A Handbook of Rice Seedborne Fungi TW Mew and P ... - IRRI books

Seedborne fungi causing foliage diseases in riceAlternaria padwickii (Ganguly) Ellissyn. Trichoconis padwickii GangulyTrichoconiella padwickii (Ganguly) JainDisease caused: stackburna. SymptomsOn leaves—large oval or circular spots with apale brown center and distinct dark brown margin.Color of center eventually becomes white andbears minute black dots.On grains—pale brown to whitish spots with blackdots at the center and dark brown border.Roots and coleoptile of germinating seedlings—dark brown to black spots that eventually coalesce.Small, discrete, and black bodies areformed on the surface of the darkened area asdecay proceeds.b. Occurrence/distributionStackburn disease is widespread in most of therice-growing countries worldwide (Fig. 4).c. Disease historyThe disease was first reported in the U.S. It resemblesblack rust of wheat on rice leaves, butonly sclerotia and mycelium were observed.Later the fungus was observed in and on riceseeds.d. Importance in crop productionStackburn leaf spot disease is not considered tobe of economic importance. However, seed infectionresults in grain discoloration, which mayreduce germination and lower grain quality. Thedisease potential of stackburn is very low and theyield loss caused by A. padwickii in literaturemay be overestimated. The effect of infectedseed on seed germination is not yet properly assessed.Detection on seeda. Incubation period on blotterA. padwickii is easily observed on seeds using theblotter method 5 d after seeding on moistenedblotter and incubated under NUV at 21 °C. Thedetection frequency is about 67.1% on seedscoming from different regions (Fig. 5a,b).b. Habit characterSeed infected with A. padwickii after incubationshows abundant aerial mycelia, hairy to cottony,profusely branched, grayish or hyaline whenFig. 4. Occurence of stackburn (Ou 1985, Agarwal and Mathur 1988, EPPO 1997).14