Field Evaluation of Root Rot Disease and Relationship Between Disease Severity and Yield in Cassava

Abstract

Reports of cassava root rot disease from different African countries have increased in recent times. Field studies were conducted from July 1998 to October 1999 to determine a reproducible disease assessment method that would allow the comparison of results from different locations and an evaluation of the relationship between disease severity and root yield. Single point disease assessments at 6, 9, 12 and 15 months after planting (MAP) were compared to multiple points assessment based on the area under a disease progress curve (AUDPC). Single point assessments at 12 and 15 MAP, and the AUDPC identified continuous variation (p ≤ 0.01) among the genotypes. However, a consistent result across trials was obtained only with the assessment based on AUDPC. Root dry yield (DYLD) at 15 MAP showed a strong negative correlation with AUDPC (r = −0.74). Regression analysis also confirmed the negative relationship between yield and root rot severity. The five genotypes compared were separated into resistant (91/02324, 30572 and 92/0427) and susceptible (92/0057 and TME-1) groups. It was concluded that root rot disease may cause significant yield loss; however, the magnitude of the yield loss will depend on the susceptibility of the cassava genotype.

Characterization of cassava (Manihot esculenta Crantz) varieties in Nigeria and Tanzania, and farmers’ perception of toxicity of cassava

“…However, the finding that none of the farmers had unharvested cassava from previous year at the time of this survey suggests that the intensity of the practice is low. Root rot (Onyeka et al, 2005) and lignification were reasons why farmers do not leave cassava roots unharvested for long periods after maturation. Thus there are limitations to the practice of delay harvesting of cassava.…”

Gender differences and challenges in cassava production and processing in Abia State, Nigeria

“…Cassava roots (traditional varieties) can be stored in the ground for up to 24 months, and some varieties for up to 36 months. Harvest may be delayed until market, processing, or other conditions are favourable (Onyeka et al, 2005). These attributes make cassava an important food security crop in Nigeria and several other sub-Saharan African countries that produce the crop.…”

Identification of levels of resistance to cassava root rot disease (Botryodiplodia theobromae) in African landraces and improved germplasm using in vitro inoculation method

“…The resistance reference (30572) was classified as moderately resistant in this study, this genotype however, showed a good level of field resistance to root rot disease in our previous study (Onyeka et al, 2005a). The performance of 30572 necessitates the need for a classification method that is independent of the control for separation of the genotypes into levels of resistance.…”

“…There have been efforts to characterise some of the African landraces and breeders' lines for resistance to other diseases of cassava (Fokunang et al, 2000), but the distribution of resistance to root rot disease in these collections remains unknown. Variations in the response of different cassava genotypes to root rot disease have been demonstrated in field studies (Onyeka et al, 2005a). However, the long growth cycle for cassava to develop storage roots for assessment and the nonuniform distribution of inoculum in the soil make field screening very difficult.…”