Agricultural Biology
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Item 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.Item 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.