H Shekara Shetty

Soil microflora and biological activities in the rhizospheres and root regions of coconut-based multistoreyed cropping and coconut monocropping systems

Abstract Microflora, enzyme activities, microbial biomass. C and N mineralization in the rhizosphere and root region soils of coconut-based multistoreyed cropping (pepper, cacao and pineapple) and coconut monocropping systems were studied. The rhizosphcres of the different crops had greater numbers of microflora than non-rhizosphcrc soils. There were fewer bacteria and fungi in the root region soils of coconut monocrop as compared to multistorcyed cropping system. The microflora, enzyme activities, C and N mineralization decreased with soil depth. Ureuse, dehydrogenase and phosphutusc activities showed variable trends in the root regions and rhizosphcres of the durerent crops. The microbial biomass in the root region soil was highest in the coconut and cacao of the multistorcyed cropping system. The organic C. total N, P and K were higher in the root region soils of multistorcyed cropping system than in the coconut monocropping system.

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.

Effect of some environmental factors on the asexual phase of Peronosclerospora sorghi

Peronosclerospora sorghi, produced a maximum of 10,800 conidia/cm2 of diseased sorghum leaves at 100% relative humidity but only about 3600 conidia at 85% relative humidity underin vitro conditions. The sporulation was totally inhibited at 80% relative humidity and below. Infected sorghum leaves kept in darkness after completion of the previous crop of the spores, did not sporulate in continuous darkness even at the optimum relative humidity and temperature. Optimum temperature for sporulation is 21–23° C, 31° C and 30° C are minimum and maximum respectively. At 26° C and above, conidiophores were malformed and produced only a few conidia. For conidial germination, 21–25° C were optimum while at 13° C conidial germination was as low as 52%. At 32° C, 80% germination was recorded but 35° C and above no germination occurred. After inoculation with conidial suspension, a minimum of 3 hr moisture was essential to induce systemic infection.

Stimulation of teliospore germination in smut fungi

Preheating and heated teliospore extracts have been found to be stimulatory to germination of the teliospores of ten different smut fungi used in this study. The effect is mostly on the percentage of germination.Maximum per cent of spore germination was observed at higher concentrations of glucose and sucrose solutions. The percentage of germination of spores of the species included was more in sucrose than in glucose. Most of the vitamins of B-complex groups stimulated the initiation of germ tube.Many of the growth regulators tried, except 2,4-dichlorophenoxy acetic acid have a stimulatory effect on teliospore germination. Higher percentage of teliospore germination was noticed in the case of gibberellic acid, followed by indole 3-acetic acid, beta-indole butyric acid and alphanaphthalene acetic acid.Ethylenediamine tetraacetic acid, furfural, fumaric acid, oxalic acid and citric acid were also stimulatory, in that order.

Carpel infection and establishment of downy mildew mycelium in pearl millet seeds

The carpels of pearl millet (Pennisetum typhoides) are infected bySclerospora graminicola. Vegetative mycelium present in the diseased mother plant infects the carpel through the stalk of the spikelet. This process may or may not cause hypertrophy. Zoospores infect the carpel through the stimga and style, without inducing hypertrophy. Infection process leading to the establishment of downy mildew mycelium in the carpellary tissue and its implications are discussed.

Factors affecting infection byPeronosclerospora sorghi on sorghum

Age of sorghum plants is important in the development of downy mildew disease incited byPeronosclerospora sorghi. Plants inoculated just after emergence and up to 4–5 leaf stage are highly susceptible. In plants inoculated after 6–7 leaf stage, systemic symptoms were not observed but only local lesions appeared. Conidial concentration of 40/seedling brings about 100% infection if the host seedlings are inoculated through root. Systemic infection occurs in 10 and 22 days depending upon the conidial concentration. Roots of the seedlings inoculated with 1000 conidia/seedling get infected earlier. Mature conidia are highly infective compared to immature or old conidia. Soil and seed-borne inoculum can initiate both systemic and local lesion type of symptoms at any growth stage of the host plant in addition to air-borne conidia. Late expression of systemic infection can result both from air-borne conidia and oospore present in the soil or seed.