Agricultural Biology

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FACTORS INFLUENCING INFECTION, SPREAD AND SEVERITY OF TWO COLLETOTRICHUM SPECIES ON COWPEA (VIGNA UNGUICULATA (L.) WALP.) UNDER DIFFERENT CROPPING SYSTEMS
(1991-04) ADEBITAN, S. A.
Screenhouse and field experiments were conducted between 1987and 1989to investigate the factors affecting infection, severity and spread of two diseases, anthracnose, caused by Colletotrichum lindemuthianum, and brown blotch, caused by Colletotrichum truncatum. The following factors were studied: reaction of cowpea genotypes to infection, methods and time of inoculation in screening cowpea seedlings for resistance; plant spacing, genotype and cropping pattern in mono-cowpea and cowpea-maize intercrop; and time of cowpea introduction into cowpea-maize association. Cowpea varieties IT82E-60, IT81D-1137, and Vita-7were most susceptible to anthracnose whereas TVx 3236, IT81D-994 and IT81D-975were most resistant. Varieties IT82E-60, IT82D-699 and Ife Brown were most susceptible to brown blotch whereas TVx 3236, Vita-7, and IT8ID-1137were most resistant. Wrapping of wounded seedlings with inoculum meal of Colletotrichum at 21 days after seedling emergence enhanced optimal conditions for infection and disease development with a clear distinction between susceptible and resistant varieties. Significantly lower incidence and severity of the diseases occurred on intercropped cowpea than monocrop. Though incidence values of 25 and 43% on pods from intercropped cowpea and sole cowpea infected with C. lindemuthianum were recorded, the results indicated that the sole cowpea had higher seed yield than the intercropped. Yield averages of 458and 678kg/ha were obtained from intercropped and sole cowpea with anthracnose infection. Increasing cowpea spacing, between- and within-rows, reduced the infection and severity of both Colletotrichum species on cowpea in maize and non-maize stands. Infection rates for the pathogens were lower on cowpea intercropped than on sole and infection rates increased as plant spacing decreased. Disease infection, severity and spread significantly increased with increase in age among all the tested varieties. Infection rates were highest on IT82E-16(semi-erect type) and lowest on IT84S-2246-4(erect type). Thus, the erect variety proved more suitable than the spreading type in reducing the spread of both diseases. Cropping pattern significantly affected the incidence and severity of the fungi on cowpea decreasing generally in the order Sole > Strip > Intrarow > Doublerow > Interrow. Planting cowpea one week before maize and planting both crops simultaneously reduced the incidence and severity of the two fungi on cowpea more than when it was introduced later into maize. Infection rates were lowest on cowpea planted simultaneously with maize.
PATHOLOGICAL ASPECTS OF SEED-BORNE MYCOFLORA OF PINUS CARIBAEA MORELET VAR. HONDURENSIS
(1990) ADEGEYE, A. O.
A survey of, the mycoflora of three seed lots of Pinus caribaea var. hondurensis was carried out using the incubation tests for the detection of seed-borne fungi on agricultural seeds. The seed-borne fungi identified were: Acromonium sp., Aspergillus flavus, A. fumigatus, A. niger, A. tamarii, Botrytis sp., Botryodiplodia theobromae, Chaetomium funicola, C. globosum, C. indicum, Cladosporium oxysporum, Dendrophoma sp., Fusarium eqruiseti, F. moniliforme var. intermedium, Gliocladium roseum, Macrophoma spp., Mucor spp., paecilomyces variotii, Penicillium citrinum, P. cyclopium, Pestalotiopsis spp., Phialophora fastigiata, Phomopsis occulta., Rhizopus sp. and Trichoderma sp. Seed-debris (pieces of cones and twigs) and stones also carried a large proportion of these pathogenic and saprophytic fungi. Using scanning electron microscope, no propagules of obligate parasitic pathogens were seen on the seed coat but spores and mycelia of some facultative pathogens were observed. Most of the seed-borne fungi were carried externally on the testa. Pinus caribaea var. hondurensis seeds inoculated with spore suspension and mycelial discs of the following fungi: Aspergillus niger, Fusarium moniliforme var. intermedium and F. eguiseti had drastic reduction in germination. F. moniliforme var. intermedium and F. eguiseti caused wilting and sudden death (damping-off) in 3 week and 3 month-old inoculated seedlings (20-60% mortality) 7 days after inoculation. Inoculated stems showed disintegration of cell-walls, parenchyma cells and fibres. Aspergillus niger had no effect on inoculated seedlings while Phialophora fastigiata had no effect on both the inoculated seeds and seedlings. Seeds which were surface sterilized for 5 minutes in 1% sodium hypochlorite and planted in autoclaved sterilized soil gave a germination percentage of 42 while seeds which were not surface sterilized but planted in sterilized soil gave 20%. Damping-off and wilting were observed in 10-12% of the seedlings which emerged from the two treatments 5-30 days after germination. Botryodiolodia theobromae, Fusarium moniliforme var. intermedium, Rhizoctonia spp. and Rhizopus spp. were isolated from the diseased seedlings. The effect of three fungicides: Benlate, Captan and Thiram in controlling the growth of the frequently occurring seed-borne fungi (Aspergillus niger. Fusarium moniliforme var. intermedium and Phialophora Fastigiata) was studied in vitro. Only Benlate at concentrations of 1 ppm and above inhibited the growth of the three fungi. Thiram inhibited the growth of Aspergillus niger and Phialophora fastigiata at 20 and 400 ppm respectively while Captan inhibited the growth of Aspergillus niger at 40 ppm.
SEASON OF HARVEST OF AMARANTHUS CRUENTUS L. IN RELATION TO SEED-BORNE MYCOFLORA AND MAJOR SHOOT DISEASES
(1990-04) ADEBANJO, A.
The quality of Amaranthus cruentus L. seeds were influenced both by seasons of harvest and varietal type. The wetness that accompanied harvests of the first (April-June) and second (August-October) seasons greatly-reduced the quality of seeds of cultivars. Quality reduction were in the form of seed malformation,-discolouration and mycelial growth on them. Fifteen fungal species were found to be associated with seeds of the cultivars used. There was a seasonal variability in the occurrence, distribution and the quantity of the seed-borne fungi. Least number and mean percentage seed infection were recorded for NHAC(100) while NHAC(30) and NHAC(33) carried the highest percentage inoculum on the seed testa. Three of the seed-borne fungi were highly pathogenic on seedlings of two of the cultivars while two of the fungi were seed transmitted. Six of these seed-borne mycoflora are new records on Amaranthus seeds in Nigeria. For the two year trials, significantly (p=0.05) least incidence (0%) of dieback, stem blight (8%) were recorded during the first season for NHAC(33) and NHAC(30) while 4% mean leaf blight was obtained from NHAC(100) in the third (December-February) season. Least mean percentage leaf blight was recorded for all the cultivars also by the third season. Conversely, the second season recorded the highest incidence of all these aerial symptoms of the disease caused by Choanephora cucurbitarum (Berk & Rav.) Thaxt. in all the cultivars. Hot water treatment of infected seeds of all cultivars at 60°C for 6 to 8 minutes completely disinfested them of the seed-borne fungi with consequent increase (>95%) in seedling emergence. Also soaking in or dusting of infected seeds with a mixture of Benlate-Captafol or single Captafol at 10g a.i./kg seed controlled the seed-borne fungi. Pre-harvest sprays of Benlate-Captafol mixture or Captafol at 3.3 kg/ha controlled inflorescence infection and seed-borne fungi with resultant yield increases and seedling emergence over the non-treated control.
STUDIES ON THE BLAST DISEASE OF SEEDLINGS OF THE OIL PALM (ELAEIS GUINEENSIS JACQ.)
(1972-12) ADERUNGBOYE, F. O.
The series of investigations carried out into the blast disease of oil palm seedlings, a disease of high economic importance, showed that the disease was widespread in nurseries throughout south-western Nigeria, The disease was prevalent between October of the year of planting and March of the following year and appeared to be severest in November and December. The incidence of the disease was lower among seedlings planted into the nursery at the beginning of the rainy season in April than, among seedlings planted in June, July or August. Coconut (Cocos nucifera Linn.) and other palms of economic and ornamental importance, for example, Are ca catechu Linn., Ptychosperma elegans Blume, and Roystonea regia (H. B. K.) Cook also showed heavy blast infection. Pythium splendens Braun (Accession No. IMI 149554) and Rhizoctonia lamellifera Small (Accession No, IMI 149556) were consistently isolated from infected roots. Pathogenicity tests with these fungi showed that the blast disease developed as a result of the co-infection of oil palm seedlings by both fungi, P. splendens was found to be more pathogenic than R. lamellifera under experimental conditions. The infective propagules of P. splendens were found to be more abundant at the ploughline depth of 9 inches than at depths of 1, 3, 6, 12, 15, 18, 24 and 36 inches. The recovery of the fungus from nursery soil by the root baiting technique was high in July-October and low in November-January. These variations in the recovery of the fungus from soil were found to correspond with variations in soil moisture but not with soil temperature. The cultural practice of incorporating organic manure with soil increased while air-drying of soil decreased the recovery value of the fungus from soil. In vitro studies on P. splendens and R. lamellifera showed that the linear growth, sporangial and sclerotial production and germination were better in agar media rich in simple sugars than those deficient in them. The best temperature range for the linear growth, sporangial and sclerotial production and germination was found to be 25-30°C. Longevity of sclerotia of R. lamellifera was highest at a relative humidity value of 95% and at a low temperature of 20°C. Soil temperature in polythene bag planting was found to be positively correlated (r = 0.7758) with the blast disease at the 1% level of significance. There was no statistically significant correlation between the disease and soil temperature or soil moisture in ground bed planting. The incidence of the blast disease was found to be higher in the subsoil and ground bed planting than in the topsoil and polythene bag planting respectively. Shading of nursery seedlings in the dry season particularly from October to December was found to be more effective than Chemical soil treatment with Femasan or Benlate in reducing the incidence of the blast disease. Soil treatment with pentachloro-nitrobenzene appeared to aggravate the disease. Extension work seedlings produced at NIFOR were found to be more resistant to the blast disease than grove palm seedlings.
STUDIES ON THE INFECTION OF YAMS BY SCUTELLONEMA BRADYS (STEINER AND LEHEW)
(1975-08) ADESIYAN, S. O.
A general survey of phytoparasitic nematodes associated with yam (Dioscorea spp.) in the Mid-Western State of Nigeria showed that Seutellonema bradys and Meloidogyne spp. were the economically important nematodes of yam tubers. S. bradys was associated with the ’dry rot' of yam tubers causing storage losses estimated between 80 and 100%. Nematodes of the genus Meloidogyne were found associated with galling of tubers of water yam (D. alata). Studies on the rate of population build-up of S. bradys in storage showed that S. bradys increased 9-fold, 8-fold and 5-fold in the tubers of D. rotundata, D. cayenensis and D. alata respectively during 6 months of storage. These increases in population influenced the severity of ’dry rot’ disease. Results of investigations into the depth of penetration of S. bradys in 5 different varieties of D. rotundata showed that there were differences in varietal susceptibility. The bulk of the nematode population was found in the periderm to a depth of between 0-1.5 cm, but depth of penetration was greater in the head portions of each of the tubers than either the middle or bottom portions. Observations on the activities of the nematodes in tuber tissues (histopathology) suggested that the 'dry rot' was mainly due to mechanical damage to the cells and the host reaction to intracellular feeding by S. bradys. Studies on changes in the carbohydrate constituents of the yam tuber infected by S. bradys showed an increase in the percentages of monosaccharides and disaccharides like sucrose, glucose and galactose, fruobose with a concomitant decrease in starch, amylose and amylopectin when compared with healthy yam. Qualitative and quantitative determination of amino acid constituents of nematode-infected tubers of white yam (D. rotundata). yellow yam (D. cayenensis) and water yam (D. alata) showed that the relative numbers of free amino acids were not materially changed following infection by 5, bradys. but a reduction occurred in the number of 'essential' amino acids in the infected tubers. Eighteen ninhydrin positive amino acids were detected in the protein hydrolysate. Except in the case of white yam and in a few other cases, increases in protein amino acids were recorded in the infected tubers of yellow and water yam. The percentage protein was also increased by infection in all species except white yam (D. rotundata). Observations on the rate of weight loss (cumulative percentage weight and mean percentage weight loss) in 3 different species of Dioscorea stored in a yam barn showed that there was a significant difference in the rate of weight loss between nematode-infected and nematode-free tubers of D. rotundata and D. cavenensis, but no significant difference was recorded between the infected and healthy yam tubers of D. alata. Estimation of the edible portions in nematode-infected and nematode-free tubers of D. rotundata. D. cavenensis and D. alata showed a significant difference in the percentage peeling losses between the infected and healthy tubers. Chromatographic analysis of the incubation solution of S. bradys showed that 5 amino acids - aspartic acid, phenylalanine, hydroxylnol acetic acid, leucine and isoleucine were discharged by this nematode. The absence of the steroid group of compounds in the nematode-infected yam tubers revealed by spectrometrie analysis might be disease-related as evidenced by its appearance in the healthy tubers. Polygalacturonase and amylase activities were detected in homogenates of S, bradys. Studies on fungi associated with the dry rot disease of yam tubers showed Aspergillus niger. Penicillium sclerotigenum. Triohoderma viride. Rhizopus nigricans and Fusarium oxvsporum. Botrvodiplodia theobromae and Fusarium moniliforme as the main species. Studies on the possible interrelationshipsbetween S. bradys and 3 fungi A. niger. P. sclerotigenum and F. oxysporum showed that the presence of the nematode seemed to increase the degree of pathogenicity of Fusarium and Penicillium species on yams. But the presence of S. bradys did not increase the degree of pathogenicity of Aspergillus niger. In greenhouse experiments, the interaction between S. bradvs and A. niger was found to be disadvantageous to the nematode. The presence of the fungus seemed to have some effect on the number of nematodes that invaded the roots and tubers and subsequently on nematode development. This was thought to be due to an anti-biotic action of A. niger on S. bradys. A host range study of 30 crop plants and weeds revealed that beniseed (Sesamum indicum L.), cowpea (Vigna unguioulata (L.) Walp.), were good alternative hosts of S. bradys. Small populations of the nematode also survived endoparasitically in the roots of Bupatorium. avnedrella. roselle faib1scus sab dar if f a L.). kenaf (Hibiscus cannabinus L.), melon (Cucurbita pepo L.); jute (Corchorus olitorius L.); yam bean (Sphenostylis stenocarpa) (Hochst ex A Rich) Harms., soko (Oelosia araentia L.) and pigeon pea (Ca.lanus ca.ian (L.) Druce). Non-hosts included maize and tobacco. Dipping nematode-infected tubers of D. alata and D. cayenensis in hot water at temperatures ranging between 50 and 60°C for 40 minutes completely eliminated the nematode. However, at temperatures above 55°C for an exposure time of 1+0 minutes, the tubers so treated suffered a physiological damage and rotted very rapidly. Temperatures between 50 and 55°C had no adverse effect on percentage emergence, growth, yield and palatability of tubers of D. alata. Field trials on chemical and cultural control of S. bradys on D. alata showed that the yield of yam was increased and the nematode population suppressed by the application of organic manure at the rate of 1.5 kg/heap or 1 ,886.3 kg/ha. Although the application of nemagon at the rate of 35.2 kg/ha. considerably suppressed nematode population, the yield of yam was significantly reduced. The results showed that there is a good deal of potential for experimentation with various cultural methods of nematode control. Studies on the effect of gamma irradiation on S. bradys showed that dosages between 5 and 15 Krad did not eliminate the nematodes completely, but suppressed sprouting and signs of deterioration in tubers. Dosages between 20 - 30 Krad eliminated about 70 - 80% of the nematode population.