Mpp-Msc-Abstracts

DEPARTMENT OF

MYCOLOGY & PLANT PATHOLOGY

M.Sc. THESIS ABSTRACTS

Out of three fungicides, Hexathir and Bavistin persisted upto 60 and 120 days, respectively in both the sterilized and unsterilized soil, whereas Aliette persisted upto 120 and 90 day, respectively under these conditions at room temperature. After 120 days, Bavistin was recovered at a level of 8.83 and 7.75 ppm in case of 200 and 100 ppm in sterile soil. In case of Aliette and Hexathir too, the recovery was more in sterilized soil. The degradation of all the fungicides was faster in the soil where microbes were added. In all the fungicides degradation increased with increase in temperature, it was minimum at 5oC and maximum at 25oC. Aliette was degraded faster at pH 4.0 and degradation increased with increase in soil pH and was minimum at pH 8.0. At pH 4.0, the growth of Phytophthora cactorum was 27.30 and 28.33 mm in post and pre-treatments on 10th day, which at pH 8.0 was 40.33 and 41.00 mm, respectively. Under different soil moisture levels, Hexathir was found to be affected most by changing moisture levels followed by Bavistin. Study on soil microflora was affected by the fungicides reveals that Bavistin at 200 ppm gave the maximum reduction of soil microflora followed by Hexathir.

The disease caused extensive losses (40.8 - 50.0%) in different locations of H.P., maximum being in Nalagarh area. Oat meal agar was the best solid medium for the growth of the pathogen. Various isolates of the pathogen differed in their pathogenicity. The pathogen overwinters in plant debris. Optimum temperature for the growth of the fungus is 20oC and pH in the range of 7.5 to 8.5. Glucose and ammonium nitrate were the best carbon and nitrogen source, respectively. Early sowing of the crop resulted in disease escape. Calixin seed dressing along with sprays gave effective control of the disease. Out of 125 lines screened against this disease, only 3 were comparatively resistant.

Storage scab produced small, smooth, brown to jet black circular spots, often shiny having intact cuticle. Artificial dip inoculation did not help in establishment of scab in storage. Scabbed apple fruits played no role as source of infection to healthy fruits in storage. Incipient scab infections carried by fruits prior to harvest resulted in scab development during storage. Red Delicious was highly susceptible to storage scab than Starking Delicious whereas, Golden Delicious was the least susceptible. Scab lesions served as the mode of entry for secondary rotting fungi. Preharvest fungicidal sprays proved effective in suppression of scab and rot development in storage. Delan (500 ppm) was most efficacious followed by Dithane M-45 (3000 ppm). The postharvest dip treatments with fungicides did not exhibit marked suppression of storage scab on test cultivars, however, significant suppression of storage rot(s) was encountered in storage.

Survey of markets and collection contents around SNS Complex, Nauni, revealed six to eight per cent fruit losses. Injuries caused by different means provided the main avenues of penetration and infection. The entry through open lenticels and stylar end(s) was selective. Maximum vegetative growth was recorded at 25oC and sporulation at 30oC. Neutral pH (7.0) yielded maximum vegetative growth and sporulation. Among nutrients, glucose supported maximum vegetative growth and sporulation, whereas, arabinose and mannitol proved poor sources for vegetative growth and sporulation, respectively. The exogenous supply of nitrogen sources revealed that potassium nitrate supported the maximum growth and sporulation of the fungus. Susceptibility to blue mould also increased as the fruit matured. Fruits of sand pear on artificial inoculation (Penicillium expansum) were significantly less susceptible than China pear. The polygalacturonase (PG) and polymethyl galacturonase (PMG) enzyme activity was significantly higher in diseased than healthy tissues. Pre-harvest sprays with 1000 ppm thiabendazole gave significant control of the blue mould rot in dip inoculated pears. The relative efficacy of different fungicides revealed that all the systemic and non-systemics gave good control as protectant (pre-inoculation treatment) than as eradicant (post-inoculation treatment). The systemic fungicides were more efficacious than non-systemics. Thiabendazole (1000 ppm) provided maximum disease control as eradicant and protectant.

Early leaf fall in June, July and August was associated with increased leaf decay and a resultant reduction in weight, area and pseudothecial productivity. Longer survival of leaves fallen in September, October and November was linked with maximum production of pseudothecia, though the leaves fallen in September were more conducive for early maturity of pseudothecia and better productivity of ascospores than being from leaves of other two months. Maximum production of pseudothecia was obtained on the leaves of Golden Delicious and in descending order on Red Delicious, Granny Smith, Tydeman’s Worcester and Red Gold. Quantitative production of primary inoculum of Venturia inaequalis was also affected by the orchard height. Only one third pseudothecia was obtained at lower elevation of 1364 m.a.s.l. at Kullu in comparison to what was obtained at 2727 m.a.s.l. (Narkanda). Shady portions of the orchard favoured better pseudothecial productivity, early maturity and higher percentage of ascospore emission. When moisture was not a limiting factor, temperature had a marked effect on the development of pseudothecia, asci and their maturity. Low temperature of 4 and 8oC were favourable for the productivity of pseudothecia in apple infusion agar plates.

Brown spot on soybean caused by Septoria glycines was prevalent in the Kangra district of Himachal Pradesh. It was not present in Mandi, Kullu, Solan and Sirmour districts. In yellow seeded cultivars the infected leaves turned yellow before shedding whereas in green seeded cultivars there was no characteristic yellowing. Potato dextrose agar and yeastal potato dextrose agar supported maximum growth. Growth was maximum in Subouraud’s medium among the liquid media studied. Czapek Dox medium supported maximum growth among different synthetic media. For growth and sporulation of the fungus the optimum temperature and pH were 20-25oC and 6.0, respectively. The conidia of S. glycines germinated between a temperature range of 20-32oC. The optimum temperature for germination was 24oC. Spore germination on sterile water and leaf exudates was similar. The periodic disease development was more when there was more rainfall. Brown spot was found to reduce soybean yields from 18.3 to 23.0 per cent. Topsin-M (0.03%), Agrozim (0.03%), Bavistin (0.03%) and Dithane M-45 (0.20%) were found to contain the disease most effectively in the field. Out of 1617 and 615 varieties/ cultivars/germplasm line tested during 1984 and 1985 seasons, none was found resistant to brown rot.

Out of four Winsconsin lines the two viz., Wisconsin 7101 and 7104 were observed to resistant whereas the other two viz., Wisconsin 7102 and 7103 remained moderately resistant, while varieties Bonneville and Kinnauri were found to be susceptible; Lincoln and GC-195 being highly susceptible during 1984-85. The 28 single crosses involving the above lines/varieties inter se developed during this programme behaved in a manner that reflected the dominance of susceptibility over resistance. The cuticular and epidermal cell wall thicknesses were found to be more in resistant isolines than in susceptible cultivars. All the F1’s derived from the susceptible x susceptible or resistant x susceptible parents remained susceptible to the disease while the ones derived exclusively from the resistant parents were, however, observed to be resistant and hence, no epistasis. The total phenolic contents were observed higher in the leaves of resistant isolines than in those of susceptible ones. The F1’s derived from the crosses involving both resistant parents showed higher contents of OD phenols than those derived from resistant x susceptible or susceptible x susceptible parents at different stages of disease recording. The level of OD phenols was found to be higher in all resistant lines than in the susceptible ones. The activity of polyphenol oxidase enzyme was found to be high at Juvenile stage and increased at mild disease stage in all the 36 populations, but at severe attack of the disease the activity of the enzyme was found to be nil in most of the population. However, the enzymatic activity was observed to be higher in resistant parents than in those of susceptible one. The F1’s derived from the crosses involving both resistant parents had higher enzymatic activity than those derived from resistant x susceptible or susceptible x susceptible at different stages of platn growth. The activity of peroxidase was found to be higher in resistant lines than in those of susceptible cultivars. All the susceptible cultivars had higher contents of ascorbic acid than those of resistant isolines.

In the mushroom beds, development of mycelial spread was drastically checked by the olive green moulds accompanied by delayed and poor pinning resulting in marked reduction in yield. Studies on the response of the competitors to variable temperatures ranging from 5-40oC indicated that maximum growth occurred at 25oC. Chaetomium species could grow on a wide range of pH levels ranging from 4-10 pH. Studies on the interaction of Chaetomium species with that of Agaricus bisporus exhibited no zone of inhibition. Studies on germination of spores indicated that the optimum temperature for both the competitors was 25oC. In pH studies on ascospore germination, 8 pH was conclusively adjudged as the optimum pH for both the species. Survival under natural conditions in soil indicated that the competitors could survive for a period of 7 months. The spores and perithecia of the mould could survive in the refrigerator at 5-10oC as well as at an ambient temperature of 15-30oC for a period of more than a year. In field trial, six promising fungicides (5 systemics and one non-systemic) were evaluated to ascertain their effect against Chaetomium species, as well as to record their effect on the yield of the mushrooms. Results obtained indicated that Captan at 1000 ppm recorded the maximum yield as compared to Bavistin, Benlate, TBZ, Topsin and Dithane M-45 at 250 ppm, which recorded yields lower than the control.

The occurrence of systemic infection of white rust caused by Albugo candida on Lepidium vir-ginicum and Capsella bursa-pastoris as well as local infection on Raphanus raphanistrum as new host of white rust are first record from India. The local lesion infection of white rust was mostly observed on abaxial leaf surface. The presence of oospores was observed only in the systemically infected plant parts. Thirteen cultivars of Brassica carinata, eighteen of B. napus and twenty six of B. juncea were found resistant to all the six isolates of A. candida under study. Similarly, fifteen cultivars of B. juncea were resistant against A. candida isolate from B. juncea out of three hundred and eighteen cultivars. Nine new biological races were identified from nine isolates from cultivated and wilt hosts for white rust. The fungicides Aliette 80 and Fuji 40 at 1000 µg/ml concentration (a.i.) were found effective in controlling the seedling infection by soaking the seed for 16 hours. Similarly, in spraying method Katazin 48, followed by Vitavax 50, Rabcide 30, Hinosan 50, Pervicur 70, Fuji 40 and Aliette 80 were found to be effective in protecting the seedlings at cotyledonary stage even at lower concentrations after 16 hours of sprayings.

The investigations were undertaken on the utilization of different agricultural wastes for the cultivation of Agaricus bisporus. At filling, the hydrogen ion concentration of different composts from 8.48 to 8.62, at spawning 7.18 to 7.38, at casing 6.90 to 7.10 and at the end of cropping 6.10 to 6.20 which has more or less followed the trend of control. Moisture content of different composts at filling ranged from 68.9 to 73.0, at spawning 68.0 to 72.0, at casing 70.8 to 78.0 and at the end of cropping 65.0 to 72.0. Different type of compost showed characteristics of a normal compost (control) with respect to colour, texture and smell of ammonia, however, pine needle and saw dust composts did not show the usual colour. The mycelium of A. bisporus could grow at a faster rate in horse manure compost followed by control, sheep manure and corn stalk compost, whereas, in other compost, it took comparatively longer period to acquire the same growth. Studies on the pre-picking pattern of different composts indicted that spawn run was completed in 15 days on all, except cattle manure, pine needle and sawdust compost where it took 16 to 17 days. Yield data obtained from formulation I clearly indicated that mean yield on horse manure and sheep manure compost was statistically at par with the control. Comparative yield data from formulation II show that corn stalk, corn cob and pea stalk composts were statistically at par with the control. Yield on paddy straw compost was statistically different from corn stalk, corn cob, pea stalk and control, however, indifferent from pine needle compost. Sawdust compost yielded the least of all the substrates tried.

Wilt incidence during the year 1985-86 ranged between 26.70 to 50.46 per cent in various gram growing areas of Himachal Pradesh. Three pathogens namely, Fusarium oxysporum f.sp. ciceri, F. solani and Sclerotium rolfsii were found associated with wilt complex disease. Disease incidence was comparative more at seedling stage and maximum at flowering and pod formation stage. The field and pot studies have shown that crops sown in the middle of October can best endure/escape the wilt attack than when even in the first week of November or sown before or after October month. Pre-emergence mortality was effectively checked by Carboxin, Mancozeb and Captan but to check post-emergence mortality carbendazim + Thiram (1:1) combination proved superior. Out of one hundred and two cultivars/lines screened under natural condition in the field and artificial condition in pot experiment, only ICC-5864 WR, ICC-10130 and ICC-2506 were resistant to wilt attack.

In all nine fungi namely, Alternaria alternata, Ascochyta rabieii, Aspergillus fumigatus, A niger, B. cinerea, Cladosporium cladosporiodes, Curvularia pallescens, Penicillium sp. and Rhizopus sp. were found associated with the seeds of chickpea of which A. rabiei was most predominant with maximum incidence of 35 per cent. Seeds having moisture level below 7.5 per cent remained free from mycoflora than those containing more than 8.5 per cent moisture. Seed dressing with captan, thiram, carbendazim and benomyl eliminated most of harmful mycoflora associated with seed including seed borne infection of A. rabiei and increased nodulation and germination remarkably.

Spray schedule recommended for the control of apple scab by this university consisting of eight sprays in a field trial reduced the intensity of all the foliar diseases and controlled scab on apple leaves (97.97%), fruits (99.30%), powdery mildew (34.90%), leaf spot diseases (85.12%), sooty blotch (89.91%) and fly speck (89.51%). Three weather parameters namely, relative humidity (70-86%), temperature (17-26oC) and high rainfall favoured the scab development both on fruits and leaves. Powdery mildew appeared at the end of April and it was maximum in the month of June when the average relative humidity mean temperature and total rainfall were 71.56 per cent, 25.01oC and 87.8 mm, respectively and decreased with increase in relative humidity and total rainfall in July and August. Leaf spots and sooty blotch and fly speck diseases of apple were maximum in the month of August and were positively correlated with relative humidity and rainfall. The ascospore maturity of Venturia inaequalis started with the silver tip stage and increased upto full bloom stage. Apple scab spray schedule suppressed the ascospore production and pseudothecia formation and also checked the various foliar diseases of apple to varying degree with a cost benefit ratio of 1:10:78. Captan, Dithane M-45 and Syllit were the most toxic fungicides for pollen germination under in vitro conditions and also under field conditions at full bloom and pink bud and full bloom stage. MBC and thiophanate methyl were the safest fungicides to the pollen.