Genetics of Pathogenicity inPuccinia coronata: The Host Range Among Grasses

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Abstract
The host range of 8 forms of P. coronata Cda. among 106 grass species in Israel was determined at the seedling stage. A few species were not susceptible to any of these cultures. Most species were susceptible to more than 1 culture and many were to all 8 cultures. Many common hosts were found, which is very important for genetic studies and for the development of hybrid rust in the field. Grasses vary in responses to the various forms of the rust pathogen; some individuals within a species being susceptible to one form and others to another form of P. coronata. The simultaneous inoculation technique was useful for identifying real common hosts. Host range for 2 forms was also determined at the adult stage. Many hosts reacted the same way at both stages. Some species, however, differed at the 2 stages, indicating some difficulties for further studies, but also suggesting the possible importance in nature of disengagement between the reactions at both stages. Several new host species and even genera were found. The host range of P. coronata in Israel was much wider than in all previous studies combined. Host ranges of the forms differed no more widely than did host ranges of races within 1 form. The use of host range of forms as an aid in the taxonomy of their hosts was invalid for P. coronata because of its very wide host range which represents all the tribes of the Festucoideae. It is postulated that the chance of the host''s exposure to the pathogens'' attack is as important in the evolution of host range as host phylogenetic relationships. The long-term association of hosts and parasites brought about this adaptation.

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