Ms. Sharada et al., INFECTION PROCESSES OF SCLEROSPORA-GRAMINICOLA ON PENNISETUM-GLAUCUM LINES RESISTANT AND SUSCEPTIBLE TO DOWNY MILDEW, Mycological research, 99, 1995, pp. 317-322
The host-pathogen interaction between pearl miller seedlings and Scler
ospora graminicola, causing downy mildew disease, was studied. Two-day
-old seedlings of pearl millet, with high resistance (0% of the plants
systemically infected), resistance (1-10%), susceptibility (11-25%) a
nd high susceptibility (> 25%) to downy mildew disease were inoculated
with zoospores of the pathogen. Infected tissues were macerated in Na
OH and stained with cotton blue in lactophenol to observe the differen
tial behaviour in germination and colonization of zoospores in tissues
of the coleoptile, mesocotyl and root regions of different lines of p
earl millet. The formation of the infection structures by the pathogen
such as appressoria, vesicles, infection hyphae, haustorial mother ce
lls and haustoria, as well as the formation of papillae in the host ce
ll walls was observed in the inoculated tissues. The percentage of hos
t cells colonized by the pathogen, and the number of haustoria formed
per 100 infected host cells were highest in the coleoptile, followed b
y the mesocotyl and root. The percentage of infected cells and the num
ber of haustoria formed were least in highly resistant and highest in
highly susceptible lines. The number of papillae, however, was maximum
in highly resistant lines, the number reducing with increasing suscep
tibility of the host to the disease. These responses may be helpful in
developing a rapid screening method to determine the resistance of pe
arl millet lines to downy mildew.