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Sorghum Stalk Rot Complex in Mindanao: Occurrence, Etiology, and Development as Affected by Various Cultural Management Practices and Weather Factors
Dissertation Abstract:
Two sorghum croppings, main crop and ratoon, were conducted to determine the pathogens causing the stalk rot complex in Mindanao as well as the effects of various cultural management practices and prevailing weather conditions on their occurrence and development.
Results showed that the three fungal pathogens were consistently associated with each other and with the stalk rot complex. These were Colletottrichum graminicola (Cesati) Wilsom which commonly cause "red rot" in sorghum stalks, Fusarium moniliforme Sheldon, and Macrophomina phaseolina (Tassi) Goid. (Rhizoctonia bataticola (Taub.) Butler) which cause charcoal rot in sorghum. Because of their synergistic relationship, their combination effect resulted in an etiological phenomenon called sorghum stalk rot complex, which became larger when two or three were associated together.
Pathogenicity tests conducted both in the field and greenhouse revealed that significantly bigger lesions occurred when the plants were inoculated in the field. Except for lesion length, no other disease parameter was significantly influenced by tillage practice. Deep plowing the field and weeding apparently limited the size of lesions or severity of infection on sorghum plants regardless of nitrogen-phosphorus-potassium (NPK) levels applied and population density maintained. Conversely, minimum tillage without weeding resulted in much larger lesion size.
Grain yield of sorghum in both croppings was higher, wherein a maximum tillage supplemented with handweeding was employed. NPK fertilizers applied at higher rates resulted in significantly higher percentage infection of stalk rot in both main drop and ratoon sorghum. However, no significant effect on the rate of infection was noted. Significantly higher yield was obtained with increasing NPK application. Population density did not have any significant effect in both percentage and rate of infection of stalk rot.
Lesion length, on the other hand, was significantly influenced by higher population density. Closer planting of sorghum promoted the increase in lesion size. Grain yield was significantly higher with increasing population density. The number of days to flowering and tillering capacity of the ratoon sorghum were significantly influenced by all treatments of tillage practice, NPK fertilizer, and population density. Plant height, however was not affected by NPK fertilizer, nor increasing population density. Only the main crop showed significantly taller plants when treated with maximum tillage and supplemented with weeding. High temperature was found to slow down infection rate. High relative humidity increased infection rate but not beyond an optimum level. High rainfall had a depressive effect on infection rate, while longer exposure to sunshine accelerated it.
