Distribution and severity of bacterial brown spot on dry beans in South Africa: An update

Abstract

Bacterial brown spot (BBS) of common bean (Phaseolus vulgaris) is a seed-borne bacterial disease caused by Pseudomonas syringae pv. syringae (Pss). Dry bean is an important field crop in South Africa and all commercially available South African dry bean cultivars are susceptible to BBS. The aim of this study was to determine the current distribution and severity of BBS in the dry bean production areas of South Africa. We surveyed 31 locations in five provinces. Disease severity was evaluated on selected plots on a 0–9 scale in four different farming systems: commercial and subsistence farms and strip and national cultivar trials. Leaves with typical BBS symptoms were harvested and transferred to the laboratory. Bacteria were isolated following standard procedure using King’s B medium. Identification of pure isolates was done using physiological and biochemical techniques. Incidence and severity values were used to calculate a disease index. BBS was observed in 88% of locations. BBS incidence was recorded in 54% to 100% of all the farming systems surveyed during the 2008/2009 and 2010/2011 seasons combined. BBS was more severe in the strip and national cultivar trials than on subsistence and commercial farms during the 2008/2009 season and more severe on the commercial farm and in national cultivar trials than on subsistence farms and strip trials during the 2010/2011 season. Findings of this study signal the importance of developing BBS-resistant dry bean cultivars for South Africa.

Assessment and characterization of mung bean (Vigna radiata) bacterial brown spot in Eastern Amhara, Ethiopia

“…Thus, the bacterial multiplication and movement within the plant cells could be reduced and lower the inoculum. This finding is in line with Muedi et al (2015) who stated that bacterial brown spot is prevalent where dry bean monocropping was practiced. There are also several studies with regard to the inhibition potential of intercrops against different pathogens in various pathosystems (Chemeda, 2003;Altieri et al, 2005;Habtamu et al, 2015).…”

“…Indirectly wet soil is good for the spread of bacterial brown spot of mung bean. The same result has been reported by Muedi et al (2015) who stated that avoiding working when soil is wet will decrease the disease severity and development as well as working when the soil is dry, which could result in reduction of disease epidemics.…”

“…This might be partly due to the high rainfall and relative humidity common in the areas, which could favor diseases infection and epidemic development. Muedi et al (2015) also obtained high disease incidence and severity of bacterial brown spot in altitude ranges of 1350-1735 m.a.s.l. due to high rainfall and relative humidity.…”

“…It could be also due to ideal moderate to warm temperature as favor for epidemics and severe localized disease outbreaks of bacterial brown spot. If environmental conditions are known to favor disease A B C development, there might be high disease incidence and severity even in high altitude areas ranging 1625-2000 (Muedi et al, 2015). Schwartz et al (2019) also reported the incidence and severity of bacterial diseases such as halo blight and bacterial brown spot outbreaks are most serious when temperatures are moderately cool and humidity is high.…”

Morpho-agronomic and genetic variation among Phaseolus vulgaris landraces from selected provinces of South Africa

“…The gene pools show variations in agronomic traits, such as seed size and shape as well as growth habits (Lei et al 2020). P. vulgaris is an important field crop in South Africa (Muedi et al 2015). The major South African provinces for small-scale farming of P. vulgaris production are Eastern Cape, KwaZulu-Natal, and Mpumalanga (Fourie 2002).…”