PREVALENCE AND INCIDENCE OF FOUR COMMON BEAN ROOT ROTS IN UGANDA.

P Paparu,S Nkalubo,F Kato,A Acur,C Mukankusi,J Nakibuule,C Acam,S Musoke

doi:10.1017/s0014479717000461

Abstract

Root rots are one of the main biotic constraints to common bean (Phaseolus vulgaris L.) production, causing losses estimated at 221 000 metric tons a year in sub-Saharan Africa. Until recently, root rots in Ugandan common bean agroecologies were mostly caused by Pythium and Fusarium spp., especially in high altitude areas. But now, severe root rots are observed in low and medium altitude agroecologies characterized by dry and warm conditions. The objective of our study was therefore to ascertain the current prevalence and incidence of common bean root rot diseases in Ugandan common bean agroecologies. Our results show that root rots were present in all seven agroecologies surveyed. Overall, the most rampant root rot was southern blight caused by Sclerotium rolfsii Sacc., followed by root rots caused by Fusarium spp., Pythium spp. and Rhizoctonia solani, respectively. Our study clearly showed the influence of environmental conditions on the prevalence and incidence of common bean root rots. While Fusarium and Pythium root rots are favoured under low air temperature and high air humidity in highland areas, high incidence of southern blight is favoured by warm and moist conditions of lowland areas. The prevalence and incidence of common bean root rots was mapped, providing a reliable baseline for future studies. Similarly, hotspots identified for common bean root rots will be a very useful resource for evaluation of germplasm and breeding lines for resistance to root rots.

Highlights

The common bean (Phaseolus vulgaris L.) is an important food crop worldwide (Wortmann et al, 1998), acclaimed for nutritive benefits such as high protein, micronutrients, vitamins and dietary fibre (Widders, 2006)
In Uganda, common bean root rots were previously known to be caused by Pythium and Fusarium spps., and the most severely affected areas were highlands, where air temperature is low and air relative humidity high (Buruchara and Rusuku, 1992; Opio et al, 2007)
Root rot prevalence Common bean root rots were observed in all sampled agroecologies (Table 1)

Summary

Introduction

The common bean (Phaseolus vulgaris L.) is an important food crop worldwide (Wortmann et al, 1998), acclaimed for nutritive benefits such as high protein, micronutrients, vitamins and dietary fibre (Widders, 2006). The most common soil-borne pathogens that cause common bean root rots include Pythium spp., Fusarium spp., Rhizoctonia solani and Sclerotium rolfsii Sacc., the asexual stage of Athelia rolfsii (Curzi) Tu and Kimbrough. These four pathogens may cause losses of up to 100% in susceptible varieties under moist conditions and impoverished soils. In Uganda, common bean root rots were previously known to be caused by Pythium and Fusarium spps., and the most severely affected areas were highlands, where air temperature is low and air relative humidity high (Buruchara and Rusuku, 1992; Opio et al, 2007).

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