Characterisation of Rhizoctonia Solani(Thanatephorus cucummeris)isolates in Manitoba

Mwiindilila, C.N. M.Sc., the University of Manitoba, February, 1984.
Characterisation of Rhizoctonia solani Isolates from Manitoba Fields.
Major Professor: C.C. Bernier

Seventy four isolates of R. solani were recovered from diseased
seedlings of rapeseed, faba bean, peas, lentils, sugarbeet,potato and
other special crops in Manitoba, in 1981 and 1982. The isolates were
grouped on the basis of the color and texture of mycelium, and the
amount and color of sclerotia produced. Mycelial zonation, the size
and distribution of sclerotia were not consistent features of any
single group and were thus not used in the assignment of isolates into
cultural morphology groups.

Isolates were also grouped according to their anastomosis groups
(AG) determined by pairing with known-AG tester cultures. All AG-4
cultures were correctly assigned to their anastomosis group on the
basis of their morphological characteristics. Other isolates,
especially slow growing cultures and those with inconsistent pigmentation,
showed overlapping cultural features and could not be correctly
assigned to their AGs on the basis of cultural morphology alone.
Isolates were distributed among anastomosis groups as follows: six in
'AG-2' composed of isolates that anastomosed with both AG-2T1 and
AG-2T2 testers; seven in AG-2T1, one in AG-2T2; four in AG-3; forty

six in AG-4; and ten in AG-5- Two of the isolates in 'AG-21 also
anastomosed with the AG-3 tester, with each other and with other
'AG-2' isolates. These isolates may belong to AG-B1, a group that has
not been reported in North America before. No AG-1 isolates were
recovered in Manitoba during 198l and 1982.


Isolates in each AG varied in pathogenic!ty from non-pathogenic to
highly pathogenic on a given host. Some isolates were pathogenic on
faba bean, peas, lentil and rapeseed, while some isolates were
pathogenic on three, two or only one of the greenhouse test hosts.
With a few exceptions, AG-4 isolates were largely pathogenic on legume
hosts, while 'AG-21 and AG-2T1 were largely pathogens of rapeseed.
AG-5 isolates were mostly non-pathogenic with the exception of a few


isolates that elicited superficial lesions on some hosts. However,
there were some AG-4 isolates that were pathogenic on legumes as well
as rapeseed, and some AG-2T1 isolates that were pathogenic on rapeseed
as well as legumes. This indicates that a certain minimum number of
isolates is required to characterise an AG's cultural features,
pathogenic!ty, or any other physiological feature under study.