Role of Panicum trypheron in annual recurrence of false smut of rice

False smut of rice caused by Ustilaginoidea virens was also found on the grass, Panicum trypheron, a common weed around paddy fields. Cross inoculation studies revealed chlamydospores from P. trypheron infected rice and vice versa. It is concluded P. trypheron is an important source of inoculum between seasons

Selection of downy mildew resistant somaclones, from a susceptible B line of pearl millet

Plants regenerated from seed-derived callus of a PNMS 6B line of pearl millet (Pennisetum glaucum (L.) R. Br.) were evaluated for their resistance induced by somaclonal variation for downy mildew disease caused by Sclerospora graminicola (Sacc.) Schroter. Among the 201 lines regenerated, only 3 lines consistently proved highly resistant (free from disease incidence) for up to 5 generations; whereas, 17 lines were resistant (disease incidence ranging from 1 to 9%). Resistance was confirmed by testing the plants under both laboratory and field conditions. The plants were evaluated for their agronomic traits

Infection processes of Sclerospora graminicola on Pennisetum glaucum lines resistant and susceptible to downy mildew

The host-pathogen interaction between pearl millet seedlings and Sclerospora 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%) and high susceptibility (> 25%) to downy mildew disease were inoculated with zoospores of the pathogen. Infected tissues were macerated in NaOH and stained with cotton blue in lactophenol to observe the differential behaviour in germination and colonization of zoospores in tissues of the coleoptile, mesocotyl and root regions of different lines of pearl millet. The formation of the infection structures by the pathogen such as appressoria, vesicles, infection hyphae, haustorial mother cells and haustoria, as well as the formation of papillae in the host cell walls was observed in the inoculated tissues. The percentage of host cells colonized by the pathogen, and the number of haustoria formed per 100 infected host cells were highest in the coleoptile, followed by the mesocotyl and root. The percentage of infected cells and the number 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 susceptibility of the host to the disease. These responses may be helpful in developing a rapid screening method to determine the resistance of pearl millet lines to downy mildew

Selection of downy mildew resistant somaclones, from a susceptible B line of pearl millet

Plants regenerated from seed-derived callus of a PNMS 6B line of pearl millet (Pennisetum glaucum (L.) R. Br.) were evaluated for their resistance induced by somaclonal variation for downy mildew disease caused by Sclerospora graminicola (Sacc.) Schroter. Among the 201 lines regenerated, only 3 lines consistently proved highly resistant (free from disease incidence) for up to 5 generations; whereas, 17 lines were resistant (disease incidence ranging from 1 to 9%). Resistance was confirmed by testing the plants under both laboratory and field conditions. The plants were evaluated for their agronomic traits

Biocontrol of downy mildew disease of pearl millet using Pseudomonas fluorescens

Pseudomonas fluorescens was tested against pearl millet downy mildew disease by treating seeds with a pure culture and formulated in talc powder. The bioagent was also tested as a foliar spray to pearl millet under greenhouse and field conditions. Treated seeds increased seedling vigour and inhibited sporulation of downy mildew pathogen. P. fluorescens controlled downy mildew disease both by seed treatment and foliar application, but efficacy was significantly higher when seed treatment was followed by a foliar application. Seed treatment was better than foliar application alone

The possible involvement of lipoxygenase in downy mildew resistance in pearl millet

The downy mildew disease, incited by Sclerospora graminicola, is a major biotic constraint for pearl millet production in the semi-arid tropics. Sources of resistance to this disease have been identified. However, the mechanism of host resistance still remains obscure. The enzyme lipoxygenase (LOX) is known to play a role in disease resistance in many host-pathosystems. In the present study, LOX activity was tested in seeds of different genotypes of pearl millet with different susceptibility to downy mildew. The LOX assay of the seeds indicated a good correlation between enzyme activity and their downy mildew reaction in the field. Maximum activity was recorded in seeds of highly resistant genotypes and minimum activity was found in the highly susceptible genotypes. Seeds obtained from plants recovered from the downy mildew disease had more LOX activity than that of the original parent seeds. Thus, in seeds, the LOX activity can be used as a biochemical marker for screening different genotypes of pearl millet for downy mildew. The study, carried out in the susceptible genotype of pearl millet seedlings, showed that LOX activity decreased after inoculating with S. graminicola zoospores when compared with uninoculated controls. However, a significant increase in the enzyme activity was observed on the second and third days after inoculation in resistant seedlings. The possible role of LOX in conferring resistance to downy mildew infection of pearl millet is discussed

Lipoxygenase activity in fresh, stored, and germinating pearl millet seeds resistant and susceptible to downy mildew disease

Lipoxygenase activity was studied in fresh, stored, and germinating pearl millet seeds of downy mildew resistant and susceptible genotypes. In both fresh and stored seeds, the enzyme activity was greater in resistant genotypes compared with that of the susceptible ones. In seeds stored for a period of 6 months, a significant reduction in the lipoxygenase activity was recorded, the reduction being greater in resistant seeds. Lipoxygenase activity decreased significantly in germinating seedlings of resistant genotypes, whereas it increased significantly in the susceptible seedlings. The high vigour in the resistant seeds of downy mildew resistant genotypes is attributed to their high enzyme activity