Resistance to Powdery Mildew in Wheat Mutants

Duggal, Vivek (1999). Resistance to Powdery Mildew in Wheat Mutants. MPhil thesis The Open University.



Suppressors of resistance genes have been reported to exist in hexaploid wheat signifying that the expression of resistance depends upon the genetic background of the plant. In 1982, ‘Hobbit sib’ hexaploid wheat, was irradiated with fast neutrons and a series of deletion mutants with increased adult plant resistance to rusts and mildew was identified. In the present study this deletion series was evaluated for mildew resistance at various growth stages to identify and characterise resistance. Two mutants, 13-54 and 13-48 were found to be significantly more resistant than the wild type at various adult and seedling growth stages with the resistance appearing to be fully activated at the seedling third leaf stage.

The third leaves of these two mutants and ‘Hobbit sib’ were used for histological studies, to determine the rate of fungal hyphae development. There were no differences in the rate of spore germination and hyphal development during the first 12 hours after inoculation (hai) but by 18 and 24 hai both the mutants had on average a slower rate of hyphal development. This demonstrates that resistance is initially expressed at the pre-haustorial or hyphal penetration stage in the two mutants. By 72 hai, there were significant differences between the proportion of germinating spores forming haustoria in the three genotypes. Large differences in the colony sizes for one mutant compared to Hobbit sib were detected indicating the possible role of post-haustorial resistance also.

To study the association of various pathogenesis related (PR) proteins with this resistance, RNA from the uninfected third leaf of the mutants and ‘Hobbit sib’, was extracted and hybridised with cDNA probes of two PR proteins; PR1 and thaumatin like (TL). The expected sized mRNA transcript bands were detected for PR-1 and TL proteins in the two resistant mutants only. The results suggested that the constitutive over-expression of PR-1 and TL might be contributing to the resistance of 13-48 and 13-54.

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