Sudheer A. Shetty

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.

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 for downy mildew resistance from the regenerants of pearl-millet

Plants were regenerated from the inflorescence explants of three B lines of pearl millet showing different degrees of susceptibility to downy mildew disease. Plants were regenerated from the embryogenic callus cultures and grown to maturity in the vicinity of other downy mildew infected plants. Progenies of disease free (R0) plants were screened for two successive generations in the disease plots. Three somaclones of 23 B (highly susceptible genotype with 97% disease incidence) showed increased level of resistance. Four disease free somaclones were obtained each from 81 B (susceptible with 15% disease incidence) and 841 B (resistant with 7% disease incidence) genotypes. When the populations of these somaclones were screened for some agronomic characters, a significant increase was observed in the population means for plant height and panicle length in two genotypes. The results manifest the genotypic differences in the extent of somaclonal variation for disease resistance and also for agronomic traits. The variants selected as downy mildew resitant were individually compared with their respective control plants for agronomic traits. Two downy mildew resistant variants retained the original characters. Thus, the present study demonstrated the existence of somaclonal variation for downy mildew resistance and some agronomic traits in pearl millet.

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.