formation and penetration of different rust isolates, but this was not related to the resistance and susceptibility of these cultivars to the rust isolates at different temperatures and different growth stages. Resistance and susceptibility were however, related to various stages in the past-entry development of the rust. Latent period seemed to be highly affected by temperature, rust isolate, host cultivar and growth stage. Reaction type on cultivars resistant as adult plants was different from that on fully susceptible ones.Resistant cultivars had significantly smaller colonies, shorter lengths of mycelium and fewer haustoria than susceptible ones. The level and type of resistance was affected by temperature, rust isolate and growth stage. Spore production was influenced by temperature with an optimum around 20° C, and was affected by rust isolate, cultivar and growth stage. In the seedling stage resistant cultivars generally produced fewer spores, smaller pustules, a smaller percentage leaf area affected, fewer pustules per leaf and per cm and fewer spores per cm than susceptible cultivars. At the adult plant stage, resistant cultivars in general produced fewer spores, had a smaller percentage leaf area affected, fewer pustules per leaf and per =2=d fewer spores per cm than susceptible ones, but as they posess the -1-,l; plant reaction type they produced large pustules and large number of sporesper pustule. Colony size, mycelium length and haustoria number were shown to be highly correlated with each other in resistant cultivars, although the correlation was weaker for susceptible cultivars. It was also showed that the correlation between these three stages and the spore production, was in general higher in resistant cultivars than that in susceptible ones.

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